Dapsone

How it works

It inhibits bacterial folate synthesis by competing with para-aminobenzoic acid for dihydropteroate synthase, and separately suppresses neutrophil function, which underlies its anti-inflammatory activity.

Prescribing in practice

• Dose-related haemolysis and methaemoglobinaemia occur, and the risk is markedly increased in glucose-6-phosphate dehydrogenase (G6PD) deficiency, so screen for G6PD status before starting.
• Dapsone hypersensitivity syndrome is a potentially fatal reaction presenting with fever, rash, and organ involvement, typically within the first weeks of treatment.
• Agranulocytosis and other blood dyscrasias can occur, warranting periodic blood count monitoring.

Monitoring

Monitor full blood count regularly and watch for clinical signs of haemolysis, methaemoglobinaemia, and hypersensitivity, particularly during the early weeks of therapy.

Counselling the patient

• Report fever, rash, sore throat, unusual tiredness, or breathlessness promptly as these may indicate a serious reaction.
• Bluish discoloration of the lips or skin may reflect methaemoglobinaemia and should be reported.

Evidence & guidelines

Use is supported by long-standing clinical experience and established UK practice, with MHRA guidance highlighting the risks of dapsone hypersensitivity syndrome and haematological effects.