Interactions between cimetidine, methylparathion, and parathion.

The purpose of this study was to determine whether cimetidine exerts a protective effect against toxicity of organophosphate pesticides requiring metabolic activation in mice and rats. In both species, pretreatment with cimetidine (75 mg/kg/ip) 30 min prior to methylparathion (MP) reduced lethality and delayed the onset of cholinergic signs of toxicity. In contrast when cimetidine was administered simultaneously with MP to mice, neither MP-induced lethality nor cholinergic signs of toxicity were altered. Moreover, cimetidine pretreatment failed to decrease parathion-induced toxicity in mice. In conclusion, pretreatment with cimetidine decreases the toxicity of MP but not of parathion in mice and rats.