Drug Breakdown: sildenafil (Viagra)

Dr Sharon Rees @reesprescribe

Day 1: #sildenafil #Viagra was originally conceived and licensed as a drug for hypertension/angina. During clinical trials, the side effect of enhancing male erectile function was reported, and further trials led to licensing for erectile dysfunction (ED) in US/Europe in 1998. #Viagra was disallowed on NHS, except in special groups, due to concerns that demand for ‘performance enhancement’ could cost >1 billion!. Restrictions were removed in 2014 after generic #sildenafil became available. Now available over the counter in UK.

Dr Sharon Rees @reesprescribe

Day 2: #Viagra dosing for ED is 25–100 mg oral once daily. Typically given as a 50mg single dose 1 hour pre-sexual activity. Maximum 1 dose/day. Unlicensed use for digital ulcers, eg in Raynaud's phenomenon. Used for pulmonary hypertension for all ages, but unlicensed under 1 year old.

Dr Sharon Rees @reesprescribe

Day 3: #Viagra has fast oral absorption (food slows especially if high fat) and a high volume of distribution. Metabolised by CYP3A4 and 2C9 (minor), which release an active metabolite with ~ 50% potency of the parent drug. Primary excretion in faeces, but about 13% is renal. Dose adjustment in severe renal impairment is recommended. T½ 3–5 hrs.