A pilot study of transdermal gabapentin in cats.

Abstract

BACKGROUND: Clinical use of gabapentin has increased; transdermal delivery in cats is incompletely studied. OBJECTIVE: To evaluate if gabapentin permeates feline skin in&#x2009;vitro and in&#x2009;vivo and to determine if pain scores improve after administration. ANIMALS: In&#x2009;vitro: cadaver skin from 6 cats; phase&#xa0;1: 8 young, healthy client-owned cats; phase&#xa0;2: 15 client-owned geriatric cats. METHODS: In&#x2009;vitro, gabapentin applied every q12h to ear or cervical skin in diffusion cells. Samples collected at 0, 2, 4, 12, and 24&#x2009;hours after application. Phase 1: Cats assigned to 1 of 4 groups: 5&#xa0;mg/kg or 10&#xa0;mg/kg applied q8h for 5&#x2009;days to either ear or cervical skin. Serum samples collected predose, and after 1 and 5&#x2009;days. Phase 2: 10&#xa0;mg/kg applied q8h for 5&#x2009;days. Two validated pain scores recorded predose, and after days 1, 5, and 8. Serum samples collected predose, and after days 1 and 5. Samples were frozen at -80&#xb0;C for concentration analysis utilizing a validated high-performance liquid chromatography mass-spectrometry method. RESULTS: Gabapentin was identified in all samples. Significant differences in gabapentin concentrations were observed from day&#x2009;1 to day&#x2009;5 (P&#x2009;<&#x2009;.02) and in pain scores from predose to day&#x2009;5 (P&#x2009;<&#x2009;.05) and day&#x2009;1 to day&#x2009;5 (P&#x2009;<&#x2009;.05). No differences in pain scores were observed from predose to day&#x2009;8 (P&#xa0;=&#xa0;.3). CONCLUSIONS AND CLINICAL RELEVANCE: Gabapentin in a transdermal base penetrates feline skin in&#x2009;vitro, is absorbed systemically in cats, and may help decrease pain scores.