COMPARATIVE PHARMACOKINETICS OF IOPHENOXIC ACID IN CATS AND BRUSHTAILPOSSUMS

The comparative plasma pharmacokinetics of iophenoxic acid was studied in the cat and brushtail possum to evaluate the suitability of this c ompound as a bait marker in these species. In cats, a mean peak plasma concentration of 946 mu g per 100 mt was obtained after administratio n of 1.5 mg kg(-1) of iophenoxic acid. However, at the same dose level in possums, mean peak plasma concentration was only 157 mu g per 100 mt. Even after administration of 10 mg kg(-1) of iophenoxic acid, the maximum peak plasma concentration in possums was only 459 mu g per 100 mt. The plasma elimination half-life for iophenoxic acid was 107 days in cats and close to one day in possums. Iophenoxic acid is therefore a suitable marker for cats but is unsuitable for use as a long-term o r quantitative bait marker for possums. Differences between the possum and other mammals in gastrointestinal physiology and plasma protein c onfiguration may account for the poor absorption and rapid elimination of iophenoxic acid in the possum.