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Sildenafil relaxes muscles and increases blood flow to particular areas of the body.
Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women.
Sildenafil inhibits phosphodiesterase type-5 (PDE5) which is responsible for cGMP degradation in the corpus cavernosum. Inhibition of PDE5 increases cGMP levels in the corpus cavernosum which results in smooth muscle relaxation and inflow of blood to the corpus cavernosum.
Rapidly absorbed after oral admin. Bioavailability: about 40%.
Widely distributed. Plasma protein binding: 96%.
Metabolised in the liver mainly by CYP3A4 and CYP2C9.
Excreted as metabolites mainly in the faeces.
Information Not Available
Headache, flushing, respiratory tract infection, angina pectoris, AV block, migraine, syncope, tachycardia, postural hypotension, MI, cerebral thrombosis, cardiac arrest, paraesthesia, tremor, depression, herpes simplex, skin ulcer, oesophagitis, abnormal LFT, rectal haemorrhage, hypoglycaemic reaction, arthritis, deafness, retinal vascular disease, photosensitivity, accidental fall.
Should be managed by standard supportive care.
Caution when used in patients with anatomical deformation of penis or conditions that may predispose them to priapism (e.g. sickle cell anaemia, myeloma, or leukaemia). Mild, transient, dose-related impairment of colour discrimination (blue/green) may occur. Hepatic or severe renal impairment, bleeding disorders, active peptic ulceration, hypotension, recent history of stroke, MI, arrhythmias, unstable angina, heart failure or retinal disorders. May cause sudden loss or decrease in hearing.
Inhibitors of CYP3A4 such as cimetidine and erythromycin are likely to reduce sildenafil clearance. CYP3A4 inducers such as rifampicin may decrease the plasma concentrations of sildenafil. Symptomatic hypotension when used with α-blockers. Plasma concentrations are increased by ritonavir.
Potentially Fatal: May potentiate hypotensive effects of of organic nitrates and nicorandil.
Concurrent admin with grapefruit juice may lead to increased plasma levels of sildenafil.
Adult: 50 mg about 1 hour before sexual intercourse. May adjust dose depending on penile response. Max: 100 mg/dose and not to be taken > once in 24 hours.
Elderly: >65 years: Lower initial dose at 25 mg.
CrCl (ml/min) Dosage Recommendation
<30 Initially, 25 mg.
Hepatic impairment: Initially, 25 mg.
For patients taking drugs which are CYP3A4 inhibitors: initially, 25 mg. For patients on ritanavir, not >25 mg every 48 hours. Patients who are stabilised on α-blocker treatment should use an initial dose of 25 mg. Higher doses should not be taken within 4 hours of an α-blocker.
May be taken with or without food
Either animal-reproduction studies have not demonstrated a foetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the 1st trimester (and there is no evidence of a risk in later trimesters).
Safety and efficacy not established
Dose selection should be cautious, usually starting at the lower end of the dosing range, reflecting the greater frequency of decreased hepatic and renal function and comorbidity.
Consider initial dose of 25 mg in patients older than 65 years of age.
Hypersensitivity. Patients concurrently or intermittently using organic nitrates in any form.
Store at 15-30°C
Store at 15-30°C