A Pfizer drug for growth hormone deficiency has bounced back from an FDA rejection to finally win regulatory approval, clearing the way for the pharmaceutical giant to compete against a smaller rival whose hormone product has a nearly two-year head start.

The Pfizer drug, somatrogon, is a version of human growth hormone engineered for once-weekly dosing. The approval announced Wednesday covers children age 3 and older. Pfizer will market the new product as Ngenla, the same brand name for the drug in other markets where it is already approved.

Growth hormone deficiency develops when the pituitary gland doesn’t secrete enough somotropin, or human growth hormone. It leads to a slower rate of growth in children and a potential delay in puberty. This rare disease can be treated with injections of engineered versions of the deficient hormone. Pfizer already markets one such product, Genotropin. But Genotropin is a daily injection and its sales have been on a steady decline as biosimilar versions eat away at its revenue. As a once weekly injectable, Ngenla offers children a less burdensome dosing regimen and it also gives Pfizer an opportunity to pick up market share.

Ngenla comes from the research of Opko Health. In 2014, Pfizer agreed to pay $295 million up front for global rights to the therapeutic candidate. The deal made Opko eligible for up to $275 million in milestone payments, plus royalties and a share of profits from sales of the drug. Opko continued to be responsible for clinical development of Ngenla while Pfizer was responsible for regulatory work and commercialization of the engineered hormone. But in early 2022, the FDA rejected a biologics license application for Ngenla, dealing a setback to the plans of Pfizer and Opko.

The FDA apparently did not ask Pfizer and Opko to run another clinical trial. The regulator’s approval is based on the same open-label Phase 3 study that was the basis of the 2021 submission. That study, which enrolled 224 pediatric patients who had not previously been treated with growth hormone therapies, compared once-weekly Ngenla to once-daily Genotropin. Results showed that Ngenla met the main goal of showing it was non-inferior to the version of the hormone injected daily, assessed by measuring annual height velocity at 12 months. Ngenla was well tolerated and its safety profile in clinical testing was comparable to that of Genotropin.

Pfizer can now prepare to offer Ngenla in the U.S. as an alternative to Skytrofa, a product from Ascendis Pharma. This once-weekly injectable human growth hormone won its FDA approval in 2021 based on trial results that compared it to daily Genotropin injections. Copenhagen-based Ascendis reported €35.7 million (about $39 million) in Skytrofa revenue for 2022.

Ngenla won regulatory approvals in Europe, Japan, Canada, and Australia last year. Pfizer expects the new product will become available in the U.S. in August.

“As a new, longer-acting option that has the ability to reduce treatment frequency from daily to weekly, Ngenla could become an important treatment option that can improve adherence for children being treated for growth hormone deficiency,” Joel Steelman, pediatric endocrinologist at Cook Children’s Health Care System and an investigator in the Ngenla clinical trial, said in a prepared statement.

Photo by Flickr user Sean MacEntee via a Creative Commons license