Antimicrobial catheter lock therapy is practiced to prevent lumenal-sourced infections of central venous catheters. Citrate has been used clinically as an anticoagulant in heparin-free catheter locks. Ethanol has also been widely studied as an antimicrobial lock solution component. This study reports on the synergy of glyceryl trinitrate (GTN) with citrate and ethanol in rapidly eradicating methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermidis, Pseudomonas aeruginosa, and Candida albicans biofilms in an in vitro model for catheter biofilm colonization. GTN has a long history of intravenous use as a hypotensive agent. It is potentially attractive as a component of a catheter lock solution because its physiologic half-life is quite short and its metabolic pathways are known. A lock containing 7% citrate and 20% ethanol required 0.01% GTN to fully eradicate biofilms of all test organisms within 2 h in the model. This GTN concentration is below the levels where clinically significant hypotensive effects are expected.