Introduction
Omnitrope (somatropin) is a recombinant human growth hormone (rhGH) that is structurally identical to the endogenous growth hormone produced by the human pituitary gland. Manufactured using recombinant DNA technology, it serves as a biosynthetic alternative to natural human growth hormone for various growth-related disorders. Omnitrope was the first biosimilar product approved by the FDA in 2006, marking a significant milestone in pharmaceutical development.
Mechanism of Action
Omnitrope exerts its effects by binding to growth hormone receptors on target cells, initiating intracellular signaling pathways that stimulate growth and metabolic processes. Its primary actions include:
- Stimulation of linear growth through activation of epiphyseal growth plates
- Promotion of protein synthesis and cellular amino acid uptake
- Enhancement of lipolysis and reduction of adipose tissue
- Antagonism of insulin action on glucose metabolism
- Promotion of sodium, potassium, and water retention
- Stimulation of collagen synthesis and bone mineralization
Indications
FDA-approved indications for Omnitrope include:
- Pediatric growth hormone deficiency (GHD)
- Turner syndrome in pediatric patients
- Prader-Willi syndrome in pediatric patients
- Idiopathic short stature in pediatric patients
- Small for gestational age (SGA) without catch-up growth by age 2-4 years
- Adult growth hormone deficiency
- Short bowel syndrome in patients receiving specialized nutritional support
Dosage and Administration
Standard Dosing:- Pediatric GHD: 0.16-0.24 mg/kg/week divided into 6-7 daily subcutaneous injections
- Turner syndrome: Up to 0.375 mg/kg/week divided daily
- Prader-Willi syndrome: 0.24 mg/kg/week divided daily
- Idiopathic short stature: Up to 0.37 mg/kg/week divided daily
- Adult GHD: Start with 0.04 mg/kg/week, titrate to maximum 0.08 mg/kg/week
- Route: Subcutaneous injection
- Sites: Rotate injection sites (thigh, abdomen, buttocks, upper arm)
- Timing: Typically administered in the evening to mimic natural growth hormone secretion patterns
- Renal impairment: Dose adjustment may be necessary
- Hepatic impairment: Use with caution
- Elderly: Start with lower doses and titrate slowly
Pharmacokinetics
Absorption:- Bioavailability: Approximately 70-90% following subcutaneous administration
- Tmax: 3-5 hours after subcutaneous injection
- Volume of distribution: 0.05-0.07 L/kg
- Does not significantly bind to plasma proteins
- Primarily metabolized in the liver via proteolytic hydrolysis
- Undergoes significant first-pass metabolism
- Half-life: 2-4 hours after subcutaneous administration
- Clearance: Primarily renal (approximately 50%)
- Elimination occurs through proteolytic degradation in renal and hepatic tissues
Contraindications
- Active malignancy
- Hypersensitivity to somatropin or any component of the formulation
- Acute critical illness due to complications after open heart or abdominal surgery, multiple accidental trauma, or acute respiratory failure
- Diabetic retinopathy with active proliferation
- Prader-Willi syndrome with severe obesity or severe respiratory impairment
- Closed epiphyses in pediatric patients
Warnings and Precautions
Boxed Warning:- Increased mortality in patients with acute critical illness
- Increased risk of neoplasms: Monitor patients with history of malignancy
- Glucose intolerance and diabetes mellitus: Monitor blood glucose regularly
- Intracranial hypertension: Monitor for headache, visual changes, nausea
- Fluid retention: May cause edema, arthralgia, carpal tunnel syndrome
- Hypothyroidism: Monitor thyroid function periodically
- Slipped capital femoral epiphysis: Monitor for hip or knee pain in children
- Pancreatitis: Monitor for severe abdominal pain
Drug Interactions
- Glucocorticoids: May inhibit growth-promoting effects
- Estrogen: Oral administration may reduce serum IGF-1 response
- Cytochrome P450 substrates: May alter metabolism of drugs metabolized by CYP450 enzymes
- Insulin: May require adjustment of insulin doses
- Anticonvulsants: May alter growth hormone clearance
Adverse Effects
Common (≥10%):- Injection site reactions (redness, swelling, pain)
- Headache
- Edema
- Arthralgia
- Myalgia
- Paresthesia
- Intracranial hypertension
- Glucose intolerance
- Slipped capital femoral epiphysis
- Progression of pre-existing scoliosis
- Pancreatitis
- Neoplasms (new or recurrence)
- Severe allergic reactions
Monitoring Parameters
Baseline Assessment:- Height, weight, growth velocity
- Bone age (in children)
- Thyroid function tests
- Fasting blood glucose and HbA1c
- IGF-1 and IGFBP-3 levels
- Fundoscopic examination
- Growth velocity every 3-6 months in children
- Glycemic control every 6 months
- Thyroid function annually
- Scoliosis screening in children
- Monitor for signs of intracranial hypertension
- Regular cancer screening as appropriate
Patient Education
Administration Instructions:- Proper injection technique and site rotation
- Storage requirements (refrigeration at 2-8°C)
- Do not freeze or shake vigorously
- Discard after 28 days after first use
- Importance of adherence to prescribed regimen
- Regular follow-up with healthcare provider
- Report any severe headaches, visual changes, or limping
- Monitor for signs of hyperglycemia
- Maintain healthy diet and exercise regimen
- Never share injection devices or needles
- Proper disposal of used needles and syringes
- Carry medical identification indicating growth hormone therapy
- Inform all healthcare providers about Omnitrope use
References
1. FDA Prescribing Information: Omnitrope (somatropin). 2022 2. Growth Hormone Research Society. Consensus guidelines for the diagnosis and treatment of growth hormone deficiency in childhood and adolescence. Journal of Clinical Endocrinology and Metabolism. 2000;85(11):3990-3993 3. Molitch ME, et al. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. 2011;96(6):1587-1609 4. Ranke MB. Treatment of children and adolescents with idiopathic short stature. Nature Reviews Endocrinology. 2013;9(6):325-334 5. Clayton PE, et al. Management of the child born small for gestational age through to adulthood: a consensus statement of the International Societies of Pediatric Endocrinology and the Growth Hormone Research Society. Journal of Clinical Endocrinology and Metabolism. 2007;92(3):804-810 6. Deal CL, et al. The 2019 Canadian Paediatric Surveillance Program (CPSP) growth hormone monitoring guidelines. Paediatrics & Child Health. 2019;24(6):372-383
This monograph is intended for educational purposes only and should not replace professional medical advice. Always consult with a qualified healthcare provider for personalized medical guidance.