Figure 4. The mean steady state volume of distribution Vss for sildenafil is L, indicating distribution into the tissues. Population Pharmacokinetics Age, gender, race, and renal and hepatic function were included as factors assessed in the population pharmacokinetic model to evaluate sildenafil pharmacokinetics in patients with PAH. The dataset available for the population pharmacokinetic evaluation contained a wide range of demographic data and laboratory parameters associated with hepatic and renal function. The major circulating metabolite results from N-desmethylation of sildenafil, and is, itself, further metabolized. Sildenafil is not expected to affect the pharmacokinetics of compounds which are substrates of these CYP enzymes at clinically relevant concentrations.Sildenafil is used to treat high blood pressure in the lungs (pulmonary hypertension). Learn more about Revatio.1 This is a generic drug. Even if this drug is covered by Medicare or your. Oral Tablet. 20 mg sildenafil oral tablet. from $ for 10 tablets. 25 mg sildenafil oral tablet. from $ for 30 tablets. 50 mg sildenafil oral tablet. from $ for 15 .  · Recommended Dosage in Adults – Oral Dosage – The recommended dosage of Sildenafil tablets are 20 mg three times a day. 3 DOSAGE FORMS & STRENGTHS. Sildenafil Tablets,USP – Sildenafil Tablets, USP are supplied as white to off white, round shaped, film-coated tablets debossed with “N7” on one side and plain on .