Dapsone (Systemic)

How it works

It suppresses neutrophil function, including myeloperoxidase activity and chemotaxis, which underlies its benefit in neutrophil-rich inflammatory skin disease, distinct from its antibacterial sulfone action.

Prescribing in practice

• Screen for glucose-6-phosphate dehydrogenase deficiency before starting, as dapsone causes dose-related haemolysis and methaemoglobinaemia that are severe in deficient patients.
• Dapsone hypersensitivity syndrome (fever, rash, eosinophilia and organ involvement) is a recognised early reaction that mandates immediate withdrawal.
• Agranulocytosis and peripheral neuropathy can occur, so any unexplained infection, bruising or motor weakness must be investigated.

Monitoring

Monitor full blood count frequently in the early months and then periodically, together with reticulocytes, methaemoglobin if symptomatic, and liver function.

Counselling the patient

• Report fever, sore throat, unusual bruising, breathlessness or blue discolouration of the lips promptly.
• Some breakdown of red blood cells is expected; tell your team if you become unusually tired or breathless.
• Do not stop the medicine abruptly without advice as your skin condition may flare.

Evidence & guidelines

Dapsone is the established first-line drug treatment for dermatitis herpetiformis based on long-standing clinical evidence and is recommended in dermatology guidance.