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Mechanism of Action
The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cGMP, producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood. Avanafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of NO by inhibiting PDE5, which is responsible for degradation of cGMP in the corpus cavernosum. Because sexual stimulation is required to initiate the local release of nitric oxide, the inhibition of PDE5 has no effect in the absence of sexual stimulation.
Studies in vitro have shown that avanafil is selective for PDE5. Its effect is more potent on PDE5 than on other known phosphodiesterases (greater than 100-fold for PDE6; greater than 1,000-fold for PDE4, PDE8 and PDE10; greater than 5,000-fold for PDE2 and PDE7; greater than 10,000-fold for PDE1, PDE3, PDE9, and PDE11). Avanafil is greater than 100-fold more potent for PDE5 than PDE6, which is found in the retina and is responsible for phototransduction. In addition to human corpus cavernosum smooth muscle, PDE5 is also found in other tissues including platelets, vascular and visceral smooth muscle, and skeletal muscle, brain, heart, liver, kidney, lung, pancreas, prostate, bladder, testis, and seminal vesicle. The inhibition of PDE5 in these tissues by avanafil may be the basis for the enhanced platelet anti-aggregatory activity of NO observed in vitro and peripheral vasodilatation in vivo.
Effects of STENDRA on Erectile Response
In a single-blind, placebo-controlled, single-dose trial of 82 patients with either organic and/or psychogenic ED, visual sexual stimulation resulted in improved erections after STENDRA administration compared to placebo, as assessed by an objective measurement of hardness and duration of erections (RigiScan®). Efficacy was assessed by RigiScan at discrete time intervals ranging from 20 – 40 minutes after dosing to 100 – 120 minutes after dosing.
Effects of STENDRA on Blood Pressure
Single oral doses of STENDRA (200 mg) administered to healthy male volunteers resulted in mean changes from baseline in systolic/diastolic blood pressure of -5.3/-3.7 mmHg at 1 hour after dosing, compared to mean changes from baseline in the placebo group of 2.7/-0.4 mmHg. The reductions in systolic/diastolic blood pressure at 1 hour after dosing of STENDRA 200 mg compared to placebo were 8.0/3.3 mmHg.
Figure 1: Median Change from Baseline in Sitting
Systolic Blood Pressure, Healthy Volunteers Day 4
Effects on Cardiac Electrophysiology
The effect of single 100 or 800 mg doses of STENDRA on the QT interval were evaluated in a randomized, double-blind, placebo, and active (moxifloxacin) –controlled crossover study in 52 healthy male subjects aged 18 to 45 years. There were no significant effects of the 100 mg dose. The mean QTc (Fridericia QT correction) for avanafil 800 mg, relative to placebo was 9.4 milliseconds (two-sided 90% CI=7.2, 11.6). An 800 mg dose of STENDRA (4 times the highest recommended dose) was chosen because this dose yields exposures greater than those observed upon co-administration of avanafil with strong CYP3A4 inhibitors. A double-blind, randomized, placebo- and active-controlled (moxifloxacin), thorough QT/QTc trial of STENDRA (100 and 800 mg) in healthy male subjects demonstrated that STENDRA did not cause any significant changes in QTc interval or ventricular repolarization.
Effects of STENDRA on Blood Pressure When Administered with Nitrates
In a clinical pharmacology trial, a single dose of STENDRA 200 mg was shown to potentiate the hypotensive effect of nitrates. The use of STENDRA in patients taking any form of nitrates is contraindicated [see CONTRAINDICATIONS].
A trial was conducted to assess the degree of interaction between nitroglycerin and STENDRA, should nitroglycerin be required in an emergency situation after STENDRA was taken. This was a single-center, double-blind, randomized, 3-way crossover trial of healthy males from 30 to 60 years of age. Subjects were divided among 5 trial groups with the trial group being determined by the time interval between treatment with trial drug and glyceryl trinitrate administration. Subjects were assigned to trial groups sequentially and hemodynamic results from the previous group were reviewed for serious adverse events (SAEs) before the next group received treatment. Each subject was dosed with all 3 study drugs (STENDRA 200 mg, sildenafil citrate 100 mg, and placebo) in random order. Subjects were administered a single dose of 0.4 mg sublingual nitroglycerin (NTG) at pre-specified time points, following their dose of trial drug (0.5, 1, 4, 8 or 12 hours). Overall, 14 (15%) subjects treated with placebo and 28 (28%) subjects treated with avanafil, had clinically significant decreases in standing SBP, defined as greater than or equal to 30 mmHg decrease in SBP, after glyceryl trinitrate administration. Mean maximum decreases are shown in Table 4.
Table 4: Mean Maximum Decreases from Baseline in
Sitting and Standing Systolic Blood Pressure/Diastolic Blood Pressure (mmHg)
following Placebo or 200 mg STENDRA with 0.4 mg sublingual nitroglycerin
|Placebo with nitroglycerin|
|STENDRA with nitroglycerin|
Like other PDE5 inhibitors, STENDRA administration with nitrates is contraindicated. In a patient who has taken STENDRA, where nitrate administration is deemed medically necessary in a life threatening situation, at least 12 hours should elapse after the last dose of STENDRA before nitrate administration is considered. In such circumstances, nitrates should still only be administered under close medical supervision with appropriate hemodynamic monitoring [see CONTRAINDICATIONS].
Effects of STENDRA on Blood Pressure When Administered with Alpha-Blockers
A single-center, randomized, double-blinded, placebo-controlled, two-period crossover trial was conducted to investigate the potential interaction of STENDRA with alpha-blocker agents in healthy male subjects which consisted of two cohorts:
Cohort A (N=24): Subjects received oral doses of doxazosin once daily in the morning at 1 mg for 1 day (Day 1), 2 mg for 2 days (Days 2 – 3), 4 mg for 4 days (Days 4 – 7), and 8 mg for 11 days (Days 8 – 18). On Days 15 and 18, the subjects also received a single oral dose of either 200 mg STENDRA or placebo, according to the treatment randomization code. The STENDRA or placebo doses were administered 1.3 hours after the doxazosin administration on Days 15 and 18. The co-administration was designed so that doxazosin (Tmax ~2 hours) and STENDRA (Tmax ~0.7 hours) would reach their peak plasma concentrations at the same time.
Cohort B (N=24): Subjects received 0.4 mg daily oral doses of tamsulosin in the morning for 11 consecutive days (Days 1 – 11). On Days 8 and 11, the subjects also received a single oral dose of either 200 mg STENDRA or placebo, according to the treatment randomization code. The STENDRA or placebo doses were administered 3.3 hours after the tamsulosin administration on Days 8 and 11. The co-administration was designed so that tamsulosin (Tmax ~4 hours) and STENDRA (Tmax ~0.7 hours) would reach their peak plasma concentrations at the same time.
Supine and sitting BP and pulse rate measurements were recorded before and after STENDRA or placebo dosing.
A total of seven subjects in Cohort A (doxazosin) experienced potentially clinically important absolute values or changes from baseline in standing SBP or DBP. Three subjects experienced standing SBP values less than 85 mmHg. One subject experienced a decrease from baseline in standing SBP greater than 30 mmHg following STENDRA. Two subjects experienced standing DBP values less than 45 mmHg following STENDRA. Four subjects experienced decreases from baseline in standing DBP greater than 20 mmHg following STENDRA. One subject experienced such decreases following placebo. There were no severe adverse events related to hypotension reported during the trial. There were no cases of syncope.
A total of five subjects in Cohort B (tamsulosin) experienced potentially clinically important absolute values or changes from baseline in standing SBP or DBP. Two subjects experienced standing SBP values less than 85 mmHg following STENDRA. One subject experienced a decrease from baseline in standing SBP greater than 30 mmHg following STENDRA. Two subjects experienced standing DBP values less than 45 mmHg following STENDRA. Four subjects experienced decreases from baseline in standing DBP greater than 20 mmHg following STENDRA; one subject experienced such decreases following placebo. There were no severe adverse events related to hypotension reported during the trial. There were no cases of syncope.
Table 5 presents the placebo-subtracted mean maximum decreases from baseline (95% CI) in systolic blood pressure results for the 24 subjects who received STENDRA 200 mg and matching placebo.
Table 5: Placebo-Subtracted Mean (95% CI) Maximum
Decreases from Baseline in Standing and Supine Systolic Blood Pressure (mmHg)
with 200 mg STENDRA
|Placebo-Subtracted Mean Value (95% CI)|
|Supine||-6.0 (-9.1, -2.9)|
|Standing||-2.5 (-6.5, 1.5)|
|Supine||-3.1 (-6.4, 0.1)|
|Standing||-3.6 (-8.1, 0.9)|
Blood pressure effects (standing SBP) in normotensive men on stable dose doxazosin (8 mg) following administration of STENDRA 200 mg or placebo, are shown in Figure 2. Blood pressure effects (standing SBP) in normotensive men on stable dose tamsulosin (0.4 mg) following administration of STENDRA 200 mg or placebo are shown in Figure 3.
Figure 2: Mean (SD) Change From Baseline in Standing
Systolic Blood Pressure Over Time Following Administration of a Single Dose 200
mg Dose of STENDRA with Doxazosin
Figure 3: Mean (SD) Change From Baseline in Standing
Systolic Blood Pressure Over Time Following Administration of a Single Dose 200
mg Dose of STENDRA with Tamsulosin
Effects of STENDRA on Blood Pressure When Administered with Enalapril
A trial was conducted to assess the interaction of enalapril (20 mg daily) and STENDRA 200 mg. Single doses of 200 mg STENDRA co-administered with enalapril caused a mean maximum decrease in supine systolic/diastolic blood pressure of 1.8/3.5 mmHg (compared to placebo), accompanied by a mean maximum increase in pulse rate of 1.0 bpm.
Effects of STENDRA on Blood Pressure When Administered with Amlodipine
A trial was conducted to assess the interaction of amlodipine (5 mg daily) and STENDRA 200 mg. Single doses of 200 mg STENDRA co-administered with amlodipine caused a mean maximum decrease in supine systolic blood pressure of 1.2 mmHg (compared to placebo), accompanied by a mean maximum increase in pulse rate of 1.0 bpm; the mean maximum decrease in diastolic blood pressure was less than that observed in the placebo group. There was no effect of STENDRA on amlodipine plasma concentrations. Concomitant amlodipine was associated with 22% and 70% increases in avanafil Cmax and AUC, respectively.
Effects of STENDRA on Blood Pressure When Administered with Alcohol
Alcohol and PDE5 inhibitors, including STENDRA, are mild systemic vasodilators. The interaction of STENDRA with alcohol was evaluated in a clinical pharmacology trial. Alcohol was administered at a dose of 0.5 g/kg, which is equivalent to approximately 3 ounces of 80-proof vodka in a 70-kg male, and STENDRA was administered at a dose of 200 mg. All patients consumed the entire alcohol dose within 15 minutes of starting. Blood alcohol levels of 0.057% were confirmed. There were no reports of orthostatic hypotension or dizziness. Additional maximum supine systolic/diastolic blood pressure decreases of 3.5/4.5 mmHg and additional maximum pulse rate increase of 9.3 bpm were observed when avanafil was taken with alcohol compared to alcohol alone. Avanafil did not affect alcohol plasma concentrations.
Effects of STENDRA on Semen
Effects of STENDRA on Vision
Single oral doses of Type 5 phosphodiesterase inhibitors have demonstrated transient dose-related impairment of color discrimination (blue/green), using the Farnsworth-Munsell 100-hue test, with peak effects near the time of peak plasma levels. This finding is consistent with the inhibition of PDE6, which is involved in phototransduction in the retina.
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.
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].
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].
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].
Effect of CYP3A4 Inhibitors on Avanafil: Strong and moderate CYP3A4 inhibitors increase plasma concentrations of STENDRA. The effect of strong CYP3A4 inhibtors, 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
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 adminstration: 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 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.
Animal Toxicology and/or Pharmacology
Repeated oral administration of avanafil in multiple species resulted in signs of centrally-mediated toxicity including ataxia, tremor, convulsion, hypoactivity, recumbency, and/or prostration at doses resulting in exposures approximately 5-8 times the MRHD based on Cmax and 8-30 times the MRHD based on AUC.
STENDRA was evaluated in 3 randomized, double-blind, placebo-controlled, parallel group trials of up to 3 months in duration. In these 3 trials, STENDRA was taken as needed at doses of 50 mg, 100 mg, and 200 mg. Patients were instructed to take 1 dose of study drug approximately 30 minutes prior to initiation of sexual activity. Food and alcohol intake was not restricted.
In addition, a subset of patients from 2 of these trials were enrolled into an open-label extension trial. In the open-label extension trial, all eligible patients were initially assigned to avanafil 100 mg. At any point during the trial, patients could request to have their dose of avanafil increased to 200 mg or decreased to 50 mg based on their individual response to treatment.
The 3 primary outcome measures were the erectile function domain of the International Index of Erectile Function (IIEF) and Questions 2 and 3 from Sexual Encounter Profile (SEP). The IIEF is a 4-week recall questionnaire that was administered at baseline and at 4-week intervals during treatment. The IIEF erectile function domain has a 30-point total score, where the higher scores reflect better erectile function. The SEP included diary-based measures of erectile function. Patients recorded information regarding each sexual attempt made throughout the trial. Question 2 of the SEP asks “Were you able to insert your penis into your partner's vagina?” Question 3 of the SEP asks “Did your erection last long enough for you to have successful intercourse?”
Results are shown from the two, Phase 3, randomized, double-blind, placebo-controlled, parallel studies, one in the general ED population (Study 1) and the other in the diabetic population with ED (Study 2).
Results in the General ED Population (Study 1)
STENDRA was evaluated in 646 men with ED of various etiologies (organic, psychogenic, mixed). The mean age was 55.7 years (range 23 to 88 years). The population was 85.6% White, 13.2% Black, 0.9% Asian, and 0.3% of other races. The mean duration of ED was approximately 6.5 years. STENDRA at doses of 50 mg, 100 mg, and 200 mg demonstrated statistically significant improvement in all 3 primary efficacy variables relative to placebo (see Table 6).
Table 6: Mean Change From Baseline for Primary
Efficacy Variables in General ED Population (Study 1)
|Placebo (N=155)||STENDRA 50 mg (N=154)||STENDRA 100 mg (N=157)||STENDRA 200 mg (N=156)|
|IIEF EF Domain Score|
|Change from baseline†||2.9||5.4||8.3||9.5|
|p-value*||0.0014||< 0.0001||< 0.0001|
|Vaginal Penetration (SEP2)|
|Change from baseline†||7.10%||18.20%||27.20%||29.80%|
|p-value*||-||0.0009||< 0.0001||< 0.0001|
|Successful Intercourse (SEP3)|
|Change from baseline†||14.10%||27.80%||43.40%||44.20%|
|p-value*||-||0.0002||< 0.0001||< 0.0001|
|† Least-square estimate from ANCOVA model
* comparison to placebo for change from baseline
Results in the ED Population with Diabetes Mellitus (Study 2)
STENDRA was evaluated in ED patients (n=390) with type 1 or type 2 diabetes mellitus in a randomized, double-blind, parallel, placebo-controlled fixed dose trial of 3 months in duration. The mean age was 58 years (range 30 to 78 years). The population was 80.5% White, 17.2% Black, 1.5% Asian, and 0.8% of other races. The mean duration of ED was approximately 6 years. In this trial, STENDRA at doses of 100 mg and 200 mg demonstrated statistically significant improvement in all 3 primary efficacy variables as measured by the erectile function domain of the IIEF questionnaire; SEP2 and SEP3 (see Table 7).
Table 7: Mean Change From Baseline for Primary
Efficacy Variables in ED Population with Diabetes Mellitus (Study 2)
|STENDRA 100 mg
|STENDRA 200 mg
|IIEF EF Domain Score|
|Change from baseline†||1.8||4.5||5.4|
|Vaginal Penetration (SEP2)|
|Change from baseline†||7.50%||21.50%||25.90%|
|Successful Intercourse (SEP3)|
|Change from baseline†||13.60%||28.70%||34.00%|
|p-value*||-||< 0.0001||< 0.0001|
|† least-square estimate from ANCOVA model
* comparison to placebo for change from baseline
Last reviewed on RxList: 11/19/2012
This monograph has been modified to include the generic and brand name in many instances.
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