No dose adjustment is required for mild to moderate hepatic impairment. What should I do if I forget a dose? In this case, just leave out the missed dose and take your next dose at the usual time. Occasionally patients may be asked to monitor their blood pressure and pulse after being newly prescribed sildenafil, after an increase in dosage, or after the addition of CYP3A4 inhibitors. The onset of action can occur within 30 minutes, while the duration of the effect can last up to 18 hours.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . Refill and transfer prescriptions online or find a CVS Pharmacy near you. Shop online, see ExtraCare deals, find MinuteClinic locations and more.  · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose.