Objective—To investigate in vitro transdermal absorption of fentanyl from patches through skin samples obtained from various anatomic regions of dogs.
Sample Population—Skin samples from 5 Greyhounds.
Procedure—Skin samples from the dogs' thoracic, neck, and groin regions were collected postmortem and frozen. After samples were thawed, circular sections were cut and placed in Franz-type diffusion cells in a water bath (32°C). A commercial fentanyl patch, attached to an acetate strip with a circular hole, was applied to each skin sample. Cellulose strips were used as control membranes. Samples of receptor fluid in the diffusion cells were collected at intervals for 48 hours, and fentanyl concentrations were analyzed by use of high-performance liquid chromatography.
Results—Mean ± SD release rate of fentanyl from the patch, defined by its absorption rate through the non–rate-limiting cellulose membrane, was linear during the first 8 hours (2.01 ± 0.05 µg/cm2 of cellulose membrane/h) and then decreased. Fentanyl passed through skin from the groin region at a faster rate and with a significantly shorter lag time, compared with findings in neck or thoracic skin samples.
Conclusions and Clinical Relevance—In vitro, fentanyl from a patch was absorbed more quickly and to a greater extent through skin collected from the groin region of dogs, compared with skin samples from the thoracic and neck regions. Placement of fentanyl patches in the groin region of dogs may decrease the lag time to achieve analgesia perioperatively; however, in vivo studies are necessary to confirm these findings.( Am J Vet Res 2004;65:1697–1700)