In a 10-patient Phase 2 proof-of-concept study in post-surgical hypoparathyroidism, 80% of participants on encaleret achieved concomitant normalization of serum calcium and 24-hour urine calcium within five days of treatment initiation, versus 0% on conventional therapy at baseline. Nine participants showed a rapid and sustained reduction in fractional excretion of calcium. No serious adverse events were reported over the brief study period.
BridgeBio disclosed the data at ASBMR and outlined plans to initiate a registrational study of encaleret in chronic hypoparathyroidism in 2026. Participants received 162 mg twice daily for up to five days, with calcitriol stopped one day prior and background calcium and calcitriol titrated based on blood calcium. The company positioned the effect as parathyroid hormone–independent, consistent with a calcium-sensing receptor antagonist acting at the kidney to reduce urinary calcium losses while maintaining normocalcemia.
Strategically, this is a bid to carve out space alongside, not just against, PTH-replacement approaches that are now reshaping the standard of care. The composite normal-serum/normal-urine calcium outcome targets a long-standing pain point in routine management, where pushing serum calcium into the normal range often drives hypercalciuria and renal morbidity. An oral, PTH-independent option could be attractive for patients with persistent hypercalciuria who are on supplements or those unwilling to use daily injectable PTH; it also sidesteps the device and cold-chain complexities that have hindered peptide therapies in the past. However, the signal comes from a tiny cohort over days, not months, leaving durability and real-world titration complexity untested.
For sites and CROs, a registrational program here will likely be operationally distinct from PTH-replacement trials. Expect composite endpoints that marry serum calcium control with urinary calcium normalization and reductions in active vitamin D and calcium supplementation, along with renal safety readouts. That requires standardized 24-hour urine collections, frequent early labs, and disciplined background therapy adjustments—workflows that favor experienced endocrine centers and central lab partnerships. Decentralized components could support adherence and symptom tracking; however, core efficacy assessments are often lab-intensive and time-consuming. Recruitment should be feasible through thyroid surgery and endocrine networks. However, the availability of an approved PTH therapy may narrow the pool of trial-ready patients unless the protocol targets those with persistent hypercalciuria or intolerance to injectables.
Regulators will look for sustained control beyond the first week, renal outcomes over longer horizons, and a safety profile that avoids swings into hypercalcemia as doses are titrated. The short Phase 2 exposure and absence of serious adverse events are encouraging, but insufficient to de-risk chronic use; gastrointestinal tolerability, effects on phosphate, and trends in kidney function will be closely scrutinized. Dose algorithms, monitoring cadence, and clear rescue criteria will be critical to site execution and to regulatory comfort.
BridgeBio also highlighted preclinical data with infigratinib in skeletal dysplasia models, reinforcing the company’s bone and mineral franchise, but the near-term pivot is the encaleret registration plan. The following milestones to watch are the Phase 3 design details, including the choice of comparator, primary endpoint hierarchy, and geographic footprint. If the registrational study confirms durable normalization of both serum and urinary calcium with manageable titration, an oral alternative could shift treatment algorithms and payer discussions. The risks are typical for a small, short POC: reproducibility at scale, maintenance of effect over months, and ensuring enrollment in a landscape where standard-of-care expectations are evolving.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
