Avogra Drug Interactions

Sildenafil metabolism is principally mediated by the cytochrome P-450 (CYP) isoforms 3A4 (major route) and 2C9 (minor route). Therefore, inhibitors of these isoenzymes may reduce sildenafil clearance.
There is a potential reduction in sildenafil clearance when co-administered with CYP3A4 inhibitors (eg, ketoconazole, erythromycin, cimetidine).
When a single 100-mg dose of sildenafil was administered with erythromycin, a specific CYP3A4 inhibitor, at steady state (500 mg twice daily for 5 days), there was a significant increase in sildenafil systemic exposure (AUC).
Co-administration of the HIV protease inhibitor saquinavir, a CYP3A4 inhibitor, at steady state (1200 mg thrice daily) with sildenafil (100-mg single dose) resulted in a significant increase in sildenafil Cmax and an increase in sildenafil AUC. Sildenafil had no effect on saquinavir pharmacokinetics. Stronger CYP3A4 inhibitors eg, ketoconazole and itraconazole would be expected to have still greater effects.
Co-administration of the HIV protease inhibitor, ritonavir, which is a highly potent P-450 inhibitor at steady state (500 mg twice daily) with sildenafil (100 mg single dose) resulted in a 4-fold increase in sildenafil Cmax and a 11-fold increase in sildenafil plasma AUC. At 24 hrs, the plasma levels of sildenafil were still approximately 200 ng/mL, compared to approximately 5 ng/mL when sildenafil was dosed alone. This is consistent with ritonavir's marked effects on a broad range of P-450 substrates. Sildenafil had no effect on ritonavir pharmacokinetics.
When the dose of sildenafil for subjects receiving potent CYP3A4 inhibitors was administered as recommended, there is a sight potentiation in the free plasma sildenafil.
Single doses of antacid (magnesium hydroxide/aluminium hydroxide) did not affect the bioavailability of sildenafil.
No interaction was seen when sildenafil (100 mg) was co-administered with amlodipine in hypertensive patients. The mean additional reduction on supine systolic blood pressure was 8 mmHg systolic and 7 mmHg diastolic.
When the α-blocker doxazosin (4 mg) and sildenafil (25, 50 or 100 mg) were administered simultaneously to patients with benign prostatic hyperplasia (BPH), additional average reductions of supine blood pressure of 7 mmHg systolic and 7 mmHg diastolic were observed.
When higher doses of sildenafil and doxazosin (4 mg) were administered simultaneously, there were infrequent reports of patients who experienced symptomatic postural hypotension within 4 hours of dosing. Simultaneous administration of sildenafil to patients taking α-blocker therapy may lead to symptomatic hypotension in some patients.