Takeda spinout Phathom's erosive esophagitis drug bests Prevacid in head-to-head phase 3 trial

Phathom Pharmaceuticals' erosive esophagitis drug vonoprazan performed as well as over-the-counter Prevacid in a head-to-head phase 3 clinical trial, potentially teeing up a 2022 application for FDA approval. 

Vonoprazan is a potassium-competitive acid blocker, or P-CAB, which is under investigation to relieve heartburn and heal all severities of erosive esophagitis. Patients with this condition have inflammation of the esophagus that is often caused by backed up stomach acids, infection, some medications and allergies.

In the phase 3 PHALCON-EE trial, vonoprazan was compared with Takeda's Prevacid, a common over-the-counter medication for reducing acid and treating the symptoms of stomach and intestinal ulcers. Phathom examined its therapy in an initial healing and maintenance phase during the study, according to a company release.

Vonoprazan met the main goal of the trial in the healing phase, by proving non-inferiority to Prevacid. Phathom's therapy saw a healing rate of 93% compared to 85% for Prevacid. The drug also met a secondary endpoint demonstrating faster healing than Prevacid in patients with moderate-to-severe disease at Week 2.

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Phathom's drug did not meet statistical significance on a secondary goal in the healing phase for onset of sustained heartburn relief by Day 3. The therapy also was unsuccessful in a measurement of vonoprazan's superiority to Prevacid at Week 2 in moderate-to-severe patients. The company blamed this blip on the testing method.

As for the maintenance phase, vonoprazan met the main goal of proving non-inferiority compared to Prevacid in the percentage of patients who maintained healing of their erosive esophagitis through Week 24. 

The side effects of vonoprazan, which include diarrhea, COVID-19 infection and gastritis, were similar to that of the already-approved Prevacid. Across both phases of the study, seven COVID-19 cases were reported including two deaths, but these adverse events were deemed unrelated to the study drug.

The results were clearly not what the market was looking for, as Phathom's shares took a dive Monday, dropping 15% to $27 as of 1:24 p.m. ET. 

Phathom will present full findings during a medical meeting next year. The results were enough to give Phathom access to $50 million from Hercules Capital.

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The company plans to apply to the FDA for approval of the drug in the first half of 2022 in healing all grades of erosive esophagitis and relief of heartburn, as well as maintenance of all grades of the condition and relief of heartburn. 

New Jersey-based Phathom was launched by Takeda and Frazier Healthcare in 2019 to focus on gastrointestinal R&D. Vonoprazan was licensed from Takeda, where it was extensively tested and approved in Japan and other Asian countries. The drug has not been approved by the FDA for any indication. 

Phathom is also testing the therapy in erosive gastroesophageal disease, nonerosive reflux disease and other acid-related disorders.