This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. The effectiveness of Sildenafil has been reviewed in clinical studies. Sildenafil is an on-demand pill that lasts for up to five hours. Ask your doctor if you have any questions. Do not use more of it and do not use it more often than your doctor ordered.AdGet Deals and Low Prices On sildenafil para hombres At Amazon. Explore Literature and Fictional Books Across a Range Of Genres and has been visited by 1M+ users in the past month. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or Missing: precio.  · For oral dosage form (tablets): Adults up to 65 years of age—50 Missing: precio.