A pilot study of transdermal gabapentin in cats

BACKGROUND: Clinical use of gabapentin has increased; transdermal delivery in cats is incompletely studied. OBJECTIVE: To evaluate if gabapentin permeates feline skin in vitro and in vivo and to determine if pain scores improve after administration. ANIMALS: In vitro: cadaver skin from 6 cats; phase 1: 8 young, healthy client-owned cats; phase 2: 15 client-owned geriatric cats. METHODS: In vitro, gabapentin applied every q12h to ear or cervical skin in diffusion cells. Samples collected at 0, 2, 4, 12, and 24 hours after application. Phase 1: Cats assigned to 1 of 4 groups: 5 mg/kg or 10 mg/kg applied q8h for 5 days to either ear or cervical skin. Serum samples collected predose, and after 1 and 5 days. Phase 2: 10 mg/kg applied q8h for 5 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°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 1 to day 5 (P < .02) and in pain scores from predose to day 5 (P < .05) and day 1 to day 5 (P < .05). No differences in pain scores were observed from predose to day 8 (P = .3). CONCLUSIONS AND CLINICAL RELEVANCE: Gabapentin in a transdermal base penetrates feline skin in vitro, is absorbed systemically in cats, and may help decrease pain scores.