Lonapegsomatropin 3 mg/cartridge (as somatropin equivalents)

Basic Info

CAS Number	1934255-39-6
Active Ingredient	Lonapegsomatropin (trade name Skytrofa), a **weekly extended-release** presentation of recombinant human growth hormone (fatty-acid modified to bind albumin and form a slow-release depot)
Dosage Form	Cartridge (lyophilised, dual chamber + injector)
Specification & Packaging	Strength: 3 mg/cartridge (as somatropin equivalents) Pack: Dual-chamber cartridge + injector Group: 05 Item No.: 51

Storage & Common Excipients

Storage Conditions	2–8 °C; **do not freeze**; during use the device may be kept at room temperature for the period stated in the label. Follow the label exactly on refrigeration and in-use limits
Common Excipients	The lyophilisate contains excipients such as mannitol, buffer, polysorbate 80 or polyoxyl castor oil and edetate disodium; the pen may contain preservatives such as m-cresol or benzyl alcohol — follow the label. Confirm against COA

Product Introduction

An **albumin-binding fatty-acid modification** (short/medium-chain fatty acid) fused to an IgG4 Fc produces a once-weekly subcutaneous injection with efficacy comparable to daily rhGH, indicated in children with growth hormone deficiency (GHD). It is the only long-acting (weekly) growth hormone in this list

Therapeutic Use

Replacement therapy for **paediatric** growth hormone deficiency (GHD); the precise indication, age range and product-selection criteria follow the locally approved label. Adult GHD indications vary by market and must be checked locally

Mode of Action

The same active moiety as daily rhGH, but albumin binding produces a prolonged concentration profile pharmacokinetically closer to physiological pulsatility; efficacy comparable to daily preparations with once-weekly dosing. Once injected, the dose cannot be adjusted within the week, so **dose selection must be carefully assessed before the first injection**

Administration & Monitoring

Subcutaneous injection on a fixed day each week (align the schedule with the missed-dose rule in the label); monitor IGF-1, height velocity and height, and bone age; during long-term therapy monitor HbA1c/fasting glucose, lipids, thyroid function, bone density, spine and femoral head (avascular necrosis), intraocular pressure and visual acuity; reassess indication and efficacy typically every 6–12 months

Important Safety Information

Prescription biologic and a **high-value, strongly regulated** product (dedicated registries with prescription and quantity reporting). Because the dose cannot be withdrawn, **the consequences of an incorrect dose selection are greater**, so the first dose warrants particular caution. Metabolic and orthopaedic risks match daily rhGH (impaired glucose tolerance, reduced bone density, intracranial hypertension); contraindicated in active malignancy; use by an athlete is absolutely a violation

Adverse Reactions

Injection-site reactions (erythema, bruising, pain — potentially more persistent than with daily preparations because of the larger injection volume); headache; oedema; arthralgia and myalgia; bone pain (relatively common with weekly dosing); raised glucose and insulin resistance; hypothyroidism; visual changes/retinal detachment; intracranial hypertension (uncommon); anti-drug antibodies (rare)

Important Risks

Non-adjustable dosing once injected (a full week must elapse); metabolic effects and impaired glucose tolerance; reduced bone density and bone pain; avascular necrosis and slipped capital femoral epiphysis; intracranial hypertension; visual impairment; theoretical tumour-related risk (IGF-1 pathway)

Contraindications

Hypersensitivity; active malignancy or ongoing chemotherapy; diagnosed intracranial hypertension; pregnancy; discontinue when final adult height is reached; contraindicated in Prader-Willi syndrome with severe upper-airway obstruction or acute respiratory infection

Special Populations

Paediatric use is the principal approved population (typically from age 2 or 3 depending on the market); contraindicated in pregnancy; dose adjustment and glucose monitoring required in diabetes or glucose intolerance; individualised dosing in children with hepatic or renal impairment; monitor bone development and density in adolescents; no routine indication in older adults

Usage Limitations

Prescription medicine and a high-value, strongly regulated category (dedicated registries, prescription and quantity reporting). Strictly no off-label use for muscle gain or anti-ageing; prohibited for competitive athletes; inject on a fixed day each week with missed-dose handling per the label; rotate injection sites; single-use devices with safe sharps disposal. Patients must be told explicitly that the dose cannot be withdrawn mid-week

Anti-Doping Testing

**Falls under the WADA Prohibited List S2.2 (growth hormone / IGF-1).** Testing uses the same strategy as for rhGH (GH-200/IGF-1 markers plus confirmation testing). Because of the extended-release kinetics, **abnormal markers persist longer**, making detection on non-dosing days more likely. Therapeutic use for genuine GHD requires a TUE and inclusion in ADAMS whereabouts monitoring

Product Quality Testing

Identification (peptide mapping/MS including fatty-acid modification site and Fc fusion confirmation), glycosylation and Fc aggregation (SEC-HPLC/CE-SDS), assay and purity, specific activity, potency, endotoxin, sterility, lyophilisate appearance and reconstitution characteristics, fill volume, mechanical and dose accuracy, stability including in-use stability, visible particles; COA