On Monday, AstraZeneca Plc (AZN) rolled out detailed results from the HICKORY Phase 3 trial of efzimfotase alfa (ALXN1850), a treatment for hypophosphatasia (HPP). HPP is an inherited metabolic disease caused by deficient activity of the enzyme alkaline phosphatase (ALP), which helps build healthy bones and supports proper muscle function.

The condition is characterized by defective mineralization, the process that hardens and strengthens bones and teeth, along with impaired calcium and phosphate regulation and functional impairments.

Here's the catch: back in March, the topline data didn't achieve statistical significance on the primary endpoint, the Six-Minute Walk Test, among adolescents and adults who had not been previously treated with Strensiq (asfotase alfa) at week 25, compared to placebo. That miss was largely attributed to stronger-than-expected placebo responses in adult-onset patients.

Clinically Meaningful Differences Achieved

But dig into the post hoc analysis and the picture gets more interesting. At week 25, 45.2% of patients treated with efzimfotase alfa achieved the minimum clinically important difference (MCID) from baseline in the 6MWT, defined as 43 meters in adolescents and 31.1 meters in adults. Compare that to 30.0% in the placebo group. That works out to 2.5-fold higher odds of achieving a clinically meaningful 6MWT response.

In the overall population at week 25, efzimfotase alfa demonstrated nominally significant improvement in the key secondary endpoint of FACIT-Fatigue, achieving an LS mean difference of 5.74 versus placebo.

Other key secondary endpoints numerically favored efzimfotase alfa, including 30-second Sit-to-Stand (30s-STS), Lower Extremity Functional Scale (LEFS), and BPI-SF Pain Severity.

Continued Improvements and Subgroup Benefits

In the open-label extension, at week 49, patients treated with efzimfotase alfa showed continued improvement across the primary and key secondary endpoints. Patients who switched from placebo to efzimfotase alfa following the randomized evaluation period at week 25 demonstrated similar improvement in these key measures of mobility, physical function, pain, and fatigue.

In a combination of prespecified subgroups of adolescents and adults with pediatric-onset HPP, efzimfotase alfa demonstrated nominally significant and clinically meaningful benefits in the primary endpoint of 6MWT, achieving an LS mean difference of 35.6 meters versus placebo at week 25, as well as the key secondary endpoints of 30s-STS and BPI-SF Pain Severity.

Efzimfotase alfa demonstrated a favorable safety profile and was generally well-tolerated across all three Phase 3 trials.

In a pooled analysis of the MULBERRY and HICKORY trials, the annualized Injection Site Reaction rate was five times lower with efzimfotase alfa compared to Strensiq in its registrational trials during the first 24 weeks of treatment.

AZN Price Action: AstraZeneca shares were up 0.15% at $159.44 during premarket trading on Monday, according to market data.