· Proper Use. Drug information provided by: Merative, Micromedex ®. Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more .Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Use the oral syringe provided with your medication to measure and take your dose. Different brands may not work the same way. Children—Use is not recommended. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. However the dose is usually not more than 40 mg 3 times a day.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 .  · Proper Use. Drug information provided by: Merative, Micromedex ®. Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more . Cost. Overdose. Ask your doctor. Q&A. Drug Images. What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a .If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. You may take this medicine with or without food. To use the oral liquid: Shake the bottle well for at least 10 seconds before each use. Read and follow these instructions carefully before you start using sildenafil and each time you get a refill of your medicine. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. The following information includes only the average doses of this medicine.