Alkermes plc (NASDAQ: ALKS) reported interim results from an ongoing long-term extension study showing that its investigational drug alixorexton sustained improvements in wakefulness and daytime sleepiness for up to nine months in adults with narcolepsy type 1 (NT1) and narcolepsy type 2 (NT2).

The interim analysis, based on a May 12, 2026 data cutoff, measured outcomes at week 24 of the long-term extension for participants who had previously completed the Vibrance-1 (NT1) and Vibrance-2 (NT2) phase 2 studies. Alixorexton is an investigational oral orexin 2 receptor agonist not yet approved by regulators.

In NT1 participants, all dose groups achieved a mean observed sleep latency of approximately 29 minutes on the Maintenance of Wakefulness Test at week 24, compared to baseline values of 1.7 to 3.4 minutes. Mean Epworth Sleepiness Scale scores fell to 7.5 from baseline scores near 19. Approximately 85% of Vibrance-1 participants enrolled in the extension, with roughly 90% remaining on treatment at the data cutoff.

In NT2 participants, mean observed sleep latency reached approximately 18 minutes at week 24, up from baseline values of 2.0 to 5.2 minutes. Mean Epworth scores declined to 8.9 from baselines near 17 to 18. About 70% of Vibrance-2 participants enrolled in the extension, with approximately 80% remaining on treatment.

Patient-reported measures of cognition and fatigue also showed sustained improvements from baseline in both NT1 and NT2 participants across all doses at week 24.

No serious treatment-emergent adverse events were reported in either group. The most common adverse events in NT1 participants were headache, micturition urgency, pollakiuria, and nasopharyngitis. In NT2 participants, common adverse events included insomnia, headache, pollakiuria, and upper respiratory tract infection.

Alixorexton is currently being evaluated in the phase 3 Brilliance Studies for NT1 and NT2, and in the phase 2 Vibrance-3 study for idiopathic hypersomnia. The U.S. Food and Drug Administration has granted the drug Breakthrough Therapy designation for NT1. Alkermes plans to present full results at an upcoming medical meeting.