Sulfone antibiotic / immunomodulator Pregnancy: In leprosy, benefits are generally considered to outweigh potential risk to the pregnant patient; some leprologists recommend folic acid 5 mg daily supplementation during pregnancy. Excreted in breast milk (a report of haemolytic anaemia in a breast-fed infant).

Dapsone

Brand names: various

Dapsone is a sulfone antibacterial and anti-inflammatory agent used in the treatment of leprosy, Pneumocystis jirovecii pneumonia prophylaxis, and dermatological conditions such as dermatitis herpetiformis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 100 mg (leprosy); 50 mg initially (dermatitis herpetiformis)

Route: Oral

Frequency: Daily (regimen varies by indication)

Adults and children over 12 years. Multibacillary leprosy (3-drug regimen): 100 mg daily for at least two years. Paucibacillary leprosy (2-drug regimen): 100 mg daily for at least 6 months. Malaria prophylaxis: 100 mg weekly with 12.5 mg pyrimethamine. Dermatitis herpetiformis: initially 50 mg daily, gradually increasing to 300 mg daily if required; once lesions subside reduce to a minimum as soon as possible, usually 25-50 mg daily. Pneumocystis carinii (jirovecii) pneumonia: in combination with trimethoprim, 50-100 mg daily; or 100 mg twice weekly, or 200 mg once weekly. Elderly: reduce dose where there is impairment of hepatic function. Tablets swallowed whole with water. Paediatric (children 6-12 years, leprosy): multibacillary 50 mg daily for at least two years; paucibacillary 50 mg daily for at least 6 months. Children under 6 years: safety and efficacy not established, no data.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to dapsone, sulfonamides, sulfones, or to any of the excipients
Severe anaemia
Porphyria
Severe glucose-6-phosphate dehydrogenase (G6PD) deficiency

Side effects

Haemolysis and methaemoglobinaemia (dose-related, most frequent); haemolytic anaemia
Agranulocytosis (rare)
Dapsone syndrome (rash, fever, eosinophilia; can progress to exfoliative dermatitis, hepatitis, psychosis; deaths recorded)
Peripheral and peripheral motor neuropathy
Hepatitis, jaundice, changes in liver function tests

Interactions

Oral typhoid vaccine: do not take until at least three days after finishing a course of dapsone (dapsone could make the vaccine less effective)
Probenecid: reduces dapsone excretion and increases dapsone plasma concentrations
Rifampicin / rifabutin: increases plasma clearance of dapsone
Saquinavir: should not be used in combination (risk of irregular heartbeat)
Trimethoprim: increased dapsone and trimethoprim concentrations reported on concurrent administration

Clinical monograph

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.

Reference: WHO leprosy; BHIVA OI; BAD; UKHSA; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways