Somatropin, rh-GH is a purified recombinant growth hormone prepared by using either Escherichia coli or mammalian-cells. Endogenous human growth hormone (hGH) is produced in the pituitary gland. Growth hormone was first isolated in 1956, and its structure was identified in 1972. Prior to 1985, growth hormone (GH) was derived from human cadavers; however, the use of human derived GH was stopped due to contamination of the product with Creutzfeldt-Jakob virus.