content: color: white to off-white crystalline powder solubility: 3.5 mg/ml in water molecular weight:666.7. sildenafil is a drug used to treat erection difficulties, such as erectile dysfunction (ed). since it first became available in 1998, the prescription drug sildenafil has helped about 16 million men around the world improve their sex lives. and no other therapy or prescription drug for erectile dysfunction has been studied as much or has the same amount of real-world experience as sildenafil since its launch. fact is, when taken correctly, sildenafil works for most men. sildenafil improves erections in most men no matter how long they have had ed, what caused it, how often they have it, or how old they are. and sildenafil has been proven to work in clinical studies of thousands of men. sildenafil is a prescription drug that works by increasing blood flow to the penis. it is not a hormone or an aphrodisiac. once you take it, sildenafil can work in as quickly as 30 minutes. sildenafil works for 4 hours so you can set your own pace. pharmacology relaxation of the smooth muscle cells of the corpus cavernosum leads to penile erection. this relaxation may be mediated by nitric oxide via cyclic guanosine monophosphate (cgmp). sildenafil is an inhibitor of type 5 -cgmp phosphodiesterase. sidenafil inhibits the breakdown of cgmp in erectile tissues and therefore aids the action of the nitric oxide/cgmp induced erection. sildenafil is well absorbed and reaches its maximum plasma levels an hour after ingestion. food delays absorption. it has a terminal half-life of 4-5 hours. there should be no accumulation of the drug if used once-daily. efficacy penile tumescence (in association with sexual stimulation) has been found to occur 30-40 minutes after dosing.