Review

Pharmacokinetics of drugs in avian species and the applications and limitations of dose extrapolation

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Abstract

The pharmacokinetic processes of drugs, i.e. absorption, distribution, metabolization and elimination, differ between birds and mammals. For instance, the clearance and volume of the distribution of aminoglycosides are lower in birds than in mammals. These pharmacokinetic differences are caused by differences in anatomy, biochemistry and physiology between birds and mammals. The species differences in pharmacokinetics and differences in the observed and predicted pharmacokinetic parameters of some drugs in birds after extrapolation from mammals (e.g. clearance of enrofloxacin, salicylic acid, meloxicam and flunixin), show that pharmacokinetic data on mammals can hardly be extrapolated to birds as such. Furthermore, differences in pharmacokinetic behavior between bird species exist as well. Therefore, the selection of an appropriate posology for birds has to be based on pharmacokinetic data of that specific bird species. In absence of these data, dose selection might be done using allometric scaling. The pharmacokinetic data are scaled in correlation to the body weight of a different bird species. In case these data are also not available, dose selection using allometric scaling with pharmacokinetic data from mammals should preferably only be done for drugs with a low toxicity.