Three Prader-Willi syndrome (PWS) patient organizations have issued a joint safety statement on diazoxide choline (Vykat XR), calling for more careful patient selection and monitoring after seven deaths and more than 100 serious adverse events were reported to the FDA's Adverse Event Monitoring System (AEMS) as of July 31, 2026. The reports do not establish that Vykat XR caused the events, and the organizations stopped short of recommending against use of the drug.
The statement from PWSA USA, the Foundation for Prader-Willi Research (FPWR), and the International Prader-Willi Syndrome Organisation (IPWSO) highlights fluid overload, respiratory and cardiac complications and recommends particular caution in patients with severe obesity, cardiac disease, edema or untreated obstructive sleep apnea. Many of the affected individuals had complex underlying conditions and multiple concurrent medications, while PWS itself carries substantial baseline respiratory and cardiovascular mortality risk.
Neurocrine Biosciences (Nasdaq: NBIX) said it remains in close contact with the FDA, patient organizations and prescribers as part of its post-marketing surveillance and maintained that Vykat XR has a favorable benefit-risk profile given the severity of PWS. The company also said it extensively reviewed adverse-event data during due diligence for its acquisition of Vykat XR developer Soleno Therapeutics, as reported by Reuters.
The reports nevertheless raise questions about Vykat XR's safety profile as use expands beyond the relatively selected population enrolled in clinical trials. Fluid retention is already a labeled risk and edema was observed during clinical development, but no deaths occurred in the pivotal study. The patient groups said post-marketing experience may increasingly include individuals with more severe obesity and cardiorespiratory disease than those represented in the pre-approval studies.
Vykat XR activates ATP-sensitive potassium channels in hypothalamic neurons to reduce the pathological hunger associated with PWS and became the first FDA-approved treatment for hyperphagia in the disorder in March 2025. Its rapid US launch subsequently made the drug the central asset in Neurocrine's USD 2.9 billion acquisition of Soleno Therapeutics, which was announced in April and completed in May 2026.
The acquisition has already been followed by regulatory complications outside the US. Shortly after the deal was announced, Soleno withdrew its European Marketing Authorization Application for Vykat XR, known as Viokat in Europe, delaying potential EU commercialization. Soleno publicly attributed the withdrawal to business and strategic considerations, although transaction filings subsequently disclosed that the company had received information from the European Medicines Agency in February that raised concerns it might not secure approval. European regulatory prospects were among the issues considered by Soleno's board during the sale process.