Methaemoglobinaemia dapsone

Dermatitis herpetiformis Dapsone is typically effective in 24 h, or sulfapyrldine. Prolonged therapy necessary, a gluten-free diet can help, Antipruritics locally as required. Not other sulphonamides benef dal effect not due to antimicrobial action. Methaemoglobinaemia may complicate dapsone therapy. 

Methaemoglobinaemia may be induced by oxidising drugs sulphonamides, nitrites, nitrates (may also occur in drinking water), primaquine, -caine local anaesthetics, dapsone, nitrofurantoin, nitroprusside, vitamin K analogues, chlorates, aniline and nitrobenzene. In the rare instance of there being urgency, methylene blue 1 mg/kg slowly i.v. benefits within 30 min. (Ascorbic acid competes directly with the chemical cause but is inadequate in severe cases, which are the only ones that need treatment.)... 

Southgate HJ, Masterson R. Lessons to be learned a case study approach prolonged methaemoglobinaemia due to inadvertent dapsone poisoning treatment with methylene blue and exchange transfusion. J R Soc Health 1999 119(l) 52-5. 

Falkenhahn M et al Unexplained acute severe methaemoglobinaemia in a young adult. Br J Anaesth 2001 Feb 86(2) 278-280. [PMID 11573675] (A young woman developed methemoglobinemia [47%] due to dapsone.)... 

Hydroxylamine is assumed to be responsible for the haematological toxicity of dapsone (methaemoglobinaemia). The findings of this study suggest that the production of this metabolite is mediated via the cytochrome P450 isoenzyme CYP2C9, which fluconazole inhibits. 

Cimetidine raises serum dapsone ievels, and may reduce methaemoglobinaemia due to dapsone. Cimetidine, ranitidine and omeprazole do not appear to affect the outcome of dapsone prophylaxis against Pneumocystis pneumonia. The absorption of dapsone does not appear to be altered by nizatidine-induced increases in gastric pH. 

The interaction between dapsone and rifampicin is established but of uncertain clinical importance. Concurrent use should be well monitored to confirm that treatment is effective. It may be necessary to raise the dosage of dapsone. It has been pointed out that there is the risk of treatment failures for Pneumocystis pneumonia as well as for leprosy. Also be alert for any evidence of methaemoglobinaemia. 

Rifampicin increases the urinary excretion of dapsone, lowers its serum ieveis and increases the risk of toxicity (methaemoglobinaemia). Simiiariy, rifabutin increases the clearance of dapsone, and may also increase its toxicity. 

Information is limited. The difference between the results of the two studies may be because the first was in AIDS patients with Pneumocystis pneumonia and the second was in asymptomatic HIV-positive patients whose drug metabolism may possibly be different. Concurrent use appears to be an effective form of treatment, but be alert for evidence of increased dapsone toxicity (methaemoglobinaemia). 

Subramaniam A, Corallo C, Nagappan R. Dapsone-associated methaemoglobinaemia in patients with a haematologic malignancy. Anaesth Intensive Care 2010 38(6) 1070-6. 

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