Daybu Clears European Review Hurdle, Marking a Limited but Critical Step for Rett Syndrome Treatment

For families affected by Rett syndrome, whether a drug can cross a regulatory threshold is often more than market news. It means there may be one more option to discuss in daily care. After re-examination on June 25, the European Medicines Agency’s Committee for Medicinal Products for Human Use (CHMP) adopted a positive opinion on Acadia’s trofinetide, recommending approval under the European brand name Daybu for the treatment of neurobehavioral symptoms associated with Rett syndrome.

This turn of events is notable because the CHMP had previously reached a negative conclusion on Daybu. In the European Medicines Agency’s June meeting highlights, the committee said that after re-examination it had changed its position and recommended granting marketing authorization, but with a restricted indication: adult and pediatric patients aged 5 years and older may use it for the treatment of neurobehavioral symptoms, including repetitive hand movements, restlessness, emotional problems, anxiety, sleep problems, and communication difficulties.

Daybu’s active ingredient, trofinetide, is not an entirely new clinical story. It is marketed in the United States under the name Daybue, and the applicant for the European filing is Acadia Pharmaceuticals (Netherlands) B.V. The CHMP positive opinion summary states that the drug will be supplied as a 200 mg/ml oral solution and already has orphan drug status. Under EU procedures, the CHMP opinion is usually sent to the European Commission for a final decision on marketing authorization.

The evidence base comes mainly from the pivotal 12-week, placebo-controlled Study 003. The European Medicines Agency said the study observed statistically significant improvements in the co-primary endpoints and key secondary endpoint, but that the magnitude of effect was small and within an acceptable range. This wording reflects a common reality in rare disease medicines: patient recruitment is limited, symptom assessment is complex, and regulators must make judgments between unmet medical need and uncertainty in the evidence.

The limitations are also clear. Common side effects listed in EMA documents include diarrhea, vomiting, and weight loss. For Rett syndrome patients and families who already require long-term care, these adverse reactions may affect real-world treatment persistence. In other words, if Daybu receives final EU approval, clinical decision-making will still not be only a question of whether it is effective, but whether the degree of symptom improvement, tolerability, and care burden can be balanced.

Rett syndrome is a rare neurodevelopmental disorder in which most patients gradually develop deterioration in language, motor, and behavioral function after early development. The reversal in Daybu’s review does not mean the disease has been fundamentally rewritten, nor should it be interpreted as a curative breakthrough. It is more like a recognition by the regulatory system that, in severe rare diseases, even limited efficacy may still create an approvable treatment position if the evidence points in a consistent direction and the risks are manageable.

The next key questions are whether the European Commission will adopt the CHMP recommendation, and how national healthcare systems will assess reimbursement and conditions of use. For rare disease drug development, Daybu’s shift from a negative opinion to a positive opinion also signals to companies and patient groups that a re-examination procedure can change the conclusion. But what ultimately determines a drug’s value is still whether, after launch, it can deliver stable, bearable, and recognizable improvement in real-world care settings.