Stabilities of dobutamine, dopamine, nitroglycerin and sodium nitroprusside in disposable plastic syringes

The solutions of dobutamine hydrochloride (5 mg/ml), dopamine hydrochloride (4 mg/ml), nitroglycerin (1 mg/ml) and sodium nitroprusside (1 mg/ml) in dextrose 5% injection were stable for 24 h when stored at 25 degrees C in 60-ml plastic syringes. For sodium nitroprusside, the syringes must be wrapped with aluminium foil (provided by the manufacturer), otherwise the loss in potency is very high (22%). There was no change in the pH values of dobutamine and dopamine solutions as well as sodium nitroprusside solutions in the prewrapped syringes. However, the pH value of nitroglycerin solutions decreased to 4.3 from 4.6 and that of sodium nitroprusside solutions in unwrapped syringes from 4.2 to 3.5; these solutions had discoloured. The chromatogram also showed new peaks from the products of decomposition. The physical appearances of the other solutions did not change.