Utility of Methylene Blue for the Reversal of Excessive Levels of Methemoglobin

Many new prophylactic and therapeutic compounds are being studied as potential sources of methemoglobin useful in counteracting the lethal effects of cyanide intoxication. The formation of methemoglobin also leads to a reduction in the blood oxygen carrying capacity which may, in extreme cases, lead to lethal consequences. The i.v. administration of Methylene blue rapidly reverses methemoglobin to hemoglobin. Unanticipated high levels of methemoglobin 65 - 85 in three sheep exposed to propiophenone derivatives led to a lethal outcome in one untreated sheep and complete recovery in two sheep which were treated with 3.0 mgkg methylene blue i.v. Methemoglobin was reduced to safe levels within minutes following administration. A similar exposure of dogs to propriophenone derivatives led to high levels 77 - 78 of methemoglobin which were readily reversed following the intravenous administration of the same dose of methylene blue.