The acute toxicity of cyclopentadienyl manganese tricarbonyl in the rat.

The acute toxicity of cyclopentadienyl manganese tricarbonyl (CMT) was studied in Sprague-Dawley rats. CMT was found to produce convulsions and pulmonary edema. The ED50s for convulsion were 32 mg/kg (95% C.I. 24-42 mg/kg) p.o. and 20 mg/kg (95% C.I. 15-26 mg/kg) i.p. The LD50s for p.o. and i.p. administration were 22 mg/kg (95% C.I. 19-26 mg/kg) and 14 mg/kg (95% C.I. 10-20 mg/kg), respectively. Approximately 13-16% of the administered dose was recovered in the urine from 0 to 48 h post-dosing. The majority of this material was present as an organometallic form of manganese other than CMT. Phenobarbital pretreatment prevented the convulsions and pulmonary damage produced by a 50 mg/kg i.p. dose of CMT. Rats pretreated with CMT (5 mg/kg, i.p.) for 3 days exhibited convulsions but no deaths after treatment with a 34 mg/kg p.o. dose of CMT. These results suggest that CMT does not require metabolic activation to produce toxic effects, and that prior exposure to CMT produces tolerance.