title: Antagonism of methomyl-induced toxicosis by diphenhydramine in rats.
abstract: The efficacy of diphenhydramine in the prevention and treatment of methomyl-induced toxicosis was evaluated in female rats. Diphenhydramine at 10 and 20 mg/kg subcutaneously (s.c.) given immediately after methomyl increased the LD(50) of methomyl (6.29 mg/kg intraperitoneally (i.p.)) in the rats by 71 and 75% respectively. Diphenhydramine at 20 mg/kg s.c. given immediately after methomyl (6 mg/kg i.p.) decreased the occurrence of cholinergic signs of toxicosis, and prevented convulsions, gasping and death by 100% in comparison with the control (methomyl-saline) group. Diphenhydramine administration at 2.5, 5 and 10 mg/kg s.c. 20 min before methomyl (8 mg/kg i.p.) significantly and dose-dependently decreased the number of convulsion episodes in rats in comparison with the control group. This effect was similar to those of atropine and diazepam pretreatments at 20 mg/kg s.c. Diphenhydramine and atropine at 20 mg/kg i.p. given 5 min after the methomyl administration (8 mg/kg i.p.) were close to each other in reducing the signs of cholinergic toxicity as well as the severity of toxicosis induced by methomyl in rats. Methomyl at 4 and 8 mg/kg i.p. significantly decreased erythrocyte (40 and 43%) and plasma (23 and 31%) cholinesterase activities in comparison with the control group. Diphenhydramine (10 mg/kg s.c.) injected 15 min before methomyl significantly decreased the inhibitory effect of methomyl (4 and 8 mg/kg i.p.) on erythrocyte cholinesterase to 17 and 27%, respectively. The inhibitory effect on plasma cholinesterase was not affected by the diphenhydramine pretreatment. The data suggest that diphenhydramine could be of therapeutic value in reducing the toxic effects of methomyl.
authors.affiliation: Department of Physiology, Biochemistry and Pharmacology, College of Veterinary Medicine, University of Mosul, P.O. Box 11136, Mosul, Iraq.
authors.forename: B K
authors.initials: BK
authors.lastname: Al-Baggou'
authors.forename: F K
authors.initials: FK
authors.lastname: Mohammad