Sildenafil citrate, marketed under brand name of VIAGRA®, is a selective cyclic GMP-specific phosphodiesterase (PDE-5) inhibitor drug that is prescribed for erectile dysfunction in men. Though most of the erectile dysfunction etiologies are psychogenic, sildenafil citrate is beneficial in physiological erectile dysfunction.
Nitric oxide is the key biochemical that increases blood flow in the penile muscles, which cause erection, and it is metabolized by c-GMP-specific phosphodiesterase. During sexual activity, nitric oxide is produced and degraded simultaneously.
Sildenafil citrate increases the activity of nitric oxide by inhibiting the degrading enzyme and thereby promotes increased blood flow in the penis and also the erection. Though rarely prescribed, sildenafil citrate is also beneficial in the treatment of pulmonary arterial hypertension (PAH) and altitude sickness (Revatio).
The intestinal absorption of sildenafil citrate is rapid, within one hour. The absorption is delayed, if used after food intake. The plasma half-life of sildenafil citrate is 3-4 hours, and then the drug may lose its potency/therapeutic activity in the body.
Primarily, sildenafil citrate is excreted in faeces and also in urine. Sildenafil citrate is a prescription drug that is sold as 25mg, 50mg and 100mg film (enteric) coated tablets. Sildenafil citrate is mostly (brand name VIAGRA) available in blue colour, in round or diamond-shaped tablets.