A low-dose sublingual formulation of zolpidem tartrate is the first agent to be approved to treat insomnia characterized by middle-of-the-night waking followed by difficulty returning to sleep, the Food and Drug Administration announced Nov. 23.

Zolpidem tartrate was first approved in the United States in 1992 as the higher-dose formulation known as Ambien.

"For people whose insomnia causes them to wake in the middle of the night with difficulty returning to sleep, this new medication offers a safer choice than taking a higher dose of zolpidem upon waking," said Dr. Robert Temple, deputy center director for clinical science in the FDA’s Center for Drug Evaluation and Research, in a statement. "With this lower dose there is less risk of a person having too much drug in the body upon waking, which can cause dangerous drowsiness and impair driving."

Intermezzo (Transcept Pharmaceuticals Inc.) should only be used when a person has at least 4 hours of bedtime remaining. It should not be taken if alcohol has been consumed or with any other sleep aid.

The recommended and maximum dose of Intermezzo is 1.75 mg for women and 3.5 mg for men, taken once per night. The recommended dose for women is lower because women clear zolpidem from the body at a lower rate than men.

Intermezzo was studied in two clinical trials involving more than 370 patients. In the studies, patients taking the drug fell back to sleep faster after awakening as compared to people taking a placebo. The most commonly reported adverse reactions in the clinical trials were headache, nausea, and fatigue.

Potential side effects include getting out of bed while not fully awake and undertaking activities that are not remembered. Reported and not remembered activities have included driving a car, making and eating food, having sex, talking on the phone, and sleepwalking. Risks of such activities increase with use of alcohol or sedating drugs.

Intermezzo is a federally controlled substance.