Neurontin®, an immediate-release (IR) formulation of gabapentin, was the first drug approved by the United States Food and Drug Administration for the treatment of postherpetic neuralgia (PHN). The effective dosing regimen of gabapentin IR (G-IR) for PHN is 1800 mg/day in three divided doses. In 2011, a gastroretentive (GR) formulation of gabapentin (G-GR, Gralise®) was approved for the treatment of PHN. The effective dosing regimen of G-GR is 1800 mg, once daily taken with the evening meal. Compared with G-IR, G-GR has an apparently better tolerability profile with a 1-2 weeks shorter titration period to reach the same therapeutically effective dose. The differences in the dosing frequency and tolerability between G-IR and GR are mainly because of the difference in formulations and thus pharmacokinetic properties. The GR formulation takes advantage of normal human gastrointestinal (GI) physiology and the unique pharmacokinetic properties of gabapentin. In this review, we compare the IR and GR formulations of gabapentin, overview the GI physiology and GR mechanism of G-GR, and describe the unique pharmacokinetic properties of gabapentin. The effect of GR formulation on efficacy and the incidence of adverse events that are commonly associated with G-IR treatment in PHN patients are also discussed.
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