The Pharmacotherapy of Blood Intoxication (Methmoglobinemia) Induce by Exposure to Ortho-Chlorobenzylidenemalononitrile (CS) in Public Protests

Background: Acquired Methemoglobinemia(MetHb) is a rare, but potentially serious and unfamiliarity with this complication may delay diagnosis and appropriate therapy.

Presentation: A case of methemoglobinemia occurring in male teenage demonstrator as a complication of re-current exposure to ortho-chlorobenzylidenemalononitrile (CS) in public protests , the patient became cyanotic with a decrease in his level of consciousness, by the effect of hydrogen cyanide as by-product of (CS), resulting in a toxic methemoglobinemia level in his blood. Methemoglobin is incapable of carrying oxygen and is formed when the ferrous iron in the heme molecule is oxidized to the ferric state. The diagnosis should be entertained when cyanosis, unresponsive to 100% oxygen therapy, appears suddenly, especially when exposure to an oxidant agent is established.

Treatment: The patient received a 1 mg/kg dose of methylene blue intravenously. A cooximetry done 1 hour later showed a methemoglobin level of 43%. A second 1 mg/kg dose of methylene blue was given and another hour later the methemoglobin level had dropped to 13%. The patient also showed clinical improvement with resolution of the cyanosis and return of his mental status to baseline.

Conclusion: Methylene blue is the specific antidote, but should be reserved for more severe cases or if co-morbid conditions make mild hypoxia un advisable.