New Hope in a Packet: How a Simple Change Offers Profound Progress for Rett Syndrome

SAN DIEGO, CA – December 12, 2025 – For families navigating the complexities of Rett syndrome, a rare and severe neurodevelopmental disorder, daily life is often a series of challenges and carefully managed routines. The condition, which primarily affects girls, robs them of acquired skills like speech and purposeful hand use, leaving them dependent on round-the-clock care. In this landscape, any innovation that eases the burden on caregivers and improves a patient’s quality of life is not just welcome—it's transformative.

This week, a significant step forward came not in the form of a brand-new molecule, but through a thoughtful redesign of an existing lifeline. Acadia Pharmaceuticals announced it has received U.S. Food and Drug Administration (FDA) approval for DAYBUE® STIX (trofinetide), a new powder-for-oral-solution formulation of the first and only approved treatment for Rett syndrome. This dye- and preservative-free powder, designed to be mixed with water-based liquids, represents a pivotal shift toward patient-centric care, offering a new level of flexibility and choice that directly addresses feedback from the Rett community.

Addressing a Critical Need: The Power of Flexibility in Daily Care

Living with Rett syndrome means contending with a host of symptoms, from debilitating motor impairments and hand stereotypies to seizures and anxiety. Administering medication can be one of the most stressful parts of a caregiver’s day, especially for patients who have difficulty swallowing or are sensitive to a medication's taste or texture. The original DAYBUE oral solution, while a breakthrough therapy, brought its own set of administration hurdles for some families.

DAYBUE STIX is engineered to overcome these exact barriers. The new powder formulation empowers caregivers to become partners in the process, allowing them to mix the medication with a small amount of a preferred water-based liquid. This seemingly simple change can make a world of difference, potentially masking an undesirable taste and adjusting the volume to make it more manageable for a child or adult to take.

“The new formulation gives us an additional option for treatment with DAYBUE, allowing us to better customize care for our patients,” explained Dr. Jennifer Martelle Tu, Director of Katie's Clinic for Rett Syndrome and an Associate Professor of Neurology at UCSF Benioff Children's Hospitals, Oakland. “We know that this kind of adaptability is something many Rett families have been seeking.”

While the new formulation is expected to have the same safety profile as the original—including common side effects like diarrhea and vomiting—the enhanced palatability and administration flexibility may indirectly improve the overall treatment experience. For a community where every small victory matters, reducing the daily struggle of medication time can free up precious energy for connection, therapy, and joy.

The Science of Sameness: How Bioequivalence Speeds Innovation

Bringing this improved formulation to market did not require years of new, large-scale clinical trials. Instead, Acadia utilized a well-established and rigorous regulatory pathway centered on the principle of bioequivalence. The FDA’s approval was based on a study demonstrating that DAYBUE STIX delivers the same amount of the active ingredient, trofinetide, into the bloodstream at the same rate as the original oral solution.

This scientific confirmation of bioequivalence is crucial. It provides assurance to physicians, patients, and caregivers that they can expect the same efficacy and safety profile that was established in the pivotal LAVENDER™ clinical study for the original liquid formulation. That study demonstrated statistically significant improvements in key behavioral and communication symptoms of Rett syndrome, offering the first real pharmacological hope for the community.

By leveraging the bioequivalence pathway, the FDA enables companies to introduce patient-friendly improvements—like changing a pill to a liquid, or a liquid to a dissolvable powder—in a much more efficient timeframe. This process acknowledges that once a drug's core safety and effectiveness are proven, subsequent innovations should focus on optimizing its delivery for the people who need it most. It's a prime example of how regulatory science can adapt to support practical, real-world progress without compromising on standards.

A Patient-Centric Strategy in a Competitive Landscape

The development of DAYBUE STIX is more than a product line extension; it's a clear signal of Acadia's long-term commitment to the rare disease community it serves. In a market where a company could simply rest on the success of a first-in-class drug, this move demonstrates a strategy of listening and responding to patient needs. This approach not only builds immense goodwill and brand loyalty but also strengthens the company's position in an increasingly competitive therapeutic area.

DAYBUE has already proven to be a significant therapy, with Acadia projecting net sales between $385 million and $400 million for 2025. This commercial success provides the financial foundation for continued investment in patient-focused innovation. Such investment is strategically vital as the treatment landscape for Rett syndrome evolves. Competitors like Anavex Life Sciences are advancing their own therapies through late-stage trials, and a wave of potentially revolutionary gene therapies from companies including Taysha Gene Therapies and Neurogene are progressing through clinical development. These gene-based treatments aim to correct the underlying genetic cause of the disorder, representing the next frontier of care. By refining its existing therapy to maximize usability and quality of life, Acadia is solidifying its role as a foundational partner for families today, even as the science of tomorrow unfolds.

Looking Ahead: A Future of Choice and Progress

Acadia has announced that DAYBUE STIX will become available on a limited basis in the first quarter of 2026, with a broader rollout planned for the second quarter. Importantly, the company will continue to offer the original oral solution, ensuring that families have a choice between the two formulations based on their individual needs and preferences. This dual offering underscores the core principle of personalized medicine: that the best treatment is the one that works best for the individual patient.

For the 6,000 to 9,000 patients in the U.S. living with Rett syndrome, the approval of DAYBUE STIX is a powerful affirmation that their experiences matter. It is a story of how impactful innovation isn't always about discovering a new molecule, but sometimes about finding a better, more compassionate way to deliver an existing one. It’s a tangible piece of progress that will make a difference in kitchens and at bedsides, lightening the load for caregivers and improving the daily lives of the people they love.