FDA Approves New Powder Formulation of Trofinetide (Daybue) for Rett Syndrome

The US Food and Drug Administration has approved Acadia Pharmaceuticals’ trofinetide (Daybue Stix) for oral solution, a dye- and preservative-free powder formulation of trofinetide for the treatment of Rett syndrome in adult and pediatric patients ≥ 2 years of age.

As described in a December 12, 2025, release from the Company, the new formulation is expected to deliver the same efficacy and safety profile of trofinetide oral solution, while offering children and adults living with Rett syndrome new flexibility and choice regarding the dose volume and taste of their trofinetide treatment.

“The new formulation gives us an additional option for treatment with DAYBUE, allowing us to better customize care for our patients,” said Jennifer Martelle Tu, MD, PhD, Director of Katie's Clinic for Rett Syndrome and Associate Professor of Neurology, UCSF Benioff Children's Hospitals, Oakland. “DAYBUE STIX is a powder for oral solution that caregivers can mix with a variety of water-based liquids providing flexibility to modify the taste and volume of their loved-one's dose. We know that this kind of adaptability is something many Rett families have been seeking.”

Trofinetide is a synthetic analog of the N-terminal tripeptide of insulin-like growth factor 1. It became the only FDA-approved treatment for Rett syndrome in 2023. The mechanism by which it exerts therapeutic effects in patients with Rett syndrome is unknown, but in animal studies, trofinetide has been shown to increase branching of dendrites and synaptic plasticity signals.

“DAYBUE, the first and only approved treatment for Rett syndrome, has provided thousands of patients an important therapeutic option,” said Catherine Owen Adams, Acadia’s Chief Executive Officer. “With the approval of DAYBUE STIX, we are building on our commitment to turn scientific promise into meaningful innovation by introducing a new formulation informed by invaluable feedback from patients, caregivers and healthcare providers.”

The efficacy and safety of this new formulation was assessed in the LAVENDER™ study in patients with Rett syndrome. The approval was informed by the results of a bioequivalence study, which demonstrated that both original trofinetide oral solution and the new trofinetide for oral solution powder formulation provide comparable exposure. This confirmed bioequivalence means patients can expect the same efficacy and safety established by the oral solution formulation when using trofinetide for oral solution powder formulation.

As described in the release from Acadia, DAYBUE STIX will be available on a limited basis starting in the first quarter of 2026 and more broadly early in the second quarter of 2026, and the current oral solution formulation will remain available.

References

1. Acadia Pharmaceuticals. Acadia Pharmaceuticals Announces FDA Approval of DAYBUE® STIX (trofinetide) for Oral Solution, a New Powder Formulation of Trofinetide for the Treatment of Rett Syndrome. December 12, 2025. Accessed December 12, 2025. https://acadia.com/en-us/media/news-releases/acadia-pharmaceuticals-announces-fda-approval-daybuer-stix

2. FDA. FDA approves first treatment for Rett Syndrome. March 13, 2023. Accessed December 12, 2025. https://www.fda.gov/drugs/news-events-human-drugs/fda-approves-first-treatment-rett-syndrome