Stock reaction and context
MBX Biosciences Inc (NASDAQ:MBX) experienced a 19.6% decline in premarket trading on Friday after releasing sustained one-year data from its once-weekly canvuparatide program for adults with chronic hypoparathyroidism. The company disclosed results from the 12-week Avail Phase 2 trial as well as one-year findings from the ongoing open-label extension study.
Trial efficacy measures
In the open-label extension, the responder rate was 57% at one year, compared with a 63% responder rate observed at 12 weeks in the randomized Phase 2 study. In the earlier 12-week trial, 63% of patients treated with canvuparatide met the primary composite endpoint versus 31% of placebo-treated patients. The primary composite endpoint was defined as maintaining albumin-adjusted serum calcium within the normal range while remaining independent from conventional therapy.
Durability and physiologic effects
Company results indicate multiple sustained physiologic effects through one year of treatment. Mean serum calcium levels were maintained within the normal range over the 12-month period. Mean 24-hour urine calcium excretion declined from baseline. In addition, mean estimated glomerular filtration rate (eGFR) increased from baseline by Week 12 in canvuparatide-treated patients and the improvement was maintained through one year.
MBX also reported evidence of restoration of systemic parathyroid hormone (PTH) activity as reflected in serum calcium normalization, reduced urinary calcium loss, and a restoration of bone metabolism markers described in the release.
Retention and safety observations
The study achieved a 90% retention rate, with patients who entered the open-label extension remaining in the study at the one-year mark. Canvuparatide was generally well tolerated over the extension period; no new safety signals emerged. Most treatment-emergent adverse events were reported as mild or moderate in severity, and the company reported no treatment-related serious adverse events. Injection site reactions were reported in 10% of patients.
Development timeline
MBX stated that its Phase 3 pivotal trial remains on schedule to initiate in the third quarter of 2026.
This article presents the company-disclosed clinical and market reaction information without additional commentary. The data described are limited to the measures and outcomes reported by the company.