If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. What special precautions should I follow? Avanafil Stendra. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Use the oral syringe provided with your medication to measure and take your dose. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* . generic Revatio and Viagra Used for Pulmonary Hypertension and Erectile Dysfunction MORE expand_more Check your prescription Prescription 20mg sildenafil (30 tablets) . Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, which is only given .