Biological and pharmacokinetic performance of two commercial formulations of ivermectin 3.15 % in bovines

Abstract

A stall test was performed to evaluate two ivermectin formulations (Ivomec Gold® and a generic one at 3.15%). Residual efficacy against larval challenges of Rhipicephalus (B.) microplus and plasmatic levels of ivermectin were studied. In both formulations residual efficacy presented a large scatter in the number of days of detachment of engorged females after treatment, discounting the residual parasitic cycle a range of 35 to 63 days was presented. Statistical analysis of the results of both formulations showed a residual period of 52 days (median) before reinfestation with larvae of R. (B) microplus. The average pharmacokinetic parameters area under the curve (AUC), represented values of 1795±188 and 1351±118, whereas plasma peaks (Tmax) occurred at 13.4±4.1 and 15.0±3.6 days post inoculation reaching maximum concentration (Cmax) of 65.4±1.5 and 41.1±0.3 ppb in Ivomec GOLD ® and generic formulation respectively. Concentrations below 10 ppb may represent the threshold below the parasitic cycle could develop and engorged ticks obtained. These results allow a better understanding to evaluate the performed of new formulations in stall and field trials to evaluate efficacy, residual efficacy and the withholding period.