organic nitrates interact with sildenafil to cause severe hypotension - concurrent use of sildenafil with nitric oxide donors or nitrites is contraindicated
other contraindications include hypotension (blood pressure below 90/50 mmHg), severe hepatic impairment, hereditary degenerative retinal disorders such as retinitis pigmentosa, recent stroke or myocardial infarction.
sildenafil should be used with caution in patients with a condition predisposing to priapism e.g. sickle cell anaemia, multiple myeloma, or leukaemia; in any patient with a penile deformity (e.g. Peyronie's disease); in those patients with active peptic ulcer disease or a bleeding disorder.
sildenafil is metabolised mainly by the cytochrome P450 system - the plasma levels of sildenafil are increased if there is concurrent use of another drug that is a cytochrome P450 inhibitor e.g. cimetidine. The manufacturer recommends that a starting dose dose of sildenafil 25mg should be considered if concurrently using a drug that is metabolised by the cytochrome P450 system.
there is no data, at present, for the use of sildenafil in males under 18 years of age, or women, and therefore sildenafil is at present contraindicated for these groups
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