FDA approves Horizant for postherpetic neuralgia indication

FDA has approved gabapentin enacarbil (Horizant, GlaxoSmithKline and XenoPort) extended-release tablets for the management of postherpetic neuralgia (PHN) in adults.

“GSK has not conducted clinical trials to compare the efficacy and safety of Horizant, and other FDA-approved PHN products,” Bradd Pavur, GSK spokesperson, told Formulary. “Horizant is not interchangeable with other gabapentin products because of differing pharmacokinetic profiles. The same dose of Horizant results in different plasma concentrations of gabapentin relative to other gabapentin products.”

The efficacy and safety of Horizant for the management of PHN was evaluated in a single, 12-week principal efficacy trial, plus 2 supportive studies that all met their respective primary end points. The 3 clinical studies involved 574 adult patients from the United States, Canada, and Germany.

The recommended dosage for the management of PHN in adults is 600 mg twice daily. Treatment should be initiated at a dose of 600 mg in the morning for 3 days followed by 600 mg twice daily (1,200 mg/day) beginning on day 4. Doses must be adjusted in patients with impaired renal function. In the 12-week, controlled study in patients with PHN, somnolence and dizziness were the most frequently reported side effects. Somnolence was reported in 10% of patients treated with 1,200 mg of Horizant per day compared with 8% of patients receiving placebo. Dizziness was reported in 17% of patients receiving 1,200 mg of Horizant per day compared with 15% of patients receiving placebo.

Horizant contains gabapentin enacarbil that becomes gabapentin, a drug used to treat seizures in people with epilepsy, when absorbed into the body. All drugs used to treat epilepsy carry warnings that they may cause suicidal thoughts and actions in a small number of people. Horizant will have the same warning, according to an FDA press release.

Horizant was FDA approved for the treatment of moderate-to-severe primary restless legs syndrome in adults on April 6, 2011.

In association with GSK’s first commercial sale of the product after approval for PHN, XenoPort is entitled to a milestone payment of $10 million from GSK.