The effects of experimental Theileria annulata
infection on the i.m. (20 mg/kg) pharmacokinetics of
oxytetracycline were investigated in crossbred calves. The serum concentration-time curves of
oxytetracycline (OTC-LA), before and after experimental
infection, were best described by a one-compartment open model. The experimental
infection by subcutaneous administration of ground-up tick supernate (GUTS), equivalent to 30 Hyalomma anatolicum anatolicum ticks infected with Theileria annulata, produced a clear temperature rise and signs of clinical disease in calves. Subsequently, haemoglobin, packed cell volume, total leucocyte count and serum Cu, Fe and Zn concentrations decreased after
infection. The absorption and elimination half-lives (t1/2 Ka and t1/2 Ke), mean absorbance time (MAT), time to peak concentration (Tmax), mean residence time (MRT), area under the serum concentration time curve (AUC infinity) and the bioavailability (F) were significantly (P < 0.05) decreased. The peak serum concentration (Cmax), however, remained unchanged after
infection. These changes may necessitate alterations in the dosage regimen of
oxytetracycline used to treat Theileria annulata
infections in cattle under field conditions.