Recurrent methemoglobinemia after acute dapsone intoxication in a child

Two cases of methemoglobinemia following zopiclone ingestion

INTRODUCTION

Most cases of methemoglobinemia result from exposure to certain medications and chemicals such as nitrates, nitrites, aniline, dapsone, phenazopyridine, benzocaine, and chlorates which oxidize the iron from the ferrous state. Intoxication with zopiclone is expected to produce drowsiness, confusion and coma but not methemoglobinemia. We report two cases of zopiclone overdose with methemoglobinemia.

CASE REPORTS

Case one: A 43-year-old woman presented to the emergency department two hours after ingesting 100 tablets of 7.5 mg zopiclone. Her initial vital signs, physical examination, chest x-ray, and electrocardiogram were normal. Two hours post-ingestion her methemoglobin level was 9.8%; 14 hours post-arrival she showed cyanosis of the lips and extremities and dyspnea after walking. The blood sample 16 hours post-ingestion was dark brown in color and the methemoglobin was 23.8%. Shortly after the second of two doses of methylene blue (1 mg/kg each) her methemoglobin was 3.6%. Case two: A 30-year-old woman came to the emergency department 50 hours after ingesting 150 to 200 tablets of 7.5 mg zopiclone. Her vital signs and physical examination were normal. Her methemoglobin level was 5.2% at 52 hours post-ingestion and it peaked at 10.4% one hour later. She recovered following symptomatic care.

DISCUSSION AND CONCLUSIONS

Methemoglobinemia has not previously been reported following acute zopiclone overdose. In our patients, there were no identifiable alternative causes explaining the methemoglobinemia and zopiclone was confirmed in both patients by laboratory analysis. These two cases suggest that zopiclone overdose is capable of producing delayed methemoglobinemia, which may be related to formation of a sufficient quantity of the N-oxide metabolite.

Methemoglobinemia: etiology, pharmacology, and clinical management

Methemoglobin (MHb) may arise from a variety of etiologies including genetic, dietary, idiopathic, and toxicologic sources. Symptoms vary from mild headache to coma/death and may not correlate with measured MHb concentrations. Toxin-induced MHb may be complicated by the drug's effect on other organ systems such as the liver or lungs. The existence of underlying heart, lung, or blood disease may exacerbate the toxicity of MHb. The diagnosis may be complicated by the effect of MHb on arterial blood gas and pulse oximeter oxygen saturation results. In addition, other dyshemoglobins may be confused with MHb. Treatment with methylene blue can be complicated by the presence of underlying enzyme deficiencies, including glucose-6-phosphate dehydrogenase deficiency. Experimental antidotes for MHb may provide alternative treatments in the future, but require further study.

Dapsone intoxication: two case reports

Two patients with dapsone intoxication, an adult and a 16-month-old child, are reported. Both developed symptomatic methemoglobin concentrations, of 35% and 37%, respectively, and improved with intravenous methylene blue. Methemoglobin levels subsequently rose in both cases to 25% at 24 and 37 hours, respectively. The recurrence of elevated methemoglobin levels resulted from either continued absorption of dapsone or its toxic metabolite from the gastrointestinal tract. Both patients were begun on serial oral activated charcoal and the child received a second methylene blue treatment. During the intoxication, serum hemoglobin concentrations dropped 2 gm with an increase in the reticulocyte count. Review of 20 cases of dapsone overdose from the literature showed that the major toxic manifestations are methemoglobinemia and hemolysis. Delayed sulfhemoglobinemia, reported in only one case, resolved spontaneously. The treatment of dapsone intoxication is intravenous methylene blue for symptomatic methemoglobinemia, gastric decontamination, and early administration of serial oral activated charcoal. Hemolysis is mild but transfusions may be required for patients with a glucose-6-phosphate dehydrogenase deficiency.