Short answer: Both are once-weekly growth hormones injected under the skin for children with growth hormone deficiency.12 Skytrofa is approved from age 1 and also for adults; Ngenla is for children 3 and older only. Skytrofa is a powder cartridge mixed by its auto-injector; Ngenla is a prefilled pen. Each label compared its drug with daily somatropin, not with the other.
| Skytrofa | Ngenla | |
|---|---|---|
| Drug | Lonapegsomatropin-tcgd1 | Somatrogon-ghla2 |
| Who | Children 1 year and older weighing at least 11.5 kg; adults with growth hormone deficiency1 | Children 3 years and older; not approved for adults2 |
| Children's label dose | 0.24 mg/kg once weekly, rounded to a cartridge strength from a weight table1 | 0.66 mg/kg of actual body weight once weekly2 |
| Device | Powder cartridge mixed and given by the Skytrofa Auto-Injector1 | Prefilled pen dosing in 0.2 mg or 0.5 mg steps2 |
| Missed dose | Give within 2 days; otherwise skip; at least 5 days between doses1 | Give within 3 days; otherwise skip2 |
| From daily growth hormone | At least 8 hours after the last daily dose1 | The day after the last daily injection2 |
| Most common in children | Viral infection 15% vs 11% on daily somatropin; fever 15% vs 9%1 | Injection site reactions 42.2% vs 25.2% on daily somatropin2 |
| Boxed warning | None1 | None2 |
Skytrofa is injected once a week at any time of day, and can be given up to 2 days before or after the usual day. A refrigerated cartridge sits out for 15 minutes first, and the auto-injector mixes the powder; a mixed cartridge is used within 4 hours.1 Ngenla is injected on the same day each week at any time of day. The day can be changed if at least 3 days pass between 2 doses, and the pen is not shaken.2
The two drugs are different molecules, so their mg doses are not interchangeable. Skytrofa's label also covers switching from another weekly growth hormone: wait at least 7 days after its last dose.1
The warnings are the shared growth hormone set: higher death rates in acute critical illness, tumors, blood sugar changes, raised pressure in the skull, low cortisol, thyroid changes, hip problems in children, scoliosis, pancreatitis and deaths in children with Prader-Willi syndrome, for which neither is approved.12 In the children's trials, thyroid problems were 6.4% on Ngenla vs 2.6% on daily somatropin; in Skytrofa's adult trial, central hypothyroidism was 7% vs 1% on placebo. These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Which, if either, fits is for your prescriber. More detail: Skytrofa side effects, Ngenla side effects, the Skytrofa and Ngenla dosing schedules, the Skytrofa and Ngenla missed-dose pages, the lonapegsomatropin and somatrogon guides, and Sogroya vs Ngenla: how do the two weekly growth hormones differ?.