Abstract

The aim of the study was to examine the interaction and toxicity between xylazine and the organophosphorus insecticide dichlorvos (DDVP) in chicks. Using the up and down method, the median lethal dose (LD₅₀) of xylazine was 62.59 mg / kg i.m., and that of dichlorvos was 6.31 mg / kg p.o. The toxic interaction between xylazine and dichlorvos was examined using a ratio of (1:1) and the (LD₅₀) value for both depending on isobolographic analysis. Antagonistic interaction was found when both of the drugs were adminstrated at the same time. Xylazine at 7.5 and 15 mg / kg i.m. significantly reduce the ratio of tremor and ataxia as well as the significant increase in the time of onset of toxicity signs when given directly after dichlorvos dosing (7 mg / kg p.o.) leading to a significant decrease in toxicity score. Xylazine at 30 mg / kg i.m. significantly reduce the ratio of convulsions and lacrimation when given directly after dichlorvos dosing as well as the significant reduction of tremor and ataxia when given (-15 and +5 minutes) according to time of dichlorvos (7 mg / kg p.o.) dosing. Xylazine at 30 mg / kg i.m. has a non – significant effect in cholinesterase (ChE) activity in plasma and brain. There was a significant decrease in the ratio of brain ChE inhibition which caused by dichlorvos (7 mg / kg p.o.) with a protection ratio of (23.33 %). The results suggest that xylazine reduce the percentage of inhibition of ChE in chicks which was caused by dichlorvos and protect them from its toxicity.