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J Vet Pharmacol Ther. 2019 Jun 10. doi: 10.1111/jvp.12767. [Epub ahead of print]

Pharmacokinetic profile of amoxicillin and its glucuronide-like metabolite when administered subcutaneously to koalas (Phascolarctos cinereus).

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Sydney School of Veterinary Science, The University of Sydney, Camperdown, NSW, Australia.
Taronga Zoo, Mosman, NSW, Australia.


Amoxicillin was administered as a single subcutaneous injection at 12.5 mg/kg to four koalas and changes in amoxicillin plasma concentrations over 24 hr were quantified. Amoxicillin had a relatively low average ± SD maximum plasma concentration (Cmax ) of 1.72 ± 0.47 µg/ml; at an average ± SD time to reach Cmax (Tmax ) of 2.25 ± 1.26 hr, and an elimination half-life of 4.38 ± 2.40 hr. The pharmacokinetic profile indicated relatively poor subcutaneous absorption. A metabolite was also identified, likely associated with glucuronic acid conjugation. Bacterial growth inhibition assays demonstrated that all plasma samples other than t = 0 hr, inhibited the growth of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 to some extent. Calculated pharmacokinetic indices were used to predict whether this dose could attain a plasma concentration to inhibit some susceptible Gram-negative and Gram-positive pathogens. It was predicted that a twice daily dose of 12.5 mg/kg would be efficacious to inhibit susceptible bacteria with an amoxicillin minimum inhibitory concentration (MIC) ≤ 0.75 µg/ml such as susceptible Bordetella bronchiseptica, E. coli, Staphylococcus spp. and Streptococcus spp. pathogens.


Phascolarctos cinereus ; amoxicillin; koala; metabolite; pharmacokinetic


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