Meta-analyses of dose-exposure relationships for gabapentin following oral administration of gabapentin and gabapentin enacarbil.

BACKGROUND: Gabapentin exposure following administration of certain doses of gabapentin or its pro-drug gabapentin enacarbil has been previously reported in the literature, with variable results.
METHODS: Meta-analyses of dose-exposure relationships were conducted to maximise precision and minimise bias. Study-level mean data for gabapentin systemic exposure, in terms of bioavailable dose and steady-state average plasma concentration, were modelled as a function of daily dose. Several linear and non-linear candidate models were tested.
RESULTS: An Emax model best described the dose-exposure relationships for gabapentin. The ED50 was 3,080 mg/day for bioavailable dose or 3,370 mg/day for steady-state concentration; and the maximum exposure was 2,340 mg/day or 16.9 mg/L. For gabapentin enacarbil, a power model was most suitable, with a power of 0.925 for bioavailable dose or 0.844 for steady-state concentration. All parameters were estimated with < 20 % standard error. Simulations confirmed that these models accurately reflected the distribution of the respective data, and bootstrapping showed high precision for the estimated dose-exposure curves.
CONCLUSION: The meta-analyses addressed issues associated with between-study variability; and confirmed the highly non-linear nature of dose-exposure relationships for gabapentin and the essentially linear relationships for gabapentin enacarbil. The resulting models could be used to simulate exposure at any clinically relevant dose and bridge therapeutic dose range between the two drugs.