Pharmacokinetics of a Single Intramuscular Injection of Amoxicillin Trihydrate in Tammar Wallabies (Macropus eugenii)
American Association of Zoo Veterinarians Conference 2006
David McLelland1,2, BSc (Vet), BVSc; Peter Holz3, BVSc, DVSc, MACVSc, DACZM; Brian Rich4, BSc, PhD; Ron Johnson5, BSc, DVM, PhD, DACVCP; Andrew Peters3, BVSc; Ian K. Barker1, DVM, MSc, PhD
1Department of Pathobiology, University of Guelph, Guelph, ON, Canada; 2Toronto Zoo, Scarborough, ON, Canada; 3Healesville Sanctuary, Healesville, VIC, Australia; 4Adelaide Zoo, Adelaide, SA, Australia; 5Department of Biomedical Sciences, University of Guelph, Guelph, ON, Canada
Abstract
Though suggested dosages for antibiotic use in marsupials have been published, there is little pharmacokinetic information in the literature. Dose regimens are largely inferred from eutherian animal literature and/or response to treatment. However, the metabolism and elimination of drugs may differ in marsupials as they have a lower metabolic rate and body temperature when compared to eutherians.
Five tammar wallabies (Macropus eugenii) were injected with amoxicillin trihydrate (Betamox, Norbrook, New Gisborne, VIC, Australia; 10 mg/kg, IM), and blood samples collected at 0, 0.5, 1, 2, 4, 8 and 10 h. Plasma concentrations of amoxicillin were measured using HPLC. Noncompartmental modeling estimated the variables (mean ± SD) for maximum plasma levels (Cmax) at 4.50±0.70 µg/ml, time to maximum plasma levels (Tmax) at 2.00±0 h, area under the curve from time 0 to infinity (AUC0-∞) at 14.76±4.15 h.µg/ml, area under the first moment curve from time 0 to infinity (AUMC0-∞) at 62.24±33.56 h.h.µg/ml, the terminal phase half-life (t½λz) at 1.88±0.60 h, and mean residence time (MRT) at 3.33±0.32 h.
Cmax, Tmax and AUC values attained in this pilot study are comparable to values attained with domestic species (dog, pig, sheep, goat) when amoxicillin trihydrate is given at similar doses and by the same route. The terminal phase half-life determined in this study is consistent with the elimination half-life in sheep and goats, however, no IV data were generated in the present study. These results could suggest a minimal depot effect in wallabies with amoxicillin trihydrate, necessitating a shorter dose interval.