Your doctor may adjust your dose as needed and tolerated. Store mixed oral liquid in the refrigerator. Slowly pull back the plunger until the required dose. You can take it up to 4 hours before you want to have sex. What is Telemedicine? How to take tablets Swallow tablets whole with a drink of water or juice but not grapefruit juice.Viagra is a phosphodiesterase type 5 (PDE5) test1.ru5 is an enzyme that affects blood flow. Potential benefits. We know that in men, Viagra dilates blood vessels and increases the flow of.  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be . Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when you get sexually excited.