Sildenafil usually should not be taken more than once every 24 hours. Follow the manufacturer’s directions to use and clean the oral syringe. Sildenafil may cause side effects. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. Make sure you have discussed any other medications you are currently taking or plan to take before starting sildenafil with your doctor and pharmacist. Tell your doctor if any of these symptoms are severe or do not go away: headache. If you are a Mayo Clinic patient, this could include protected health information.$ retail Save 91% $ Get free savings Most popular Safeway $ retail Save 94% $ Get free savings Low price Walgreens $ retail Save 94% $ Get free savings directions Closest store Rite Aid. 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 adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels.  · Medically reviewed by test1.ru Last updated on Applies to the following strengths: 10 mg/mL; 10 mg/ mL; 20 mg; 25 mg; 50 mg; mg Usual Adult Dose for: Erectile Dysfunction Pulmonary Hypertension Usual Geriatric Dose for: Erectile Dysfunction Additional dosage information: Renal .