General

In vitro and in vivo preclinical, and clinical testing have demonstrated that Protropin^® (somatrem for injection), is therapeutically equivalent to pituitary-derived human growth hormone. Treatment of children who lack adequate endogenous growth hormone secretion with Protropin resulted in an increase in growth rate and an increase in insulin-like growth factor-I levels similar to that seen with pituitary-derived human growth hormone.

Actions that have been demonstrated for Protropin, somatropin and/or pituitary-derived human growth hormone include:

A. Tissue Growth--1) Skeletal Growth: Protropin stimulates skeletal growth in children with growth failure due to a lack of adequate secretion of endogenous growth hormone. Skeletal growth is accomplished at the epiphyseal plates at the ends of a growing bone. Growth and metabolism of epiphyseal plate cells are directly stimulated by growth hormone and one of its mediators, insulin-like growth factor-I. Serum levels of insulin-like growth factor-I are low in children and adolescents who are growth hormone deficient, but increase during treatment with Protropin. New bone is formed at the epiphyses in response to growth hormone. This results in linear growth until these growth plates fuse at the end of puberty. 2) Cell Growth: Treatment with pituitary-derived human growth hormone results in an increase in both the number and the size of skeletal muscle cells. 3) Organ Growth: Growth hormone of human pituitary origin influences the size of internal organs, including kidneys, and increases red cell mass. Treatment of hypophysectomized or genetic dwarf rats with somatropin results in organ growth that is proportional to the overall body growth.

B. Protein Metabolism--Linear growth is facilitated in proof by growth hormone- stimulated protein synthesis. This is reflected by nitrogen retention as demonstrated by a decline in urinary nitrogen excretion and blood urea nitrogen during growth hormone therapy.

C. Carbohydrate Metabolism--Growth hormone is a modulator of carbohydrate metabolism. For example, children with inadequate secretion of growth hormone sometimes experience fasting hypoglycemia that is improved by treatment with growth hormone. Protropin therapy may decrease glucose tolerance. Administration of Protropin to normal adults and patients who lacked adequate secretion of endogenous growth hormone resulted in increases in mean serum fasting and postprandial insulin levels. However, mean glucose and hemoglobin A_1C levels remained in the normal range.

D. Lipid Metabolism--Acute administration of pituitary-derived human growth hormone to humans resulted in lipid mobilization. Nonesterified fatty acids increased in plasma within two hours of pituitary-derived human growth hormone administration. In growth hormone deficient patients, long-term growth hormone administration often decreases body fat. Mean cholesterol levels decreased in patients treated with growth hormone.

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