Pfizer is reporting positive topline results for its anticonvulsant pregabalin for a new indication. Currently sold under the brand name Lyrica, the agent has met each of its three co-primary endpoints for restless legs syndrome.

Pregabalin is typically used for the treatment of neuropathic pain, as an adjunct therapy for partial seizures, or for fibromyalgia.

The new phase 3 trial enrolled more than 700 patients who were randomly assigned to receive placebo, pregabalin 300 mg a day, pramipexole 0.25 mg a day, or pramipexole 0.5 mg a day.

Investigators report that the year-long trial, which is known as A0081186, showed significant benefit with pregabalin.

The drug was associated with a statistically significant improvement compared with placebo as measured by the International Restless Leg Group Rating Scale. In addition, patients on active treatment were more likely to respond to treatment compared with those receiving placebo, as measured by the Clinical Global Impression Improvement Scale.

Pregabalin was also associated with a statistically significant reduction in the rate of augmentation or worsening of symptoms compared with pramipexole 0.5 mg.

The most common adverse events for pregabalin were dizziness, somnolence, fatigue, headache, and nasopharyngitis.

Topline results from a previous phase 3 study in restless legs syndrome showed that pregabalin demonstrated statistically significant improvements in the primary endpoint of sleep maintenance compared with placebo.

In that trial, known as A0081185, adverse events were similar to those in the subsequent trial. In addition, nausea, dry mouth, upper respiratory tract infection, and disturbance of attention were reported.

Like gabapentin, pregabalin binds to the alpha2-delta subunit of the voltage-dependent calcium channel in the central nervous system. Pregabalin decreases the release of neurotransmitters such as glutamate, noradrenaline, and substance P.

Pfizer says it has no plans to seek regulatory approval for an indication in restless legs syndrome at this time. The patent for pregabalin is scheduled to expire in October 2013.

Pregabalin is one of four drugs that a subsidiary of Pfizer in 2009 pleaded guilty to misbranding "with the intent to defraud or mislead." Pfizer illegally promoted these drugs, prompting false claims to government healthcare programs for uses that were not approved by the US Food and Drug Administration. Pfizer agreed to pay $2.3 billion in settlement and entered a corporate integrity agreement.

Allison Shelley • Medscape Medical News © 2011 WebMD, LLC