Assessment of diphenhydramine effects against acute poisoning induced by the organophosphate insecticide dichlorvos in chicks

Objective: The study was designed to assess the protective and ameliorative effects of the antihistamine diphenhydramine against a model of acute organophosphate insecticide (dichlorvos) poisoning in 7-14 day-old chicks. Material and Methods: The acute (24 h) oral me dian lethal doses (LD50) of dichlorvos either alone or with concomitant diphenhydramine (10 mg kg-1, i.m.) or atropine (2 mg kg 1, i.m.) were determined in the chicks by the up-and-down method. The protective and ameliorative effects of diphenhydramine on the signs of dichlorvos poisoning were examined and compared with those of atropine. Plasma and whole brain cholinesterase activities of chicks treated with diphen hydramine and/or dichlorvos were measured by an electrometric method. Results: Diphenhydramine at 10 mg kg-1, intramuscularly (i.m.) im mediately after oral dosing with dichlorvos increased the oral LD50 value of the insecticide from 6.49 to 17.14 mg kg-1, whereas atropine at 2 mg kg-1, i.m. increased it to 22.55 mg kg-1. The oral dosing of dichlorvos at 8 mg kg-1 caused acute signs of cholinergic poisoning in the chicks. The best effective dosage of diphenhydramine was at 10 mg kg-1, i.m. immediately after the oral dichlorvos dosing, which significantly in creased the latencies to onset of signs of poisoning and significantly prevented the 2 h and 24 h lethalities. Diphenhydramine also significant ly decreased the occurrence of signs of poisoning and reduced total toxicity score in the chicks. Diphenhydramine, similar to atropine, given at times of -15, 0 and + 5 min relative to the time of dichlorvos dosing also ameliorated dichlorvos-induced poisoning in the chicks to vary ing extents. Dichlorvos alone at the oral doses of 2 and 4 mg kg-1 significantly reduced cholinesterase activity in the plasma and whole brain. Diphenhydramine at 10 mg kg-1, i.m. immediately after oral dichlorvos dosing at 4 mg kg-1 significantly but partially ameliorated cholinester ase inhibition caused by the insecticide in the whole brain of the chicks. Conclusion: The results suggest that diphenhydramine has protective and ameliorative effects against a model of acute organophosphate poisoning in chicks.