Disc's Bitopertin Hits All Phase 3 Goals in Rare Light Disorder

Disc Medicine reported on October 19 that its oral drug bitopertin met all primary and secondary endpoints in APOLLO, a pivotal Phase 3 trial in erythropoietic protoporphyria (EPP). The company plans to go back to the FDA with the data before the end of 2026.

What happened

APOLLO was a randomized, double-blind, placebo-controlled study. It enrolled 183 people aged 12 or older with EPP or X-linked protoporphyria at sites in the US, Canada, Europe and Australia. Patients took 60 mg of bitopertin or a placebo once a day for six months.

The trial had two co-primary endpoints, and the company said both were met:

• Blood PPIX: whole-blood metal-free protoporphyrin IX fell by 41.4% compared with placebo.
• Time in light: in the sixth month, average total time in light without pain rose by 12.2 hours compared with placebo.

On secondary endpoints, Disc reported that the rate of phototoxic reactions was 71% lower than with placebo. In adults, daily sunlight time before early warning symptoms rose by 56 minutes compared with placebo.

Dizziness was the most common side effect, reported by 50% of people on bitopertin. The company said it was mostly mild or moderate and usually passed. No one on bitopertin stopped treatment because of a side effect.

Why it matters

EPP is a rare genetic disease. A buildup of PPIX makes sunlight exposure painful. Standard care centres on staying out of the sun.

According to Dermatology Times, the only FDA-approved therapy for EPP is Scenesse, a surgically implanted hormone. Bitopertin is a pill designed to adjust heme production, with the aim of lowering PPIX.

The result also matters for Disc's regulatory path. In February 2026, the FDA turned down the company's earlier application, which sought accelerated approval. The agency accepted that bitopertin lowers PPIX. It said the earlier trials did not show that lower PPIX led to benefits tied to sunlight exposure. The FDA said at the time that APOLLO results could support traditional approval.

APOLLO measured both PPIX and time in light, which goes to the gap the FDA described. Bitopertin is still investigational and is not approved anywhere.

What it means for people in the industry

Disc plans to resubmit its new drug application by the end of 2026 and expects an FDA decision by mid-2027. The company said fuller APOLLO data will come at a future medical meeting.

Things to watch include the FDA's response to the resubmission and the detailed data release. The company did not announce hiring or site plans with the results.

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Sources

• Disc Medicine bitopertin meets Phase 3 trial goals, Stock Titan (Disc Medicine Form 8-K and press release)
• Bitopertin Meets All End Points in Phase 3 APOLLO Trial for EPP, Dermatology Times
• Disc Medicine Receives Complete Response Letter from FDA for Bitopertin for the Treatment of EPP, Disc Medicine