Evaluation of an osmotic pump for fentanyl administration in cats as a model for nondomestic felids.

OBJECTIVE To evaluate the reliability of an SC implanted osmotic pump (OP) for fentanyl administration in cats and to compare serum concentrations of fentanyl delivered via an OP and a transdermal patch (TP). Animals-8 spayed female cats. PROCEDURES In a crossover design, cats received fentanyl at 25 microg/h via a TP or an OP. All cats were anesthetized for the pump or patch placement (0 hours) and again when it was removed (96 hours). Venous blood samples were collected for measurement of serum fentanyl concentrations at 0, 6, 12, 24, 36, 48, 72, and 96 hours and at 24 and 48 hours after device removal. After a 3-week washout period, the experiment was repeated with each cat receiving the other treatment. RESULTS Mean serum fentanyl concentrations at 24, 36, 72, and 96 hours were greater when the OP was used than when the TP was used. Mean residence time and half-life were greater when the TP was used. Fentanyl concentration changed significantly faster in initial and elimination phases when the OP was used. Marked interindividual variation in serum fentanyl concentrations was evident with both administration methods. No adverse effects were evident with either method. CONCLUSIONS AND CLINICAL RELEVANCE Use of the OP to administer fentanyl to cats resulted in a shorter initial lag phase to a therapeutic serum concentration, higher bioavailability, and faster elimination after removal, compared with use of a TP. These advantages, in addition to the inability of cats to remove the OP, may make OPs useful for fentanyl administration in nondomestic felids.