Gabapentin enacarbil (XP-13512) is a prodrug for the anticonvulsant and analgesic gabapentin, offering sustained dose-proportional exposure and predictable bioavailability.

Gabapentin enacarbil demonstrated active apical to basolateral transport across Caco-2 cell monolayers and pH-dependent passive permeability across artificial membranes. XP13512 inhibited uptake of (14)C-lactate by human embryonic kidney cells expressing monocarboxylate transporter type-1, and direct uptake of prodrug by these cells was confirmed using liquid chromatography-tandem mass spectrometry. XP13512 inhibited uptake of (3)H-biotin into Chinese hamster ovary cells overexpressing human sodium-dependent multivitamin transporter (SMVT) [1].

In 4 studies of healthy volunteers (136 subjects total), the pharmacokinetics of Gabapentin enacarbil immediate- and extended-release formulations were compared with those of oral gabapentin. Gabapentin enacarbil immediate-release (up to 2800 mg single dose and 2100 mg twice daily) was well absorbed (>68%, based on urinary recovery of gabapentin), converted rapidly to gabapentin, and provided dose-proportional exposure, whereas absorption of oral gabapentin declined with increasing doses to <27% at 1200 mg. Compared with 600 mg gabapentin, an equimolar Gabapentin enacarbil extended-release dose provided extended gabapentin exposure (time to maximum concentration, 8.4 vs 2.7 hours) and superior bioavailability (74.5% vs 36.6%) [2].