• Metabolism: Dapsone is slowly and nearly completely absporbed from GI tract, and distributed throughout the body. It is acetylated in the liver to monoacetyl and diacetyl derivatives. The major metabolite of dapsone is monoacetyldapsone. The rate of acetylation of dapsone is genetically determined and is subject to interindividual variation, although the rate is usually constant for each individual. The drug also is hydroxylated in the liver to hydroxylamine dapsone (NOH-DDS). NOH-DDS appears to be responsible for methemoglobinemia and hemolysis induced by the drug. The metabolites are excreted moslty in the urine. Only minor amounts of dapsone are excreted in feces. (A617, A618). Route of Elimination: Renal Half Life: 28 hours (range 10-50 hours)
• Uses/Sources: For the treatment and management of leprosy and dermatitis herpetiformis. Dapsone is mainly employed for its actions against mycobacterium leprae. It is also used with pyrimethamine in the treatment of malaria, and of Pneumocystis carinii pneumonia (PCP) (A308, L1039).
• Health Effects: Methemoglobinemia and hemolysis are the main risks of acute intoxication. Hemolytic anemia, agranulocytosis, aplastic anemia and other blood dyscrasias may occur in chronic poisoning. Target organs are central and peripheral nervous systems, blood, liver and skin. Methemoglobinemia is the principal and constant feature of dapsone poisoning. Hemolytic anaemia and agranulocytosis may occur with the relatively low doses used for leprosy and malaria, whereas peripheral neuropathy and hepatitis are only observed with the higher doses used in the treatment of dermatitis herpetiformis. (L1040).
• Symptoms: Overdosage might be expected to produce nasal congestion, syncope, or hallucinations. Measures to support blood pressure should be taken if necessary.
• Treatment: Administer charcoal as a slurry following oral or parenteral exposure. (T36)
• Route of Exposure: Ingestion (L1039, T14); dermal (L1039, T14) ; eye contact (L1039, T14); inhalation (L1039, T14) Bioavailability is 70 to 80% following oral administration.

• Carcinogenicity: 3, not classifiable as to its carcinogenicity to humans. (L135)
• Toxicity: LD50: 496 mg/kg (Oral, Mouse)

Dapsone acts against bacteria and protozoa in the same way as sulphonamides, that is by inhibiting the synthesis of dihydrofolic acid through competition with para-amino-benzoate for the active site of dihydropteroate synthetase. The anti-inflammatory action of the drug is unrelated to its antibacterial action and is still not fully understood.