Bosentan

How it works

It blocks endothelin-1 at both ETA and ETB receptors on vascular smooth muscle and endothelium, reducing the vasoconstriction and proliferation that drive raised pulmonary vascular resistance.

Prescribing in practice

• Bosentan is hepatotoxic and teratogenic: liver transaminases must be monitored and reliable contraception used, with pregnancy excluded before and during treatment.
• It induces CYP3A4 and CYP2C9, reducing the efficacy of hormonal contraceptives and interacting with ciclosporin, glibenclamide and warfarin.
• Avoid co-administration with ciclosporin and glibenclamide, and use with caution alongside other potentially hepatotoxic drugs.

Monitoring

Liver transaminases should be measured before starting and at regular intervals throughout treatment, with haemoglobin also checked periodically as anaemia can occur.

Counselling the patient

• Women must use reliable non-hormonal contraception and report a missed period.
• Attend for regular blood tests to monitor the liver.
• Report jaundice, dark urine, nausea or undue tiredness promptly.

Evidence & guidelines

Randomised placebo-controlled trials in pulmonary arterial hypertension demonstrated improved exercise capacity and haemodynamics, supporting its established place in specialist treatment pathways.