Growth Hormone (Somatropin)

Somatropin is synthetic human growth hormone.
Growth hormone, also known as somatotropin, is a protein hormone of about 190 amino acids that is synthesised and secreted by cells called somatotrophs in the anterior pituitary. It has a significant role in the control of several complex processes, including growth and metabolism.
It has two distinct types of effects:

• Direct effects are the result of growth hormone binding its receptor on target cells. Fat cells (adipocytes), for example, have growth hormone receptors, and growth hormone stimulates them to break down triglyceride and suppresses their ability to take up and accumulate circulating lipids.
• Indirect effects are mediated primarily by an insulin-like growth factor-I (IGF-I). This hormone is secreted from the liver and other tissues in response to growth hormone. A majority of the growth promoting effects of growth hormone is actually due to IGF-I acting on its target cells.

• Genotropin®
• Humatrope®¹
• Norditropin®
• NutropinAq®
• Saizen®
• Zomacton®

• Usually, growth hormone treatment should be stopped after the first year if the extra height gain is not at least half the height gain in the year before treatment began.
• For a child who continues treatment after the first year, treatment should be stopped, after discussion with the child and carer, when the expected final height has nearly been reached, or when the child has grown less than 2 cm in 1 year.
• Alternatively, treatment should be continued until the person can be seen by an adult endocrinologist
• The doctor who is treating a child with Prader-Willi syndrome should consider the amount of fat in the body as well as height when considering when to stop treatment with growth hormone. This is because children with Prader-Willi syndrome often have too much body fat.
• The doctor should consider stopping treatment with growth hormone before a child has reached final height if the child is not taking the treatment regularly.
• If a child with chronic renal insufficiency has a kidney transplant, growth hormone treatment should be stopped. It should not usually be started again until at least 1 year after the transplant. This is so that doctors can see whether the child's growth catches up after the transplant.

Although it has been shown that physicians value even small gains, as final height approaches an additional 20% expenditure may be needed to gain the last 1% to 3% of adult height.³
A proportion of children with growth hormone deficiency (GHD) have persistence of GHD as young adults. To date, no markers have been shown in childhood to have predictive value in determining persistence of GHD into adult life. Children with GHD are more likely to have persistent severe GHD in adult life when the diagnosis is associated with other pituitary hormone deficiencies, abnormal pituitary neuroimaging, induced puberty, early age of diagnosis, and lower peak GH response at the first dynamic GH test in childhood.⁴

• The level of growth hormone should be checked.
• If the peak growth hormone response is less than 9 mU/litre in the insulin tolerance test or a similar low result in another reliable test, then growth hormone treatment should be given until what is known as adult peak bone mass is achieved (this happens at around age 25 years).
• After adult peak bone mass has been achieved an assessment of whether it is appropriate to continue with the human growth hormone treatment should be made, in line with the three measures described above.

NICE has recommended that the first stages of growth hormone treatment (starting treatment, adjusting the dose to suit the person, and assessing how well it is working) should be carried out by a consultant endocrinologist who has a special interest in growth hormone disorders. If, after the first stages, the growth hormone is to be prescribed by the persons GP, then the GP and consultant should share the persons care.

• Breast-feeding
• Diabetes mellitus - adjustment of hypoglycaemic therapy may be necessary
• Disorders of the epiphysis of the hip - should be monitored for limping
• History of malignant disease
• Initiation of treatment close to puberty not recommended in child born small for gestational age
• Papilloedema
• Relative deficiencies of other pituitary hormones, particularly hypothyroidism - regular thyroid function tests recommended
• Resolved intracranial hypertension
• Silver-Russell syndrome

Contraindications

• Rotate subcutaneous injection sites to prevent lipoatrophy
• Headache
• Fundoscopy for papilloedema recommended if severe or recurrent headache
• Visual problems
• Nausea and vomiting - if papilloedema confirmed consider benign intracranial hypertension
• Peripheral oedema
• Arthralgia, myalgia, carpal tunnel syndrome
• Paraesthesia
• Antibody formation
• Hypothyroidism
• Insulin resistance, hyperglycaemia,⁷ hypoglycaemia
• Leukaemia:
  • This has been reported as a cluster of cases in children receiving growth hormone.
  • Further evidence appears to show no increased risk for the development of de-novo cancers in those treated with GH, unless there is an underlying predisposition.^8,9