The intravenous pharmacokinetics of diminazene in healthy dogs.

Diminazene remains one of South Africa's most commonly used antiprotozoal agents for the management of babesiosis in dogs. Although the drug has been on the market for over 40 years, its intravenous pharmacokinetics are poorly known. To better understand the pharmacokinetics of the drug Berenil, it was reconstituted in sterile water and administered intravenously to 6 adult German shepherd dogs. All 6 dogs demonstrated the previously described secondary peak in the plasma concentration versus time profile. The plasma pharmacokinetics for diminazene are described by both non-compartmental and compartmental models. From non-compartmental analysis, the area under curve to the last sample point (AUClast), clearance (CL) and volume of distribution (Vz) were 4.65 +/- 1.95 ng/ml/h, 0.77 +/- 0.18 l/kg/h and 2.28 +/- 0.60 l/kg, respectively. For compartmental modelling, the plasma concentrations were fitted to both a 2-compartmental open model and a recirculatory enterohepatic model. From the recirculation model, the rate of release and re-entry into the central compartment varied markedly with the rate of release from the gall bladder (Ttom) being estimated at 27 +/- 20.90 h. Once released, drug re-entry into the central compartment was variable at 9.70 +/- 5.48 h. With normal biliary excretion time being about 2 h, this indicates that the redistribution cannot be occurring physiologically from the bile. Although it was not possible to identify the site from which sequestration and delayed release is occurring, it is believed that it is most likely from the liver. The study therefore showed that the secondary peak described for the pharmacokinetics of intramuscular administered diminazene in the dog is not related to biphasic absorption.