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Home » Drug Information » FDA Approved Drugs » 2012
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Horizant (gabapentin enacarbil)

The following drug information is obtained from various newswires, published medical journal articles, and medical conference presentations.

Company: GlaxoSmithKline
Approval Status: Approved June 2012
Treatment Area: postherpetic neuralgia

General Information

Horizant (gabapentin enacarbil) is an extended-release formulation of gabapentin enacarbil, a prodrug of gabapentin. The precise mechanism by which gabapentin is efficacious in PHN is unknown. Gabapentin is structurally related to the neurotransmitter gamma-aminobutyric acid (GABA) but has no effect on GABA binding, uptake, or degradation.

Horizant is specifically indicated for the management of postherpetic neuralgia (PHN) in adults.

Horizant is supplied as an extended release tablet for oral administration. The recommended initial dose is 600 mg with food in the morning for 3 days, followed by an increase to 600 mg twice daily with food beginning on day 4.

Clinical Results

FDA Approval
The FDA approval of Horizant for PHN was based on the results of one 12-week clinical trial. The multicenter, randomized, double-blind, parallel-group, placebo-controlled study evaluated the efficacy, safety, and dose response of 3 maintenance doses of Horizant (1,200, 2,400, and 3,600 mg/day, with 107, 82, and 87 adult subjects in each dosing group, respectively). Placebo was administered to 95 subjects. Subjects were required to have a minimum baseline 24-hour average Pain Intensity Numerical Rating Scale (PI-NRS) intensity score of at least 4.0 on the 11-point numerical PI-NRS. Following a 1-week baseline period during which subjects were screened for eligibility, subjects completed a 1-week up-titration period followed by a 12 week maintenance treatment period, and then a 1-week down-titration period. Treatment with Horizant statistically significantly improved the mean pain score and increased the proportion of subjects with at least a 50% reduction in pain score from baseline at all doses tested. A benefit over placebo was observed for all 3 doses of the drug as early as Week 1 and maintained to the end of treatment.

Side Effects

Adverse reactions associated with the use of Horizant may include, but are not limited to, the following:

  • dizziness
  • somnolence
  • headache

Mechanism of Action

Horizant is an extended-release formulation of gabapentin enacarbil, a prodrug of gabapentin. The precise mechanism by which gabapentin is efficacious in PHN is unknown. Gabapentin is structurally related to the neurotransmitter gamma-aminobutyric acid (GABA) but has no effect on GABA binding, uptake, or degradation.

Literature References

Backonja MM, Canafax DM, Cundy KC. Efficacy of gabapentin enacarbil vs placebo in patients with postherpetic neuralgia and a pharmacokinetic comparison with oral gabapentin. Pain Med. 2011 Jul;12(7):1098-108

Additional Information

For additional information regarding Horizant or postherpetic neuralgia, please visit the Horizant web page.