Keywords : LD50
Iraqi Journal of Veterinary Sciences,
Metronidazole is antimicrobial drug for human and animal use, The more characteristic side effect associated with use high dose of metronidazole is neurotoxic signs, some of these signs that recorded in animal represented by ataxia and tremor, there is limited information is available on the pharmacological profile of metronidazole in birds The aim of our study explain some of its neurological effect in chicks by its interaction with one of organophosphorus insecticide chlorpyrifos that have well-known excitatory effect on nervous system. Median Lethal Doses (LD50) of metronidazole and chlorpyrifos were determined depending on up and down method. The intraperitoneal and oral LD50 of metronidazole were 516.9 mg/kg, 3061.8 mg/kg respectively. The oral LD50of chlorpyrifos was 13.705 mg/kg, intraperitoneal treatment of metronidazole with Oral treatment of chlorpyrifos in ratio 1:1, 1: 0.5, and 0.5:1, respectively of LD50at the same time increased LD50for metronidazole and chlorpyrifos and the isobolographic analysis showed that the points of interaction occurred above the diagonal line connecting between LD50 of each; while oral treatment of metronidazole and chlorpyrifos in ratio 1:0.5 LD50at the same time decreased LD50for metronidazole and chlorpyrifos and the point of interaction was above the diagonal line connecting between LD50 of each in conclusion we found that isobolografhic analysis for metronidazole and chlorpyrifos in different percentages and routs of treatment reveal to antagonist effect despite the similarity in the toxic signs.