Nitroglycerin absorption from transdermal systems: formulation effects and metabolite concentrations.

We recently compared plasma concentrations of nitroglycerin and its two dinitrate metabolites in 16 healthy male subjects after application of two controlled-release transdermal formulations of the drug. Analysis of the resulting plasma concentration-time curves indicated that the two formulations did not produce equivalent concentrations of parent drug or either of the dinitrate metabolites during the initial period of dosing. In addition, both formulations produced concentrations of the two dinitrate metabolites that exceeded the concentration of the parent drug by severalfold. Even if the pharmacologic effect of the dinitrate metabolites is low compared to that of nitroglycerin, these higher concentrations may contribute to the effect of nitroglycerin. Scrutiny of the ratio of 1,2-glyceryl dinitrate to 1,3-glyceryl dinitrate in the 16 subjects confirmed previous observations that preferential formation of the 1,2-glycerol dinitrate metabolite may occur depending on the route of administration. This ratio may thus be indicative of the bioavailability of nitroglycerin following transdermal application. Additional data suggesting racial differences in nitroglycerin absorption after transdermal application are presented.