ELFABRIO Approval Offers Blueprint for Small-Population Biologic Trials

Chiesi Farmaceutici S.p.A. secured FDA approval for ELFABRIO (pegunigalsidase alfa-iwx) on May 9, 2023, establishing a regulatory precedent that biologics manufacturers targeting rare disease populations will need to study closely. The approval rested on a combined dataset from just 93 patients across two trials, a scale that places acute pressure on trial design integrity, endpoint selection, and demographic representativeness under 21 CFR Part 211 and ICH Q10 frameworks.

ELFABRIO is an enzyme replacement therapy (ERT) indicated for adult patients with Fabry disease, an inherited lysosomal storage disorder caused by deficiency of alpha-galactosidase-A, resulting in pathological accumulation of globotriaosylceramide (Gb3) in renal, cardiac, neurological, and gastrointestinal tissues. The therapy is administered as an intravenous infusion every two weeks at an approved dose of 1.0 mg/kg. Doses of 0.2 mg/kg and 2.0 mg/kg evaluated in Trial 1 have not been established as safe or effective and are not approved.

Trial architecture and its implications for process validation: Trial 1 was a single-arm study enrolling 16 ERT-naive patients or those without ERT exposure for more than 26 weeks, conducted across 13 sites in 6 countries. Efficacy was assessed at six months using renal biopsy to quantify Gb3 deposition in kidney tissue. Trial 2 enrolled 77 patients previously treated with agalsidase beta, randomized against that comparator over 24 months across 28 sites in 12 countries, with endpoints including estimated glomerular filtration rate and safety and tolerability data.

• No comparator group was included in Trial 1
• Trial 2 used agalsidase beta as the active comparator
• The approved dose was identified through a dose-ranging design within Trial 1

For QA directors and regulatory affairs leads, the ELFABRIO dossier illustrates how FDA is willing to accept renal biopsy as a surrogate efficacy endpoint in rare disease ERTs when patient population constraints limit conventional trial power. Manufacturers developing biologics for similarly small populations should note the agency's acceptance of a 16-patient single-arm study as the primary efficacy basis, provided the mechanistic rationale and endpoint sensitivity are well-characterized. Sterility assurance and comparability protocols for the biologic manufacturing process remain critical given the intravenous route of administration and the vulnerable patient population.

Source: FDA Drug Trials Snapshot for ELFABRIO, original approval date May 9, 2023, published April 29, 2026. Refer to the ELFABRIO Prescribing Information for all approved conditions of use.