Short answer: Somatrogon has a half-life of about 37.7 hours (effective half-life, children). Levels peak median 11 hours (6 to 25 hours) after a dose. People vary, so treat these as estimates.
Somatrogon is a long-acting form of growth hormone. It is human growth hormone joined to extra protein pieces taken from hCG, which slow its removal so one injection lasts a week. It is sold as Ngenla (Pfizer), injected under the skin once a week, and is approved only for children.
Also known as: Ngenla, somatrogon-ghla.
Ngenla comes as ready-to-use prefilled pens: 24 mg/1.2 mL (dialed in 0.2 mg steps) and 60 mg/1.2 mL (0.5 mg steps). It is injected under the skin of the belly, thighs, buttocks or upper arms once a week on the same day, at any time of day, rotating the site. If a dose needs more than one injection, each goes in a different site. The pen is not shaken. A missed dose can be given within 3 days; after that it is skipped.
If you also use a powder peptide, the free peptide reconstitution calculator handles the vial math.
The Ngenla label approves somatrogon for children 3 years and older with growth failure from too little growth hormone. It is not approved for adults. Label dosing is 0.66 mg/kg of actual body weight once a week, then adjusted by growth. Children switching from daily growth hormone start the day after their last daily shot.
The label has no boxed warning. Its warnings, shared with daily growth hormone, cover higher death rates when started during acute critical illness (where it is not used), severe allergic reactions, growth of existing tumors and second tumors in childhood cancer survivors, higher blood sugar, raised pressure in the skull, fluid retention, low cortisol and thyroid changes, hip problems and scoliosis in children, pancreatitis, fat changes at injection sites, and sudden death in children with Prader-Willi syndrome. An eye exam is done before starting. In the 12-month trial against daily somatropin, injection site reactions were the most common side effect (42.2% vs 25.2%), mostly pain at the site. Full numbers are on the Ngenla side effects, Ngenla dosing schedule, missed Ngenla dose and Ngenla storage pages, and Sogroya vs Ngenla compares the two.
The Ngenla label says levels rise slowly after an injection under the skin and peak 6 to 25 hours later, with a median of 11 hours. The mean effective half-life estimated in children with growth hormone deficiency was 37.7 hours, which the label says allows weekly dosing.
Numbers shown are taken from the source above. Half-life varies from person to person and with injection site.
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