Bitopertin Met Primary and Secondary Endpoints in Phase 3 EPP Trial

Oral bitopertin (Disc Medicine) met both co-primary endpoints and all secondary endpoints in the phase 3 APOLLO trial in adults and adolescents with erythropoietic protoporphyria (EPP), including X-linked protoporphyria (XLP), Disc Medicine announced in topline results.

Bitopertin is an investigational glycine transporter 1 inhibitor designed to modulate heme biosynthesis and is not approved in any jurisdiction, according to the company. EPP results in accumulation of protoporphyrin IX (PPIX), which causes severe, painful reactions to sunlight. The randomized, double-blind APOLLO trial enrolled 183 patients aged 12 years or older with EPP or XLP in the US, Canada, Europe, and Australia, who received bitopertin 60mg or placebo once daily for 6 months.

Compared with placebo, bitopertin was associated with a 41.4% reduction in whole-blood metal-free PPIX from baseline and a 12.2-hour increase in average monthly total time in light without pain during month 6, the co-primary endpoints. Secondary endpoints, including the incidence of phototoxic reactions, cumulative time in light without pain over 6 months, and, in adults, average daily sunlight exposure time to prodrome, also significantly favored bitopertin. Exploratory quality-of-life measures favored bitopertin as well. The company did not report effect sizes for the secondary endpoints or CIs for any endpoint.

The company described bitopertin as generally well tolerated. Dizziness was the most common treatment-emergent adverse event, occurring in 50% of bitopertin recipients; it was mild or moderate and generally transient. No treatment-emergent adverse events above grade 3 occurred. Placebo-group adverse event rates were not reported.

Disc said it plans to resubmit a new drug application to the FDA by the end of 2026, with an FDA decision anticipated by mid-2027, and to present more detailed APOLLO data at a future medical conference.

Source: Disc Medicine. Disc Medicine announces success on all primary and secondary endpoints in the pivotal phase 3 APOLLO trial of bitopertin in adults and adolescents with erythropoietic protoporphyria (EPP). News release. Disc Medicine; October 19, 2026. Accessed October 19, 2026.