Effects of sildenafil citrate (Viagra) combined with nitrate on the heart

Background-Sildenafil citrate (Viagra) is indicated for the treatment of er ectile dysfunction. Large and sudden decreases in systemic blood pressure w ere reported in a substantial number of patients taking sildenafil citrate combined with nitroglycerin. We studied the effect of sildenafil citrate on the relationship between changes in systemic blood pressure and coronary b lood flow. Methods and Results-Healthy male beagles were used to assess systemic blood pressure, pulmonary arterial pressure, and flow in the left circumflex art ery tin which a critical stenosis was established) and left anterior descen ding coronary artery. After measurement of the hemodynamic variables, 2 mg/ kg sildenafil citrate was administered via a nasogastric tube. Hemodynamic changes were monitored for 1 hour. Subsequently, the acute effect of nitrat e combined with sildenafil citrate was studied by the bolus injection of 0. 2 mg isosorbide dinitrate before and after sildenafil citrate. Systemic blo od and pulmonary arterial pressures and circumflex flow did not change duri ng this study; however, left anterior descending coronary arterial flow inc reased from 16.0+/-5.8 to 24.6+/-8.7 mL/min 1 hour after administration of sildenafil citrate. The prolongation of systemic blood pressure decrease an d the circumflex flow decrement induced by isosorbide dinitrate after silde nafil citrate were significantly larger and longer than those before silden afil citrate. Conclusions-Sildenafil citrate had the effect of vasodilation in a normal c oronary artery; however, a combined effect with nitrate resulted in large a nd protracted decreases in systemic blood pressure and coronary blood flow in vessels with critical stenosis.