Epilepsy Drug Cuts Sleep Apnea by 47% in Trial

An Unexpected Discovery

A drug long used to treat childhood epilepsy has emerged as a surprisingly potent weapon against obstructive sleep apnea (OSA) — one of the world's most widespread and undertreated chronic conditions. Results from the FLOW trial, a large European phase 2 study published in The Lancet, show that sulthiame reduced the frequency of breathing interruptions during sleep by up to 47% in patients with moderate to severe OSA, compared with placebo.

The FLOW Trial: Scale and Design

The multicenter, randomized, double-blind, placebo-controlled trial enrolled 298 adults with untreated moderate-to-severe obstructive sleep apnea across 28 clinical sites in five European countries: Spain, France, Belgium, Germany, and the Czech Republic. Participants were assigned to one of three once-daily doses of sulthiame — 100 mg, 200 mg, or 300 mg — or a placebo, taken at bedtime for 15 weeks.

The primary endpoint was reduction in the apnea-hypopnea index (AHI), a standard measure of how many times per hour a patient's breathing is disrupted. The results were dose-dependent and striking: the 100 mg group saw a 17.8% reduction, the 200 mg group 34.8%, and the 300 mg group 39.9%. Using a stricter oxygen-desaturation threshold, the highest-dose group achieved nearly 47% fewer interruptions than the placebo arm.

How the Drug Works

Sulthiame is a carbonic anhydrase inhibitor, a class of compounds that alter the body's carbon dioxide sensitivity and respiratory drive. In the context of sleep apnea, the drug appears to stabilize neural control of breathing and strengthen upper airway muscles, reducing the tendency of the throat to collapse during sleep — the root cause of obstructive apnea. Patients also demonstrated measurably improved nighttime oxygen saturation levels and reported less daytime sleepiness.

"We have been working on this treatment strategy for a long time, and the results show that sleep apnea can indeed be influenced pharmacologically. It feels like a breakthrough," said Jan Hedner, senior professor of pulmonary medicine at the University of Gothenburg and Sahlgrenska University Hospital, who led the research.

Why It Matters: The CPAP Problem

An estimated one billion people worldwide live with some form of sleep apnea, yet the condition remains severely underdiagnosed and poorly managed. The current standard of care — continuous positive airway pressure (CPAP) therapy — is effective but cumbersome: it requires wearing a mask connected to an air pump every night. Studies consistently find that roughly half of patients abandon CPAP within a year due to discomfort, noise, or the psychological burden of the device.

A simple, once-daily pill could transform adherence and access, particularly in low- and middle-income countries where CPAP equipment is often unaffordable. Sulthiame is an off-patent compound already approved for epilepsy in several countries, which could accelerate regulatory pathways and reduce costs.

Safety and the Road Ahead

Side effects in the FLOW trial were generally mild to moderate and consistent with the known pharmacology of carbonic anhydrase inhibitors: tingling sensations (paresthesia), headaches, mild fatigue, and occasional nausea. No serious drug-related adverse events were reported.

However, researchers caution that phase 3 trials — involving larger, more diverse patient populations over longer periods — are still required before sulthiame can be approved specifically for sleep apnea. The company Apnimed, which is co-developing the drug for this indication, has signaled plans to advance to phase 3 studies. If those trials confirm the FLOW findings, sulthiame could become the first approved pharmacological treatment for obstructive sleep apnea — a milestone that has eluded medicine for decades.