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Prescribing Information
GENOTROPIN® (somatropin [rDNA origin] for injection)
Clinical Pharmacology
Return to the GENOTROPIN Product Center

Mechanism of Action

In vitro, preclinical, and clinical tests have demonstrated that GENOTROPIN lyophilized powder is therapeutically equivalent to human growth hormone of pituitary origin and achieves similar pharmacokinetic profiles in normal adults. In pediatric patients who have growth hormone deficiency (GHD), have Prader-Willi syndrome (PWS), were born small for gestational age (SGA), have Turner syndrome (TS), or have Idiopathic short stature (ISS), treatment with GENOTROPIN stimulates linear growth. In patients with GHD or PWS, treatment with GENOTROPIN also normalizes concentrations of IGF-I (Insulin-like Growth Factor-I/Somatomedin C). In adults with GHD, treatment with GENOTROPIN results in reduced fat mass, increased lean body mass, metabolic alterations that include beneficial changes in lipid metabolism, and normalization of IGF-I concentrations.

In addition, the following actions have been demonstrated for GENOTROPIN and/or somatropin.

Pharmacodynamics

Tissue Growth
A. Skeletal Growth: GENOTROPIN stimulates skeletal growth in pediatric patients with GHD, PWS, SGA, TS, or ISS. The measurable increase in body length after administration of GENOTROPIN results from an effect on the epiphyseal plates of long bones. Concentrations of IGF-I, which may play a role in skeletal growth, are generally low in the serum of pediatric patients with GHD, PWS, or SGA, but tend to increase during treatment with GENOTROPIN. Elevations in mean serum alkaline phosphatase concentration are also seen.

B. Cell Growth: It has been shown that there are fewer skeletal muscle cells in short-statured pediatric patients who lack endogenous growth hormone as compared with the normal pediatric population. Treatment with somatropin results in an increase in both the number and size of muscle cells.

Protein Metabolism
Linear growth is facilitated in part by increased cellular protein synthesis. Nitrogen retention, as demonstrated by decreased urinary nitrogen excretion and serum urea nitrogen, follows the initiation of therapy with GENOTROPIN.

Carbohydrate Metabolism
Pediatric patients with hypopituitarism sometimes experience fasting hypoglycemia that is improved by treatment with GENOTROPIN. Large doses of growth hormone may impair glucose tolerance.

Lipid Metabolism
In GHD patients, administration of somatropin has resulted in lipid mobilization, reduction in body fat stores, and increased plasma fatty acids.

Mineral Metabolism
Somatropin induces retention of sodium, potassium, and phosphorus. Serum concentrations of inorganic phosphate are increased in patients with GHD after therapy with GENOTROPIN. Serum calcium is not significantly altered by GENOTROPIN. Growth hormone could increase calciuria.

Body Composition
Adult GHD patients treated with GENOTROPIN at the recommended adult dose (see DOSAGE AND ADMINISTRATION) demonstrate a decrease in fat mass and an increase in lean body mass. When these alterations are coupled with the increase in total body water, the overall effect of GENOTROPIN is to modify body composition, an effect that is maintained with continued treatment.

Pharmacokinetics

Absorption
Following a 0.03 mg/kg subcutaneous (SC) injection in the thigh of 1.3 mg/mL GENOTROPIN to adult GHD patients, approximately 80% of the dose was systemically available as compared with that available following intravenous dosing. Results were comparable in both male and female patients. Similar bioavailability has been observed in healthy adult male subjects.

In healthy adult males, following an SC injection in the thigh of 0.03 mg/kg, the extent of absorption (AUC) of a concentration of 5.3 mg/mL GENOTROPIN was 35% greater than that for 1.3 mg/mL GENOTROPIN. The mean (± standard deviation) peak (Cmax) serum levels were 23.0 (± 9.4) ng/mL and 17.4 (± 9.2) ng/mL, respectively.

In a similar study involving pediatric GHD patients, 5.3 mg/mL GENOTROPIN yielded a mean AUC that was 17% greater than that for 1.3 mg/mL GENOTROPIN. The mean Cmax levels were 21.0 ng/mL and 16.3 ng/mL, respectively.

Adult GHD patients received two single SC doses of 0.03 mg/kg of GENOTROPIN at a concentration of 1.3 mg/mL, with a one- to four-week washout period between injections. Mean Cmax levels were 12.4 ng/mL (first injection) and 12.2 ng/mL (second injection), achieved at approximately six hours after dosing.

There are no data on the bioequivalence between the 12 mg/mL formulation and either the 1.3 mg/mL or the 5.3 mg/mL formulations.

Distribution
The mean volume of distribution of GENOTROPIN following administration to GHD adults was estimated to be 1.3 (± 0.8) L/kg.

Metabolism
The metabolic fate of GENOTROPIN involves classical protein catabolism in both the liver and kidneys. In renal cells, at least a portion of the breakdown products are returned to the systemic circulation. The mean terminal half-life of intravenous GENOTROPIN in normal adults is 0.4 hours, whereas subcutaneously administered GENOTROPIN has a half-life of 3.0 hours in GHD adults. The observed difference is due to slow absorption from the subcutaneous injection site.

Excretion
The mean clearance of subcutaneously administered GENOTROPIN in 16 GHD adult patients was 0.3 (± 0.11) L/hrs/kg.

Special Populations

Pediatric: The pharmacokinetics of GENOTROPIN are similar in GHD pediatric and adult patients.

Gender: No gender studies have been performed in pediatric patients; however, in GHD adults, the absolute bioavailability of GENOTROPIN was similar in males and females.

Race: No studies have been conducted with GENOTROPIN to assess pharmacokinetic differences among races.

Renal or hepatic insufficiency: No studies have been conducted with GENOTROPIN in these patient populations.

Table 2 Mean SC Pharmacokinetic Parameters in Adult GHD Patients

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenicity studies have not been conducted with GENOTROPIN. No potential mutagenicity of GENOTROPIN was revealed in a battery of tests including induction of gene mutations in bacteria (the Ames test), gene mutations in mammalian cells grown in vitro (mouse L5178Y cells), and chromosomal damage in intact animals (bone marrow cells in rats). See PREGNANCY section for effect on fertility.


GENOTROPIN Safety Information
 

Important Safety Information

Contraindications

Somatropin should not be used for growth promotion in pediatric patients with closed epiphyses.

Somatropin is contraindicated in patients with active proliferative or severe nonproliferative diabetic retinopathy.

Somatropin is contraindicated in patients with active malignancy. Because growth hormone deficiency may be a sign of pituitary or other brain tumors, the presence of such tumors should be ruled out before treatment is initiated. Somatropin should not be used in patients with any evidence of progression or recurrence of an underlying intracranial tumor.

Somatropin should not be used to treat patients with acute critical illness due to complications from surgery, trauma, or respiratory failure; the safety of continuing somatropin treatment for approved uses in patients who develop these illnesses has not been established.

Somatropin is contraindicated in patients with Prader-Willi syndrome who are severely obese or have respiratory impairment (see WARNINGS).

Additional Safety Information

Monitor patients with glucose intolerance closely; dosage of antihyperglycemic drug may need to be adjusted. Monitor carefully if somatropin is administered in combination with glucocorticoid therapy and/or other drugs metabolized by the CP450 pathway.

In childhood cancer survivors, an increased risk of a second neoplasm, in particular meningiomas, has been reported in patients treated with somatropin after their first neoplasm, particularly those who were treated with cranial radiation.

Intracranial hypertension (IH) has been reported in a small number of patients treated with somatropin. If papilledema is observed during somatropin treatment, treatment should be stopped and reassessed. Patients with Turner syndrome and Prader-Willi syndrome may be at increased risk for the development of IH.

Patients treated with somatropin should have periodic thyroid function tests and thyroid hormone replacement therapy should be initiated or adjusted when indicated.

In patients with multiple hormone deficiencies, standard hormonal replacement therapy should be monitored closely when somatropin therapy is administered.

Progression of scoliosis can occur in patients who experience rapid growth. Patients with scoliosis should be monitored for manifestation or progression during GH therapy.

Slipped capital femoral epiphyses may occur more frequently in patients with endocrine disorders or in patients undergoing rapid growth.

Somatropin should be used during pregnancy only if clearly needed and with caution in nursing mothers because it is not known whether somatropin is excreted in human milk.

In clinical trials with GENOTROPIN in pediatric GHD patients, the following events were reported infrequently: injection site reactions, including pain or burning associated with the injection, fibrosis, nodules, rash, inflammation, pigmentation, or bleeding; lipoatrophy; headache; hematuria; hypothyroidism; and mild hyperglycemia.

In clinical studies of 273 pediatric patients born SGA treated with GENOTROPIN, the following clinically significant events were reported: mild transient hyperglycemia; 1 patient with benign intracranial hypertension; 2 patients with central precocious puberty; 2 patients with jaw prominence; and several patients with aggravation of preexisting scoliosis, injection site reactions, and self-limited progression of pigmented nevi. Anti-hGH antibodies were not detected in any of the patients treated with GENOTROPIN.

Deaths have been reported with the use of a growth hormone in pediatric PWS patients with severe obesity, history of upper airway obstruction or sleep apnea, and/or unidentified respiratory infection. Therefore, all patients with PWS should be evaluated and monitored for signs of upper airway obstruction, sleep apnea, and respiratory infections, and have effective weight control.

In clinical trials with GENOTROPIN in pediatric patients with PWS, the following drug-related events were reported: edema, aggressiveness, arthralgia, benign intracranial hypertension, hair loss, headache, and myalgia.

Somatropin may increase the occurrence of otitis media in Turner syndrome patients.

In 2 clinical studies with GENOTROPIN in pediatric patients with Turner syndrome, the most frequently reported adverse events were respiratory illnesses (influenza, tonsillitis, otitis, sinusitis), joint pain, and urinary tract infection. The only treatment-related adverse event that occurred in more than 1 patient was joint pain.

In 2 clinical studies with GENOTROPIN in pediatric patients with ISS, the most commonly encountered adverse events included upper respiratory tract infections, influenza, tonsillitis, nasopharyngitis, gastroenteritis, headaches, increased appetite, pyrexia, fracture, altered mood, and arthralgia.

In clinical trials with GENOTROPIN adults with GHD, the majority of side effects were symptoms of fluid retention, including peripheral swelling/edema, arthralgia, pain and stiffness of the extremities, myalgia, paresthesia, and hypoesthesia.

In women on oral estrogen replacement, a larger dose of somatropin may be required to achieve the defined treatment goal (see DOSAGE AND ADMINISTRATION).

Elderly patients may be more sensitive to the action of somatropin, and therefore may be more prone to develop adverse reactions.

The cartridges of GENOTROPIN contain m-Cresol and should not be used by patients with a known sensitivity to this preservative.

Subcutaneous injection of somatropin at the same site repeatedly may result in tissue atrophy. This can be avoided by rotating the injection site.

Health care providers should supervise the first injection and provide appropriate training and instruction for the proper use of all devices for GENOTROPIN.

Rx only

 

Please see full prescribing information.

GENOTROPIN®somatropin [rDNA origin] for injection

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