A Pfizer biologic drug developed to offer more convenient dosing for children with growth hormone deficiency has been turned down by the FDA.
Pfizer disclosed the regulatory action late Friday. FDA complete response letters are not public documents, and the company did not say what concerns or questions were raised by the agency about the drug, somatrogon. Pfizer only said it is evaluating the FDA’s comments and will work with the agency to determine the path forward for the drug.
Growth hormone deficiency is a rare disease that affects both children and adults. In children, the condition leads to growth and development problems. Growth hormone deficiency that develops in adults can cause an increase in fat and a decrease in muscle mass, as well as high cholesterol levels. Genetic mutations can cause growth hormone deficiency; when it is acquired, the cause can be linked to trauma, infection, radiation therapy, or a tumor in the brain. In some cases, there is no known cause.
Treatment for the deficiency is injections of human growth hormone, typically given daily. Pfizer already markets one such product, Genotropin, a drug that generated $427 million in revenue in 2020. Somatrogon is a version of human growth hormone engineered to offer a long-acting effect that permits once-weekly dosing. The drug is administered via a pre-filled injection pen. In Phase 3 testing in children, somatrogon met the main goal of showing that it was not inferior to daily injections of Genotropin as assessed by measuring the rate of height growth at 12 months. Patients in the clinical trial tolerated somatrogon well and adverse events reported in the clinical trial were comparable across both arms.
Patients already have a new option for once-weekly human growth hormone injections. Last August, the FDA approved Skytrofa, which was developed by Copenhagen, Denmark-based Ascendis Pharma. The regulatory decision made the product the first once-weekly product approved for treating growth hormone deficiency in children. On Jan. 13, European regulators approved the Ascendis drug in the same indication. Pivotal pediatric clinical trials are underway in Japan and China. Also, a global Phase 3 study is evaluating Skytrofa as a treatment for adult human growth hormone deficiency.
Pfizer acquired global rights to somatrogon in a 2014 deal that paid Opko Health $295 million up front. An additional $275 million is tied to regulatory milestones, and the deal also puts Opko in line for royalties and a share of profits from the product’s sales. Under the terms of the agreement, Opko was responsible for clinical development of the drug while Pfizer would handle regulatory and commercialization work, including manufacturing.
Though the complete response letter for somatrogon is a setback, Pfizer is pressing onward with commercialization and regulatory applications in other markets. The drug is approved in Japan, where it is marketed under the name Ngenla. It’s also approved for use in Canada and Australia. A regulatory decision in Europe is expected early this year.