The US Food and Drug Administration (FDA) today approved a first-in-class insomnia drug called suvorexant (Belsomra, Merck) after the manufacturer lowered the dosages to satisfy the agency's safety concerns.

Last July, Merck announced that the FDA had declined to approve suvorexant until the starting dose for most patients was 10 mg. The agency also said that proposed upper-limit doses of 30 mg for elderly patients and 40 mg for nonelderly patients were unsafe.

In a news release today, the FDA said it had approved suvorexant at 4 different strengths — 5 mg, 10 mg, 15 mg, and 20 mg. The total dosage in 1 day should not exceed 20 mg.

Merck noted in its own news release today that the recommended dose is 10 mg for most patients, just as the FDA insisted.

Suvorexant, an orexin receptor antagonist, is the first drug of its kind to be approved for patients with insomnia. It alters the signaling of orexins, neurotransmitters responsible for regulating the sleep-wake cycle.

The FDA determined that suvorexant was effective based on 3 clinical trials involving more than 500 participants. Those receiving suvorexant nodded off more quickly and spent less time awake for the rest of the night compared with participants given a placebo. Drowsiness was the most commonly reported adverse event for clinical trial participants taking suvorexant, which is classified as a Schedule IV controlled substance.

In next-day driving tests that the FDA asked Merck to perform, both male and female participants who took the 20-mg dose proved to be impaired drivers. The FDA advises physicians to caution patients at this dosage level against next-day driving or other activities requiring full alertness. Patients taking lower doses also should know about the risk for impaired driving the day after because sensitivity to the drug varies from person to person.

"Using the lowest effective dose can reduce the risk of side effects, including next-morning drowsiness," said Ellis Unger, MD, director of the Office of Drug Evaluation I in the FDA's Center for Drug Evaluation and Research, in the agency's news release.

More information about today's decision is available on the FDA Web site.