Pharmacology · Antileprosy drugs
Dapsone !
A sulfone used in leprosy multidrug therapy and dermatitis herpetiformis. It can cause haemolysis, especially in G6PD deficiency, and methaemoglobinaemia.
Updated 2026-11-01
Also called: Diaminodiphenylsulfone (DDS)
Mechanism of action
Dapsone resembles para-aminobenzoic acid (PABA) and competes with it at dihydropteroate synthase, so the bacterium cannot make folate, much like the sulfonamides. Separately, it calms neutrophils (it inhibits myeloperoxidase and the respiratory burst), which explains its use in neutrophilic skin diseases such as dermatitis herpetiformis.
- Dapsone imitates PABA
- It blocks dihydropteroate synthase
- No folate: the bacillus stops multiplying
Pharmacokinetics
- Absorption
- Rapid and almost complete by mouth
- Metabolism
- Liver, including acetylation
- Elimination
- Urine, mostly as metabolites
- Half-life
- Long and variable: about 10 to 50 hours
Indications
- Leprosy, all forms, within multidrug therapy Leprosy (Hansen disease) →
- Dermatitis herpetiformis Dermatitis herpetiformis →
- Pneumocystis pneumonia: alternative agent (dapsone is active against Pneumocystis jirovecii) Pneumocystis pneumonia (PCP) →
- Prophylaxis of toxoplasmosis Toxoplasmosis →
Adverse effects
Common
- Dose-related haemolysis
- Methaemoglobinaemia (bluish lips, breathlessness)
- Nausea, headache
- Rash
Contraindications
- Hypersensitivity to dapsone or its derivatives
Key interactions
- Rifampicin
- Lowers dapsone levels markedly; in leprosy MDT no change is needed
- Trimethoprim
- Both drugs can raise each other's levels
- Folate antagonists such as pyrimethamine
- More blood reactions: closer blood counts
What is monitored
- G6PD testing before starting whenever possible
- Frequent blood counts, most often in the first months
- Liver tests when feasible
- Signs of methaemoglobinaemia (cyanosis, breathlessness)
Administration and safety
- By mouth; also in leprosy MDT blister packs
- A topical gel form exists for acne; it is a different use
- Severe anaemia is corrected before starting
Nursing care
- Confirm the G6PD result before the first dose when available
- Teach to report sore throat, fever, pallor, bruising or rash
- Watch for bluish lips or breathlessness (methaemoglobinaemia)
- Explain that leprosy reactions are not allergy and do not mean MDT is stopped
Pregnancy and breastfeeding
Used in pregnancy only if clearly needed; it passes into breast milk in substantial amounts and can cause haemolysis in the newborn.
Test yourself
Think of the answer, then tap the question to see it.
How does dapsone stop M. leprae?
It imitates PABA and blocks dihydropteroate synthase, so the bacillus cannot make folate.
A patient on dapsone has bluish lips and normal oxygen on the blood gas. What do you suspect?
Methaemoglobinaemia caused by dapsone.
Which skin disease responds well to dapsone besides leprosy?
Dermatitis herpetiformis, thanks to its anti-neutrophil effect.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - DAPSONE 100MG tablet DAPSONE 25MG tablet (DailyMed (U.S. National Library of Medicine), 2026); Leprosy (World Health Organization (WHO), 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 65 (McGraw Hill, 2023).
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