Investing.com -- Shares of Harmony (JO: HARJ ) Biosciences (NASDAQ: HRMY ) plummeted 17% following the announcement that the U.S. Food and Drug Administration (FDA) issued a Refusal to File (RTF) letter regarding the company's submission for pitolisant, aimed at treating excessive daytime sleepiness (EDS) in adult patients with idiopathic hypersomnia (IH).

The RTF letter represents a regulatory hurdle, delaying Harmony's plans to expand the use of pitolisant. Despite the decline in stock price, Harmony maintains its 2025 net revenue guidance of $820-$860 million, indicating confidence in its long-term strategy and existing product offerings. The company's CEO, Jeffrey M. Dayno, M.D., expressed disappointment with the FDA's decision but reaffirmed the commitment to developing Pitolisant HD, a higher-dose formulation of the drug with a provisional patent extending to 2044. Harmony anticipates initiating a Phase 3 registrational trial for Pitolisant HD in IH by the fourth quarter of 2025, with a target Prescription Drug User Fee Act (PDUFA) date in 2028.

While the primary outcome for EDS between pitolisant and placebo in the randomized withdrawal phase of the Phase 3 INTUNE Study did not achieve statistical significance, the open-label phase showed patient improvements on the Epworth Sleepiness Scale that were considered clinically meaningful. Harmony's Chief Medical (TASE: PMCN ) and Scientific Officer, Kumar Budur, M.D., M.S., remains optimistic about the upcoming Phase 3 trial design, which is expected to effectively demonstrate pitolisant's benefit for IH patients.

Harmony Biosciences currently markets pitolisant as WAKIX® in the U.S. for the treatment of EDS or cataplexy in adult patients with narcolepsy and for EDS in pediatric patients 6 years of age and older with narcolepsy. However, the drug is not approved for IH, the indication for which the RTF letter was received.

Despite the setback, Harmony emphasizes its diversified pipeline and commitment to advancing science in sleep/wake and rare neurological disorders as key components of its long-term vision. The company is focused on executing its strategic priorities and delivering sustained growth.

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