FDA approves new fibromyalgia therapy.(NEWS)

Milnacipran, a norepinephrine-serotonin reuptake inhibitor, has been approved by the Food and Drug Administration for the management of fibromyalgia in adults, the third drug approved for this indication.

Approval was based on the results of two phase III studies of a total of 2,084 patients with fibromyalgia, which found that during 3-6 months of treatment, those (1,460 patients) treated with 100 mg or 200 mg of milnacipran per day experienced statistically significant and clinically meaningful improvements in pain, patient global assessment, and physical function, compared with those on placebo.

Milnacipran is a dual reuptake inhibitor that preferentially blocks reuptake of norepinephrine three times as much as it blocks reuptake of serotonin. Milnacipran, approved on January 14, is expected to be available in pharmacies in March, according to Forest Laboratories Inc. and Cypress Bioscience Inc., which developed the drug and will market it under the trade name Savella.

The two studies "used a very strictend point to define someone as a responder to the drug," said Dr. Daniel Clauw, professor of medicine in the division of rheumatology at the University of Michigan, Ann Arbor, and the lead investigator in one of the studies. To be a responder, they had to have a 30% improvement in pain as well as say they were doing much better on the drug than before starting the drug and also had to have a clinically meaningful improvement in function, he said in an interview.

"This shows that when some individuals take this drug, they feel much better overall, not just regarding pain, which makes us think that this drug and others that lead to these global improvements are attacking the root cause of fibromyalgia rather than just covering up symptoms such as pain."

Although the drug's label says the exact mechanism of action in inhibiting pain is unknown, milnacipran "almost certainly" works by increasing central nervous system levels of norepinephrine and serotonin, noted Dr. Clauw, also director of the chronic pain and research center at the university. "Both of these neurotransmitters, especially norepinephrine, are known to play a critical role in pain transmission, and it is thought that the primary mechanism of action is that raising these neurotransmitter levels in the brain causes increased activity down descending--from the brain to spinal cord--analgesic pathways, thus inhibiting the upward transmission of pain."

Pregabalin (Lyrica) was approved for treating fibromyalgia in 2007, followed by duloxetine (Cymbalta), which, like milnacipran, is an inhibitor of neuronal serotonin and norepinephrine reuptake, in June 2008.