J Emerg Med 2013 Feb 11;44(2):381-4. Epub 2012 May 11.
National University Hospital, 5 Lower Kent Ridge Road, Singapore 119074, Singapore.
Background: Chlorate poisoning as a cause of methemoglobinemia is regarded in current literature to be resistant to treatment by methylene blue due to the oxidizing and denaturing properties of the chlorate anion, and often leads to severe renal and hematological complications with a high mortality rate. Recent case studies suggest practitioners have eschewed the use of methylene blue in such situations.
Objectives: This report describes a case of chlorate poisoning presenting as severe methemoglobinemia successfully treated with methylene blue alone, believed to be a first in reported literature.
Case Report: A 34-year-old male construction worker presented 4 h after accidental ingestion of an industrial chemical, with giddiness and breathlessness. Physical examination did not reveal any abnormal cardiorespiratory findings, although arterial blood gas analysis and pulse oximetry revealed an "oxygen saturation gap." Methemoglobin levels were found to be severely elevated at 66.8% 6 h after ingestion, and the patient was promptly treated with methylene blue. Clinical examination and laboratory tests suggested the absence of hemolysis at the time of treatment. The patient was discharged after a brief and uneventful hospital stay. Subsequent tests revealed the chemical ingested to be sodium chlorate.
Conclusion: The successful outcome in our case suggests that a window of opportunity as long as 6 h may exist during which treatment of chlorate poisoning with methylene blue may be of clinical value. We postulate that the absence of significant hemolysis and hematological alterations at the time of antidote administration may be a necessary prerequisite for treatment success.