Slovak, J. E., & Costa, A. P. (2021). A pilot study of transdermal gabapentin in cats. Journal of Veterinary Internal Medicine, jvim.16137.
Gabapentin is a commonly used drug in feline medicine for both pain control and anxiolysis. As with most drugs, oral administration of gabapentin to cats may in some cases be difficult. Transdermal administration of medications provides an alternative route that may be applicable for some drugs, whereby dug may be suspended in a base, applied to the skin (usually on the inner ear) and thereby absorbed into circulation.
The purpose of this study was to determine the bioavailability of gabapentin in a proprietary transdermal base (lipoderm) and to further evaluate its analgesic efficacy by this route. This study was designed in two phases, the first an in vitro study and the second a two-phase in vivo study.
The first phase of the study used feline skin collected from cadavers of cats deceased for unrelated reasons. Transdermal gabapentin was applied to the skin using “Franz diffusion cells”, and the concentration absorbed into an electrolyte solution on the other side was measured using HPLC. In this phase, gabapentin was detected in all samples at all time points. This suggested that transdermal application was feasible.
During the first portion of the in vivo phase, transdermal gabapentin was applied to the ears or cervical skin of healthy cats at concentrations of 5 or 10 mg/kg every 8 hours. Eight cats were enrolled into this phase. Blood samples were collected 1 and 5 days after collection. Gabapentin was detected in all samples at both time points. No difference was noted in concentration based on dose or location.
In the final phase, client owned cats with chronic pain were enrolled and treated with transdermal gabapentin at 10mg/kg every 8 hours. 15 cats were enrolled into this phase of the study. Blood samples were collected 1 and 5 days after collection and pain scores assessed. Gabapentin was detected in all samples at all time points, with a significant increase in concentration from day 1 to day 5. A significant difference in pain scores was noted between day 1 to 5, with a gradual decrease.
The authors of this study concluded that transdermal application of gabapentin in a lipoderm base is able to attain therapeutic blood levels and reduce pain scores in treated cats.
There were several limitations to this study. Its small sample size was to be expected given that it was a pilot study, however still may limit data analysis. The study was not controlled, and so the efficacy of gabapentin to treat pain was not able to be accurately assessed. The effects of long term administration has also not been investigated. There is also no current data on what the optimal serum gabapentin level is. Another potential concern is the practicality of this- gabapentin is generally well tolerated mixed into food and is often easily administered to cats, and so in many cases transdermal administration may not be needed. However, in cases where it is helpful, this medication administration route may be helpful.
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