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Phase 2 trial shows bitopertin reduces protoporphyrin-IX in adults with erythropoietic protoporphyriaExperimental drug bitopertin reduces key protein in adults with light sensitivity disorder

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Key Takeaway
Consider bitopertin's phase 2 efficacy in reducing protoporphyrin-IX as preliminary, pending larger confirmatory trials.

This phase 2 randomized controlled trial evaluated the efficacy and safety of bitopertin, a glycine transporter 1 inhibitor, in 75 adults with erythropoietic protoporphyria. Participants were randomized to receive once-daily oral bitopertin 20 mg (n=26), 60 mg (n=25), or placebo (n=24) for 17 weeks. The primary outcome was the percentage change from baseline in whole-blood metal-free protoporphyrin-IX levels at day 121.

For the primary outcome, bitopertin 20 mg reduced protoporphyrin-IX by 29.6% versus placebo (P = .004), and the 60 mg dose reduced it by 49.8% (P < .001). The incidence of phototoxic reactions was also reduced with bitopertin, though specific incidence rates and statistical significance were not reported. The study reported bitopertin was well tolerated with no notable safety concerns identified, though detailed adverse event data were not provided.

Key limitations include the small sample size, short 17-week follow-up period, and lack of formal statistical adjustments for multiple pairwise comparisons between groups. As a phase 2 trial, these results are preliminary. No disease-modifying therapies are currently approved for erythropoietic protoporphyria, so this represents an investigational approach. The findings support further study of bitopertin in larger phase 3 trials with longer follow-up to confirm efficacy and establish a comprehensive safety profile.

Researchers conducted a 17-week study to see if a new oral drug, bitopertin, could help adults with erythropoietic protoporphyria (EPP). EPP is a rare disorder where sunlight causes severe, burning pain. The study involved 75 adults who took either a 20 mg dose, a 60 mg dose, or a placebo pill daily. The main goal was to see if the drug lowered levels of a protein in the blood called protoporphyrin-IX, which causes the light sensitivity.

By the end of the study, both doses of bitopertin significantly reduced this protein level compared to the placebo. The higher dose reduced it by nearly 50%. The study also found that people taking bitopertin had fewer painful skin reactions to light. The drug was reported to be well-tolerated with no major safety concerns identified during the trial.

It is important to be cautious about these results. This was a phase 2 trial, which means it was relatively small and only lasted about four months. The researchers noted the study was too short to know about long-term safety or benefits, and the small number of people means the findings need to be confirmed. Currently, there are no approved drugs that modify the course of EPP.

For now, this research shows bitopertin is a promising candidate that successfully lowered a key marker of the disease in a short-term study. The next steps will require much larger and longer trials to see if reducing this protein reliably leads to less pain and more time in the sun for people living with EPP.

What this means for you:
An experimental drug reduced a key marker of a rare light sensitivity disorder in a small, short-term study. More research is needed.

Study Details

Study typeRct
Sample sizen = 26
EvidenceLevel 2
Follow-up3.9 mo
PublishedApr 2026
View Original Abstract ↓
BACKGROUND: Erythropoietic protoporphyria is a rare genetic disorder of heme biosynthesis characterized by protoporphyrin-IX accumulation, painful phototoxic reactions, and hepatobiliary disease, for which no disease-modifying therapies are approved. OBJECTIVE: To evaluate the efficacy and safety of bitopertin, an inhibitor of glycine transporter 1, in adults with erythropoietic protoporphyria. METHODS: In this randomized, double-blind, phase 2 study, patients received once-daily oral bitopertin 20 mg, bitopertin 60 mg, or placebo for 17 weeks. The primary endpoint was percentage change from baseline in whole-blood metal-free protoporphyrin-IX levels at day 121. RESULTS: Patients received bitopertin 20 mg (n = 26), 60 mg (n = 25), or placebo (n = 24). At day 121, the percentage change from baseline in whole-blood metal-free protoporphyrin-IX versus placebo was -29.6% (P = .004) with bitopertin 20 mg and -49.8% (P < .001) with bitopertin 60 mg. Bitopertin was associated with a reduced incidence of phototoxic reactions. Bitopertin was well tolerated with no notable safety concerns identified. LIMITATIONS: Small sample size, short follow-up period, and no formal adjustments for between-group multiple-pairwise comparisons. CONCLUSIONS: Bitopertin significantly reduced protoporphyrin-IX levels, showed improved measures of sunlight tolerance, and had a favorable safety profile in patients with erythropoietic protoporphyria.
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