1.1. Disease Prevalence and Incidence

Growth hormone (GH) is produced by the pituitary gland and plays a role in achieving normal growth in children, and also plays a role in the regulation of protein, lipid and carbohydrate metabolism during both childhood and adult life.¹ Growth hormone deficiency (GHD) is observed in both children and adults. The majority of adult GHD (76%) cases are associated with pituitary tumours and subsequent surgery and radiotherapy. Other causes of this condition include non-pituitary tumours, head injury, and vascular lesions; it can also occur idiopathically.² Clinical manifestations in adults include decreased lean body and muscle mass, increased fat mass, reduced bone mineral density (BMD), lipid profile changes, and psychiatric symptoms.^3,4 Diagnosis of adult GHD is usually based on a medical history (childhood-onset GHD, hypothalamic–pituitary disease or surgery, cranial irradiation, or traumatic brain injury) and biochemical tests (GH stimulation tests).^2,4,5 In a European study, the prevalence of hypopituitarism was estimated at 29 to 45 per 100,000, and the incidence at 4.2 cases per 100,000 per year.² There are no data on prevalence or incidence of GHD in Canada.

1.2. Standards of Therapy

Once GHD is diagnosed, patients may receive replacement therapy with recombinant human growth hormone (also called somatropin) under the supervision of an endocrinologist.² The goals of replacement therapy are to correct the metabolic, functional, and psychological abnormalities associated with adult GHD.⁴ For young adults with persistent GHD after attaining final height, it is recommended that GH treatment should be continued to achieve full somatic development, including the accrual of maximal bone and muscle mass. Elderly patients with proven GHD should be treated with GH, usually with lower doses (concordant with the physiological decrease in GH secretion).^2,4

Each somatropin product is biosynthesized using recombinant DNA technology and has a sequence identical to that of human GH produced by the pituitary gland.¹ Many studies have suggested similarities in the clinical effectiveness and safety profile of the various available somatropin products.^6,7 Somatropin products that have been approved by Health Canada as replacement of endogenous growth hormone in adults with GHD (either adult or childhood-onset) include Humatrope, Nutropin, Omnitrope, Saizen, and Genotropin.^8,9

Somatropin products are considered safe for both short and long-term use.^10,11 Doses of somatropin should be adjusted based on patients’ age, weight, sex, risks of adverse effects, and insulin-like growth factor-1 (IGF-1) levels, and the use of somatropin should be monitored regularly.^2,5

1.3. Drug

The Genotropin brand of somatropin was initially approved by Health Canada in 1998 for long-term therapy in patients with GHD, both adults and children.¹² At present, Genotropin is also indicated for short children born small for gestational age, Turner syndrome, and idiopathic short stature.¹³ It is administered subcutaneously at a dose of 0.15 mg to 0.3 mg per day for adult GHD. The final dose should be individually increased as required with respect to age and gender to a maximum daily maintenance dose of 1.33 mg.⁸