Abstract
Providing adequate pain relief to non-domestic felids is challenging, and alternative methods are needed for reliable, non-stressful delivery of analgesics. Transdermal fentanyl patches have been used to provide pain relief to domestic cats, but their disadvantages include being easily removed and providing unreliable blood levels.1,2 Alzet® osmotic pumps (Figure 1) have been used to deliver constant infusions of medications to laboratory animals and have potential for administration of analgesics to exotic cats.
Figure 1. Cutaway section of osmotic pump
As a model for non-domestic felids, eight domestic cats received either a transdermal fentanyl patch (25 µg/h size; Fentanyl Transdermal System, Mylan Pharmaceuticals Inc., Morgantown, West Virginia 26505 USA) applied to the lateral thorax or an osmotic pump (10 µl/h; Model 2ML1, Durect Corp., Cupertino, California 95014 USA, www.alzet.com) loaded with fentanyl (2.5 mg/ml; Fentanyl citrate, USP, Spectrum Chemical MFG Corp., Gardena, California 90248 USA) placed subcutaneously over the back. After a 3-week wash-out period, each cat received the alternate treatment. Blood samples for radioimmunoassay (Coat-a-Count® Fentanyl, Diagnostics Products Corporation, Los Angeles, California 90045 USA) were collected periodically for 4 days, after which the pump/patch was removed.
Though inter-individual variation was observed using either method, the osmotic pumps resulted in higher fentanyl concentrations than those produced by the patches. The pumps were well tolerated by the cats, easy to place, and easy to remove. Though more studies are needed, Alzet® osmotic pump delivery of fentanyl may be appropriate for exotic felid post-surgical analgesia.
Acknowledgments
This study was supported by a grant from the Morris Animal Foundation. The authors thank Tami Moyers and Nancy Zagaya for technical assistance and Joseph Bartges for the use of his research animals.
Literature Cited
1. Lee, D.D., M.G. Papich, and E.M. Hardie. 2000. Comparison of pharmacokinetics of fentanyl after intravenous and transdermal administration in cats. Am. J. Vet. Res. 61: 672–677.
2. Scherk-Nixon, M. 1996. A study of the use of a transdermal fentanyl patch in cats. J. Am. Anim. Hosp. Assoc. 32:19–24.