Lessons to be learned: a case study approach: prolonged methaemoglobinaemia due to inadvertent dapsone poisoning;...

The authors present a case of methaemoglobinaemia of acute onset, with an unusually 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 instead of an antispasmodic that had been prescribed for a spinal condition; this was because the tablets had been incorrectly labelled and dispensed in a pharmacy. The patient took increasing doses of the presumed 'antispasmodic' tablets as they seemed to lack clinical effect, thus further exacerbating the toxic consequences. Moreover, the patient brought his wrongly labelled tablets into hospital and was allowed to use them there, contrary to normal hospital policy. As treatment for the methaemoglobinaemia both bolus and continuous infusions of methylene blue were used, which probably contributed to the severe haemolysis which followed. Furthermore, the development of a rare side effect of dapsone toxicity, namely that of a sensorimotor neuropathy, is reported.