Background: Methaemoglobinaemia is an infrequent condition. It can be congenital or be induced by several toxic compounds. In methaemoglobin (metHb) the iron in the haem moiety of haemoglobin is oxidized from the ferrous (Fe2+) to the ferric state (Fe3+). This complex is dark brown and unable to transport oxygen. Combined with a leftward shift in the oxyhaemoglobin dissociation curve this leads to decreased tissue oxygenation with subsequent hypoxic features in patients.
Case reports: We report two cases of dapsone-induced methaemoglobinaemia. The blood, mucosa and nail beds adopted a brown-bluish appearance which was used diagnostically. One patient was treated effectively with repeated injections of methylene blue, which reduces methaemoglobin. In the other patient, the methaemoglobin level declined with a T50 of 50 hours. Both patients had few symptoms and made an uneventful recovery.
Interpretation: The hypoxia in methaemoglobinaemia may be effectively treated with methylene blue. Repeated injections may be necessary.