(Updates with company comment)
By Toni Clarke
WASHINGTON Aug 13 (Reuters) - The U.S. Food and Drug Administration said on Wednesday it has approved a new insomnia drug made by Merck & Co.
The drug, to be called Belsomra, is the first in a new class of sedatives that block chemicals in the brain called orexins that help keep people awake.
Belsomra, known generically as suvorexant, has the potential to cause next-day sleepiness and impaired driving. As a result, the FDA said, no more than one pill should be taken per night and the dose should not exceed 20 milligrams.
The FDA had asked Merck to study the next-day driving performance of people who took the drug amid concerns the sedative could lead to next-day drowsiness.
The test showed impaired driving in patients who took 20 milligrams of the drug. Patients therefore "should be cautioned against next-day driving or activities requiring full mental alertness," the FDA said in a statement.
Even those who take a lower dose should be made aware of the potential for next-day driving impairment because individuals may respond differently to any given drug, the agency said.
The FDA approved the drug in 5, 10, 15 and 20 milligram doses.
Merck said it expects the drug to be available in late 2014 or early 2015, once the Drug Enforcement Administration has made its final decision on the scheduling of the drug.
The FDA recommended that Belsomra be listed as a controlled substance because it can be addictive and has the potential to be abused. The DEA has proposed that the drug be given a Schedule IV designation.
Schedule 1 drugs have the greatest potential for abuse while Schedule V drugs have the least potential.
Merck's shares rose 1.4 percent on the New York Stock Exchange on Wednesday to close at $57.85.
Merck had originally proposed that non-elderly adults start on 20 milligrams and increase to 40 milligrams if needed. It recommended that elderly patients start by taking 15 milligrams and increase to 30 if necessary.
FDA officials said at an advisory committee meeting in May 2013 that there was little evidence to show the drug was more effective at higher doses and considerable evidence to show it was less safe.
"Using the lowest effective dose can reduce the risk of side effects, such as next-morning drowsiness," said Dr. Ellis Unger, an official in the FDA's drugs division.
Merck said on Wednesday that the recommended dose of Belsomra is 10 milligrams within 30 minutes of going to bed, with at least seven hours before a patient needs to wake up. The drug is designed for people who have difficulty getting to sleep and staying asleep.