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Pfizer and OPKO Health’s once weekly treatment for pediatric growth hormone deficiency (GHD) will not be imminently approved by the U.S. FDA in a notable setback for the two companies.

According to Pfizer, the FDA issued a complete letter of response (CRL) to the application at the end of last week. No explanation of the reason for the approval delay was given, but Pfizer is apparently “evaluating the FDA’s comments and will work with the agency to determine an appropriate path forward,” according to a press statement issued by the big pharma.

“We remain confident in the potential treatment benefits that somatrogon has to offer patients around the world,” said Brenda Cooperstone, Chief Development Officer, Rare Disease, Pfizer Global Product Development. “We will work closely with the FDA to determine the best path forward to bring this important once-weekly treatment option to pediatric growth hormone deficiency patients and their families.”

The once weekly hormone therapy, somatrogon, designed to treat GHD, has recently been approved in Japan, Canada and Australia. It also had a positive opinion from the Committee for Medicinal Products for Human Use of the European Medicines Authority, an early nod that almost always signals imminent approval by the regulatory agency.

OPKO received an upfront payment of $295 million from Pfizer in 2014 to develop somatrogon, and had the potential to receive up to an additional $275 million upon achievement of regulatory milestones such as market approvals. Pfizer has the exclusive license to commercialize somatrogon around the world.

The treatment has had its ups and downs during development, with a Phase III trial failure in 2016 followed by more positive results for another Phase III trial announced in 2019.

This regulatory setback will be good news for Danish competitor Ascendis, which received FDA approval for its GHD treatment lonapegsomatropin (brand name Skytrofa) towards the end of last summer.

Pediatric GHD is a rare disorder caused by inadequate secretion of growth hormone by the pituitary gland. It causes short stature and can also result in delayed puberty and other physical health problems. It can be genetic or environmental in cause and impacts between one in 4000 and one in 10,000 children.

There are several recombinant growth hormone therapies that are already approved and on the market, including Pfizer’s own Genotropin, so an important factor in new therapies being submitted for approval for GHD is improved performance. Past trials suggest lonapegsomatropin has the advantage over somatrogon in this regard, as it showed better growth performance in comparison with Genotropin.

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