Background: Gabapentin absorption is mediated by a saturable transporter system located in the upper gastrointestinal tract, indicating a short window of absorption. Therefore, conventional sustained formulations would likely result in decreased bioavailability, as the dosage form would pass through the window of absorption before the drug could be completely released.
Objective: The aim of this study was to compare the pharmacokinetics of an oral, gastric-retentive, gabapentin extended-release (G-ER) formulation with a gabapentin immediate-release (G-IR) formulation after single and multiple daily doses in healthy subjects.
Methods: In this open-label, multiple-dose, 3-way crossover, exploratory study, healthy male and female subjects (aged 18-65 years) were randomized to receive doses of 1800 mg G-ER in accordance with the following regimens: G-ER QD (8 pm), G-ER BID in divided doses (600 mg at 8 am and 1,200 mg at 8 pm), or G-IR TID (600 mg at 8 am, 2 pm, and 8 pm) on day 1 and on days 4 through 8 of each study period. The subjects underwent a 10-day washout between study periods. Gabapentin plasma concentrations were measured in serial plasma samples collected >or=48 hours following dosing on days 1 and 8 using a validated high performance liquid chromatography/tandem mass spectrometry system with a lowest limit of quantitation of 75 ng/mL. Adverse events (AEs) were monitored and documented throughout the confinement in the clinic and washout phases of each study period.
Results: Of the 24 subjects enrolled in the study, 21 (11 males, 10 females; mean age, 37 years [range, 23- 60 years]; mean height, 172 cm [range, 158-188 cm], mean weight, 77 kg [range, 56-95 kg]; mean body mass index, 26.2 kg/m2 [range, 21.5-29.7 kg/m2]) completed the study. The completing subjects consisted of 8 whites, 7 blacks, 3 Asians, and 3 Hispanics. At steady state, exposure of both G-ER regimens (QD and BID) appeared similar compared with that of G-IR. However, BID dosing resulted in apparently lower C(max) (mean ratio: 81%; CI 90%, 76%-86%) and greater C(min) values (mean ratio: 118%; CI 90%, 107%-130%), while G-ER QD dosing was associated with numerically greater C(max) (mean ratio: 116%; CI 90%, 109%-123%), and lower C(min) values (mean ratio: 52%; CI 90%, 48%-56%) compared with G-IR TID during a 24-hour dosing period. A total of 47 treatment-emergent AEs occurred in 17 patients during the study. The most common AEs were headache (25% G-ER BID divided dose, 10% G-ER QD dosing, and 14% in G-IR TID dosing), dizziness (6%, 0%, and 19%), and muscle cramp (19%, 0%, and 10%). AEs were most prevalent in the G-IR study group.
Conclusions: This exploratory study found that in these healthy subjects, the daily exposure provided by less frequent G-ER dosing was not significantly different from same daily dose with G-IR, administered more frequently. The G-ER BID dosing resulted in less fluctuation, while the G-ER QD dosing produced higher maximum concentrations compared with a G-IR TID regimen.