In vitro effect of additives in benzodiazepine solutions on the superoxide anion-generating system in polymorphonuclear leucocytes

Inhibitory effects of diazepam and flunitrazepam on the superoxide anion (O₂^-) -generating system in granulocytes were examined for their clinical relevance. When the effects of commercial solutions and pure preparations were compared using porcine and human polymorphonuclear leucocytes in vitro, the solutions were found to be more inhibitory than the pure drugs by 4-11 times, indicating that inhibition was caused mainly by the additives in the solutions. Concentrations of the additives required for 50% maximal inhibition of the system were 2.3, 7.5 and 0.9 μl ml^-1 for propylene glycol, ethanol and benzyl alcohol, respectively, while those of pure diazepam and flunitrazepam were 220 and 190 μg ml^-1, respectively, under comparable conditions. However, plasma concentrations of the benzodiazepines and their additives during clinical use were far less than these inhibitory concentrations, indicating that they had no appreciable effect on the O₂^--generating system in polymorphonuclear leucocytes of patients.