WO2007061868A2 - Treatment of stereotypic, self-injurious and compulsive behaviors using specific serotonin reuptake inhibitors and antagonists of nmda receptors - Google Patents

Abstract

A combination of a specific serotonin reuptake inhibitor (SSRI) and an NMDA receptor antagonist can be used in methods of treatment, for reducing the frequency of stereotypic behaviors in animals and for reducing the frequency of analogous compulsive behaviors in humans, for example, those that have been said to be a manifestation of, or related to, obsessive-compulsive disorder.

Description

TREATMENT OF STEREOTYPIC, SELF-INJURIOUS AND

COMPULSIVE BEHAVIORS USING

SPECIFIC SEROTONIN REUPTAKE INHIBITORS AND ANTAGONISTS OF

NMDA RECEPTORS RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/742,805, filed December 5, 2005 and U.S. Provisional Application No. 60/737,710 filed November 17, 2005. The entire teachings of the above applications are herein incorporated by reference.

BACKGROUND OF THE INVENTION

Stereotypic behavior in animals (also called "repetitive" or "compulsive" behavior) has been defined by some researchers as acts that are repetitive and constant, which may appear to serve no obvious purpose, and may even be injurious. One of the most common of these behaviors is, for example, crib-biting by horses — grabbing and biting of the feed bin or of parts of the structure in which the horse is housed (also called "cribbing" — see U.S. 4,692,451 for a description of this behavior, associated behaviors, and resulting problems). Another common behavior in dogs is compulsive licking of itself — even to the point of aggravating a sore ("lick granuloma" or "acral lick"). Stereotypies may show some degree of variation, and may be unlike the more typical behaviors such as cribbing and licking, in that they have no features of repetitive motion, but are characterized rather by motionless staring or a frozen body position. The repetitive behaviors of animals and the compulsive behaviors of humans have both responded to treatment with some of the same drugs. See, e.g., regarding treatment of acral lick with drags that have shown benefit in human obsessive- compulsive disorder (OCD), Rapoport, J.L., CHn. Neurophar., 15:Suppl. 1 Pt A:261A- 262A, 1992; Rapoport, J.L. et al, Arch. Gen. Psychiatry, 49:517-521, 1992. See also Smith, K.C. and Pittlekow, M.R., J. Am. Dermatol, 20:860-861, 1989, wherein it was reported that onychophagia and skin picking responded to treatment with (-) enantiomers of opioid antagonists, which have been effective also in compulsive hair pulling in cats, feather picking in birds, acral lick in dogs and cribbing in horses (Dodman, N.H., Vet. International 5:13-20, 1994; Dodman , N.H. et al., J. Am. Vet. Med. Assoc. ./93:815-819, 1988; Turner, R., Proceedings of Annual Conference of the Association of Avian Veterinarians: August 31-September 4, 1993, Nashville, TN, pp. 116-118). See also U.S.4,692,451 , the contents of which are incorporated herein by reference in their entirety. In addition, serotonin reuptake inhibitors (SRIs), including selective serotonin reuptake inhibitors (SSRIs) and clomipramine, are the first-line of pharmacotherapy in the treatment of obsessive-compulsive disorder. For a review see Kaplan, A. and Hollander, E., Psychiatr, Serv. 54(8): 1111-1118, 2003. Studies of this type provide justification for the conclusion that the same underlying physiological processes are involved in causation of the animal and human behaviors. Therefore, the behaviors should all respond positively to similar methods of therapy.

SUMMARY OF THE INVENTION The invention relates to a method for treating a disorder in animals, variously termed repetitive, stereotypic, or compulsive behavior, and which can also be self- injurious, by administering to the animal, by one or more appropriate routes and by appropriate doses, an effective amount of one or more NMDA receptor antagonists. In some cases, the composition comprises one or more NMDA receptor antagonists that are not haloperidol. In some cases the composition comprises one or more NMDA receptor antagonists, and does not comprise an opioid receptor agonist or antagonist which is primarily (-) enantiomer. In some cases the composition comprises one or more NMDA receptor antagonists, but does not comprise an opioid receptor agonist or antagonist of either (+) or (-) enantiomer. The invention also relates to a method for treating obsessive, repetitive, stereotypic or compulsive behaviors in mammals, by administering to the mammal by one or more appropriate routes and by appropriate doses, an effective amount of a selective serotonin reuptake inhibitor (SSRI) and an NMDA receptor antagonist. In one embodiment, the SSRI used in the method is fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram or escitalopram and, in a particular embodiment, the SSRI is fluoxetine. The NMDA antagonist for use in combination with the SSRI is as described above, that is, in some cases the NMDA receptor antagonist is not haloperidol or an opioid receptor agonist or an antagonist which is primarily (-) enantiomer. The invention, more particularly, is a method for treating compulsive behaviors in horses, such as crib biting, wind sucking, stall walking, weaving, head bobbing, pawing, tonguing, self-biting, flank sucking, and head shaking, by administering to the horse an effective amount of an SSRI and an effective amount of NMDA receptor antagonist. In another particular embodiment, the invention is a method for treating compulsive behaviors in dogs, such as compulsive licking (acral lick), tail chasing and whirling, pacing, fly chasing, shadow or light chasing, excessive barking, stone eating, excessive drinking, and excessive eating, comprising administering to the dog an effective amount of an SSRI and an effective amount of NMDA receptor antagonist. Also an embodiment of the invention is a method for treating compulsive behaviors in cats, such as wool sucking, compulsive licking, tail chasing, hoarding, pacing, excessive marking, compulsive masturbation, and compulsive aggression. A further embodiment of the invention is a method for treating compulsive behaviors in birds, such as feather and skin picking. The compulsive behaviors in both cats and birds are treated by administering an effective amount of an SSRI and an effective amount of NMDA receptor antagonist.

The invention relates to a method for treating a disorder (or more than one disorder, as it is possible that two or more can occur together) in humans, variously termed repetitive, stereotypic, or compulsive behavior, and which can also be self- injurious, by administering to the human, by one or more appropriate routes and by appropriate doses, an effective amount of an SSRI in combination with an effective amount of NMDA receptor antagonist, thereby relieving the frequency and/or intensity of the compulsion and reducing the frequency and/or intensity of the behavior.

Examples of the human behaviors which can be treated by these methods include, but are not limited to: obsessive-compulsive disorder (with its various manifestations of checking, counting, washing to remove contamination, etc.), trichotillomania, psychogenic excoriation, nail biting, compulsive exercising, smoking compulsion, drug (opioid) addiction, and alcohol addiction. These compulsive behaviors may be related also to compulsive gambling, compulsive shopping, and eating disorders.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph in which cumulative crib-bites per time after administration of D-methadone (diamonds), as well as the rate of crib-bites per 5-mmute interval (squares) are plotted, showing the effect of D-methadone on the rate of compulsive crib- biting in horses.

FIG. 2 is a bar graph in which the cumulative number of turns of the stall in 30 minutes are plotted for a stall-walking horse observed before and after the injection of dextromethorphan. Dextromethorphan-HBr, 1.0 mg/kg Lv., was injected after 30 minutes of control observations. "Saline" indicates the number of turns by the horse, observed in 30 minutes after injection of saline. "Dextro" indicates the number of turns by the horse, observed in 30 minutes after injection of dextromethorphan.

FIG. 3 is a bar graph showing the time spent in three typical behaviors in four experiments in which the effect of dextromethorphan on a shadow-chasing dog was tested on four consecutive days. Back slash hatching indicates "searching"; forward hatching indicates "fixated"; white indicates "resting." Dextromethorphan-HBr, 2 mg per kg p.o. was administered twice daily, and testing was carried out one hour after the morning dose. Bars indicate the total time of each of three behaviors during the first 10 minutes after the beginning of testing. Time not accounted for was spent in moving about the room, usually out of range of the camera.

FIG. 4 is a graph of the cumulative number of scratches by a mouse, plotted at 10 minute intervals, when naltrexone (10 mg/kg; squares), dextromethorphan (10 mg/kg; triangles), or no compound (control; diamonds) was injected into the mouse 10 minutes before injection of compound 48-80. FIG. 5 A is a graph of the cumulative number of scratches by a mouse, plotted at 10 minute intervals, when haloperidol (2.0 mg/kg; triangles), dextromethorphan (20 mg/kg; squares), or naloxone (20 mg/kg; diamonds) was injected into the mouse 10 minutes after injection of compound 48-80.

FIG. 5B is a graph of the cumulative number of scratches by a mouse, plotted at 10 minute intervals, when (+) methadone (5.0 mg/kg; squares), (+) methadone (10 mg/kg; triangles), or saline (control; diamonds) was injected into the mouse 30 minutes after injection of compound 48-80.

FIGs. 6A-6C are a series of graphs of the cumulative number of scratches by a mouse, plotted at 5 minute intervals for 30 minutes, when fluoxetine at 10 mg/kg (FIG. 6A) or memantine at 2 mg/kg (FIG. 6B) and 5 mg/kg (FIG. 6C) is injected into the mouse 5 minutes prior to injection of serotonin.

FIGs. 7A-7B are a series of graphs of the cumulative number of scratches by a mouse, plotted at 5 minute intervals for 30 minutes, when a combination of memantine at 2 mg/kg and fluoxetine at 0.1 mg/kg (FIG. 7A) or memantine at 5 mg/kg and fluoxetine at 5 mg/kg (FIG. 7B) is injected into the mouse 5 minutes prior to injection of serotonin.

FIGs. 8A- 8B are a series of graphs of the cumulative number of scratches by a mouse, plotted at 5 minute intervals for 30 minutes, when fluoxetine at 10 mg/kg (FIG. 8A) or 20 mg/kg (FIG. 8B) is injected into the mouse 5 minutes prior to injection of compound 48-80.

FIGs. 9A-9C are a series of graphs of the cumulative number of scratches by a mouse, plotted at 5 minute intervals for 30 minutes, when fluoxetine at 5 mg/kg (FIG. 9A) or memantine at 5 mg/kg (FIG. 9B) or a combination of memantine at 5 mg/kg and fluoxetine at 5 mg/kg (FIG. 9C) is injected into the mouse 5 minutes prior to injection of compound 48-80.

FIGs. 10A- 1OB are a series of graphs of the cumulative number of scratches by a mouse, plotted at 5 minute intervals for 30 minutes, when a combination of fluoxetine at 10 mg/kg and memantine at 2 mg/kg (FIG. 10A) or at 5 mg/kg (FIG. 10B) is injected into the mouse 5 minutes prior to injection of compound 48-80. FIG. 11 is a graph illustrating the response of all dogs treated with memantine. FIG. 12 is a graph illustrating the change in the behavior of dogs that responded to treatment with fluoxetine and memantine.

FIG. 13 is a graph illustrating the change in the behavior of dogs that responded to treatment with memantine alone. FIG. 14 is a graph illustrating the change in behavior of Dog 1 due to the addition of fluoxetine and dextomethorphan to memantine treatment.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to methods of treating animals displaying various types of repetitive and/or compulsive (frequently also called stereotypic) behaviors using compounds that are characterizable as NMDA receptor antagonists (having specific binding activity to NMDA receptors and/or the ability to block activation of the NMDA ligand-gated channel by an activating compound) in combination with compounds known as SSRIs.

Compulsive Behaviors

Compulsive or stereotypic behaviors in dogs can be put into several categories. "Grooming behaviors" can include, for example, lick granuloma (acral lick), compulsively licking objects, self-scratching, chewing feet, hair and nails, etc., flank sucking and air licking. "Locomotory behaviors" can include, for example, running and jumping, pacing, head shaking, paw shaking, tail swishing, freezing, whirling, tail chasing, walking in a pattern, as along a fence, digging and floor scratching. "Vocalization behaviors" include, for example, rhythmic barking, growling or snarling at self, barking at food, crying and howling. "Predatory behaviors" include, for instance, staring, air batting, jaw snapping, pouncing, prey chasing or searching, ducking, and fly chasing. "Eating and drinking behaviors" include, for example, excessive drinking, polyphagia, excessive drooling, gravel and dirt eating, stone chewing, wool sucking, and eating fabrics. "Sexual behaviors" include, for example, compulsive mounting and masturbating. See, for tables compiling the observed behaviors of not only cats and dogs, but also horses, primates and other species Dodman, N.H., "Veterinary Models of Obsessive-Compulsive Disorder," Chapter 16, pp. 319-334 In Obsessive-Compulsive Disorders: Practical Management (M.A. Jenike et ah, eds.), Moseby, Boston, 1998. See also N.H. Dodman et al, "Veterinary Models of OCD₅" Chapter 6, pp. 99-143, In Obsessive-Compulsive Disorders: Diagnosis, Etiology and Treatment, (E. Hollander et al. , eds.), Marcel Dekker, New York, 1997. See also Tables 1 and 2 in Luescher, U.A. et al, "Stereotypic or Obsessive-Compulsive Disorders in Dogs and Cats," In Veterinary Clinics of North America: Small Animal Practice, 21(2):401-413 (March, 1991).

Cats can exhibit behaviors similar to those seen in dogs, with the most common behaviors being those related to grooming, such as excessive self-licking and hair chewing. Other repetitive behaviors are tail chasing, hoarding, wool sucking, pacing, excessive marking, compulsive masturbation, and compulsive aggression.

Horses have not been observed to display compulsive predatory behaviors, but can also suffer from species-typical compulsive behaviors, such as cribbing, wind sucking, stall walking, weaving, head bobbing, pawing, lip flapping/tonguing, head shaking, flank biting, trichotillomania, and masturbation.

Birds, especially those of the order Psittaci, which includes parakeets, cockatoos, lories, macaws, and South American and African parrots, are subject to compulsive behaviors, particularly feather pulling and skin picking, but also route tracing, spot picking, masturbation and regurgitation.

Compulsive behaviors exhibited by animals of the porcine species include bar biting, vacuum chewing, and chain chewing.

Animals of the ovine and bovine species can exhibit behaviors similar to those seen in other species. These include tonguing and compulsive sucking, weaving, hair licking, and masturbation.

Bears in captivity have developed pacing behaviors.

Primates in captivity have been observed to have the following compulsive behaviors: hair pulling and skin picking (categorized as" grooming" behaviors), self sucking, licking and chewing ("consummatory" behaviors), self-directed aggression ("aggressive" behavior), masturbation and rectal probing (sexual behaviors), and bouncing in place and somersaulting (locomotory behaviors).

Humans, as would be expected, have developed a great variety of compulsive behaviors, compared to those of the animals. Common human behaviors include: paraphilias (sexual); self-directed aggression and pyromania (aggressive); checking, list- making, performing rituals, praying, avoidance of contamination (fear and avoidance); skin/nose picking, trichotillomania (grooming); gambling, hoarding ("predatory"); whirling, tics, compulsive exercising (locomotor); and binge eating (consummatory) and excessive counting, blinking and staring. This list, like the lists of behaviors of the animals given above, is not intended to be complete or limiting, as variations with each individual animal or human are possible. Further descriptions of human compulsive behaviors can be found in Diagnostic and Statistical Manual of Mental Disorders (DSM-rV™), American Psychiatric Association, 1994.

Stereotypic animal behaviors have been compared to obsessive-compulsive disorder and disorders involving similar repetitive or compulsive behaviors in humans. As Freud described compulsive behavior, "the patient is impelled to perform actions which not only afford him no pleasure but from which he is powerless to desist." It has been hypothesized that a more satisfactory definition of stereotypies or compulsive behaviors would encompass both the animal and human syndromes, by being based on common, specific neuropathologic differences in the brains of animals or humans manifesting these behaviors, compared to animals or humans that do not manifest such behaviors. See discussion in Luescher, U.A. et at, "Stereotypic or Obsessive- Compulsive Disorders in Dogs and Cats," In Veterinary Clinics of North America: Small Animal Practice, 21(2.):401-413 (March 1991).

The similarities have led some to refer to not only the human behaviors, but also the animal behaviors, as "compulsive" behaviors or "obsessive-compulsive disorders." See Overall, K.L., Canine Practice, 17:39-42, 1992; Dodman, N.H. and B. Olivier, CNS Spectrums, 1 (2): 10-15, 1996. It has been proposed that acral lick in dogs, and compulsive bar biting and chain chewing of tethered sows, as well as several other behaviors of animals, might serve as useful models of human obsessive-compulsive disorder (Dodman, N.H. and B. Olivier, CNS Spectrums, l(2):10-15, 1996). Compulsive self-grooming behaviors in animals, in particular, have been compared with trichotillomania in humans (Moon-Fanelli, A. A. et al., Chapter 3, pp. 63-92 In Trichotillomania, (DJ. Stein et al., eds.), American Psychiatric Press, Inc., Washington, D. C. The serotonin reuptake inhibitor citalopram has been found to be useful in the treatment of OCD and possibly compulsive hair-pulling in humans, and has been used successfully, in the majority of the dogs in the study reported, to treat acral lick dermatitis (Stein, DJ. et al, Depression and Anxiety, 8:39-42, 1998). These data provide evidence that acral lick dermatitis can be a useful animal analog of OCD.

Similarities that can be observed among the repetitive animal behaviors, and between the repetitive behaviors of animals and the repetitive behaviors of humans, suggest a common etiology. In addition, there are studies that link one human syndrome to another. Neurologic disorders such as epilepsy, Sydenham's chorea, and toxic and vascular lesions of the basal ganglia have been found concurrently with OCD (Freeman, J. et al, Paediatrics, 35:42-49, 1965; Kettle, P. and I. Marks, Br. J. Psychiatry, 149:315-319, 1989), leading to the suggestion that repetitive behaviors may be a sign of acquired disease. Observation of increased rates of OCD in Tourette syndrome (TS) patients, increased prevalence of tics and TS in OCD patients, and the increased familial rates of OCD and TS in first-degree relatives of both TS and OCD probands lead to the conclusion that there is a genetic association between the two disorders (Leonard, HX. , et al, Am. J. Psych, 149:1244-1251, 1992; Leonard, H.L., et al, Adv. Neurol, 58:83- 93, 1992). A study of the incidence of OCD in the first degree relatives of trichotillomania patients found a higher lifetime prevalence of OCD in this group than in the relatives of normal controls (Lenane, M. C. et al, J. Child Pyschol. Psychiatry, 33(5):925-933, 1992). Attention deficit/hyperactivity disorder occurs frequently with Tourette syndrome (see, for example, Harris, E.L. et al, J. Int. Neuropsychol Soc, 1(6):511-516, 1995).

NMDA Receptor Antagonists iV-methyl-D-aspartic acid (NMDA) selectively activates a major subclass of glutamatergic excitatory amino acid receptors in the vertebrate central nervous system (CNS). The NMDA receptor is a ligand-gated channel that is activated by the coagonists glutamate (or selectively in vitro by NMDA) and glycine acting at a strychnine-insensitive glycine site (Wong, E.H.F. and J. A. Kemp, Annu. Rev. Pharmacol. Toxicol, 31:401-425, 1991). It is further subject to regulation by a voltage- dependent block of the channel by Mg²⁺, a voltage-independent action of Zn²⁺, the redox state of the receptor, arachidonic acid, ethanol, neurosteroids, pH and polyamines. Although the exact structure of NMDA receptors is still a matter of debate, NMDA-sensitive ionotropic glutamate receptors probably consist of tetrameric, heteromeric, subunit assemblies that have different physiological and pharmacological properties and are differentially distributed throughout the central nervous system. The NMDA receptors are positively modulated by glycine, by polyamines (spermine and spermidine), by histamine and, under some conditions, by cations. NMDA receptors are coupled to glutamate-gated high conductance channels permeable to K⁺, Na⁺, and Ca⁺⁺ , that are critical for long-term potentiation, and are selectively activated by the artificial glutamate analog N-methyl-D-aspartate. There is evidence that NMDA receptors play an important role in learning and in other phenomena in the brain, such as drug dependence and addiction, chronic pain, and CNS development, as well as in normal or disturbed synaptic transmission in some areas of the CNS. See, for review on NMDA receptors, Danysz, W. and Parsons, C. G., Pharmacological Reviews, 50(4):597- 664, 1998.

An NMDA receptor antagonist is any one of a number of agents which has been shown to bind to NMDA receptors and/or block any of the sites that bind glycine, glutamate, NMDA or phencyclidine (PCP). Blocking the NMDA receptor sites has the effect of preventing the creation of an action potential in the cell. NMDA receptor antagonists include those compounds that preferentially bind to NMDA receptors, but may also have other activities.

NMDA receptor antagonists include the following: previously identified competitive and non-competitive antagonists of NMDA receptors, which may bind, for instance, at the glycine site (on the NRl subunit) and/or at the glutamate recognition site (on the NR2 subunit). Preferred NMDA receptor antagonists are those that have the ability to cross the blood-brain barrier and also demonstrate a low incidence of side effects. Such NMDA receptor antagonists can include, for example, compounds known as arylcyclohexylamines such as the anesthetic ketamine, neuroleptics such as haloperidol (Coughenour, L.L. and JJ. Corden, J. Pharmacol. Exp. Ther., 280:584-592, 1997) and the anti-Parkinson drug amantadine. Ifenprodil and eliprodil are neuroprotective agents whose mechanism of action has been attributed to their NMDA antagonist properties (Scatton, B. et al, pp. 139-154 In Direct and AlIo steric Control of Glutamate Receptors, Palfreyman, M. G. et al, eds., CRC Press, 1994). Trifluperidol and haloperidol have been shown to have a similar selectivity for the NRla/NR2B receptor subtype expressed in Xenopus oocytes (Ilyin, V. et al, Soc. Neurosci. Abstracts, 21 :835, 1995. Memantine, felbamate, ifenprodil, eliprodil, CGS19755, remacemide, and CNS 1102 are also antagonists of NMDA receptors (Lipton, S.A. and P.A. Rosenberg, New England Journal of Medicine, 330 (9):613-622, 1994). A large number of NMDA receptor antagonists have been synthesized and tested for interaction with the NMDA receptor complex, and research into the synthesis and improvement of NMDA receptor antagonists is continuing. See, for example, U.S. 5,783,700, WO 97/10240, U.S. 5,710,168, WO 98/03189, and DE 19601782.

NMDA receptor antagonists also include newer preparations under development e.g., CP 101, 606 (Di, X. et al, Stroke. 28:2244-2251, 1997) Bin CL (Grauert, M. et al, J. Pharmacol. Exp. Ther., 285:767-776, 1998); AR-R15896AR (Palmer, CG. et al, J. Pharmacol Exp. Ther., 288:121-132, 1999) LY274614 (Tiseo, PJ. and Inturrisi C.E., J. Pharmacol. Exp. Ther., 264:1090-1096, 1993); and NMDA antagonists that act on the glycine B site (Danysz, W. and CG. Parsons, Pharmacol Rev., 50:597-664, 1998). Many different types of assays, with many variations of each type, have been used by those of skill in the art to test compounds for the properties of an NMDA receptor antagonist. Triton-treated membrane fractions prepared from rat telencephalon (including cortex, hippocampus, and striatum) can be used in binding assays to determine K_D's of compounds; the effects of various compounds on [³H] glycine binding can be determined, yielding a K₁, (Kessler, M. et al, J. Neurochem, 52:1319-1328, 1989). Ebert, B. et al (Eur. J. Pharmacol. MoI Pharmacol, 208:49-52, 1991) have described assays that determine K₁ values of compounds by evaluating their affinities to membrane fractions isolated from various parts of the rat brain. It was found that the test compounds showed markedly lower affinity for the MK-801 binding sites in the rat cerebellum compared to MIC-801 binding sites in the cortex (approximately 25-fold lower). K_D values were similar for rat cortex, hippocampus, striatum, midbrain and medulla pons, although B_max values (indicating density of binding sites) for these tissues varied considerably.

In other types of tests of compounds for properties of NMDA receptor antagonists, onset and relief of block of NMDA-induced voltage-clamped neuron currents can be measured after application of a compound (Mealing, G.A.R. et al, J. Pharmacol. Exp. Ther., 288:204-210 (1999); Mealing, G.A.R. et al, J. Pharmacol. Exp. Ther., 281 :376-383 (1997)). Trapping of block by NMDA antagonists has been studied by a method described also in Mealing, G.A.R. et al, J. Pharmacol. Exp. Ther., 288:204-210 (1999) and in Blanpied, T.A. et al, J. Neurophysiol, 77:309-323 (1997), measuring current amplitudes on rat cortical neurons. Tests of the effectiveness of NMDA receptor antagonists as antinociceptive agents are the rat tail-flick test and the formalin test, both described in Shimoyarna, N. et al, J. Pharmacol. Exp. Ther., 283:648-652 (1997). Other assays for NMDA receptor binding and effects of this binding are referred to in the review by Danysz and Parsons, Pharmacological Reviews, 50(4):597-664, 1998.

Preferred NMDA receptor antagonists are those which have a K_D in an NMDA receptor binding assay greater than 10 μM and less than or equal to 100 μM, more preferred are those NMDA receptor antagonists which have a K_D greater than 1 μM and less than or equal to 10 μM, even more preferred are those NMDA receptor antagonists which have a K_D greater than 100 nM and less than or equal to 1 μM, still more preferred are those NMDA receptor antagonists which have a K_D greater than 10 nM and less than or equal to 100 nM, and most preferred are those NMDA receptor antagonists which have a K₀ equal to or less than 10 nM.

There is evidence for three major categories of opioid receptors in the central nervous system. These have been designated μ, K, and δ. Binding to the opioid receptors can be measured in assays such as those described in Kristensen, K. et al, Life Sciences, 55(2):PL45-PL50 (1994), using bovine caudate nucleus. Opioid receptor binders (which act either as an agonist or antagonist) are those compounds that bind to opioid receptors with a dissociation constant of less than about 100 nM. Preferably, opioid receptor binding molecules bind to opioid receptors with a K_D of less than 10 nM. A given opioid drug may interact to a variable degree with all three types of receptors and act as an agonist, partial agonist, or antagonist, at each type of receptor. The antagonist naloxone binds with high but variable affinity to all of these receptors. The term "naloxone-sensitive" is sometimes used synonymously with "opioid" in describing the actions of a given compound. See Jaffe, J.H. and W.R. Martin, "Opioid Analgesics and Antagonists," pp. 485-521 In The Pharmacological Basis of Therapeutics, (A.G. Gilman et ah, eds.), 8th ed., Pergamon Press, New York, 1990. Compounds classified as opioids have the ability to bind to opioid receptors. These can be natural or synthetic compounds. It has been found that some opioids tested for binding to the NMDA receptor are NMDA receptor antagonists (Ebert, B. et al, Biochemical Pharamacology. 56:553-559, 1998). Within the class of compounds that are opioids and are NMDA receptor antagonists is a subset of compounds that can exist as (-) and (+) forms. Where the enantiomers have been tested for binding affinity to NMDA receptors, both have been found to have binding activity; for some of these compounds, the (+) enantiomer has been demonstrated as having a higher affinity for NMDA receptors (Gorman, A.L., et al, Neurosci. Lett., 223:5-8, 1997; Choi, D. W. and V. Viseskul, Eur. J. Pharmacol, 155:27-35, 1988; Craviso, G.L. and Musacchio, J.M., Molec. Pharmacol. Exp. Ther., 264:1090-1096, 1993).

While Applicants do not wish to be bound by a single mechanism of action of the methods of the claims, one hypothesis that explains the results observed in the Examples is that both narcotic agonists and narcotic antagonists can bind to NMDA receptors and act as antagonists of NMDA receptors. Support for this hypothesis can be found in the scientific literature: (1) narcotic agonists and antagonists bind to NMDA receptors (see study of inhibition of binding of [³H] dextromethorphan in Craviso, G.L. and J.M. Musacchio, Molec. Pharmacol, 23:629-640, 1983); (2) both (+) and (-) enantiomers can bind to NMDA receptors, with the (+) enantiomer in most cases having a higher affinity for the NMDA receptor (see Craviso, G.L. and Musacchio, J.M. Molec. Pharmacol, 23:629-640, 1983); also see study of inhibition of binding of MK-801 to NMDA receptors in synaptic membranes from rat forebrain in Gorman, A.L. et ah, Neurosci. Lett, 223:5-8, 1997); (3) like compounds previously characterized as

NMDA antagonists, narcotic agonists and antagonists can protect cultured neurons from glutamate toxicity (Choi, D.W. and Viseskul, V. Eur. J Pharmacol, 155:27-35, 1988).

Assuming that both (+) and (-) enantiomer of narcotic antagonists decrease stereotypic behaviors by blocking NMDA receptors, there are considerable advantages to be gained by employing (+) enantiomers. These are: (1) there is no induction of narcotic receptors; (2) narcotics can be employed for pain relief if necessary (e.g. oral surgery or other surgery), as (+) enantiomers of narcotic antagonists do not block narcotic analgesia. The (+) enantiomers, unlike some known NMDA antagonists, readily cross the blood brain barrier. They do not produce toxic side effects like dizocilpine (MK-801). There is much experience with dextromethrophan as an antitussive with very little toxicity. Furthermore, there is considerable experience in treating addiction with (-) naltrexone and with racemic methadone. Toxicity of these substances is minimal.

Substituting (+) methadone for racemic methadone or (-) acetyl-1 methadol in the treatment of narcotic addicts would have many advantages, including: 1) decreased craving without maintaining addiction; 2) no tolerance, and therefore lower doses; 3) no problems with security or drug diversion; and 4) less difficulty in weaning addicts. Block of NMDA receptors should also decrease craving for cocaine and alcohol (Sass, H. et al., Arch. Gen. Psychiarty, 53:673-680, 1996; Mitchem, L.D. et al, Pharmacol Biochem. Behavior, 62:97-102, 1999).

Preferred NMDA antagonist compounds to be used in the treatment of repetitive behavior disorders include (+) enantiomers of both natural and synthetic opioids, such as dextromethorphan, dextrorphan, (+) methadone and (+) pentazocine; (+) enantiomers of synthetic narcotic antagonists such as (+) naloxone, (+) naltrexone, (+) nalmefene, and (+) diprenorphine. NMDA receptor antagonists and/or compositions to be used in methods described herein for the treatment of stereotypic, self-injurious and compulsive behaviors in animals and in humans include NMDA receptor antagonists or compositions comprising NMDA receptor antagonists; NMDA receptor antagonists or those compositions comprising NMDA receptor antagonists, wherein the NMDA receptor antagonist or composition does not comprise haloperidol; those NMDA receptor antagonists or compositions comprising NMDA receptor antagonists, wherein the NMDA receptor antagonist or composition does not comprise haloperidol and does not comprise primarily (-) enantiomer of an opioid receptor agonist or antagonist; NMDA receptor antagonists or compositions comprising NMDA receptor antagonists, wherein the NMDA receptor antagonist or composition does not comprise haloperidol, and does not comprise an opioid receptor agonist or antagonist as (-) or (+) enantiomer; also, NMDA receptor antagonists or compositions comprising a compound selected from the group consisting of: dextromethorphan, dextrorphan, naltrexone, naloxone, methadone, pentazocine, nalmefene, diprenorphine, nalorphine, hydromorphone, oxymorphone, hydrocodone, oxycodone, buprenorphine, butorphanol, nalbuphine, fentanyl, metazocine, cyclazocine, etazocine, and a combination of any of the preceding, wherein the compounds are predominantly (+) enantiomer.

Further compounds which can be used, preferably topically, in a composition for the treatment of behaviors such as psychogenic excoriation and scratching associated with pruritus are compounds such as loperamide, MK-801, and ketamine, wherein the compound is primarily (+) enantiomer, of those that are optically active.

SSRIs

Selective serotonin reuptake inhibitors (SSRIs) are a class of compounds that regulate serotonin (5-HT). They are part of a larger class of serotonin reuptake inhibitors (SRIs); however, SSRIs have increased specificity and, therefore, increased tolerability as compared to other SRIs (e.g., clomipramine and tri-cyclic antidepressants). It is believed that the mechanism of action of SSRIs involves blocking neuronal uptake of serotonin through their inhibition of transporter proteins that facilitate the uptake of serotonin by neurons. This inhibition of serotonin uptake results in increased levels (i.e., bioavailability) of serotonin in the extracellular brain space. (See Celada, P. etal, Rev. Psychiatr. Neurosci 29 (4). -252-265, 2004.) Some SSRIs include: fluoxetine (Prozac®), sertraline (Zoloft®), paroxetine (Paxil®), fluvoxamine (Luvox®), citalopram (Celexa®) and escitalopram (Lexapro®).

In addition to being a treatment for depression, SSRIs are one of the primary treatments for obsessive-compulsive disorder. It is thought that serotonin plays an important role in OCD through its inhibition of excessive activity of excitatory neurons of the orbitofrontal cortex. Thus, the SSRIs' increase of serotonin levels in OCD patients is believed to lead to a decrease in symptoms clinically. Though SSRIs have fewer side effects than other SRIs, when administered at therapeutic levels they can still cause adverse side effects that include gastrointestinal disturbances (e.g., nausea, diarrhea and constipation), headache, insomnia, anxiety, restlessness and sexual dysfunction. Further, studies have shown that much higher doses of SSRIs are necessary to treat obsessive-compulsive disorder as compared to many psychiatric and/or depressive disorders, resulting in an increased frequency of these adverse effects in patients having OCD (see Dougherty, DD et al., J. CHn. Psychol. 60(1 l):l 195-1202, 2004). There is also a longer latency period for OCD patient response to SSRIs, oftentimes 2 to 5 times longer than the time required for a therapeutic response in depressive patients (see Husted, DS and Shapira, NA, CNS Spectr. 9(H):$33-847,

2004). Hence, lower dosage levels of and a quicker response to SSRI treatment in OCD would be desirable.

In addition, many patients, approximately 40% to 60%, become resistant and/or refractory to SSRI treatment, where adequate treatment is defined as a decrease in the symptoms OCD to a level that is tolerable to the patient and allows the patient to function (e.g., a 25% to 35% decrease in the patient's Yale-Brown Obsessive- Compulsive Scale (Y-BOCS) score). (See Husted DS and Shapira NA, CNS Spectrums 9(11):833-847, 2004.) As used herein, patients SSRI "treatment-resistant" are those for whom at least two adequate therapeutic trials of SSRIs have failed (i.e., patients have had less than a 25% reduction in Y-BOCS score and/or still experience significant OCD-related impairment). Id₁ As used herein, patients deemed SSRI "treatment- refractory" constitute those with a greater degree of resistance, that is, those who have failed a number of therapeutic trials of SSRIs, standard augmentation strategies and behavioral therapies and/or those who have some response to treatment, yet continue to experience significant impairment from their OCD symptoms. Id. Thus, a better response by a greater number of patients to SSRI treatment of OCD is also desirable. Accordingly, in the present invention, an effective amount of an SSRI and an effective amount of an NMDA antagonist are administered to treat an animal having . obsessive-compulsive disorder. Any SSRI can be used in the combination therapy and preferred SSRI compounds to be used in the treatment of repetitive behavior disorders include fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram and escitalopram. In a particularly preferred embodiment, fluoxetine is the SSRI compound and memantine is the NMDA receptor antagonist used in the treatment of obsessive- compulsive disorder in an animal. In another embodiment, the patient to which the SSRI and NMDA receptor antagonist are administered is not treatment-resistant to the SSRI and, in still another embodiment, the subject is not treatment-refractory to the SSRI.

Subjects for Treatment

Animals to be treated for repetitive behaviors include, but are not limited to, birds and mammals, for example, captive "wild" birds and mammals, such as those living in zoos or animal preserves, especially species that are predatory or can be predatory, such as feline, canine and ursine species, domestic animals, such as those raised for meat or furs (e.g., chickens, pigs, cattle, minks), and those animals kept as pets or for recreational purposes, such as rats, mice, cats, dogs, horses, and various types of birds, such as parrots, cockatoos, parakeets, pigeons and the like.

"Horses" as used herein includes those domesticated animals that are usually called "horses," but also those animals that are sometimes classified by size as being ponies or miniature horses.

"Of an equine species" refers herein not only to horses, donkeys, and the like but also to equine hybrids, such as mules and hinnies.

Similarly, "of a canine species" refers herein not only to domestic dogs, but also to wild dogs and canine hybrids.

Stereotypic movement disorder of humans is characterized by "repetitive, seemingly driven, and nonfunctional motor behavior (e.g., hand shaking or weaving, body rocking, head banging, mouthing of objects, self-biting, picking at skin or bodily orifices, hitting own body)." The severity of the behavior is such that it interferes with normal activities or results in bodily injury if preventive measures were not used. Self- injurious behaviors occur in certain medical conditions associated with mental retardation (e.g., fragile X syndrome, de Lange syndrome, and Lesch-Nyhan syndrome, characterized by self-biting). See pages 118-121 In Diagnostic and Statistical Manual of Mental Disorders (DSM-IV™), American Psychiatric Association, 1994.

Smoking compulsion in humans is the urge to perform the act of smoking (tobacco cigarettes, cigars, or tobacco contained in another vessel or vehicle). The act of smoking is the physical manipulation of the cigarette or other tobacco vehicle and the conscious control of breathing that is normally performed in the course of taking in and blowing out the tobacco smoke, primarily involving the hands and mouth, in a kind of ritual. Smoking compulsion usually accompanies the well-documented nicotine addiction resulting from frequent and habitual tobacco smoking, but can be thought of as a compulsion which is separate from the craving satisfied by the administration of nicotine by a route other than smoking. This compulsion to smoke may be responsible for the failure of the simple administration of decreasing doses of nicotine (by transdermal patch or by nicotine-containing chewing gum, for example) to wean smokers from their smoking habit. Psychogenic excoriation (also sometimes referred to as neurotic excoriation or pathologic skin picking) is a human disorder characterized by excessive scratching, picking, gouging, or squeezing the skin, and occurs in approximately 2% of dermatology clinic patients, mostly female (Gupta, M.A. et at, Compr. Psychiatry, 27:381-386, 1986). It has been Irypothesized that psychogenic excoriation is an impulse control disorder which is related to obsessive-compulsive disorder, or which is a manifestation of obsessive-compulsive disorder (McElroy, SX. et al, J. Clin. Psychiatry, 55:33-53, 1994). Patients with psychogenic excoriation have responded to serotonin reuptake inhibitors such as fluoxetine and sertraline (Gupta, M.A. and A.K. Gupta, Cutis, 51:386-387, 1993; Stein, DJ. et al, Psychosomatics, 34:177-181, 1993; Phillips, K.A. and S.L. Taub, Psychopharmacol Bull, 31 :279-288, 1993; Kalivas, J. et al, Arch. Dermatol, 132:589-590, 1996). In a study of fluvoxamine (a selective serotonin reuptake inhibitor used in the treatment of OCD) for the treatment of psychogenic excoriation, patients showed significant improvement (Arnold, L.M. et al, Journal of Clinical P sychopharmacology, 19:15-18, 1999). hi what can also be considered a related self-injurious behavior, scratching associated with pruritis has been shown to respond to peripherally acting opiates, such as loperamide (U.S. 5,849,761; U.S. 5,849,762). An animal model, using injections of a chemical irritant, can be used to test the effectiveness of agents to treat scratching associated with pruritis (Kuraishi, Y. et al, European Journal of Pharmacology, 275: 229-233, 1995).

Thus, OCD in humans can be manifested by a number of behaviors including checking, counting, cleaning and washing to remove contamination, hoarding, doing projects repeatedly and excessively performing rituals involving tapping or touching objects, counting, praying, list-making, blinking and staring.

Compositions, Doses and Routes of Administration

An effective amount of an agent, a compound or a drug is an amount that produces a measurable improvement in the condition to be treated (e.g., a reduction in the frequency of the behavior exhibited in the human or animal, compared to the frequency of behaviors exhibited in a human or animal left untreated or sham-treated). An NMDA receptor compound primarily in the (+) form can be from greater than 50% to 100% (+) enantiomer. Similarly, a compound that is primarily (-) can be from greater than 50% (in a racemic mixture) to 100% (-) enantiomer. Compositions comprising primarily the (+) form of an opioid can have greater than 50% to 60% (+) enantiomer, but preferably have greater than 60% to 70% (+) enantiomer, more preferably greater than 70% to 80% (+) enantiomer, still more preferably greater than 80% to 90% (+) enantiomer, and most preferably, more than 90% (+) enantiomer. In addition, the dosage of NMDA receptor antagonist used in the method can be an effective amount of any those compounds described previously (see NMDA receptor antagonists). For instance, in the case that the NMDA receptor antagonist memantine is administered with the SSRI, it can be administered at a concentration of about 5 to 40 mg/day.

Similarly, SSRI compounds can be administered to a particular animal with the NMDA receptor antagonist at the concentration deemed appropriate by one with skill in the art to treat a particular manifestation of obsessive-compulsive disorder. The chosen SSRI is preferably used in combination with an NMDA receptor antagonist at a concentration less than that used when the SSRI is administered alone to treat repetitive and/or compulsive behaviors (e.g., concentrations below 80 mg/day fluoxetine, 200 mg/day sertaline, 60 mg/day paroxetine, 300 mg/day fluvoxamine, 60 mg/day citalopram and 30 mg/day escitalopram). (See Dougherty, DD et al, J. Clin. Psychol. 60(ll):l \95-l202, 2004). Thus, in the case that the SSRI used in the method is fluoxetine, it would preferably be administered with an NMDA receptor antagonist (e.g., memantine), at a concentration of about 20 to 40 mg/day.

The amount of the SSRI and NMDA compounds used will vary depending on the size, age, body weight, general health, sex, and diet of the host, and the time of administration, the biological half-life of the compound, and the particular characteristics and symptoms of the disorder to be treated. Adjustment and manipulation of established dose ranges are well within the ability of those of skill in the art, and preferably minimize side effects and toxicity. The SSRI and NMDA receptor antagonist compounds can be administered on varying schedules depending on several factors that are best assessed by one with skill in the art for a particular patient. In one embodiment, an effective amount of the SSRI and an effective amount of an NMDA receptor antagonist compound are administered once per day (i.e., once in a 24 hour period). The two compounds can be administered simultaneously (i.e., concurrently) as either separate pharmaceutical excipients or as one joint composition. In a particular embodiment, a composition comprised of an SSRI and one or more NMDA antagonists is administered to an animal to treat stereotypic and/or compulsive behaviors.

Alternatively, the chosen SSRI and NMDA receptor antagonist compounds can be administered sequentially, that is, as separate compositions administered one after the other. The amount of time between administration of each composition will vary according to a patient's tolerance of the compounds and therapeutic need(s). hi most cases, there would be little time delay between administration of the SSRI and NMDA receptor antagonist, meaning one compound would be administered directly after the other. Regardless of the schedule of administration, the compounds are preferably administered within the same 24 hour time period. The order in which the compounds are administered would generally be of less importance if the two compounds are administered sequentially with little time delay between their administration; however, it may be necessary for the skilled artisan to determine the most desirable order in which to give the two compounds if dosing intervals of the two compounds are varied.

The two agents to be used in methods of treating an animal for a repetitive and/or compulsive behavior disorder can be employed in combination with a non-sterile or sterile carrier or carriers for use with cells, tissues or organisms, such as a pharmaceutical carrier suitable for administration to a human or animal subject. Hence, the invention also relates to pharmaceutical compositions comprising an effective amount of an SSRI inhibitor, an effective amount of one or more NMDA receptor antagonists and a pharmaceutically acceptable carrier. Such compositions for use in the method comprise, for instance, a media additive or a therapeutically effective amount of an agent and a pharmaceutically acceptable carrier or excipient. Such carriers may include, but are not limited to, saline, buffered saline, dextrose, water, ethanol, surfactants, such as glycerol, excipients such as lactose and combinations thereof. The formulation can be chosen by one of ordinary skill in the art to suit the mode of administration. The chosen route of administration will be influenced by such factors as the solubility, stability and half-life of the agent, for instance. Agents to be used in the treatment of a repetitive and/or compulsive behavior disorder may be employed alone or in conjunction with other compounds, such as other therapeutic compounds. The pharmaceutical compositions may be administered in any effective, convenient manner, including administration by topical, oral, anal, vaginal, intravenous, intraperitoneal, intramuscular, subcutaneous, intranasal, transdermal or intradermal routes, among others. In therapy or as a prophylactic, the active agents may be administered to a subject as an injectable composition, for example as a sterile aqueous dispersion, preferably isotonic, or "packaged" as liposomes or microspheres.

When injectable compositions are desired, the functional NMDA receptor antagonists and SSRIs of the present invention may be formulated, for example, into preparations for injection by dissolving, suspending or emulsifying them in an aqueous or non-aqueous solvent, such as vegetable oil, synthetic aliphatic acid glycerides, esters of higher aliphatic acids or propylene glycol; and if desired, with conventional additives such as solubilizers, isotonic agents, suspending agents, emulsifying agents, stabilizers and preservatives. Alternatively, if one wishes to prepare an oral dosage form containing one of the functional antagonists herein encompassed, commonly used and pharmaceutically acceptable tableting excipients, such as lactose, microcrystalline cellulose, corn starch, stearic acid, or the like, may be used, if desired, to prepare such dosage forms.

Alternatively, the composition may be formulated for topical application, for example, in the form of ointments, creams, lotions, eye ointments, eye drops, ear drops, mouthwash, impregnated dressings and sutures and aerosols, and may contain appropriate conventional additives, including, for example, preservatives, solvents to assist drag penetration, and emollients in ointments and creams. Such topical formulations may also contain compatible conventional carriers, for example cream or ointment bases, and ethanol or oleyl alcohol for lotions.

EXEMPLIFICATION

Example 1 : Treatment of cribbing in horses

Horses were admitted to the Large Animal Hospital of Tufts University School of Veterinary Medicine or were tested in their home barn. Cribbing straps and food were removed prior to testing. Control rates of crib-biting were observed and recorded for 5 minute intervals for one hour or more after an intravenous injection of 0.15 M saline. Test drugs were administered orally (by gavage) or by injection into the jugular vein. Solutions were made up with physiological saline and sterilized by filtration through a 0.2 micron filter (Millipore).

For the experimental data shown in Figure 1 , after establishment of a stable control rate of approximately 10 crib-bites per minute, 50 mg of D-methadone-HCl in 25 ml saline was injected i.v. In Figure 1, the cumulative number of crib-bites was plotted against time as was the rate per 5 minute interval (Shuster, L. and N.H. Dodman, pp. 185-202, In Psychopharmacology of Animal Behavior Disorders, (N.H. Dodman and L. Shuster, eds.), Blackwell Scientific, Maiden, MA, 1998). The rate decreased between the second and the fifth 5-minute interval following injection. The control rate then resumed during the next 80 minutes of observation. Horses were observed continuously during scoring for side effects that might be attributed to the treatment. These included changes in posture, disposition and motor activity. See also Table 1.

Example 2: Treatment of stall-walking in horses

Dextromethorphan-HBr, 1.0 mg/kg i.v., was injected after 30 minutes of control observations, to test its effect on a stall-walking horse. When measuring "stall walking" locomotor activity, each circuit around the stall was scored as one rotation. Cumulative rotations per 5 minute interval were plotted against time to establish the rate of circling.

The results of the experiment are plotted in Figure 2. See also Table 1.

Table 1 Effect of some Drug Treatments on the Rate of Crib Biting

Example 3: Treatment of light/shadow-chasing in dogs

Behavior of a shadow-chasing dog was filmed with a video camera for 10 minutes after the onset of testing in the owner's home. To stimulate the dog, the owner moved around a flashlight beam on the floor for 5 seconds. The typical response after the light' was turned off was frantic searching for the light followed by fixed staring at the floor. Dextromethorphan-HBr, 2 rng per kg p.o. was administered twice daily and testing was carried out one hour after the morning dose. Results are shown in Figure 3.

Example 4: Mouse Model for Pruritus

The animals used were BALB/c male mice, weighing 27-33 g. One mouse was used per compound tested, except for two control mice receiving saline; two different mice were tested with (+) methadone, each with a different dose. Compound 48/80 (Kuraishi, Y. et ah, European Journal of Pharmacology, 275:229-233, 1995), 0.5 mg/ml in saline, was injected subcutaneously in a volume of 0.1 ml, between the shoulder blades of the mouse. Test compounds, dissolved in saline, were injected intraperitoneally in a volume of 0.1 ml per 1O g, either 10 minutes before or 30 minutes after injection of compound 48/80. The cumulative number of scratches with a hind leg were recorded at 10 minute intervals for 60 minutes following the injection of compound 48/80. See Tables 2 and 3, as well as Figures 4, 5A and 5B, showing the effectiveness of the compounds tested: naltrexone, dextromethorphan, (+) methadone, haloperidol, and (+) naloxone.

Table 2

Effect of NMDA Blockers on Pruritus in Mouse: Blocker Administered 10

Minutes Before 48/80

Table 3

Effect of NMDA Blockers on Pruritus in Mouse: Compound Administered 30

Minutes After 48/80

Example 5: Treatment of Compulsive Scratching in Mice Using an SSRI and NMDA Receptor Antagonist

Compulsive scratching was produced by injecting mice subcutaneously with either serotonin or compound 48-80 which degranulates mast cells to release serotonin. The cumulative number of scratches with a hind leg was recorded at 5 minute intervals for the next 30 minutes. Treated animals were injected intraperitoneally 5 minutes prior to inducer with fluoxetine, memantine or a combination of both drugs. Controls received saline intraperitoneally. Mean values were calculated, and the significance of differences between the treated and control groups was determined with Student's t-test or by the non-parametric Mann- Whitney U Test (p ≤ 0.05).

Fluoxetine given alone decreased scratching, but only at relatively high doses (see FIGs. 6A, 8 A-8B and 9A). Memantine, when give alone at both 2 mg/kg and 5 mg/kg demonstrated little effect (see FIGs. 6B-6C and 9B). When lower doses were given, p-values generally did not achieve significance because of small sample size and considerable individual variability among controls (see Table 4). When the two drugs were combined, lower doses of each did significantly decrease compulsive scratching (see Table 4) induced by both serotonin (see FIGs. 7A-7B) and compound 48-80 (see FIGs. 9C and 10A). Even when combined with fluoxetine, higher doses of memantine were more effective at decreasing compulsive scratching (see FIGs. 10A- 10B). Except for decreased motor activity by mice injected with higher does of fluoxetine, there were few overt side effects among the treated animals.

Table 4

Effect of a Combination of an SSRI and an NMDA Receptor Antagonist on Compulsive Scratching in Mouse

Sub-cutaneous injections: 0.1 niL serotonin (0.4 mg/niL) or 0.1 mL of 48-80 (1.0 mg/mL). * indicates p ≤ 0.5. Example 6: Treatment of Obsessive-Compulsive Disorder in Dogs Using an SSRI and memantine

The effect of the NMDA receptor antagonist memantine on dogs of differing breeds and having various types of repetitive, self-injurious or obsessive-compulsive disorders was evaluated. (See Table 5 for treatment data and dog characteristics).

Table 5 Treatment data for dogs with OCD

Some dogs were already being treated with fluoxetine, while other dogs had received no previous treatment. Memantine at 0.5 mg/kg was administered to the dogs. Those dogs already being treated with fluoxetine were required to be on that treatment for more than 6 weeks before the addition of memantine treatment. Those dogs that had been treated wiih fluoxetine for less than 6 weeks were continued on fluoxetine until stable for 6 weeks. Response of the dogs to the treatments was evaluated by the dogs' owners based on the frequency and intensity of the compulsive behavior (see Table 6).

Table 6 Scoring of dogs treated for OCD

Of those dogs already being treated with fluoxetine, the owners scored their behavioral difference compared to their behavior before memantine treatment was begun. Weekly behavioral scores were created by calculating the average score for seven days.

Nearly 45% of the dogs responded to memantine treatment (see FIG. 11). In those dogs that responded to memantine treatment, the dogs already being treated with fluoxetine (dogs 5 and 8) had 100% improvement with the addition of memantine. In other words, the addition of memantine cured the dogs of their obsessive-compulsive/ repetitive behaviors (see FIG. 12). Responders treated with memantine alone (dogs 1 and 3) also saw some improvement in their behaviors (see FIG. 13). The addition of fluoxetine treatment in week 3 further decreased the repetitive behavior of dog 1 (see FIG. 13).

Dog 1, which responded to memantine treatment alone, was also further treated with other NMDA receptor antagonists when repetitive behaviors began to increase again (i.e., slippage). The addition of fluoxetine and dextromethorphan resulted in improvement in the spinning behavior of dog 1 (see FIG. 14).

In the improved dogs, a response was typically seen within the first 5 days of treatment. Ambulatory and predatory compulsive disorders such as light/shadow chasing and spinning improved, while only one oral compulsive behavior like licking or flank sucking improved. Although the sample size was small, memantine was helpful in some cases of canine obsessive-compulsive disorder. Improvement in the obsessive- compulsive behaviors in those dogs refractory to SSRI treatment was significant, as no other known treatment is available to these animals.

Example 7: Treatment of humans with an SSRI and memantine

Memantine was administered to several patients that had been refractory to SSRl treatment (e.g., PROZAC®, PAXIL® AND ZOLOFT®) for several months to several years. The Yale-Brown Obsessive Compulsive Score (Y-BOCS) of these patients was taken before and after addition of memantine treatment to the SSRI treatment (see Table 7). AU patients saw a decrease in their Y-BOCS, some as significantly as 73% (e.g., patient 3). The decrease in Y-BOCS score was, on average, about 50%. Verbally, patients 1, 2, 3 and 5 reported a huge improvement clinically in their obsessive- > compulsive behaviors. As these patients were refractory and/or resistant to SSRI treatment and had no other treatment options available to them, improvement in their symptoms of obsessive-compulsive disorder meant an very significant improvement in their quality of life.

Table 7 Treatment of humans with an SSRI and memantine

AU references cited herein not previously specifically stated as being incorporated by reference are hereby incorporated by reference in their entirety.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method for treating obsessive-compulsive disorder in an animal comprising administering to the animal an effective amount of a specific serotonin reuptake inhibitor (SSRI), its derivatives or pharmaceutically acceptable salts thereof and an effective amount of an NMDA receptor antagonist, its derivatives or pharmaceutically acceptable salts thereof.

2. The method of claim 1 wherein the SSRI_. is one selected from the group consisting of fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram and escitalopram.

3. The method of claim 2 wherein the SSRI is fluoxetine.

4. The method of claim 1 wherein the NMDA receptor antagonist is one selected ^• from the group consisting of memantine, methadone, milnaciprin, dextromethorphan, dextrophan, naloxone, naltrexone and nalmefene.

5. The method of claim 4 wherein the NMDA receptor antagonist is primarily the (+) enantiomer of an opioid receptor antagonist.

6. The method of claim 4 wherein the NMDA receptor antagonist is memantine.

7. The method of claim 4 wherein the animal treated for obsessive-compulsive disorder is a human.

8. The method of claim 7 wherein the SSRI and NMDA receptor antagonist are administered on a dosage schedule selected from the group consisting of simultaneously and sequentially.

9. The method of claim 7 wherein the SSRI and NMDA receptor antagonist are administered at least once per day.

10. A method for treating obsessive-compulsive disorder in an animal comprising administering to the animal an effective amount of fluoxetine and an effective amount of memantine.

11. The method of claim 10 wherein the animal is a human.

12. The method of claim 11 wherein about 20 milligrams per day (mg/day) to about

40 mg/day of fluoxetine and about 5 mg/day to about 40 mg/day of memantine are administered.

13. The method of claim 12 wherein the fluoxetine and memantine are administered on a dosage schedule selected from the group consisting of simultaneously and sequentially.

14. The method of claim 12 wherein the fluoxetine and memantine are administered at least once per day.

15. A method for treating obsessive-compulsive disorder in a subject comprising administering to the subject an effective amount of an SSRI, its derivatives or pharmaceutically acceptable salts thereof and an effective amount of an NMDA receptor antagonist, its derivatives or pharmaceutically acceptable salts thereof, wherein the subject is not treatment-resistant to the SSRI or the subject is not treatment-resistant to the SSRI.

16. A method for treating obsessive-compulsive disorder in an animal comprising administering to the animal an effective amount of an SSRI, its derivatives or pharmaceutically acceptable salts thereof and an effective amount of an NMDA receptor antagonist, its derivatives or pharmaceutically acceptable salts thereof, wherein the NMDA receptor antagonist does not comprise haloperidol.

17. A pharmaceutical composition comprising an effective amount of an SSRI, an effective amount of one or more NMDA receptor antagonists and a pharmaceutically acceptable carrier.

18. The pharmaceutical composition of claim 17 for use in treating an animal with obsessive-compulsive disorder.

19. The pharmaceutical composition of claim 18 wherein the animal is a human.

20. The pharmaceutical composition of claim 17 wherein the SSRI is one selected from the group consisting of fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram and escitalopram.

21. The pharmaceutical composition of claim 20 wherein the SSRI is fluoxetine.

22. The pharmaceutical composition of claim 21 wherein the one or more NMDA receptor antagonists are selected from the group consisting of memantine, methadone, milnaciprin, dextromethorphan, dextrophan, naloxone, naltrexone and nalmefene.

23. The pharmaceutical composition of claim 22 wherein the NMDA receptor antagonist is memantine.

24. The pharmaceutical composition of claim 23 wherein the SSRI is fluoxetine and the NMDA receptor antagonist is memantine.

25. The pharmaceutical composition of claim 24 wherein about 20 mg/day to about 40 mg/day of fluoxetine and about 5 mg/day to about 40 mg/day of memantine are administered.

26. A method for treating obsessive-compulsive disorder in an animal comprising administering to the animal the pharmaceutical composition of Claim 17.