Lessens to be learned: a case study approach: Prolonged methaemoglobinaemia due to inadvertent dapsone poisoning; treatment with methylene blue and exchange transfusion

The authors present a case of methaemoglobinaemia of acute onset, with an u nusually protracted course. The long persistence of this disorder led to a search for the cause which was eventually traced to medication with dapsone . The latter was found to be inappropriately being taken by the patient ins tead of an antispasmodic that had been prescribed for a spinal condition; t his was because the tablets had been incorrectly labelled and dispensed in a pharmacy. The patient took increasing doses of the presumed 'antispasmodi c' tablets as they seemed to lack clinical effect, thus further exacerbatin g the toxic consequences. Moreover, the patient brought his wrongly labelle d tablets into hospital and was allowed to use them there, contrary to norm al hospital policy. As treatment for the methaemoglobinaemia both bolus and continuous infusions of methylene blue were used, which probably contribut ed to the severe haemolysis which followed. Furthermore, the development of a rare side effect of dapsone toxicity, namely that of a sensorimotor neur opathy, is reported.