Efficacy and safety of givosiran in Japanese patients with acute hepatic porphyria: clinical findings from an expanded access study.

Acute hepatic porphyria (AHP), a rare genetic disorder, causes life-threatening porphyria attacks and chronic pain and impairs daily functioning and quality of life. Recently, a new siRNA therapy, givosiran, became available for AHP. This open-label, multicenter, single-arm study expanded access to givosiran and further explored its safety and efficacy in 10 Japanese patients with AHP. Participants received monthly subcutaneous injections of givosiran (2.5 mg/kg). Three patients were continued from the phase III ENVISION study of givosiran, and seven were newly recruited. Assessments comprised clinical AHP features, urinary aminolevulinic acid (ALA) and porphobilinogen (PBG) levels, use of hemin to treat attacks, and the Givosiran Patient Experience Questionnaire (GPEQ). Urinary ALA and PBG levels remained at or below upper limits of normal levels throughout the study. The GPEQ showed symptomatic improvement in eight participants. Of the eight adverse events, five were deemed by the investigator to be related to givosiran. One patient experienced two attacks, which required urgent healthcare visits but no hemin use. Generally, the safety profile was consistent with that previously observed. All adverse events were nonserious, and no deaths occurred. The study indicates that monthly givosiran administration is safe and clinically useful in Japanese patients with AHP.