Scandinavian researchers writing in The Lancet gave a warm review to an investigational drug for migraine, but patients in the United States, at least, will have a wait before it reaches them.
Merck manufactures the drug, called telcagepant, and was initially expected to seek approval from the U.S. Food and Drug Administration last year.
An online Lancet review by researchers from Sweden and Norway touted telcagepant as holding out hope for migraine patients with acute attacks that fail to respond to migraine medications known as triptan drugs, such as Zomig and Imitrex. One major concern of these drugs has been their tendency to cause narrowing of the blood vessels, a process known as vasoconstriction.
"Telcagepant does not cause vasoconstriction, a major limitation in the use of triptans," wrote Dr. Lars Edvinsson of University Hospital in Lund, Sweden, and Dr. Mattias Linde of Norwegian University of Science and Technology in Trondheim.
"Telcagepant might provide hope for those who have a poor response to, or are unable to use, older drugs."
But elevations in certain liver enzymes among some telcagepant trial participants caused Merck to hold back in the U.S., fearing an application would be rejected. In September, the company announced that it was meeting with FDA officials to discuss how to proceed.
As a result, a Merck spokeswoman told MedPage Today, the company will sponsor another clinical safety study to begin this year. She said the trial was still being designed, and the protocol would be posted to the Clinicaltrials.gov Web site about the time enrollment begins.
No other information, such as the projected completion date, is available at this time, the spokeswoman said.
The group of drugs called CGRP receptor antagonists, to which telcagepant belongs, represents a new front in the war on migraine, as Edvinsson and Linde explained.
The receptor appears throughout the nervous system, both central and peripheral, and researchers believe it helps regulate vascular tone, pain signaling, motor function, and other activities with neurologic components.
A variety of studies have implicated it specifically in migraine, notably findings that CGRP levels rise in cranial blood and saliva during attacks.
But the two researchers said the clinical findings with telcagepant were marred by the liver abnormalities, which they called "slightly disturbing."
A 12-week phase IIa trial was stopped a year ago when some patients showed these liver problems toward the end of the study.
Edvinsson and Linde also noted that relatively high doses of the drug are needed to reduce migraines -- more than 100 mg, compared with 5 mg for zolmitriptan.
"Outstanding questions include whether CGRP receptor antagonists can be combined with triptans to give more effective therapy and whether they will be of value in patients who do not respond to a triptan," the researchers wrote.
"Additionally, effectiveness of triptans in children has not been proven, a group that might benefit after such research."