Usage
Somatropin is a synthetic human growth hormone (hGH) prescribed for various medical conditions related to growth hormone deficiency or insufficiency. It is a growth hormone agonist, classified as an endocrine agent.
Somatropin’s mechanism of action involves mimicking the effects of naturally occurring hGH, stimulating cell growth and regeneration in various tissues by binding to cell surface receptors specific to growth hormone. This action promotes protein synthesis, increases fat breakdown for energy, and impacts carbohydrate metabolism.
Alternate Names
Somatropin is also known as recombinant human growth hormone (rhGH). Several brand names exist, including but not limited to Genotropin, Humatrope, Norditropin, Omnitrope, Saizen, Serostim, Tev-Tropin, Zorbtive and Zomacton.
How It Works
Pharmacodynamics: Somatropin binds to specific cell surface receptors, primarily on liver cells, leading to the production of insulin-like growth factor 1 (IGF-1). IGF-1 mediates many of the growth-promoting effects of somatropin, including bone growth, protein synthesis, and organ growth.
Pharmacokinetics:
- Absorption: Subcutaneous administration provides slow and sustained absorption.
- Metabolism: Primarily metabolized in the liver and kidneys.
- Elimination: Excreted through both renal and hepatic pathways. Specific details on CYP enzyme involvement are limited.
Mode of Action: Somatropin interacts with dimerized growth hormone receptors on cell surfaces, activating intracellular signaling pathways that lead to increased gene transcription, protein synthesis, and cell growth.
Receptor Binding: Binds to the growth hormone receptor, a transmembrane protein.
Enzyme Inhibition/Neurotransmitter Modulation: Specific enzyme inhibition or neurotransmitter modulation is not the primary mechanism of somatropin action.
Dosage
Dosage is highly individualized and should be determined and monitored by a physician experienced in growth hormone therapy. The following are general guidelines, and specific product information should always be consulted:
Standard Dosage
Adults:
- Growth Hormone Deficiency: Initial dose: 0.15-0.3 mg/day subcutaneously. Titrate upward every 1-2 months based on clinical response and IGF-1 levels. Maintenance doses vary widely between individuals. Women may require higher doses than men. Patients older than 60, obese individuals, or those with diabetes/glucose intolerance may start with a lower dose (0.1-0.2 mg/day).
Children:
- Growth Hormone Deficiency: 0.16-0.24 mg/kg/week subcutaneously, divided into 6-7 daily doses.
- Turner Syndrome: Up to 0.375 mg/kg/week subcutaneously, divided into 3-7 weekly doses.
- Idiopathic Short Stature: Up to 0.47 mg/kg/week subcutaneously, divided into 6-7 daily doses.
- Small for Gestational Age: Up to 0.48 mg/kg/week subcutaneously, divided into 6-7 daily doses. Recent literature suggests higher initial doses (e.g., 0.067 mg/kg/day) in very short or older/pubertal children. Younger children (less than 4 years old) with less severe short stature may start at a lower dose (0.033 mg/kg/day).
- Prader-Willi Syndrome: 0.16-0.24 mg/kg/week subcutaneously, divided into 6-7 daily doses.
Special Cases:
- Elderly Patients: Start at a lower dose with smaller increments.
- Patients with Renal Impairment: Dose adjustments based on renal function may be necessary, but specific guidelines are limited.
- Patients with Hepatic Dysfunction: Dose adjustments may be needed, but specific guidelines are limited.
- Patients with Comorbid Conditions: Patients with diabetes, glucose intolerance, or obesity may require lower initial doses and careful monitoring. Dosage adjustments may be required for those on oral estrogen therapy.
Clinical Use Cases
Somatropin is not typically used for acute conditions like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. Its use focuses on long-term growth promotion or hormone replacement.
Dosage Adjustments
Dose adjustments are based on individual patient response, including clinical improvement and serum IGF-1 levels. Consider renal or hepatic dysfunction, metabolic disorders, age, gender, and concomitant medications when modifying dosage.
Side Effects
Common Side Effects:
- Injection site reactions (pain, redness, swelling, itching)
- Headache
- Muscle or joint pain
- Edema
- Carpal tunnel syndrome
- Numbness/tingling in extremities
Rare but Serious Side Effects:
- Intracranial hypertension (papilledema, visual changes, headache, nausea, vomiting)
- Pancreatitis (sudden severe abdominal pain, nausea, vomiting)
- Hypothyroidism
- Hyperglycemia
- Allergic reactions (rash, itching, difficulty breathing)
Long-Term Effects:
- Increased risk of certain cancers
- Glucose intolerance/diabetes
- Musculoskeletal complications
Adverse Drug Reactions (ADR):
- Systemic hypersensitivity reactions
Contraindications
- Active malignancy
- Acute critical illness following open heart surgery, abdominal surgery, multiple trauma, or acute respiratory failure
- Closed epiphyses (in children for growth promotion)
- Active proliferative or severe non-proliferative diabetic retinopathy
- Prader-Willi syndrome with severe obesity or respiratory impairment
- Hypersensitivity to somatropin or excipients (e.g., benzyl alcohol, metacresol)
Drug Interactions
- Glucocorticoids: May attenuate the growth-promoting effects of somatropin.
- Oral Estrogens: May reduce the response to somatropin, requiring dose adjustment.
- Insulin/Oral Hypoglycemics: May require adjustment due to somatropin’s effects on glucose metabolism.
- Cytochrome P450 Interactions: While somatropin is primarily metabolized in the liver and kidneys, specific CYP interactions have not been extensively characterized. Consult specific drug information for potential interactions with other medications metabolized by CYP enzymes.
Pregnancy and Breastfeeding
- Pregnancy: Limited human data. Animal studies have not shown significant adverse developmental effects. Use only if clearly needed.
- Breastfeeding: It is unknown if somatropin is excreted in human milk. While limited data suggest no adverse effects, exercise caution, especially when nursing a newborn or preterm infant.
Drug Profile Summary
- Mechanism of Action: Mimics endogenous hGH, stimulating cell growth and regeneration via IGF-1.
- Side Effects: Injection site reactions, headache, muscle/joint pain, edema, carpal tunnel syndrome, intracranial hypertension, pancreatitis, hypothyroidism, hyperglycemia, allergic reactions.
- Contraindications: Active malignancy, acute critical illness, closed epiphyses, proliferative diabetic retinopathy, hypersensitivity.
- Drug Interactions: Glucocorticoids, oral estrogens, insulin/oral hypoglycemics.
- Pregnancy & Breastfeeding: Limited human data, use cautiously.
- Dosage: Individualized based on age, condition, and response; refer to detailed dosage guidelines.
- Monitoring Parameters: Growth parameters (height, weight, growth velocity), IGF-1 levels, glucose levels, thyroid function tests.
Popular Combinations
Somatropin is typically used as monotherapy. Concomitant use of other hormones may be necessary in patients with multiple hormone deficiencies.
Precautions
- Monitor for potential side effects, particularly intracranial hypertension, pancreatitis, and glucose intolerance.
- Pre-screening for pre-existing conditions and concomitant medications is crucial.
- Exercise caution in patients with diabetes or a history of glucose intolerance.
- Regular monitoring of growth parameters and IGF-1 levels is essential.
- Rotate injection sites to avoid lipodystrophy.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Somatropin?
A: Somatropin dosing is individualized based on the patient’s age, condition, and response to therapy. Refer to the detailed dosage guidelines provided above for specific recommendations for adults and children.
Q2: What are the most common side effects of Somatropin?
A: Common side effects include injection site reactions (pain, redness, swelling), headache, muscle or joint pain, fluid retention (edema), and carpal tunnel syndrome.
A: Serious side effects include intracranial hypertension (visual changes, severe headaches, nausea, vomiting), pancreatitis (severe abdominal pain), and allergic reactions. Seek immediate medical attention if any of these occur.
Q4: Is Somatropin safe to use during pregnancy?
A: Limited human data are available regarding Somatropin use during pregnancy. Animal studies haven’t shown significant adverse effects, but it should be used only if clearly needed. Discuss the risks and benefits with your doctor.
Q5: Can Somatropin be used in patients with diabetes?
A: Patients with diabetes or glucose intolerance may require lower initial doses and careful monitoring of blood glucose levels. Dose adjustments of insulin or oral hypoglycemic medications may be necessary.
Q6: How is Somatropin administered?
A: Somatropin is administered via subcutaneous injection. Rotate injection sites to minimize the risk of lipodystrophy.
Q7: What are the contraindications for Somatropin use?
A: Somatropin is contraindicated in patients with active malignancy, acute critical illness, closed epiphyses (in children for growth promotion), proliferative diabetic retinopathy, and hypersensitivity to the drug or its components.
Q8: How long is Somatropin treatment typically continued?
A: Treatment duration varies depending on the condition being treated. For growth hormone deficiency in children, treatment may continue until near-final adult height is achieved or epiphyseal closure occurs. Adult growth hormone deficiency may require lifelong treatment.
Q9: What should be monitored during Somatropin treatment?
A: Monitor growth parameters (height, weight, growth velocity) regularly, along with IGF-1 levels, glucose levels, and thyroid function. Regular assessment for side effects is also essential.
