Lonapegsomatropin (Skytrofa)
A once-weekly prodrug that releases unchanged somatropin over the week.
Checked 2026-10-22 against the US label Researched and written by Kymata Health Editorial Report an error
- Sold as
- Skytrofa
- Full name
- lonapegsomatropin-tcgd
- Maker
- Ascendis Pharma
- Status
- Prescription only; US label since 2021
- Sport
- WADA S2, prohibited at all times
What is lonapegsomatropin?
Short answer
Lonapegsomatropin is somatropin attached to a large polyethylene-glycol carrier by a linker that breaks at a steady rate in the body. As it breaks, it releases ordinary somatropin, so one injection covers a week. Ascendis Pharma sells it as Skytrofa, for children and, since 2025, adults with GH deficiency.
How it lasts a week
The label describes somatropin conjugated to a 4 × 10 kDa methoxy-polyethylene-glycol carrier through the TransCon linker (63 kDa in all). The linker cleaves itself with first-order kinetics, releasing fully active 22 kDa somatropin, so what reaches the GH receptor is the native hormone. (Skytrofa label)
Who is Skytrofa approved for?
The US label's indications, in its own terms.
US label indications
2- Children 1 year and older who weigh at least 11.5 kg, with growth failure from too little GH
- Adults with growth hormone deficiency (adult indication approved 28 July 2025)
What dose does the Skytrofa label give?
What the label states, for the patients it covers. Not a dose for anyone reading this: the prescriber sets it.
On the label
| Label wording, summarised | Source |
|---|---|
| Adults: 1.4 mg weekly at ages 30 to 60; 2.1 mg weekly under 30 or with oral estrogen; 0.7 mg weekly over 60; label maximum 6.3 mg weekly. | (Skytrofa label) |
| Children: 0.24 mg/kg once weekly. | (Skytrofa label) |
How long does lonapegsomatropin last, and when is IGF-1 checked?
Pharmacokinetics
| Measure | Label value | Source |
|---|---|---|
| Half-life (children) | 30.7 h (prodrug); about 25 h (released somatropin) | (Skytrofa label) |
| Time to peak (adults) | 31 h (prodrug); 13 h (released somatropin) | (Skytrofa label) |
| IGF-1 | Peaks about 2 days after a dose; weekly average about 4.5 days after | (Skytrofa label) |
IGF-1 timing The label says to draw the IGF-1 sample 4 to 5 days after the prior dose when adjusting the adult dose. (Skytrofa label)
What are the warnings for Skytrofa?
From the current US label. A clinician weighs them for each patient.
Status Prescription only. Skytrofa has had a US label since 2021 (Ascendis Pharma). WADA prohibits it at all times (S2). (Skytrofa label; WADA Prohibited List 2026)
Warnings shared by every growth hormone label
| Topic | What the labels say |
|---|---|
| Acute critical illness | Contraindicated after open-heart or abdominal surgery, multiple trauma or acute respiratory failure; two ICU trials found higher mortality with GH. |
| Active cancer | Contraindicated with active malignancy; a preexisting one must be inactive and treated. Childhood cancer survivors given head radiation had more second tumours, mostly meningiomas. |
| Prader-Willi syndrome | Deaths reported in children with severe obesity, airway obstruction, sleep apnea or respiratory infection. |
| Glucose | Can lower insulin sensitivity and unmask impaired glucose tolerance or diabetes. |
| Intracranial hypertension | Papilledema, headache and visual changes, usually in the first 8 weeks; eye exams before and during treatment. |
| Fluid retention | Edema, joint and muscle pain, carpal tunnel: usually transient and dose dependent. |
| Adrenal and thyroid | May unmask low cortisol (central hypoadrenalism) or central hypothyroidism; thyroid tests during treatment. |
| Children: hips and spine | Slipped capital femoral epiphysis and progression of scoliosis during rapid growth. |
| Other | Pancreatitis (rare), lipoatrophy at a repeated site, contraindicated in active proliferative or severe non-proliferative diabetic retinopathy. |
Frequently asked questions
Questions
- Is lonapegsomatropin a different hormone from somatropin?
- No. It is a carrier-bound form that releases unchanged somatropin as its linker breaks; the carrier is what makes it last a week.
- Is Skytrofa approved for adults?
- Yes, for adults with growth hormone deficiency since 28 July 2025, as well as for children 1 year and older who weigh at least 11.5 kg.
- When is IGF-1 checked on Skytrofa?
- The label times the blood draw 4 to 5 days after the previous dose.
- Is lonapegsomatropin banned in sport?
- Yes. WADA lists lonapegsomatropin under S2, prohibited at all times.
The growth hormone family
GH itself, the drugs that make the pituitary release more of it, and IGF-1 downstream. Half-lives are human values.
Three ways to raise GH
| Class | Acts on |
|---|---|
| GHRH analog | GHRH receptor on the pituitary (cAMP) |
| Ghrelin-receptor agonist | Ghrelin receptor (GHS-R1a) in hypothalamus and pituitary |
| Growth hormone (daily) | GH receptor directly; bypasses the pituitary |
| Growth hormone (weekly) (this page) | GH receptor directly, released over a week |
| IGF-1 | IGF-1 receptor, downstream of GH |
Compared
16 agents| Agent | Class | Labelled product | Half-life (human) | Taken |
|---|---|---|---|---|
| Somatropin (rhGH) | Growth hormone (daily) | Genotropin, Humatrope, Norditropin, Omnitrope, Zomacton, Serostim | 2 to 3.8 h (SC, across labels) (Humatrope label) | Daily injection (label) |
| Somapacitan | Growth hormone (weekly) | Sogroya | about 2 to 3 days (adults) (Sogroya label) | Weekly injection (label) |
| Somatrogon | Growth hormone (weekly) | Ngenla | 37.7 h (effective, children) (Ngenla label) | Weekly injection (label) |
| Lonapegsomatropin | Growth hormone (weekly) | Skytrofa | about 31 h (prodrug, children) (Skytrofa label) | Weekly injection (label) |
| Tesamorelin | GHRH analog | Egrifta SV, Egrifta WR | 8 to 38 min (by formulation and study) (Egrifta WR label) | Daily injection (label) |
| Sermorelin | GHRH analog | None | 6 to 7 min IV (EU product information) (Geref 50 SPC (HPRA)) | Daily injection in studies |
| CJC-1295 with DAC | GHRH analog | None | 5.8 to 8.1 days (Teichman 2006, JCEM) | Weekly or every other week in studies |
| CJC-1295 without DAC (mod GRF 1-29) | GHRH analog | None | No human value published | No human study published |
| Ipamorelin | Ghrelin-receptor agonist | None | 2 h (IV infusion) (Gobburu 1999, Pharm Res) | Single IV infusions in the human study |
| GHRP-2 | Ghrelin-receptor agonist | None | No human value published | IV test doses in studies |
| GHRP-6 | Ghrelin-receptor agonist | None | 2.5 h (IV) (Cabrales 2013, Eur J Pharm Sci) | IV test doses in studies |
| Hexarelin | Ghrelin-receptor agonist | None | No human value published | IV test doses in studies |
| MK-677 (ibutamoren) | Ghrelin-receptor agonist | None | No human value published | Daily by mouth in studies; GH raised over 24 h |
| Macimorelin | Ghrelin-receptor agonist | Macrilen | 4.1 h (Macrilen label) | One oral dose, as a diagnostic test (label) |
| Mecasermin (rhIGF-1) | IGF-1 | Increlex | 5.8 h (children) (Increlex label) | Twice daily with a meal (label) |
| IGF-1 LR3 | IGF-1 | None | No human value published | No human study published |
GH axis guides5
- Growth hormone: the GH axisHow GH is controlled, every agent compared
- GH pulse simulatorDose times against the natural sleep and exercise GH pulses, modelled from half-lives
- Long-acting growth hormones explainedThree once-weekly products, three different ways of making GH last a week.
- Somatropin brands comparedOne molecule, several names, and which are still on the US market.
- IGF-1 monitoring on GH-axis treatmentWhy IGF-1 is the test, when to draw it on weekly GH, and what the labels say to do with it.