Sildenafil

How it works

It selectively inhibits PDE5, the enzyme that breaks down cyclic GMP, thereby enhancing nitric oxide-mediated smooth muscle relaxation and increasing blood flow into the corpus cavernosum during sexual stimulation.

Prescribing in practice

• It is absolutely contraindicated with nitrates or nicorandil because the combination can cause profound, potentially fatal hypotension.
• It should be avoided or used with caution in recent stroke or myocardial infarction, significant cardiovascular disease and severe hepatic impairment.
• Caution and dose consideration apply with alpha-blockers and potent CYP3A4 inhibitors owing to additive hypotension and increased exposure.

Monitoring

Assess cardiovascular fitness for sexual activity before prescribing and review efficacy and tolerability rather than relying on routine laboratory monitoring.

Counselling the patient

• Never take this with nitrate heart medicines or recreational nitrates ('poppers').
• Seek urgent medical help for an erection lasting several hours or for sudden loss of vision or hearing.
• It works only with sexual stimulation and a high-fat meal can delay its onset.

Evidence & guidelines

Sildenafil is an established first-line PDE5 inhibitor for erectile dysfunction; see NICE guidance and the SPC for indications and cautions.