Influence of dimethoate on pyrantel concentration in rat liver

The aim of the study was to evaluate the influence of dimethoate on pyrantel concentrations in the liver after coadministration of dimethoate and pyrantel embonate. Rats were given intragastrically or in drinking water pyrantel or pyrantel and dimethoate, on different regimes of dosing. In the first group, after administration of pyrantel embonate at a dose of 1 000 mg/kg, the maximum concentration of pyrantel in the liver was 440 ng/g and the half-life in the terminal phase was 151 h. After simultaneous administration of pyrantel and dimethoate, the maximum concentration of pyrantel decreased to 174 ng/g; however, the half-life did not change. Administration of a 2.5 times lower dose caused a nonproportional lowered maximum concentration of pyrantel and a statistically significant increase in its rate of elimination. The influence of dimethoate on pyrantel concentration in rat liver was similar after pyrantel administration both at a dose of 400 mg/kg and 1 000 mg/kg. The obtained results show that dimethoate probably does not influence pyrantel biotransformation; however, they can suggest the inhibition of absorption of this compound and changes in its body distribution.