Once-Weekly Pediatric Growth Hormone Snags FDA Approval

— Somatrogon injection given go-ahead after initial FDA rejection last year

FDA APPROVED somatrogon (Ngenla) over a photo of a female physician measuring the height of a little girl.

The FDA approved long-acting injectable somatrogon (Ngenla) for pediatric human growth hormone deficiency, developers Pfizer and OPKO Health announced this week.

Somatrogon is indicated for children ages 3 and up with growth failure due to inadequate endogenous growth hormone secretion.

Support for the approval came from a phase III trial involving treatment-naive children ages 3 to 12 years. The 224-patient study compared once-weekly somatrogon with once-daily somatropin. At 12 months, somatrogon was non-inferior to somatropin in terms of height velocity (10.10 vs 9.78 cm/year, respectively) and for the secondary endpoint of change in bone maturation.

"The approval of Ngenla will be significant for children with growth hormone deficiency in the U.S. It holds potential to reduce the treatment burden that can come with daily growth hormone injections," said investigator Joel Steelman, MD, of Cook Children's Health Care System in Fort Worth, Texas, in a statement.

"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," he added.

Slowly replacing once-daily options, the injectable joins other long-acting pediatric growth hormones recently approved for once-weekly dosing, including lonapegsomatropin (Skytrofa) and somapacitan (Sogroya).

Somatrogon's approval was a long time coming. Pfizer and OPKO filed for approval back in January 2021, but a year later the sponsors were hit with a complete response letter rejecting the treatment -- the companies didn't give details as to why the FDA initially turned down the agent.

Patients switching to somatrogon from a daily growth hormone should initiate treatment on the day following their last daily injection. The injection should be administered once weekly, on the same day each week, at any time of the day in the abdomen, thighs, buttocks, or upper arms with weekly rotation of injection site, according to the label.

Single-use, pre-filled pens of the human growth hormone analog will come in strengths of 24 mg/1.2 mL (20 mg/mL; delivering the dose in 0.2 mg increments) and 60 mg/1.2 mL (50 mg/mL; delivering the dose in 0.5 mg increments). The recommended dose is 0.66 mg/kg based on actual body weight but can be individualized based on the growth response.

The therapy is contraindicated in children with acute critical illness, hypersensitivity to somatrogon or its excipients, closed epiphyses, active cancers, active proliferative or severe non-proliferative diabetic retinopathy, as well as those with Prader-Willi syndrome who are severely obese or have severe respiratory impairment.

Common adverse events in the phase III trial (≥5%) were injection site pain, nasopharyngitis, headache, and pyrexia. Most events were of mild or moderate intensity; between-group rates of adverse events were similar, though severe events occurred slightly more often in the somatrogon group (8.3% vs 5.2% with once-daily somatropin).

Somatrogon is expected to be available in August 2023, said Pfizer.