Sildenafil Citrate is a selective inhibitor of cyclic guanosine monophosphate (cGMP) specific phosphodiesterase type 5 (PDE5). Sildenafil Citrate is designated chemically as 1-[[3-(6,7 dihydro-1-methyl-7-oxo-3-propyl-1 H- pyrazolo [4,3-d] pyrimidin-5-yl)-4-ethoxyphenyf] sulfonyl]-4-methylpiperazine citrate with a molecular weight of 666.7

Sildenafil is a unique medicine in the group that helps the erection of penis and stay rigid enough to complete the sexual activity on stimulation. It does not increase the desire to have sexual intercourse nor it induces fertility. The drug acts by enhancing the smooth muscle relaxant effects of Nitric Oxide that is normally released in response to stimulation. Comit dilates the arteries in the penis and thus allows filling of blood into the sinusoids. As the penis hardens, the veins are compressed restricting the blood flow out of the penis; the filling of blood in the penile spaces causes erection.

This drug is rapidly absorbed after anal administration, with absolute bioavailability of about 40%. It has a rapid onset of action usually within one hour of taking the dose. Sildenafil is widely distributed into tissues and is approximately 96% bound to plasma proteins. It is metabolized predominantly by hepatic metabolism and is converted to an active metabolite. Both Sildenafil and Its metabolite have a plasma half-life of approximately 4 hours. Therefore, it is not expected to accumulate when taken more than once daily. Sildenafil is ' excreted predominantly as metabolite in the faeces and to a lesser extent in the form of urine. Clearance may be reduced in the elderly and the patients with severe renal or hepatic impairment.

The evaluation of Erectile Dysfunction should include a determination of potential underlying causes and the identifications of appropriate treatment following complete medical assessment. The cardiovascular risks of sexual activity may be advisable because of their underlying cardiovascular status. Caution is required in patients with renal or hepatic impairment and dosage reduction may be necessary. Care is also needed in patients with anatomical and hematological disorders, which may predispose them to Priapism (painful erection greater than 6 hours in duration) and may be advisable in those with bleeding disorders or active peptic ulceration. The safety of Sildenafil is uncertain in patients with hypotension (BP < 90 / 95) or hypertension (BP > 170 / 110) a recent history of stroke or myocardial infarction.

Prolonged erection greater than 4 hours and Priapism have been reported infrequently. In an event, an erection persists longer than 4 hours; the patient should seek immediate medical assistance. If Priapism is not treated immediately, it could result in penile tissue damage and permanent loss of potency.

Low Blood Pressure, mild and transient headache, flushing and dyspepsia and increased sensitivity to light, urinary or respiratory tract infection, Priapism. Acute myocardial infarction after taking Sildenafil has been noted in US.

The usual dose of Sildenafil is 50mg to be taken about one hour before sexual intercourse. The dose may be increased to 10Omg once a day or decreased to 25mg in case of elderly patients and in those with severe renal or hepatic impairment and could later be increased according to response if appropriate.