16 HOW SUPPLIED/STORAGE AND HANDLING

These effects on the metabolite are not expected to be of clinical consequence. Given sildenafil peak plasma concentrations of approximately 1 µM after recommended doses, it is unlikely that VIAGRA will alter the clearance of substrates of these isoenzymes.

Pregnancy & Lactation

In addition, in a study performed in healthy male volunteers, co-administration of the HIV protease inhibitor saquinavir, also a CYP3A4 inhibitor, at steady state (1200 mg tid) with Viagra (100 mg single dose) resulted in a 140% increase in sildenafil Cmax buy sildenafil uk and a 210% increase in sildenafil AUC. Viagra had no effect on saquinavir pharmacokinetics. A stronger CYP3A4 inhibitor such as ketoconazole or itraconazole could be expected to have greater effect than that seen with saquinavir. Population pharmacokinetic data from patients in clinical trials also indicated a reduction in sildenafil clearance when it was co-administered with CYP3A4 inhibitors (such as ketoconazole, erythromycin, or cimetidine) [see Dosage and Administration (2.4) and Drug Interactions (7.4)]. In another study in healthy male volunteers, co-administration with the HIV protease inhibitor ritonavir, which is a highly potent P450 inhibitor, at steady state (500 mg bid) with VIAGRA (100 mg single dose) resulted in a 300% (4-fold) increase in sildenafil Cmax and a 1000% (11-fold) increase in sildenafil plasma AUC.

Erectile Dysfunction

At 24 hours 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 P450 substrates. VIAGRA had no effect on ritonavir pharmacokinetics [see Dosage and Administration (2.4) and Drug Interactions (7.4)]. Although the interaction between other protease inhibitors and sildenafil has not been studied, their concomitant use is expected to increase sildenafil levels. In a study of healthy male volunteers, co-administration of sildenafil at steady state (80 mg t.i.d.) with endothelin receptor antagonist bosentan (a moderate inducer of CYP3A4, CYP2C9 and possibly of CYP2C19) at steady state (125 mg b.i.d.) resulted in a 63% decrease of sildenafil AUC and a 55% decrease in sildenafil Cmax. In a study of healthy male volunteers, sildenafil (100 mg) did not affect the steady state pharmacokinetics of the HIV protease inhibitors, saquinavir and ritonavir, both of which are CYP3A4 substrates.

• Numerous drug interaction studies have been conducted with sildenafil.
• Co-administration with nitrates causes synergistic blood pressure lowering.
• This interaction can lead to life-threatening hypotension and cardiovascular collapse.
• Alpha-blockers (e.g., tamsulosin) can enhance the blood pressure-lowering effect.
• A separation of at least 4 hours between alpha-blocker and sildenafil dose is advised.
• HIV protease inhibitors significantly increase sildenafil AUC (up to 11-fold).
• A maximum sildenafil dose of 25mg in a 48-hour period is recommended with ritonavir.
• Other CYP3A4 inhibitors require similar dose reductions and cautious use.
• No significant interaction was observed with tolbutamide, warfarin, or alcohol.
• Alcohol can increase the potential for orthostatic hypotension and dizziness.
• Always assume a potential interaction exists with any new medication.

VIAGRA (50 mg) did not potentiate the increase in bleeding time caused by aspirin (150 mg).

Sildenafil at steady state, at a dose not approved for the treatment of erectile dysfunction (80 mg t.i.d.) resulted in a 50% increase in AUC and a 42% increase in Cmax of bosentan (125 mg b.i.d.).

• The societal impact of sildenafil has been profound since its introduction.
• It helped destigmatize the discussion and treatment of erectile dysfunction.
• It spawned a multi-billion dollar market for sexual health pharmaceuticals.
• The "Viagra" brand name became one of the most recognized in the world.
• It led to increased research and development in urology and sexual medicine.
• It also raised important questions about medicalization and lifestyle drugs.
• Direct-to-consumer advertising for ED treatments became widespread.
• It prompted debates about insurance coverage for quality-of-life medications.
• The success of sildenafil accelerated research into other PDE5 inhibitors.
• It highlighted the importance of serendipity in drug discovery.
• Its impact extends beyond medicine into cultural and social spheres.

Sildenafil was not carcinogenic when administered to rats for 24 months at a dose resulting in total systemic drug exposure (AUCs) for unbound sildenafil and its major

metabolite of 20- and 38- times, for male and female rats, respectively, the exposures observed in human males given the Maximum Recommended Human Dose (MRHD) of 100 mg.

Dosing & Uses

Absorption and Distribution: VIAGRA is rapidly absorbed. When VIAGRA is taken with a high fat meal, the rate of absorption is reduced, with a mean delay in Tmax of 60 minutes and a mean reduction in Cmax of 29%. Based upon measurements of sildenafil in semen of healthy volunteers 90 minutes after dosing, less than 0.001% of the administered dose may appear in the semen of patients. Metabolism and Excretion: Sildenafil is cleared predominantly by the CYP3A4 (major route) and CYP2C9 (minor route) hepatic microsomal isoenzymes. The major circulating metabolite results from N-desmethylation of sildenafil, and is itself further metabolized.

How should I store sildenafil?

This metabolite has a PDE selectivity profile similar to sildenafil and an in vitro potency for PDE5 approximately 50% of the parent drug. Plasma concentrations of this metabolite are approximately 40% of those seen for sildenafil, so that the metabolite accounts for about 20% of sildenafil's pharmacologic effects. After either oral or intravenous administration, sildenafil is excreted as metabolites predominantly in the feces (approximately 80% of administered oral dose) and to a lesser extent in the urine (approximately 13% of the administered oral dose). Similar values for pharmacokinetic parameters were seen in normal volunteers and in the patient population, using a population pharmacokinetic approach. Geriatrics: Healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil, resulting in approximately 84% and 107% higher plasma AUC values of sildenafil and its active N-desmethyl metabolite, respectively, compared to those seen in healthy younger volunteers (18–45 years). Sildenafil was not carcinogenic when administered to mice for 18–21 months at dosages up to the Maximum Tolerated

Dose (MTD) of 10 mg/kg/day, approximately 0.4 times the MRHD on a mg/m2 basis in a 50 kg subject.

• Special populations require careful consideration before prescribing.
• In elderly patients (65+), clearance may be reduced; start with a lower dose.
• No dose adjustment is typically needed for patients with mild renal impairment.
• For moderate renal impairment (CrCl 30-80 mL/min), caution is advised.
• In severe renal impairment (CrCl <30 mL/min), a 25mg dose is often recommended.
• For hepatic impairment (Child-Pugh A and B), a 25mg starting dose is advised.
• Sildenafil is not recommended for patients with severe hepatic impairment.
• Safety and efficacy in pediatric patients for ED have not been established.
• Revatio is approved for pediatric PAH patients aged 1 year and older.
• The dose for pediatric PAH is based on body weight and must be carefully calculated.
• Use during pregnancy is only for PAH and requires a careful risk/benefit analysis.

In clinical studies, VIAGRA was assessed for its effect on the ability of men with erectile dysfunction (ED) to engage in

If you take too much

Due to age-differences in plasma protein binding, the corresponding increase in the AUC of free (unbound) sildenafil and its active N-desmethyl metabolite were 45% and 57%, respectively [see Dosage and Administration (2.5), and Use in Specific Populations (8.5)] Renal Impairment: In volunteers with mild (CLcr=50–80 mL/min) and moderate (CLcr=30–49 mL/min) renal impairment, the pharmacokinetics of a single oral dose of VIAGRA (50 mg) were not altered. In volunteers with severe (CLcr <30 mL/min) renal impairment, sildenafil clearance was reduced, resulting in approximately doubling of AUC and Cmax compared to age-matched volunteers with no renal impairment [see Dosage and Administration (2.5), and Use in Specific Populations (8.6)]. In addition, N-desmethyl metabolite AUC and Cmax values significantly increased by 200% and 79%, respectively in subjects with severe renal impairment compared to subjects with normal renal function. Hepatic Impairment: In volunteers with hepatic impairment (Child-Pugh Class A and B), sildenafil clearance was reduced, resulting in increases in AUC (85%) and Cmax (47%) compared to age-matched volunteers with no hepatic impairment. The pharmacokinetics of sildenafil in patients with severely impaired hepatic function (Child-Pugh Class C) have not been studied [see Dosage and Administration (2.5), and Use in Specific Populations (8.7)].

Sildenafil may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

Therefore, age >65, hepatic impairment and severe renal impairment are associated with increased plasma levels of sildenafil. A starting oral dose of 25 mg should be considered in those patients [see Dosage and Administration (2.5)]. Sildenafil metabolism is principally mediated by CYP3A4 (major route) and CYP2C9 (minor route). Cimetidine (800 mg), a nonspecific CYP inhibitor, caused a 56% increase in plasma sildenafil concentrations when co-administered with VIAGRA (50 mg) to healthy volunteers. When a single 100 mg dose of VIAGRA was administered with erythromycin, a moderate CYP3A4 inhibitor, at steady state (500 mg bid for 5 days), there was a 160% increase in sildenafil Cmax and a 182% increase in sildenafil AUC. sexual activity and in many cases specifically on the ability to achieve and maintain an erection sufficient for satisfactory sexual activity.

VIAGRA was evaluated primarily at doses of 25 mg, 50 mg and 100 mg in 21 randomized, double-blind, placebo-controlled

• Numerous clinical guidelines mention the use of sildenafil for ED and PAH.
• The American Urological Association (AUA) guidelines include sildenafil as first-line therapy.
• The European Association of Urology (EAU) guidelines provide similar recommendations.
• For PAH, guidelines from the ACCP and ESC/ERS recommend PDE5 inhibitors.
• Sildenafil is often recommended as monotherapy or in combination for PAH.
• Guidelines emphasize the importance of patient assessment and counseling.
• They recommend starting with the lowest effective dose and titrating as needed.
• Guidelines caution against use in patients with cardiovascular instability.
• Regular follow-up is recommended to assess efficacy and adverse effects.
• Treatment should be part of a comprehensive management plan for the condition.
• Guidelines are regularly updated as new evidence emerges from clinical trials.

trials of up to 6 months in duration, using a variety of study designs (fixed dose, titration, parallel, crossover).

5.6 Combination with Other PDE-5 inhibitors

The mean times (adjusted for baseline) to onset of limiting angina were 423.6 and 403.7 seconds for sildenafil (N=70) and placebo, respectively. These results demonstrated that the effect of VIAGRA on the primary endpoint was statistically non-inferior to placebo. Effects of VIAGRA on Vision: At single oral doses of 100 mg and 200 mg, transient dose-related impairment of color discrimination was detected using the Farnsworth-Munsell 100-hue test, with peak effects near the time of peak plasma levels. Subjects in the study reported this finding as difficulties in discriminating blue/green. An evaluation of visual function at doses up to twice the maximum recommended dose revealed no effects of VIAGRA on visual acuity, intraocular pressure, or pupillometry.

Patient resources

VIAGRA is rapidly absorbed after oral administration, with a mean absolute bioavailability of 41% (range 25–63%). The pharmacokinetics of sildenafil are dose-proportional over the recommended dose range. It is eliminated predominantly by hepatic metabolism (mainly CYP3A4) and is converted to an active metabolite with properties similar to the parent, sildenafil. Both sildenafil and the metabolite have terminal half lives of about 4 hours. Mean sildenafil plasma concentrations measured after the administration of a single oral dose of 100 mg to healthy male volunteers is depicted below: Figure 5: Mean Sildenafil Plasma Concentrations in Healthy Male Volunteers. VIAGRA was administered to more than 3,000 patients aged 19 to 87 years, with ED of various etiologies (organic, psychogenic, mixed) with a mean duration of 5 years.

Usual Geriatric Dose for Erectile Dysfunction

Concomitant administration of strong CYP3A4 inducers, such as rifampin, is expected to cause greater decreases in plasma levels of sildenafil. Single doses of antacid (magnesium hydroxide/aluminum hydroxide) did not affect the bioavailability of VIAGRA. In healthy male volunteers, there was no evidence of a clinically significant effect of azithromycin (500 mg daily for 3 days) on the systemic exposure of sildenafil or its major circulating metabolite. Pharmacokinetic data from patients in clinical trials showed no effect on sildenafil pharmacokinetics of CYP2C9 inhibitors (such as tolbutamide, warfarin), CYP2D6 inhibitors (such as selective serotonin reuptake inhibitors, tricyclic antidepressants), thiazide and related diuretics, ACE inhibitors, and calcium channel blockers. The AUC of the active metabolite, N-desmethyl sildenafil, was increased 62% by loop and potassium-sparing diuretics and 102% by nonspecific beta-blockers.

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