WO2011076852A2

WO2011076852A2 - Medical device with bypass arrangement

Info

Publication number: WO2011076852A2
Application number: PCT/EP2010/070497
Authority: WO
Inventors: Philip Albert Sparholt
Original assignee: Novo Nordisk A/S
Priority date: 2009-12-22
Filing date: 2010-12-22
Publication date: 2011-06-30
Also published as: WO2011076852A3

Abstract

A mixing device (1) adapted for separate storage of substances and sterile mixing is provided. The mixing device (1) is of the dual chamber type, having an extended bypass arrangement enabling fluid flow round a front stopper (7) after priming and insertion of an infusion set.

Description

MEDICAL DEVICE WITH BYPASS ARRANGEMENT

FIELD OF THE INVENTION

The present invention relates to a medical device which is adapted to store substances in separate chambers and which is capable of mixing the substances in a simple manner to produce an administrable drug.

BACKGROUND OF THE INVENTION

Some pharmaceutical drugs adapted for parenteral administration are only stable in the administrable form a relatively short period of time. For convenience reasons and in order to extend the shelf life of such a drug it is sometimes preferred to store individual constituents of the drug separately and to mix them only just before a dose is needed.

Traditionally, a mixing of constituents stored in separate vials is performed using a syringe with a needle to withdraw the one constituent from the one vial and inject it into the other vial containing the other constituent. The syringe with the attached needle is then used to withdraw from this vial the desired amount of drug to be injected into the patient. This kind of manual operation may bring about some uncertainty as to the exact concentration of the resulting drug, because it can be difficult to completely empty a vial. Moreover, since the first constituent is withdrawn from one vial and transported to another vial via a syringe with a needle, typically including a penetration of two rubber septa in order to establish fluid connection to the respective vial interiors, both sterility and safety may be compromised.

Dedicated mixing devices exist which provide for a semi-automated mixing procedure that does not involve moving a needle between separate vials. These devices are typically prefilled with specific volumes of the constituents to be mixed, and the constituents are arranged separately until the user starts using the device. At this point by one or more relatively simple operations the user is able to mix the constituents in the device without having to worry about sterility or about obtaining the right concentration of the end product.

US 4,226,236 discloses a dual chamber mixing and delivery device containing a powdered drug and a liquid diluent which are initially separated by a slidable stopper. The stopper is positioned proximally of a bypass channel in the device housing. By advancement of a rear piston the stopper is moved to a position within the bypass channel allowing for passage of the diluent round the stopper and thereby for mixing of the two components. When the diluent has been transferred to the powdered drug chamber and the mixing is complete the rear piston is in physical contact with the stopper. Further advancement of the piston in the device will lead the stopper to expel the final product through an outlet.

Such a dual chamber mixing and delivery device is commonly used in the medical area. If, for example, the final product is to be administered intravenously a delivery means such as a hypodermic needle or an infusion set may be attached to the device outlet to convey the liquid drug to the subject. Before insertion of an infusion needle into the vein it is imperative to remove air from the entire delivery line, i.e. to make sure that no air is introduced into the bloodstream. This can be done relatively easily by holding the device with the outlet end facing upwards and advancing the rear piston in the device housing a distance sufficient for the mixed product to displace the air and fill the lumen of the delivery means. In US 4,226,236 when the piston is so advanced the stopper is advanced an equivalent distance. Notably, during this advancement the stopper will move into sealing contact with the inner wall of the housing distally of the bypass channel, thereby effectively separating the drug chamber from the bypass channel.

In order to avoid a situation where the drug is inadvertently administered in e.g. the subcutaneous tissue it is desirable to be able to check whether the infusion needle when inserted is correctly positioned in a vein. In a single chamber syringe such a check could be performed by pulling the piston backwards to thereby create a partial vacuum in the delivery line. This would cause a small volume of fluid from the body to be aspirated into the device, and by viewing the colour of the fluid it could be determined if it contained blood. However, for a device of the kind disclosed in US 4,226,236 since the stopper is in sealing contact with the inner wall of the device housing following the described priming action and the piston is not mechanically engaged with the stopper it is in practice impossible to retract the stopper in a controllable manner. In other words, it is not possible to perform this check when using such a device. EP 0 144 551 discloses a dual chamber mixing device with vein indication test capacity. The device as such resembles the device disclosed in US 4,226,236. However, the arrangement of the bypass zone in the cylindrical barrel has been specifically adapted to the contents of the device such that after mixing of the separately stored components the combined volume of the components is approximately equal to the volume of the chamber defined between the stopper and the distal end of the barrel when the stopper is within the bypass zone. This means that upon mixing allegedly no air is left in the barrel. To assure that no air is introduced into the bloodstream, however, it may be necessary to prime the device after attachment of a delivery means. Doing this requires expelling a small volume of the mixed product through the outlet to flush the lumen of the delivery means, thereby causing the stopper to be moved out of the bypass zone to take up a more distal position in the barrel. Upon insertion of the delivery means it is therefore not possible to retract the stopper to perform an aspiration. Apart from this the specific adaptation of the device to its contents may put restrictions on the use of it in relation to mixing of other substances or other volumes, potentially requiring the manufacturing of a completely new device if such other use is desired.

It is further sometimes necessary to check if the infusion needle is correctly positioned in the vein even during an administration. This is for example the case if e.g. due to sudden movements of the subject under treatment there may be doubt as to whether the infusion needle has been either pulled out of the vein or perhaps completely transpierced the vein. During administration the stopper will naturally be positioned even further distally of the bypass section than after the priming of the delivery line, since more drug has been expelled from the device. In the above described devices it will obviously not be possible to controllably retract the stopper at such a point given the shortcomings in relation to retracting the stopper immediately after priming of the delivery line.

Hence, while overcoming some drawbacks of the traditional way of mixing separately stored substances the prior art dual chamber mixing devices do not provide a ready procedure for ensuring a correct insertion of a primed delivery element. They do further not provide for a simple check of whether the delivery element is in fact still

appropriately positioned at a later point in time during the administration procedure.

SUMMARY OF THE INVENTION

Having regard to the above it is an object of the invention to provide a medical device which is capable of mixing two separately stored substances in a safe and sterile manner, thereby producing a final administrable product.

It is a further object of the invention to provide a medical mixing device which can be used for IV drug delivery and which allows a user to perform a fast and simple check of whether a corresponding infusion needle has been properly inserted into a vein. It is an even further object of the invention to provide a medical mixing device of the above type which offers the user a possibility of checking for correct delivery both prior to and during an administration.

In the disclosure of the present invention, aspects and embodiments will be described which will address one or more of the above objects or which will address objects apparent from the below disclosure as well as from the description of exemplary embodiments.

In accordance with the principles of the invention a check procedure for ensuring correct placement of a primed delivery member in the body is enabled by arranging one or more bypass sections in a dual chamber device such that a partial vacuum can be established in the delivery line when desired simply by the user reversing the movement needed for administration of the drug.

In one aspect of the invention a medical device is provided, comprising a body having a proximal end portion, a distal end portion and a wall extending therebetween. The body may be cylindrical having a longitudinal main axis. The device has at least one bypass section, a bypass section e.g. being in the form of a longitudinally extending

enlargement of the inside diameter of the body. An outlet is provided in fluid

communication with the distal end portion, and a slidable stopper is arranged in the body between the outlet and the proximal end portion. In the initial stage, i.e. in a storage situation, the stopper may be positioned proximally of the proximal most bypass section. A user operable piston is arranged between the stopper and the proximal end portion. Thereby, a rear variable volume chamber is defined between the piston and the stopper. A front variable volume chamber is defined by the stopper, a portion of the wall, and the outlet. The two variable volume chambers are adapted to store respective substances to be mixed during use of the device. The stopper is movable from an initial position in which at least a portion of the stopper is in sealing contact with the wall to a first intermediate position in which fluid communication between the rear chamber and the front chamber is established via the bypass section. When the stopper is in the first intermediate position the substance from the rear chamber is free to flow to the front chamber to mix with the substance in the front chamber, thereby producing a final administrable product. The stopper is further movable from the first intermediate position to a second intermediate position, the axial distance between these two intermediate positions corresponding to a priming volume of air and/or of the

administrable product being expelled through the outlet. When the stopper is in the second intermediate position it is positioned in a bypass section enabling liquid transport round the stopper, and at least a portion of the piston is in sealing contact with the wall.

The stopper may be further movable from the second intermediate position to an end position at the distal end portion in which the device is emptied (to the degree practically possible) of the administrable product. Alternatively, the second intermediate position may be an end position of the stopper.

The outlet may be adapted to receive a portion of a delivery means for establishing fluid connection to a subject, such as a hypodermic needle or an infusion set, or is at least adapted to be fluidly coupled with such a delivery means. The delivery means comprises a lumen capable of containing a volume of material. A coupling between the outlet and the delivery means may comprise a Luer type connection, a bayonet coupling, a screw thread, or indeed any suitable means known in the art of medical devices.

The medical device itself may be a syringe type device, in which case a piston rod may be attached to the piston, or a cartridge type device, e.g. adapted for use in connection with an injection device comprising actuation means such as a piston rod for executing the movements of the piston. These actuation means may be operated manually by a user or automatically by the injection device upon some signal from a user.

In the present context the term "a priming volume" should be understood as a volume capable of priming either the device alone or the device and the delivery means, i.e. a volume providing for removal of all residual air from either the front chamber or the entire delivery line. It is emphasized that "a priming volume" also covers a volume which is greater than the minimum volume needed to prime both the device and the delivery means.

When using a device as the above described once the substances have been mixed and a priming volume has been expelled through the outlet it is not necessary to retract the stopper in order to perform an aspiration to check for correct subsequent placement of a delivery element, e.g. an infusion needle, in the body. The user operable piston can simply be retracted, leaving the stopper in place in the bypass section, whereby a partial vacuum will be established just behind, or proximal of, the stopper in the chamber between the piston and the stopper. This partial vacuum will cause body fluid from the compartment in which the infusion needle is positioned to be sucked into the device, whereby it will be visually evident if the needle is positioned in a vein. The check is relevant in relation to IV delivery for ensuring proper placement of the infusion needle in a vein, but also in relation to e.g. subcutaneous and intramuscular delivery, where it is desired to ensure that the needle is not positioned in a blood vessel. The colour of the aspirated liquid is indicative of whether access to the bloodstream is established. An absence of blood in the device is evidence that the needle has not been placed in a blood vessel. Notably, the retraction of the piston can be carried out using only a small force as long as the stopper is in a bypass section and a portion of the piston is in sealing contact with the wall.

A bypass section enabling transport of a liquid substance round the stopper may extend longitudinally in parallel with the main axis. Alternatively, or additionally, a bypass section may extend longitudinally in a spiralling or partly spiralling manner about the main axis.

The stopper may be a conventional type rubber piston having a longitudinal extent which is smaller than the longitudinal extent of each of the at least one bypass sections to thereby enable liquid passage round the stopper when positioned in a bypass section. A conventional type rubber piston is an attractive solution since it is less costly than a custom-fabricated piston.

The substances to be mixed in the device may be two liquids or a solid material and a liquid, such as a powder and a solvent, and the volume of the mixed product is either equal to or smaller than the volume of the front chamber immediately after transfer of the one substance from the rear chamber to the front chamber. If the volume of the mixed product is smaller than the volume of the front chamber immediately after mixing of the substances, either air or both air and a volume of the mixed product will be expelled through the outlet in order to prime the device (or the device and the delivery means). If the volume of the mixed product is equal to the volume of the front chamber then only a volume of the mixed product will be expelled. It is noted that it may be relevant to only prime the device itself, i.e. to not also prime a delivery means, because some users prefer to prime the delivery means, e.g. an infusion set, with blood being pumped out of the vein after insertion of the delivery needle.

The outlet may initially be covered by a sterile barrier, such as e.g. a septum or a plug, and may be exposed to the surroundings only just prior to use of the device, e.g . by removal of the plug.

In a particular embodiment of the invention the device comprises a bypass section extending continuously between a first end and a second end, the first end being positioned distally of the stopper when the stopper is in the storage position. The stopper extends between a proximal face facing the proximal end portion of the body and a distal face facing the distal end portion of the body, and the first end is positioned distally of at least the proximal face of the stopper. The second end is positioned distally of the distal face of the stopper when the stopper is in the second intermediate position, which second intermediate position corresponds to a volume of the mixed product having been expelled through the outlet.

The total longitudinal, or axial, extent of the piston and the stopper may substantially equal or exceed the longitudinal distance between the first end and the second end of the bypass section. Thereby, sealing contact between the piston and the wall is guaranteed for any position of the stopper within the bypass section (i.e. where the proximal face is positioned distally of the first end and the distal face is positioned proximally of the second end).

The first end of the bypass section may e.g. be positioned in the vicinity of the mid section of the device, and the second end may in principle be positioned at any appropriate point distally thereof, e.g. at the distal end portion.

With a device of this kind aspiration can be performed at practically all stages during the administration since the stopper will be within the bypass section at any, or substantially any, position from the first intermediate position to the end position. Further, the device is not restricted to contain certain substances of certain specific volumes. Rather, it may be used with a plurality of different substances in different volumes because the construction allows for aspiration at basically any point before and during administration, independent of the volume of the final mixed product.

In an alternative embodiment of the invention the device comprises two bypass sections arranged longitudinally offset from one another.

In one version thereof the two bypass sections are arranged serially, i.e. such that the distal end of the proximal most bypass section is positioned proximally of the proximal end of the distal most bypass section.

The proximal most bypass section may e.g. be positioned in the vicinity of the mid section of the device, and the distal most bypass section may in principle be positioned at any appropriate place distally thereof, e.g . in the vicinity of the distal end portion. The distal most bypass section may in particular be positioned such that when the stopper has been moved from the first intermediate position to the second intermediate position and the axial distance thereby travelled by the stopper corresponds to a volume of the mixed product sufficient to flush the lumen of an attached delivery means has been expelled through the outlet, the stopper is positioned within the distal most bypass section. One specific example of that is when the axial distance travelled by the stopper from the first intermediate position to the second intermediate position has caused a volume of the mixed product equal to, or substantially equal to, the volume of the lumen of the delivery means to be expelled through the outlet.

In this embodiment the combined longitudinal extent of the piston and the stopper may substantially equal or exceed the longitudinal extent of each of the bypass sections.

A device of this kind will enable the user to perform an aspiration to check for correct placement of the delivery element at least immediately after a priming of the delivery line.

In the present specification reference to a certain aspect or a certain embodiment (e.g. "an aspect", "a first aspect", "one embodiment", "an exemplary embodiment", or the like) signifies that a particular feature, structure, or characteristic described in connection with the respective aspect or embodiment is included in at least that one aspect or embodiment of the invention, but not necessarily in all aspects or

embodiments of the invention. It is emphasized, however, that any combination of features, structures and/or characteristics described in relation to the various aspects and embodiments of the invention is encompassed by the invention unless otherwise indicated herein or clearly contradicted by context.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with references to the drawings, wherein

Figs, la - lh show cross-sectional views of a medical device according to an

embodiment of the invention in different stages during use,

Figs. 2a - 2h show cross-sectional views of a medical device according to another embodiment of the invention in different stages during use, and Fig. 3 shows a cross-sectional view of a medical device according to yet another embodiment of the invention.

In the figures like structures are mainly identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS When in the following relative expressions, such as "forwards" and "backwards", are used, these refer to the appended figures and not necessarily to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only. Fig. la shows a dual chamber mixing device 1 in accordance with one embodiment of the invention in a situation right before mixing. The device 1 comprises a cylindrical barrel with a wall 2 extending between a proximal end portion 3 and a distal end portion 4. An outlet 5 is arranged at the distal end portion 4, and a coupling part 6 is provided for coupling with an infusion set (not shown). The device 1 contains a front stopper 7 which together with a distal portion of the wall 2 and the outlet 5 defines a front chamber 8 containing a powdered drug (not shown). A piston 9 is arranged behind the front stopper 7 in such a manner that a rear chamber 11 is provided between the two. The rear chamber 11 holds a liquid solvent (not shown) adapted to be mixed with the powdered drug. A piston rod 10 is coupled to the piston 9 allowing a user to move the piston 9 both forwards and backwards in the barrel. An elongated bypass 12 is provided between the front stopper 7 and the distal end portion 4.

In use of the device 1, after having removed a protective plug (not shown) originally covering the outlet 5, the piston rod 10 is moved forwards as indicated by the arrow in Fig. lb. Thereby, the piston 9 will pressurise the solvent in the rear chamber 11, causing the front stopper 7 to move forwards in the barrel. When the front stopper 7 reaches a position within the bypass 12 fluid communication is established between the rear chamber 11 and the front chamber 8, and the solvent is free to move round the front stopper 7. The continued pressure from the piston 9 will force the solvent into the front chamber 8, as indicated by the flow arrow F_mix, where it will mix with the powdered drug to form a final administrable product (not shown). When all of the solvent has been thus transferred to the front chamber 8 the rear chamber 11 is collapsed, and the piston 9 abuts the front stopper 7 (Fig. lc). The infusion set is now attached to the coupling part 6 and the piston rod 10 is moved further forwards leading the piston 9 and the front stopper 7 to expel any air from the front chamber 8 out through the outlet 5 and through the lumen of the infusion set.

When the front stopper 7 has been moved a distance corresponding to the lumen of the infusion set having been flushed by the administrable product the cannula part of the infusion set can be inserted into a vein of a subject without any risk of introducing air into the bloodstream. The front stopper 7 may then be in the position shown on Fig. Id. After insertion of the infusion cannula if the user wants to perform a check for correct placement in the vein he simply pulls the piston rod 10 backwards (Fig. le). Thereby, the piston 9 and the front stopper 7 will part and a new rear chamber 21 will form between them. The total axial length of the front stopper 7 and the piston 9 is greater than the axial extent of the bypass 12. Because the front stopper 7 is positioned in the bypass 12 and the piston 9 is in sealing contact with the wall 2 at any time during the retraction of the piston rod 10 a partial vacuum is created in the front chamber 8 and in the infusion set, sucking a volume of body fluid into the device 1. A flow of liquid round the front stopper 7 will take place, as indicated by flow arrow F_asp (Fig. If), and the user will be able to identify, by looking at the colour of this liquid, if blood has entered the device 1.

If the liquid is coloured red the user can assume an intravenous placement of the cannula and can then begin to infuse the administrable product (Fig. lg). Fig. lh shows the device 1 after emptying, where the front stopper 7 has been advanced all the way down the barrel to a position at the distal end portion 4. The retraction of the piston rod 10 can be carried out with very little force because the front stopper 7 is positioned in the bypass 12, allowing liquid to flow around it, and the device 1 therefore provides for a simple and easy way of checking for correct placement of an infusion element in a vein.

Fig. 2a shows a dual chamber mixing device 100 in accordance with another

embodiment of the invention in a situation right before mixing. The device 100 comprises a cylindrical barrel with a wall 102 extending between a proximal end portion 103 and a distal end portion 104. An outlet 105 is arranged at the distal end portion 104, and a coupling part 106 is provided for coupling with an infusion set (not shown). The device 100 contains a front stopper 107 which together with a distal portion of the wall 102 and the outlet 105 defines a front chamber 108 containing a powdered drug (not shown). A piston 109 is arranged behind the front stopper 107 in such a manner that a rear chamber 111 is provided between the two. The rear chamber 111 holds a liquid solvent (not shown) adapted to be mixed with the powdered drug. A piston rod 110 is coupled to the piston 109 allowing a user to move the piston 109 both forwards and backwards in the barrel. A front bypass 113 and a rear bypass 112 are provided between the front stopper 107 and the distal end portion 104. The two bypass sections 112, 113 are shown in a serial in-line arrangement. However, it is understood that they can, as an alternative, be arranged circumferentially set apart.

In use of the device 100, after having removed a protective plug (not shown) originally covering the outlet 105, the piston rod 110 is moved forwards as indicated by the arrow in Fig. 2b. Thereby, the piston 109 will pressurise the solvent in the rear chamber 111, causing the front stopper 107 to move forwards in the barrel. When the front stopper 107 reaches a position within the rear bypass 112 fluid communication is established between the rear chamber 111 and the front chamber 108, and the solvent is free to move round the front stopper 107. The continued pressure from the piston 109 will force the solvent into the front chamber 108, as indicated by the flow arrow F_mix, where it will mix with the powdered drug to form a final administrable product (not shown). When all of the solvent has been thus transferred to the front chamber 108 the rear chamber 111 is collapsed, and the piston 109 abuts the front stopper 107 (Fig. 2c). The infusion set is now attached to the coupling part 106 and the piston rod 110 is moved further forwards leading the piston 109 and the front stopper 107 to expel any air from the front chamber 108 out through the outlet 105 and through the lumen of the infusion set.

The axial distance between the front bypass 113 and the rear bypass 112 is fitted such that when the front stopper 107 moves from a position within the rear bypass 112 to a position within the front bypass 113 (Fig. 2d) a volume of the administrable product in the front chamber 108, which volume is sufficient to flush the attached infusion set, is expelled through the outlet 105.

The cannula part of the infusion set can now be inserted into a vein of a subject without any risk of introducing air into the bloodstream. After insertion of the infusion cannula if the user wants to perform a check for correct placement in the vein he simply pulls the piston rod 110 backwards (Fig. 2e). Thereby, the piston 109 and the front stopper 107 will part and a new rear chamber 121 will form between them. The total axial length of the front stopper 107 and the piston 109 is greater than the axial extent of each of the rear bypass 112 and the front bypass 113. Because the front stopper 107 is positioned in the front bypass 113 and the piston 109 is in sealing contact with the wall 102 at any time during this retraction of the piston rod 110 a partial vacuum is created in the front chamber 108 and in the infusion set, sucking a volume of body fluid into the device 100. A flow of liquid round the front stopper 107 will take place, as indicated by flow arrow F_asp (Fig. 2f), and the user will be able to identify, by looking at the colour of this liquid, if blood has entered the device 100.

If the liquid is coloured red the user can assume an intravenous placement of the cannula and can then begin to infuse the administrable product (Fig. 2g). Fig. 2h shows the device 100 after emptying, where the front stopper 107 has been advanced all the way down the barrel to a position at the distal end portion 104.

Fig. 3 shows a dual chamber mixing device 200 in accordance with yet another embodiment of the invention in a situation right before mixing. The device 200 comprises a cylindrical barrel with a wall 202 extending between a proximal end portion 203 and a distal end portion 204. An outlet 205 is arranged at the distal end portion 204, and a coupling part 206 is provided for coupling with an infusion set (not shown).

The device 200 contains a front stopper 207 which together with a distal portion of the wall 202 and the outlet 205 defines a front chamber 208 containing a powdered drug (not shown). A piston 209 is arranged behind the front stopper 207 in such a manner that a rear chamber 211 is provided between the two. The rear chamber 211 holds a liquid solvent (not shown) adapted to be mixed with the powdered drug. A piston rod 210 is coupled to the piston 209 allowing a user to move the piston 209 both forwards and backwards in the barrel. An elongated bypass 212 is provided between the front stopper 207 and the distal end portion 204.

The mixing device 200 resembles the previously described mixing device 1, the only difference being that the bypass 212 extends all the way to the distal end portion 204. The use of the device 200 is in principle identical to the use of the device 1. However, due to the configuration and the arrangement of the bypass 212 aspirations are possible until the point where the entire, or substantially the entire, administrable product has been expelled through the outlet 205. The user is thereby able to check if the infusion element is correctly positioned in a vein at any time during the administration.

The device 1, 100, 200 may be delivered from the manufacturer with a separate piston rod 10, 110, 210 adapted to be coupled to the piston 9, 109, 209 by the user just before use. Alternatively, the piston rod 10, 210, 210 is pre-attached to the piston 9, 109, 209 upon delivery.

Claims

1. A medical device comprising :

- a body comprising a proximal end portion, a distal end portion, and a wall

extending therebetween,

- an outlet in fluid communication with the distal end portion,

- a slidable stopper arranged between the outlet and the proximal end portion,

- a piston arranged between the stopper and the proximal end portion, the piston being operable by a user to move selectively towards the outlet and towards the proximal end portion,

- a first variable volume chamber defined by the stopper, a portion of the wall, and the outlet, the first variable volume chamber being adapted to store a first substance,

- a second variable volume chamber located between the stopper and the piston and adapted to store a second substance to be mixed with the first substance to thereby produce an administrable product, and

- one or more bypass sections, wherein the stopper is adapted to be moved from an initial position in which at least a portion of the stopper is in sealing contact with the wall to a first intermediate position in which the second substance is capable of moving from the second variable volume chamber to the first variable volume chamber, wherein the stopper is further adapted to be moved from the first intermediate position to a second intermediate position, thereby causing a priming volume of air and/or of the administrable product to be expelled through the outlet, and wherein when the stopper is in the second intermediate position the stopper is positioned in a bypass section enabling liquid transport round the stopper, and at least a portion of the piston is in sealing contact with the wall.

2. A medical device according to claim 1, wherein the outlet is adapted to be fluidly coupled with delivery means for establishing fluid connection to a subject, the delivery means comprising a lumen, and wherein the priming volume of the administrable product being expelled through the outlet when the stopper is moved from the first intermediate position to the second intermediate position is equal to or larger than the volume of the lumen.

3. A medical device according to claim 2, wherein the delivery means comprises a hypodermic needle.

4. A medical device according to claim 2, wherein the delivery means comprises an infusion set.

5. A medical device according to any of the preceding claims, wherein the stopper has a proximal face and a distal face, and wherein the one or more bypass sections comprises one bypass section having a first end and a second end, the first end being positioned distally of the proximal face when the stopper is in the initial position, and the second end being positioned distally of the distal face when the stopper is in the second intermediate position.

6. A medical device according to claim 5, wherein the second end is positioned at the distal end portion.

7. A medical device according to claim 5 or 6, wherein the combined longitudinal extent of the piston and the stopper equals or exceeds the longitudinal extent of the bypass section.

8. A medical device according to any of claims 1 - 4, wherein the one or more bypass sections comprise two bypass sections arranged longitudinally offset from one another.

9. A medical device according to claim 8, wherein the two bypass sections are arranged serially.

10. A medical device according to claim 8 or 9, wherein one of the two bypass sections has a first end and a second end, the second end being positioned at the distal end portion, and wherein the combined longitudinal extent of the piston and the stopper equals or exceeds the longitudinal extent of each of the bypass sections.