As in the other titration studies, patients were started on 50 mg and allowed to adjust the dose up to mg or down to 25 mg of VIAGRA; all patients, however, were receiving 50 mg or mg at the end of the study. The pharmacokinetics of sildenafil are dose-proportional over the recommended dose range. A stronger CYP3A4 inhibitor such as ketoconazole or itraconazole could be expected to have greater effect than that seen with saquinavir. Do not take it more than 3 times a day. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. 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.Viagra is available in three strengths: 25 milligrams (mg), 50 mg, and mg. What are the typical dosages of Viagra? Typically, your doctor will start you on the recommended . Most men aged 18 and over can take sildenafil for erectile dysfunction. Most adults and children aged 1 year and over can take sildenafil for pulmonary hypertension. Who may not be able to take sildenafil. Sildenafil is not suitable for some people. To make sure it’s safe for you, speak to your doctor or pharmacist before taking sildenafil if you. Erectile dysfunction is when a man has difficulty getting an erection or keeping it long enough for sex. It’s also known as ED or impotence. It happens when not enough blood flows to the penis, preventing an erection. The frequency increases with age, affecting about 50% of men over age 40*; however younger men may also experience ED.