Sexual activity may be a strain on your heart, especially if you have heart disease. In some patients, the use of VIAGRA with alpha-blockers can lead to a drop in blood pressure or to fainting medicines called HIV protease inhibitors, such as ritonavir Norvir , indinavir sulfate Crixivan , saquinavir Fortovase or Invirase , or atazanavir sulfate Reyataz some types of oral antifungal medicines, such as ketoconazole Nizoral and itraconazole Sporanox some types of antibiotics, such as clarithromycin Biaxin , telithromycin Ketek , or erythromycin other medicines that treat high blood pressure other medicines or treatments for ED VIAGRA contains sildenafil, which is the same medicine found in another drug called REVATIO. Online pharmacies can be broadly categorized as: Mail-order pharmacies are operated by pharmacy benefits managers PBMs on behalf of health insurers or providers. They require a prescription for any controlled substance and have a licensed pharmacist to answer questions rather than support staff. Sildenafil usually should not be taken more than once every 24 hours. What side effects can this medication cause?The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your. Sildenafil citrate is a white to off-white crystalline powder with a solubility of mg/mL in water and a molecular weight of VIAGRA is formulated as blue, film-coated rounded-diamond-shaped tablets equivalent to 25 mg, 50 mg and mg of sildenafil for oral administration. AdDon’t go to the pharmacy without checking prices at GoodRx® first. No commitment or fees. Find the lowest price in your neighborhood & use our free coupons to save up to 80%Service catalog: Prescription Coupons, Prescription Discounts, Online Doct.