Mean STENDRA plasma concentrations measured after the administration of a single oral dose of 50 or 200 mg to healthy male volunteers are depicted in Figure 4. The pharmacokinetics of STENDRA are dose proportional from 12.5 to 600 mg.

Figure 4: Plasma Avanafil Concentrations (mean ± SD) Following a Single 50 mg or 200 mg STENDRA Dose

Absorption and Distribution

STENDRA is rapidly absorbed after oral administration, with a median Tmax of 30 to 45 minutes in the fasted state. When STENDRA (200 mg) is taken with a high fat meal, the rate of absorption is reduced, with a mean delay in Tmax of 1.12 to 1.25 hours and a mean reduction in Cmax of 39% (200 mg). There was an approximate 3.8% decrease in AUC. The small changes in avanafil Cmax and AUC are considered of minimal clinical significance; therefore, STENDRA may be administered with or without food. The mean accumulation ratio is approximately 1.2. Avanafil is approximately 99% bound to plasma proteins. Protein binding is independent of total drug concentrations, age, renal and hepatic function.

Based upon measurements of avanafil in semen of healthy volunteers 45-90 minutes after dosing, less than 0.0002% of the administered dose appeared in the semen of patients.

Metabolism and Excretion

Avanafil is cleared predominantly by hepatic metabolism, mainly by the CYP3A4 enzyme and to a minor extent by CYP2C isoform. The plasma concentrations of the major circulating metabolites, M4 and M16, are approximately 23% and 29% that of the parent compound, respectively. The M4 metabolite has an in vitro inhibitory potency for PDE5 18% of that of avanafil and M4 accounts for approximately 4% of the pharmacologic activity of avanafil. The M16 metabolite was inactive against PDE5.

Avanafil was extensively metabolized in humans. After oral administration, avanafil is excreted as metabolites predominantly in the feces (approximately 62% of administered oral dose) and to a lesser extent in the urine (approximately 21% of the administered oral dose). STENDRA has a terminal elimination half-life of approximately 5 hours.

Geriatric

The pharmacokinetics of a single 200 mg STENDRA administered to fourteen healthy elderly male volunteers (65-80 years) and eighteen healthy younger male volunteers (18-43 years of age) were compared. AUC0-inf increased by 6.8% and Cmax decreased by 2.1% in the elderly group, compared to the younger group. However, greater sensitivity to medications in some older individuals should be considered [see Use in Specific Populations (8.5)].

Renal Impairment

The pharmacokinetics of a single 200 mg STENDRA administered to nine patients with mild (creatinine clearance greater than or equal to 60 and less than 90 mL/min) and to ten patients with moderate (creatinine clearance greater than or equal to 30 to less than 60 mL/min) renal impairment were evaluated. AUC0-inf decreased by 2.9% and Cmax increased by 2.8% in patients with mild renal impairment, compared to healthy volunteers with normal renal function. AUC0-inf increased by 9.1% and Cmax decreased by 2.8% in patients with moderate renal impairment, compared to healthy volunteers with normal renal function. There is no data available for subjects with severe renal insufficiency or end-stage renal disease on hemodialysis [see Use in Specific Populations (8.6)].

Hepatic Impairment

The pharmacokinetics of a single 200 mg STENDRA administered to eight patients with mild hepatic impairment (Child-Pugh A) and eight patients with moderate hepatic impairment (Child-Pugh B) were evaluated. AUC0-inf increased by 3.8% and Cmax decreased by 2.7% in patients with mild hepatic impairment, compared to healthy volunteers with normal hepatic function. AUC0-inf increased by 11.2% and Cmax decreased by 51% in patients with moderate hepatic impairment, compared to healthy volunteers with normal hepatic function. There is no data available for subjects with severe hepatic impairment (Child-Pugh Class C) [see Use in Specific Populations (8.7)].

Drug Interaction Studies

Clinical Studies

Effect of CYP3A4 Inhibitors on Avanafil: Strong and moderate CYP3A4 inhibitors increase plasma concentrations of STENDRA. The effect of strong CYP3A4 inhibitors, ketoconazole and ritonavir, and moderate CYP3A4 inhibitor, erythromycin, on avanafil pharmacokinetics was studied in an open-label, randomized, one-sequence crossover, three-way parallel study.

Strong CYP3A4 Inhibitors

Fifteen healthy male volunteers received 400 mg ketoconazole (2 tablets containing 200 mg ketoconazole) once daily for 5 days (Days 2-6) and a single 50 mg avanafil on Days 1 and 6. Twenty-four hour pharmacokinetics of avanafil on Days 1 and 6 were compared. Co-administration with the strong CYP3A4 inhibitor ketoconazole resulted in an approximate 13-fold increase in AUC0-inf and 3.1-fold increase in Cmax. Fourteen healthy male volunteers received 300 mg ritonavir (3 tablets containing 100 mg ritonavir) twice daily for 1 day (Day 2), 400 mg twice daily for 1 day (Day 3), 600 mg twice daily for 5 days (Days 4-8), and a single 50 mg avanafil on Days 1 and 8. Twenty-four hour pharmacokinetics of avanafil on Days 1 and 8 were compared. Co-administration with the strong CYP3A4 inhibitor ritonavir resulted in an approximate 13-fold increase in AUC0-inf and 2.4-fold increase in Cmax of avanafil.

Moderate CYP3A4 Inhibitors

Fifteen healthy male volunteers received 500 mg erythromycin (2 tablets containing 250 mg erythromycin) every 12 hrs for 5 days (Days 2-6) and a single 200 mg avanafil (2 tablets containing 100 mg avanafil) on Days 1 and 6. Twenty-four hour pharmacokinetics of avanafil on Days 1 and 6 were compared. Co-administration with the moderate CYP3A4 inhibitor erythromycin resulted in an approximate 3.6-fold increase in AUC0-inf and 2.0-fold increase in Cmax of avanafil.

Effect of Avanafil on Other Drugs: 

Warfarin 

The effect of avanafil on warfarin pharmacokinetics and pharmacodynamics was evaluated in a double-blind, randomized, placebo-controlled, two-way crossover study. Twenty-four healthy male volunteers were randomized to receive either 200 mg avanafil or matching placebo for 9 days. On Day 3 of each period, volunteers received a single 25 mg warfarin. Pharmacokinetics of R- and S-warfarin, PT, and INR prior to warfarin dosing and up to 168 hrs after warfarin administration were compared. Platelet aggregation prior to warfarin dosing and up to 24 hrs after warfarin administration were compared. PT, INR, and platelet aggregation did not change with avanafil administration: 23.1 sec, 2.2, and 75.5%, respectively. Co-administration with avanafil resulted in an approximate 1.6% increase in AUC0-inf and 5.2% decrease in Cmax of S-warfarin.

Omeprazole, Rosiglitazone, and Desipramine

The effect of avanafil on the pharmacokinetics of omeprazole (a CYP2C19 substrate), rosiglitazone (a CYP2C8 substrate), and desipramine (a CYP2D6 substrate) was evaluated in an open-label, three cohort, crossover study. Nineteen healthy male volunteers received a single 40 mg omeprazole delayed-release capsule once daily for 8 days (Days 1-8), and a single 200 mg avanafil on Day 8. Twelve hour pharmacokinetics of omeprazole on Days 7 and 8 were compared. Co-administration with avanafil resulted in an approximate 5.9% increase in AUC0-inf and 8.6% increase in Cmax of omeprazole. Twenty healthy male volunteers received a single 8 mg rosiglitazone tablet then a single 200 mg avanafil. Twenty-four hour pharmacokinetics of rosiglitazone with and without avanafil were compared. Co-administration with avanafil resulted in an approximate 2.0% increase in AUC0-inf and 14% decrease in Cmax of rosiglitazone. Twenty healthy male volunteers received a single 50 mg desipramine tablet then a single 200 mg avanafil tablet 2 hours after desipramine. Ninety-six hour pharmacokinetics of desipramine with and without avanafil were compared. Co-administration with avanafil resulted in an approximate 5.7% increase in AUC0-inf and 5.2% increase in Cmax of desipramine.

In vitro studies

Avanafil had no effect on CYP1A1/2, 2A6, 2B6 and 2E1 (IC50 greater than 100 micromolar) and weak inhibitory effects toward other isoforms (CYP2C8, 2C9, 2C19, 2D6, 3A4). Major circulating metabolites of avanafil (M4 and M16) had no effect on CYPs 1A, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4. Avanafil and its metabolites (M4 and M16) are unlikely to cause clinically significant inhibition of CYPs 1A, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 or 3A4.