Sildenafil or other phosphodiesterase type-5 inhibitors may potentiate the hypotensive effects of organic nitrates. Use of the two drugs between sildenafil and nicorandil should be avoided as the former may enhance the hypotensive effect of nicorandil. Symptomatic hypotension may also occur when sildenafil are given with alpha blockers. Drugs including cimetidine, delavirdine, erythromycin, itraconazole, ketoconazole, and HIV-protease inhibitors that inhibit the cytochrome P450 isoenzyme CYP3A4, may reduce the clearance of phosphodiesterase type-5 inhibitors. Hence, it required a reduction in dosage. Besides, the plasma concentrations of sildenafil are significantly increased by ritonavir and grapefruit juice whereas the plasma concentrations of sildenafil are likely decreased by inducers of CYP3A4 such as rifampicin. Thus, such combinations should not be given, unless necessary.
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