Influence of ethanol on the delivery of intravenous nitroglycerin solutions

In order to evaluate the surface tension lowering effect of ethanol in intravenous nitroglycerin solutions of varying concentrations, drop size was measured in intravenous transfusion sets that should deliver 60 drops/ml. Ethanol 5% solutions led to a significant decrease in drop volume and a concomitant increase in the number of drops per unit volume, up to 79 drops/ml were observed. The surface tension lowering effect may account for decreases of up to 25% in delivered nitroglycerin when drop counting infusion pumps are used, and may be a factor in the development of apparent tolerance to intravenous nitroglycerin.