Vykat Defends $107M Franchise as Eight Deaths Cloud Approved Benefit-Risk

Neurocrine Defends Vykat Amidst New Patient Death and Safety Concerns

Neurocrine Biosciences is defending its Prader-Willi syndrome therapy, Vykat, following another patient death, bringing the total reported deaths to eight. The company reiterated confidence in the drug's benefit-risk profile and the FDA-approved label, urging appropriate monitoring. Despite safety concerns, Vykat generated $107 million in the third quarter, contributing to Neurocrine's total revenue of $1.1 billion. Neurocrine plans a new study in 2027 to explore dosing and safety in patients with complex health issues, clarifying it was not an FDA request. This comes after the $2.9 billion acquisition of Soleno Therapeutics in April 2026, which brought Vykat into Neurocrine's portfolio.

• Neurocrine Biosciences confirmed an eighth patient death associated with its Prader-Willi syndrome drug, Vykat, since its approval in 2025. Despite this, the company maintains confidence in the drug's safety profile, emphasizing that the FDA-approved label provides clear guidance for safe and effective use in the indicated patient population, contingent on appropriate monitoring and patient selection.
• In response to ongoing safety concerns and analyst inquiries during its third-quarter earnings call, Neurocrine announced plans for a new study in 2027. This study will investigate dosing and safety specifically in Prader-Willi patients with complex health issues, aiming to build further evidence. The company clarified that this initiative is proactive and not a direct request from the FDA.
• The safety concerns have led to tempered growth expectations from analysts, with BMO Capital Markets anticipating increased patient discontinuations in late 2026 and early 2027. Clinicians have previously warned about seven deaths and over 100 serious adverse events, including edema, respiratory, and cardiac complications, particularly in patients with pre-existing obesity, severe breathing issues, or underlying heart problems.

Vykat's Safety Profile: What the Data Shows

In the 13-week randomized, double-blind, placebo-controlled Phase 3 DESTINY PWS trial in participants aged 4 years and older, diazoxide choline extended-release tablet (DCCR) was generally well tolerated, with 83.3% in the DCCR group experiencing a treatment-emergent adverse event and 73.8% in the placebo group (not significant). In the long-term open-label assessment of 125 participants receiving DCCR for up to 52 weeks in DESTINY PWS and/or its open-label extension, DCCR administration to people with PWS was well-tolerated and associated with broad-ranging improvements in the syndrome.

The reported adverse event profile was consistent across studies. Common treatment-emergent adverse events included hypertrichosis, peripheral edema, and hyperglycemia. In the single-center Phase II pilot study in 13 overweight or obese adolescent and adult subjects, the most common adverse events were peripheral edema and transient increases in glucose, and many of the adverse events were common medical complications of PWS and diazoxide.

Treatment persistence supported tolerability in the long-term setting, with adverse events infrequently resulting in discontinuation (7.2%). In the pilot proof-of-concept study, DCCR treatment appeared to address unmet needs including hyperphagia and aggressive behaviors, and sustained administration of DCCR has the potential to reduce disease severity and the burden of care for families.

Addressing Unmet Needs in Prader-Willi Syndrome

Prader-Willi syndrome remains difficult to treat because hyperphagia and obesity drive premature mortality from diabetes mellitus, metabolic syndrome, sleep apnea, respiratory insufficiency, and cardiovascular disease, while therapeutic options remain limited. The control of hyperphagia and improving food-related behaviors are the most important unmet needs in PWS and could be addressed with the development of a new therapeutic agent.

• Absence of broadly effective pharmacotherapy for hyperphagia and weight control. No widely accepted consensus guideline exists concerning anti-obesity medications in children with PWS, and studies on metformin, topiramate, liraglutide, and setmelanotide are still limited. In DESTINY PWS, a 13-week, randomized, double-blind, placebo-controlled, phase 3 trial in 127 participants aged 4 years and older, diazoxide choline extended-release tablet (DCCR) did not significantly improve hyperphagia in the primary analysis (HQ-CT least-square mean [SE] -5.94 [0.879] vs -4.27 [1.145]; P = .198), but did so in participants with severe hyperphagia and in the pre-COVID analysis. In the 12-week COMPASS PWS study in 175 participants randomized 1:1 to carbetocin 3.2 mg TID nasal spray (n = 85) and placebo (n = 90), the least squares mean change (standard error) in HQ-CT was -4.8 (0.8) and -5.1 (0.8), respectively, with treatment difference of 0.3 (95% confidence interval: -1.8, 2.4; P = 0.79) that was not statistically significant, with no separation for any secondary or exploratory endpoint.

• Safety limitations that halted promising mechanisms. MetAP2 inhibition with beloranib produced statistically significant improvements in hyperphagia-related behaviours and weight loss, with improvement in HQ-CT total score greater in the 1.8 mg (mean difference -6.3, 95% CI -9.6 to -3.0; P = .0003) and 2.4 mg groups (-7.0, 95% CI -10.5 to -3.6; P = .0001) vs placebo, but dosing was stopped early due to an imbalance in venous thrombotic events in beloranib-treated participants (2 fatal events of pulmonary embolism and 2 events of deep vein thrombosis) compared with placebo. Growth hormone therapy can trigger or worsen obstructive sleep apnea or hypoventilation in some patients, may contribute to adenotonsillar hypertrophy, and has reports of sudden death within the first 6 months of treatment in children with Prader-Willi syndrome, mostly associated with severe obesity, requiring polysomnography to assess need for adenotonsillectomy before initiating recombinant human growth hormone therapy and close monitoring during treatment.

• Poor durability of diet, lifestyle, and surgical approaches. Subjects with PWS will become severely obese unless food intake is strictly controlled, and once obesity develops it is difficult to maintain control of food intake, with successful weight loss and maintenance hardly accomplished. Parents experienced difficulties with children still stealing food, and especially lowering carbohydrates was considered challenging, while combined dietary and lifestyle intervention resulted in decreased BMI, although BMI returned to baseline values on long-term follow-up. Bariatric surgery literature in hypothalamic obesity is largely limited to case reports and series with short term follow-up, making it difficult to draw conclusions as to long term safety and efficacy.

• Trial design constraints in a heterogeneous rare disease. Developing clinical trials is complicated by varied genotype and phenotypic differences, including paternal 15q11-q13 deletion observed in about 60% of individuals, maternal disomy 15 found in approximately 35% of cases, and imprinting center defects, with behavior problems impacted by genetic subtypes. A small-scale clinical study may indicate a positive outcome but have too small of a sampling population to adequately evaluate unwanted outcomes, and enrollment in the CARE-PWS phase 3 trial was stopped prematurely because of onset of the COVID-19 pandemic.

Understanding Safety Signals in Prader-Willi Trials

Safety signals in Prader-Willi syndrome trials vary by therapeutic mechanism, with metabolic, respiratory, and vascular events most closely monitored. Growth hormone studies report long-term respiratory and glycemic risks, while diazoxide choline, carbetocin, and other investigational agents show distinct tolerability profiles.

• Diazoxide choline extended-release tablet (DCCR): Common treatment-emergent adverse events included hypertrichosis, peripheral edema, and hyperglycemia, with adverse events infrequently resulting in discontinuation (7.2%). The pilot study reported peripheral edema and transient increases in glucose as the most common adverse events, and the 16-week randomized withdrawal study reported adverse events were similar with both treatments, with no serious adverse events in the DCCR arm.

• Growth hormone / somatropin: In KIGS, there were five cases of sudden death (age range 3-15 years), with three obese (weight for height > 200%) and causes including bronchopneumonia, respiratory insufficiency and sleep apnoea; scoliosis was the most commonly reported adverse event (n = 24), with four children developing hyperglycaemia and six having presumptive diabetes (type 2 in five, and one case of type 1). In PATRO Children, adverse events were reported in 192 patients (81.7%) and serious adverse events in 96 patients (40.9%), with the most frequent treatment-related serious adverse events being sleep apnea syndrome (n = 11; 4.7%), tonsillar hypertrophy (n = 4; 1.7%), and adenoidal hypertrophy (n = 4; 1.7%), plus treatment-related scoliosis in two patients, impaired glucose tolerance in one patient and type 2 diabetes mellitus in another patient.

• Growth hormone tolerability in adults and registries: The United States multicenter trial reported mildly progressive ankle edema as the most serious treatment-emergent adverse event (five patients), without glucose impairment. The Japanese Phase 3 study reported treatment-emergent adverse events in five (83.3%), five (71.4%), and 19 (95.0%) participants in the GH-naïve pediatric cohort, GH-treated pediatric cohort, and adult cohort, respectively, with three participants reporting four serious treatment-emergent adverse events, and none were treatment related. The 10-year LG Growth Study reported adverse events in 34.2% of patients, adverse drug reactions in 7.0%, serious adverse events in 3.2%, and serious adverse drug reactions in 0.3%, with the most frequent adverse event being scoliosis (1.6%), followed by headache (0.8%) and injection site pain (0.5%).

• Carbetocin and beloranib: The CARE-PWS Phase 3 trial reported the most common adverse event during the placebo-controlled period was mild to moderate flushing, while the 14-day trial reported incidence of adverse events was similar between treatment groups. Beloranib reported injection site bruising as the most frequent adverse event, with dosing stopped early due to an imbalance in venous thrombotic events in beloranib-treated participants (2 fatal events of pulmonary embolism and 2 events of deep vein thrombosis) compared with placebo.

• Neurobehavioral and metabolic agents: Guanfacine-extended release reported no serious adverse events, with fatigue/sedation as the only adverse event significantly associated with treatment. Aripiprazole for temper outbursts reported adverse effects from mild to partly serious extent in 60% of cases, with increased daytime sleepiness as the major adverse effect and discontinuation in only 20% of cases. Liraglutide reported gastrointestinal disorders as the most common adverse events.