Nifedipine stability in cardioplegic solution.

The stability of nifedipine in cardioplegic solution was studied. Cardioplegic solutions containing nifedipine at 275 and 500 micrograms/liter were stored in plastic bags covered in brown plastic wrappers (1) under normal room light at 25 degrees C and (2) in a dark refrigerator at 4 degrees C. Samples were removed periodically for 48 hours. Infusions of cardioplegic solution containing 275 micrograms/liter were simulated using tubing and flow rates of 100, 200, and 300 ml/min; bags were covered with aluminum foil, while tubing was exposed to normal room lighting or yellow lighting, which does not degrade nifedipine. Gas chromatography was used for nifedipine assays. Nifedipine degraded more rapidly at 25 degrees C than at 4 degrees C. However, even when protected from light and refrigerated, nifedipine concentrations declined to less than 90% of original potency by approximately six hours after preparation. There was no significant degradation during the simulated infusion regardless of light exposure or flow rate. Cardioplegic solutions containing nifedipine should be prepared immediately before the surgical procedure, refrigerated until use, and protected from light until administration.