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# FDA Rejects Commissioner's Voucher Drug
- URL: https://www.fdaweb.com/fda-rejects-commissioners-voucher-drug/
- Published: 2026-02-13T12:00:00.000Z
- Updated: 2026-09-14T13:33:48.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5160671

FDA has issued Disc Medicine a [complete response letter](https://download.open.fda.gov/crl/CRL%5FNDA220707%5F20260213.pdf?ref=fdaweb.com) (CRL) for its experimental therapy bitopertin, indicated for treating erythropoietic protoporphyria, or EPP. The Watertown, MA-based company was seeking accelerated approval under the Commissioner’s National Priority Voucher pilot program.

The letter said FDA had concluded that while mid-stage trial data showed the drug significantly reduced a key biomarker associated with the rare blood disorder, the application did not adequately demonstrate that biomarker changes were reasonably likely to predict clinical benefit, according to the company.

In its review, FDA agreed that results from the Phase 2 AURORA and BEACON studies provided sufficient evidence that bitopertin significantly lowered whole blood metal-free protoporphyrin IX, or PPIX, a toxic heme precursor that accumulates in patients with EPP, the company says. Elevated PPIX levels are linked to the severe photosensitivity that characterizes the disease.

However, the agency determined that the trials did not show a clear association between the percentage reduction in PPIX and improvements in sunlight exposure–based endpoints measured in the studies, the company says. Although FDA acknowledged the “strong mechanistic and biological plausibility” of using PPIX as a biomarker in protoporphyria, it said the data did not establish that the magnitude of PPIX reduction observed would predict clinical benefit under the accelerated approval standard. While the agency acknowledged the biomarker effect, it has held firm that correlation with real patient outcomes is essential, likely setting a clearer precedent for how surrogate endpoints are evaluated in rare diseases going forward.

FDA also indicated that results from the ongoing Phase 3 APOLLO study could potentially support a traditional approval. Disc said enrollment in the APOLLO study is expected to be completed in March 2026, several months ahead of schedule, with topline data anticipated in the fourth quarter of 2026\. If the APOLLO results are supportive, Disc plans to resubmit its application in response to the CRL and expects a potential updated FDA decision by mid-2027.