Lonapegsomatropin-Tcgd

Introduction Overview

Generic Name

lonapegsomatropin-tcgd

Brand Name

Skytrofa

Dosage Form

Injection for subcutaneous use (0.7 mg, 1.4 mg, 1.8 mg, 2.1 mg, 2.5 mg, 3 mg, 3.6 mg, 4.3 mg, 5.2 mg, 6.3 mg, 7.6 mg, 9.1 mg, 11 mg, 13.3 mg)

Drug Class

Growth hormones

Pharmacokinetics

Absorption:
Skytrofa is administered via subcutaneous injection, which facilitates absorption directly into the systemic circulation, bypassing the gastrointestinal tract and thus avoiding first-pass metabolism. Once administered, the polyethylene glycol (PEG) carrier temporarily attached to the somatropin molecule protects it from rapid renal clearance. This PEGylation extends the half-life of the active growth hormone to approximately 25 hours, allowing for a once-weekly dosing regimen. The absorption profile is characterized by a gradual release of the active somatropin as the prodrug slowly cleaves in vivo, resulting in sustained plasma concentrations that maintain therapeutic IGF-1 levels.

Distribution:
After systemic absorption, somatropin distributes throughout extracellular fluid compartments, targeting growth hormone receptors primarily in the liver and peripheral tissues. The PEGylation of lonapegsomatropin reduces renal filtration and minimizes rapid clearance, enabling prolonged plasma exposure. Volume of distribution is consistent with endogenous growth hormone, distributing mainly to vascular and interstitial spaces rather than accumulating extensively within tissues. Binding to growth hormone receptors occurs in multiple tissues where it stimulates downstream effects.

Metabolism:
Lonapegsomatropin acts as a prodrug, undergoing enzymatic cleavage to release active somatropin. The PEG carrier is metabolized via predictable enzymatic pathways involving cleavage of the linker molecule, after which free somatropin engages the growth hormone receptor. The metabolic degradation of somatropin occurs predominantly through proteolytic breakdown by cellular enzymes, similar to endogenous growth hormone metabolism. The liver and peripheral tissues participate in somatropin metabolism, generating smaller peptides and amino acids which are reused or excreted.

Elimination:
The PEGylation of lonapegsomatropin markedly slows renal clearance, enabling extended circulatory half-life compared to daily somatropin products. The prolonged elimination half-life of approximately 25 hours allows for weekly dosing. Metabolites, including PEG fragments and degraded somatropin peptides, are excreted via renal and biliary routes. Consistent elimination kinetics support stable plasma concentrations and predictable dosing. Pharmacokinetic studies demonstrate no significant accumulation with repeated weekly administration at prescribed doses.

Dosage Forms

Available Dosage Forms:
Skytrofa is available as a lyophilized powder in a single-dose, dual-chamber prefilled cartridge containing lonapegsomatropin-tcgd (the active prodrug) and a diluent (water for injection). The dual-chamber cartridge facilitates in-device reconstitution prior to injection. The cartridge is intended for use with the Skytrofa Auto-Injector, an electronic, reusable subcutaneous injection device.

The available strengths of Skytrofa injection cartridges include: 0.7 mg, 1.4 mg, 1.8 mg, 2.1 mg, 2.5 mg, 3 mg, 3.6 mg, 4.3 mg, 5.2 mg, 6.3 mg, 7.6 mg, 9.1 mg, 11 mg, and 13.3 mg.

Dosages for Adults and Adolescents:
In children 1 year and older weighing at least 11.5 kg with inadequate endogenous growth hormone secretion, the recommended initial dose is 0.24 mg/kg once weekly. Dose should be individualized and titrated based on growth response and clinical parameters.

Adults with growth hormone deficiency require dosing adjustment based on age and estrogen status: adults aged 30-60 years not taking oral estrogen begin at 1.4 mg weekly; adults under 30 or those taking estrogen at any age start at 2.1 mg weekly; adults over 60 years not on estrogen start at 0.7 mg weekly. Dose can be titrated monthly guided by IGF-1 serum concentrations and clinical response, with a maximum dose of 6.3 mg once weekly.

Specific Patient Populations:
For pediatric patients, growth failure due to endogenous GH deficiency is the indication, with dosing adjusted for body weight and monitored for efficacy and safety. For adults with GHD, titration considers age, sex, and concurrent hormone therapies; close monitoring of IGF-1 and side effects is essential. Transitioning patients from daily somatropin to Skytrofa requires an 8-hour gap post last dose. If switching from other long-acting GH therapies, a 7-day washout period is recommended. Injection sites should be rotated to reduce risk of lipoatrophy. The device and cartridge design facilitate patient or caregiver self-administration under healthcare guidance.

Mechanism Of Action

Skytrofa (lonapegsomatropin-tcgd) acts as a long-acting prodrug of somatropin, a recombinant human growth hormone. Upon subcutaneous injection, the PEGylated prodrug undergoes controlled enzymatic cleavage releasing unmodified somatropin systemically. This somatropin molecules bind specifically to growth hormone receptors (GHR) on target cells, initiating downstream signaling cascades.

At the molecular level, somatropin binds the extracellular domain of the GHR, leading to receptor dimerization and activation of the associated Janus kinase 2 (JAK2). Activated JAK2 phosphorylates Signal Transducers and Activators of Transcription (STATs), particularly STAT5, which translocate to the nucleus and modulate transcription of genes involved in growth and metabolism. This leads to increased production of Insulin-like Growth Factor 1 (IGF-1), primarily in the liver, a key mediator of many growth hormone effects.

Consequently, IGF-1 stimulates cellular proliferation, differentiation, and metabolism in various tissues including bone, muscle, and adipose tissue. It promotes linear growth in children by enhancing chondrocyte proliferation and matrix synthesis in growth plates. In adults with growth hormone deficiency, somatropin improves protein synthesis, promotes lipolysis reducing adiposity especially trunk fat, and enhances glucose metabolism, contributing to improved body composition and physical function.

Comparatively, Skytrofa shares the same somatropin active moiety as other recombinant human growth hormone therapies (e.g., Humatrope, Genotropin), but its distinctive PEGylation prolongs half-life, allowing once-weekly dosing versus traditional daily injections. Clinical trials demonstrate that its mechanism effectively stimulates growth velocity and metabolic benefits equivalent or superior to daily somatropin. Research supports its efficacy and safety from Phase 3 clinical trials, establishing its role as an effective and more convenient option for growth hormone replacement therapy.

Pharmacological Actions

Stimulates growth and development by mimicking endogenous human growth hormone activity.
Induces hepatic production of Insulin-like Growth Factor 1 (IGF-1), a critical mediator of growth.
Promotes longitudinal bone growth through chondrocyte proliferation and differentiation.
Enhances protein synthesis leading to increased muscle mass and physical strength.
Facilitates lipolysis resulting in reduction of body fat, particularly visceral adipose tissue.
Improves carbohydrate metabolism by modulating gluconeogenesis and insulin sensitivity.
Increases bone mineralization and density supporting skeletal health.
Modulates metabolism by increasing energy expenditure and improving body composition in adults with deficiency.
Reduces trunk fat and improves lipid profiles in adults with growth hormone deficiency.
Exhibits prolonged pharmacodynamic effects due to extended release from PEGylated prodrug.
Activates growth hormone receptor-mediated JAK2-STAT signaling pathways for gene transcription.
Facilitates anabolic effects contributing to tissue repair and regeneration.
Supports neurophysiological functions including cognitive benefits seen in GH deficiency states.
Bypasses rapid renal clearance through PEGylation, enabling weekly dosing.
Demonstrates comparable efficacy and safety to daily somatropin therapy but with improved adherence potential.

Therapeutic Or Clinical Uses

Treatment of growth failure in children aged 1 year and older with inadequate endogenous growth hormone secretion.
Replacement therapy for growth hormone deficiency in adults.
Management of pediatric growth hormone deficiency to improve linear height velocity.
Improvement of body composition in adults with GHD by reducing fat mass and increasing lean muscle mass.
Use as an alternative to daily somatropin injections providing once-weekly dosing convenience.
Treatment to normalize metabolism abnormalities associated with growth hormone deficiency in adults.
Potential use in children who have growth hormone deficiency secondary to pituitary disorders or idiopathic GHD.
Restoration of normal physiological GH levels in adults to reverse GH deficiency symptoms such as low energy and decreased bone density.
Adjunct management of metabolic complications due to chronic GHD.
Facilitation of normal development and maintenance of muscle strength in both pediatric and adult GHD patients.
Improvement in exercise capacity and quality of life for adults with growth hormone deficiency.
Reduction in visceral adiposity contributing to decreased cardiovascular risk in adult GHD.
Support for catch-up growth in pediatric patients with documented GH deficiency.
Clinical use in patients who have discontinued or transitioned from daily somatropin or other GH therapies.
Utilized as the only FDA-approved long-acting growth hormone therapy with demonstrated superior efficacy in children (according to Phase 3 heiGHt trial).

Side Or Adverse Effects

Viral infections including upper respiratory tract infections such as common cold in children.
Common pediatric adverse events including fever, cough, nausea, vomiting, diarrhea, and stomach pain.
Joint pain and arthritic symptoms such as stiffness or discomfort reported in pediatric patients.
Bleeding tendencies manifesting as nosebleeds or petechiae (pinpoint red or purple skin spots).
Fluid retention leading to swelling or edema, particularly in extremities (legs, ankles, feet) in adults.
Serious allergic reactions including hives, facial swelling, or difficulty breathing requiring emergency intervention.
Musculoskeletal pain including hip or knee pain, possibly causing limp gait.
Neurological symptoms such as numbness or tingling in hands, wrists, or fingers indicative of carpal tunnel syndrome.
Severe peripheral edema or puffiness in hands and feet signaling possible overdose or intolerance.
Behavioral changes including mood disturbances or altered cognition.
Visual disturbances or unusual headaches suggesting increased intracranial pressure.
Signs of pancreatitis characterized by severe upper abdominal pain radiating to the back, nausea, and vomiting.
Hyperglycemia manifestations including increased thirst, urination, dry mouth, and fruity breath odor.
Intracranial hypertension presenting with severe headache, tinnitus, dizziness, nausea, and vision problems.
Symptoms of adrenal insufficiency such as extreme weakness, dizziness, weight loss, and skin color changes.

Precautions

Avoid use in patients with known hypersensitivity to somatropin, lonapegsomatropin, or any component of Skytrofa.
Exercise caution in patients with acute critical illness, particularly post open-heart surgery, abdominal surgery, or multiple injuries.
Do not administer to patients with acute respiratory failure due to increased risk of adverse outcomes.
Avoid use in patients with active malignancy; tumor status should be stable or in remission prior to initiation.
Use with caution in patients with diabetic retinopathy to prevent worsening eye complications.
Contraindicated in patients with Prader-Willi syndrome who are obese or have severe respiratory compromise including sleep apnea.
Screen for past history of cancer, brain tumors, or pituitary disorders prior to therapy initiation.
Monitor thyroid function in patients with hypothyroidism as GH therapy may alter thyroid hormone levels.
Rotate injection sites to reduce risk of local lipoatrophy or injection site reactions.
Ensure patients or caregivers are trained on proper use of the Skytrofa Auto-Injector device.
Notify healthcare provider immediately if symptoms of intracranial hypertension or pancreatitis develop.
Evaluate compliance and other causes of poor growth if inadequate response observed in pediatric patients.
Reassess pediatric patients once epiphyseal closure occurs before continuing adult GH replacement.
Advise patients not to share injection devices to prevent infections.
Avoid reusing needles or syringes and comply with proper sharps disposal regulations.

Warnings

Seek immediate medical attention for signs of allergic reactions including hives, facial swelling, or difficulty breathing.
Discontinue and evaluate if severe upper abdominal pain suggestive of pancreatitis occurs.
Monitor for symptoms of intracranial hypertension such as headaches, ringing in ears, dizziness, visual changes.
Be alert for hyperglycemia signs including increased thirst and urination; adjust diabetic medications accordingly.
Watch for worsening or new onset vision problems and unusual headaches.
Discontinue in presence of severe swelling or puffiness indicative of fluid retention complications.
Avoid use in patients with active cancer or progression of pre-existing malignancies.
Not recommended during acute critical illnesses or multiple trauma as it may increase mortality risk.
Pregnancy and breastfeeding data are limited; use only if benefits outweigh potential risks.
Patients with Prader-Willi syndrome with obesity or severe respiratory impairment should not receive Skytrofa.
Monitor injection sites for lipoatrophy or local adverse reactions due to repeated administration.
In pediatric patients, failure to improve growth velocity should prompt evaluation for alternative causes.
Close monitoring of IGF-1 levels is essential to avoid overdose and potential adverse effects.
Adhere to recommended dosing intervals to minimize risk of accumulation and toxicity.
Avoid sudden discontinuation without medical advice to prevent adverse withdrawal effects.

Contraindication

Hypersensitivity to somatropin, lonapegsomatropin-tcgd, or any ingredient in Skytrofa.
Acute critical illness following open heart surgery, abdominal surgery, or multiple accidental trauma.
Acute respiratory failure where GH therapy has been associated with increased mortality.
Active malignancy or progression of cancer; GH therapy may promote tumor growth.
Diabetic retinopathy with active eye disease worsened by GH administration.
Prader-Willi syndrome in patients who are obese or have severe respiratory compromise including sleep apnea.
Patients with closed epiphyses without reevaluation for adult GH deficiency.
Use in combination with other unapproved growth hormone formulations or therapies.
Known sensitivity to polyethylene glycol or related excipients in the formulation.
Use in pediatric patients under 1 year or those weighing less than 11.5 kg (not studied and not recommended).

Drug Interactions

Hormonal contraceptives and hormone replacement therapy may alter GH metabolism affecting dose requirements.
Insulin and oral hypoglycemic agents may require adjustment due to altered glucose metabolism from GH therapy.
Concurrent steroid medications (e.g., prednisone, dexamethasone, methylprednisolone) can antagonize GH effects.
Drugs metabolized via cytochrome P450 enzymes may interact with GH altering drug clearance or efficacy.
Use with other growth hormone therapies requires proper washout periods to avoid overdose or toxicity.
Potential interaction with drugs affecting fluid balance, exacerbating edema or swelling.
Concurrent diabetes treatment regimens may need close monitoring owing to risk of hyperglycemia.
Avoid simultaneous use with somatropin-sensitive medications to prevent additive adverse effects.
Other biologics may interact altering immunogenicity and efficacy.
Medications affecting thyroid function may influence GH effects and require dose adjustments.
Frequent monitoring of IGF-1 and clinical response is necessary when multiple drug interactions are expected.
Limited data on interactions with herbal supplements; caution advised with products affecting endocrine system.
Drugs that induce or inhibit liver enzymes may modify GH metabolism and plasma concentrations.
Patients should inform healthcare providers of all prescription, over-the-counter, and herbal medications.
Use the Drugs.com Drug Interaction Checker for updated and personalized interaction assessment.

Preparations Of The Drug

Skytrofa is formulated as a white to off-white lyophilized powder in a dual-chamber prefilled cartridge.
One chamber contains lonapegsomatropin-tcgd powder; the other contains sterile water for injection as diluent.
Cartridges are single-dose and designed for use exclusively with the Skytrofa Auto-Injector device.
Available dosage strengths include 0.7 mg, 1.4 mg, 1.8 mg, 2.1 mg, 2.5 mg, 3 mg, 3.6 mg, 4.3 mg, 5.2 mg, 6.3 mg, 7.6 mg, 9.1 mg, 11 mg, and 13.3 mg.
The Auto-Injector electronically mixes and prepares the injection immediately prior to administration.
The device provides automated dose delivery with safety features and feedback confirming complete dosing.
Skytrofa cartridges are stored refrigerated between 2°C to 8°C and protected from light in the outer carton.
Cartridges may be stored at room temperature up to 30°C for up to 6 months if removed from refrigeration.
Once removed from refrigeration, write the removal date on the carton; do not use beyond 6 months or expiration date.
The solution after mixing should be clear or opalescent; do not use if cloudy or containing particulate matter.
The formulation contains only lonapegsomatropin-tcgd as active ingredient and water for injection as inactive.
Cartridges are for single patient use; do not share injection devices or cartridges.
Dispose of needles and syringes in designated sharps containers following regulations.
The Auto-Injector enables patient or caregiver self-administration outside clinical settings after proper training.
The product is manufactured by Ascendis Pharma Endocrinology Division A/S, Denmark.