Comparison of the toxicity of methylcyclopentadienyl manganese tricarbonyl with that of its two major metabolites.

Pneumotoxicity and lethality resulting from administration of methylcyclopentadienyl manganese tricarbonyl (MMT) and its 2 major metabolites in rats were compared. Following i.p. injection, MMT was found to have an LD50 value of 12.1 mg/kg. Neither of the metabolites appeared to have significant acute toxicity even when doses as high as 250 mg/kg were given. This impressive difference in toxicity may be due in part to changes in solubility of the metabolites, allowing for (1) decreased distribution into the central nervous system, coupled with (2) a more rapid excretion rate. This suggests that the oxidative metabolism of MMT that results in the formation of these metabolites is an important detoxifying pathway.