FDA Rejects Disc Medicine's Bitopertin for Rare Blood Disorder Under Fast-Track Program

Disc Medicine said on Friday the U.S. Food and Drug Administration declined to approve its drug bitopertin to treat a rare genetic disorder, sending its shares down 21%, with additional after-market declines reaching 31.6% to $48.90. The FDA issued a Complete Response Letter on February 13, 2026, rejecting the company's accelerated approval bid for bitopertin in erythropoietic protoporphyria over concerns that reductions in protoporphyrin IX had not been shown to reliably predict clinical benefit.

The drug was being reviewed under the FDA's national priority voucher program, which fast-tracks the process to one to two months from the typical 10-12 months. This marks the first time the agency has declined a drug submitted through the newly implemented program designed to accelerate drug reviews. In December, the FDA had previously approved a generic antibiotic through the same fast-track program.

The company was testing bitopertin as a treatment for erythropoietic protoporphyria, a blood disorder which makes patients extremely sensitive to sunlight. The condition leads to the buildup of protoporphyrin in the blood, leading to extreme sensitivity to sunlight, which can cause painful skin reactions. Erythropoietic protoporphyria is a rare genetic metabolic disorder caused by a deficiency of the ferrochelatase enzyme, with hypersensitivity of the skin to sunlight as the major symptom.

Disc said the agency concluded the two mid-stage trials did not show a clear link between the reduction in patients' protoporphyrin levels and their tolerance to sunlight. Reviewers pushed back bitopertin's review by two weeks on concerns about trial data and its risk for abuse. The delay was due to the agency's concerns over whether pain-free time in the sun – a secondary trial goal – was a statistically solid measure of efficacy, or if other biomarker data could justify approval.

The FDA requested additional clinical endpoint evidence, indicating it wants to see results from the ongoing Phase 3 APOLLO trial and updated safety data before reconsidering. The company on Friday said the issue raised by the regulator is "readily addressable" as it expects results from its ongoing late-stage study in the fourth quarter.

On February 17, 2026, Disc Medicine planned a conference call to address the Complete Response Letter, prompting the company to prioritize completing APOLLO enrollment by March 2026 and delivering topline data in the fourth quarter of 2026 for use in a resubmission. Disc Medicine said on Tuesday it will pursue a traditional U.S. approval pathway for its rare disease drug after the Food and Drug Administration declined to approve the treatment under the new fast-track review program.

Disc plans to respond to the FDA's rejection letter once the late-stage study is completed and expects an updated FDA decision by mid-2027. For a resubmission, Disc will need to run an adequate and well-controlled study that uses clinical endpoints to measure the efficacy of bitopertin.

The CEO said the policy debate over accelerated approval has stretched across multiple U.S. administrations, and recent regulatory decisions suggest an increasingly stringent view on when such approvals are appropriate. The decision adds to evidence of internal agency turbulence and a meaningful shift in approval standards for rare-disease therapies. The rejection is not the end of the world for Disc, as the late-stage trial if positive should support full approval.

The FDA's stance underscores a higher evidentiary bar for approval, potentially delaying bitopertin's market entry but clarifying the regulatory path and placing greater emphasis on APOLLO's co-primary endpoints that link biomarker reductions to improvements in sunlight tolerance. For investors and patients, the outcome of APOLLO has become a pivotal inflection point for Disc's EPP program and its broader positioning in the rare disease hematology space, as successful data could both satisfy regulators and validate the company's biomarker-driven approach.

Disc Medicine, Inc. is a biopharmaceutical company focused on developing treatments for hematologic diseases, including rare disorders such as erythropoietic protoporphyria. Its pipeline includes bitopertin and other candidates like DISC-0974 and DISC-3405, targeting serious blood-related conditions where there are limited existing therapeutic options.