Efzimfotase alfa
An investigational treatment for Hypophosphatasia.
The same compound appears under different names depending on the context. Here is how to identify Efzimfotase alfa wherever you encounter it, plus the key facts at a glance.
- Generic name
- Efzimfotase alfa
- Development code
- ALXN1850
- Drug class
- Enzyme replacement therapy
- Manufacturer
- Alexion, AstraZeneca Rare Disease
- How it's taken
- Subcutaneous injection once every 2 weeks (investigational; weight-band doses of 20 mg, 35 mg or 50 mg in Phase 3)
Alexion's next-generation enzyme replacement for hypophosphatasia, injected under the skin once every 2 weeks instead of 3 to 6 times a week. The FDA accepted its application under priority review on September 18, 2026 for patients aged 2 and older, including adults with adult-onset HPP, with a decision expected in the first half of 2027.
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Where Efzimfotase alfa fits
If approved as filed, efzimfotase alfa would be the first HPP treatment for patients aged 2 and older regardless of when their disease began, closing the gap for adults with adult-onset HPP who today have no approved drug, and it would offer people on Strensiq a switch from 3 to 6 injections a week to 1 every 2 weeks. The HICKORY miss on its primary endpoint, driven by the adult-onset group, is the main question for the FDA review.
How Efzimfotase alfa works
Like Strensiq, efzimfotase alfa supplies the alkaline phosphatase enzyme that people with HPP lack, so the body can clear the inorganic pyrophosphate that blocks bone from hardening[1]. The difference is how long it lasts. It was engineered to stay active in the body for longer, which allowed the Phase 3 trials to give fixed doses of 20 mg, 35 mg or 50 mg by weight band once every 2 weeks, rather than the weight-based doses 3 or 6 times a week that Strensiq requires[4].
AstraZeneca says it was designed for a broad range of patients aged 2 and older, including people without obvious bone changes on X-ray, and reports that across the pooled MULBERRY and HICKORY trials the annualized rate of injection site reactions was 5 times lower than in Strensiq's registrational trials, with a median of 98.8% of days free of injection site reactions[2].
Mechanism: Second-generation recombinant tissue-nonspecific alkaline phosphatase enzyme replacement, engineered for a longer half-life so it can be injected subcutaneously once every 2 weeks
Side effects and safety
No FDA label exists yet, so what is known comes from AstraZeneca's press releases and presentations. The company describes the safety profile as favorable and generally well tolerated across all 3 Phase 3 trials[2]. In CHESTNUT, children who switched from Strensiq had treatment-emergent adverse events at a similar rate to those who stayed on Strensiq (90.5% versus 86.4%)[3].
Injection site reactions, the dominant problem with Strensiq, were about 5 times less frequent per year in the pooled analysis[2]. Because this is the same class of enzyme replacement as Strensiq, the risks that carry a boxed warning there, anaphylaxis and other hypersensitivity reactions, plus lipodystrophy, calcium deposits in the eye and kidney, and antibodies that blunt the drug's effect, remain the questions the FDA review will address; the trial exclusion criteria barred anyone with a history of allergy to asfotase alfa or ALXN1850[4].
The full adverse event tables have not been published.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Efzimfotase alfa
In the Phase 3 trials it was given as a subcutaneous injection once every 2 weeks at 20 mg, 35 mg or 50 mg depending on body weight, and AstraZeneca describes it as intended for self-administration[4][1]. The final dose, device and instructions will be set by the FDA label if it is approved.
Availability and cost
Not yet priced. As a biologic enzyme replacement from the maker of Strensiq, it is likely to be priced as an orphan drug; dosing by weight band every 2 weeks rather than by exact weight several times a week may change how cost scales with a child's growth, but AstraZeneca has said nothing about price.
How hypophosphatasia treatments compare
Hypophosphatasia has 1 FDA-approved medicine, Strensiq, and a successor enzyme from the same company, efzimfotase alfa, that the FDA is reviewing with a decision expected in the first half of 2027. Both replace the missing alkaline phosphatase enzyme; they differ in how often they are injected and in which patients they were studied. Your metabolic bone specialist will weigh when your HPP began, your age and your injection site history. Adults with adult-onset HPP have no approved drug today and are managed with supportive care.
Hypophosphatasia has 1 FDA-approved treatment: Strensiq (asfotase alfa, approved 2015). Also compared, not FDA-approved for hypophosphatasia: Efzimfotase alfa (no brand yet) (efzimfotase alfa (ALXN1850), Under FDA review (decision expected first half of 2027)). Strensiq is typically used as perinatal/infantile-onset and juvenile-onset hpp at any current age; not approved for adult-onset hpp.
| Drug | How it works | How it’s given | How often | Where you get it | Who it is for | FDA status |
|---|---|---|---|---|---|---|
Strensiq asfotase alfa | Enzyme replacement: a bone-targeted copy of tissue-nonspecific alkaline phosphatase that clears the pyrophosphate blocking bone mineralization | Subcutaneous injection from a vial and syringe (self or caregiver injected after training) | 3 times a week (2 mg/kg) or 6 times a week (1 mg/kg); up to 3 times a week at 3 mg/kg in perinatal and infantile-onset HPP | Home, after supervised first doses | Perinatal/infantile-onset and juvenile-onset HPP at any current age; not approved for adult-onset HPP | 2015 |
Efzimfotase alfa (no brand yet) efzimfotase alfa (ALXN1850) You are here | Enzyme replacement: a longer-acting second-generation alkaline phosphatase from the same company | Subcutaneous injection (studied as self-administered) | Once every 2 weeks at a fixed dose by weight band (20 mg, 35 mg or 50 mg in Phase 3) | Home (if approved as studied) | Under FDA review for all patients aged 2 and older, including adult-onset HPP; filed on the HICKORY, MULBERRY and CHESTNUT trials | Under FDA review (decision expected first half of 2027) |
This chart is for education only and is not medical advice. Efzimfotase alfa is investigational in the United States; its dosing, who it will be approved for and its side effects will be set by the FDA label if it is approved. Strensiq figures come from its prescribing information. Talk with a metabolic bone specialist about your own situation.
Clinical trial results
Three Phase 3 trials support the application[1]. MULBERRY (NCT06079359) randomized 29 children aged 2 to under 12 who had never had Strensiq, 2 to 1 against placebo for 24 weeks; the primary endpoint, the Radiographic Global Impression of Change score for rickets, improved by a median of 1.67 points versus 0 on placebo (median difference 1.67, 95% CI 0.66 to 2.00, p=0.0003), and the Rickets Severity Score also improved (median difference -1.00, p=0.0008), with a 6-minute walk gain of 34.5 m that was not statistically significant[3].
CHESTNUT (NCT06079372) switched 43 children already on Strensiq to efzimfotase alfa or kept them on Strensiq; adverse event rates were similar and bone scores held steady[3]. HICKORY (NCT06079281) randomized 124 adolescents and adults who had never had Strensiq, 2 to 1 against placebo. Its primary endpoint, change in 6-minute walk distance at week 25, favored the drug by 17.05 m but did not reach statistical significance (p=0.1675); AstraZeneca attributes this to an unexpectedly strong placebo response in the adult-onset group[2].
Fatigue improved on the FACIT-Fatigue scale (5.74 points, nominal p=0.0016), 45.2% of treated patients versus 30.0% on placebo reached a clinically meaningful walk gain in a post hoc analysis, and in the prespecified pediatric-onset subgroup (60 patients) the walk gain was 35.6 m (nominal p=0.0386)[2]. In the adult-onset subgroup (64 patients) the walk distance did not improve (-2.70 m) although fatigue did (7.41 points, nominal p=0.0021)[2].
All 3 trials continue as open-label extensions, with walk distance still improving at week 49 in people who stayed on the drug[2].
Development history
ALXN1850 came out of Alexion's effort to improve on asfotase alfa, which it has sold as Strensiq since 2015. A Phase 1 dose-escalation study in adults with HPP was published in 2024[7]. The Phase 3 program began in January 2024 (HICKORY), April 2024 (CHESTNUT) and May 2024 (MULBERRY)[4].
AstraZeneca presented MULBERRY and CHESTNUT results at the International Conference on Children's Bone Health on June 28, 2026, announced on September 18, 2026 that the FDA had accepted the BLA with priority review and a target decision in the first half of 2027, and presented the HICKORY results at the ASBMR meeting on October 11, 2026[3][1][2].
Applications are also under review in Japan and other markets[1]. No decision had been announced as of October 18, 2026.
Explore Hypophosphatasia trials
Other Hypophosphatasia treatments
Where to access Efzimfotase alfa
Investigational: available only through clinical trial enrollment
Efzimfotase alfa has not been approved by the FDA and is not available by prescription. The only way for a patient to receive Efzimfotase alfa today is by enrolling in an active clinical trial and meeting that trial's eligibility criteria. Decisions about trial participation should be made with the specialist who manages the patient's condition and knows their current treatment.
Primary active trial
ClinicalTrials.gov record NCT06079281
Investigator: Kathryn Dahir, MD · Vanderbilt Health, Program for Metabolic Bone Disorders (HICKORY lead investigator)
View full trial record on ClinicalTrials.gov →Trial status, site list, and eligibility are pulled from ClinicalTrials.gov. Confirm current recruitment status and nearest site directly with the study team before traveling.
Common questions about Efzimfotase alfa
▸What is Efzimfotase alfa?
Alexion's next-generation enzyme replacement for hypophosphatasia, injected under the skin once every 2 weeks instead of 3 to 6 times a week. The FDA accepted its application under priority review on September 18, 2026 for patients aged 2 and older, including adults with adult-onset HPP, with a decision expected in the first half of 2027.
▸How does Efzimfotase alfa work?
Like Strensiq, efzimfotase alfa supplies the alkaline phosphatase enzyme that people with HPP lack, so the body can clear the inorganic pyrophosphate that blocks bone from hardening[1]. The difference is how long it lasts. It was engineered to stay active in the body for longer, which allowed the Phase 3 trials to give fixed doses of 20 mg, 35 mg or 50 mg by weight band once every 2 weeks, rather than the weight-based doses 3 or 6 times a week that Strensiq requires[4]. AstraZeneca says it was designed for a broad range of patients aged 2 and older, including people without obvious bone changes on X-ray, and reports that across the pooled MULBERRY and HICKORY trials the annualized rate of injection site reactions was 5 times lower than in Strensiq's registrational trials, with a median of 98.8% of days free of injection site reactions[2].
▸What are the side effects of Efzimfotase alfa?
No FDA label exists yet, so what is known comes from AstraZeneca's press releases and presentations. The company describes the safety profile as favorable and generally well tolerated across all 3 Phase 3 trials[2]. In CHESTNUT, children who switched from Strensiq had treatment-emergent adverse events at a similar rate to those who stayed on Strensiq (90.5% versus 86.4%)[3]. Injection site reactions, the dominant problem with Strensiq, were about 5 times less frequent per year in the pooled analysis[2]. Because this is the same class of enzyme replacement as Strensiq, the risks that carry a boxed warning there, anaphylaxis and other hypersensitivity reactions, plus lipodystrophy, calcium deposits in the eye and kidney, and antibodies that blunt the drug's effect, remain the questions the FDA review will address; the trial exclusion criteria barred anyone with a history of allergy to asfotase alfa or ALXN1850[4]. The full adverse event tables have not been published.
▸How is Efzimfotase alfa taken?
▸Is Efzimfotase alfa FDA approved?
Not yet. Efzimfotase alfa is under FDA review for Hypophosphatasia; AstraZeneca (Alexion) has filed an application and a decision is expected in the first half of 2027. The FDA calendar page tracks the outcome.
▸When will the FDA decide on efzimfotase alfa?
AstraZeneca said on September 18, 2026 that the FDA accepted the application with priority review and that the action date falls in the first half of 2027. The company has not disclosed an exact day.
▸How is efzimfotase alfa different from Strensiq?
Both replace the same missing enzyme. Efzimfotase alfa is engineered to last longer, so it was given once every 2 weeks in trials instead of 3 or 6 times a week, and it was studied in adults with adult-onset HPP, a group Strensiq's label does not cover. AstraZeneca reports about 5 times fewer injection site reactions per year than in Strensiq's trials.
▸Did the HICKORY trial succeed?
Partly. The primary endpoint, 6-minute walk distance at week 25 in adolescents and adults, improved by 17.05 m over placebo but did not reach statistical significance (p=0.1675). Fatigue improved significantly, and people with pediatric-onset HPP gained 35.6 m in a prespecified subgroup, while the adult-onset subgroup did not improve its walk distance. AstraZeneca filed on all 3 trials together.
▸Can I join an efzimfotase alfa trial now?
The 3 Phase 3 trials finished enrolling and are listed as active, not recruiting. People already enrolled continue in open-label extensions. Ask your HPP specialist about expanded access if the drug is approved for an age group or form that does not match your situation.
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- AstraZeneca · 2026-09-18. Efzimfotase alfa granted Priority Review in the US as treatment for patients with hypophosphatasia aged 2 years and older. https://www.astrazeneca-us.com/media/press-releases/2026/Efzimfotase-alfa-granted-Priority-Review-in-the-US-as-treatment-for-patients-with-hypophosphatasia-aged-2-years-and-older.html
- AstraZeneca · 2026-10-11. Efzimfotase alfa showed numerical improvement in Six-Minute Walk Test achieving mean difference of 17.05 metres vs placebo in treatment-naive adolescents and adults with hypophosphatasia at week 25 in HICKORY Phase III trial. https://www.astrazeneca.com/media-centre/press-releases/2026/efzimfotase-alfa-showed-numerical-improvemen-6-minute-walk-test-vs-placebo-treatment-naive-adolescents-adults-hpp-hickory-phiii-trial.html
- AstraZeneca · 2026-06-28. Efzimfotase alfa demonstrated improvements in bone health in treatment-naive paediatric patients with hypophosphatasia at week 25 in MULBERRY Phase III trial. https://www.astrazeneca.com/media-centre/press-releases/2026/efzimfotase-alfa-demonstrated-improvements-in-bone-health-in-treatment-naive-patients-with-hypophosphatasia-at-week-25-in-mulberry-phase-iii-trial.html
- ClinicalTrials.gov · 2026-06-22. Phase 3 Study of ALXN1850 Versus Placebo in Adolescent and Adult Participants With HPP Who Have Not Previously Been Treated With Asfotase Alfa (HICKORY). https://clinicaltrials.gov/study/NCT06079281
- ClinicalTrials.gov · 2026-05-28. Phase 3 Study of ALXN1850 in Treatment-Naive Pediatric Participants With HPP (MULBERRY). https://clinicaltrials.gov/study/NCT06079359
- ClinicalTrials.gov · 2026-05-05. Phase 3 Study of ALXN1850 in Pediatric Participants With HPP Previously Treated With Asfotase Alfa (CHESTNUT). https://clinicaltrials.gov/study/NCT06079372
- PubMed Central · 2024. Safety, pharmacokinetics, and pharmacodynamics of efzimfotase alfa, a second-generation enzyme replacement therapy: phase 1, dose-escalation study in adults with hypophosphatasia. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11425692/