Skin permeation and antinociception of topical gabapentin formulations

Chronic pain affects greater than 116 million Americans each year. Even with the best pain management approaches, many chronic pain patients still suffer from moderate to severe pain. An alternative therapy to treat chronic pain includes compounded topical formulations of common analgesics. Compounded dosage forms of gabapentin are commonly used for pain management, however, the penetration and efficacy of gabapentin in these compounded topical formulations has not been fully studied. In this study, the transdermal penetration of gabapentin was studied in Franz diffusion cells using porcine skin. Gabapentin was compounded in two commercially available bases; Lipobase, Lipoderm, and a standard poloxamer lecithin organogel. The penetration and retention of gabapentin in the skin was dependent upon the base. The most rapid and greatest penetration and retention of gabapentin in the skin occurred with a poloxamer lecithin organogel base. Lipobase and Lipoderm bases produced slow and smaller penetration and retention of gabapentin as compared to poloxamer lecithin organogel base. Gabapentin 1% and 5% compounded in Lipoderm were tested in the in vivo preclinical formalin pain model. Topical 5% gabapentin produced a similar reduction in nociception in both Phase 1 and Phase 2 of the formalin response as systemic subcutaneous gabapentin (100 mg/kg). Topical 1% gabapentin reduced Phase 2, but not Phase 1 formalin-induced nociceptive behaviors. These findings suggest that topical administration of gabapentin may produce local antinociception.