Medication Summary
Somatostatin analogues are the most effective medical therapies for growth hormone (GH) excess. After transsphenoidal surgery, these agents are generally a first-line treatment, followed by a dopamine-receptor agonist or GH receptor antagonist. [58]
The most extensively studied and used somatostatin analogue, octreotide, binds to the somatostatin receptor subtypes II and V, inhibiting GH secretion.
Prolactin levels are often adequately suppressed with dopamine-receptor agonists. However, circulating GH and insulinlike growth factor ̶ I (IGF-I) levels rarely normalize with these agents.
Somatostatin Analogs
Class Summary
Like natural somatostatin, octreotide inhibits the secretion of GH, insulin, and glucagon. After an intravenous administration, basal serum GH, insulin, and glucagon levels fall. Octreotide also inhibits prolactin release by means of vasoactive intestinal peptide (VIP) ̶ and thyrotropin-releasing hormone (TRH) ̶ mediated secretion of prolactin. Octreotide is used to treat acromegaly and several hormone-secreting tumors.
Octreotide (Sandostatin, Mycapssa)
Octreotide acts primarily on somatostatin receptor subtypes II and V, inhibiting GH secretion. It also has a multitude of other endocrine and nonendocrine effects, including inhibition of glucagon, VIP, and gastrointestinal peptides.
The SC product is administered 3 times per day. The long-acting somatostatin analogue given IM every 4 weeks. It results in similar improvements in GH/IGF-I concentration as octreotide but is associated with fewer adverse effects. A trial of short-acting somatostatin analogue is necessary to confirm the patient's ability to tolerate this compound.
Do not administer octreotide LAR in the deltoid area, because of significant discomfort at the injection site. Gluteal injection sites should be alternated.
An oral twice daily product is also available.
Lanreotide (Somatuline Depot)
Lanreotide, an octapeptide analogue of natural somatostatin, is indicated for long-term treatment of acromegaly in patients who experience inadequate response to other therapies. It inhibits a variety of endocrine, neuroendocrine, exocrine, and paracrine functions. Lanreotide elicits high affinity for human somatostatin receptors 2, 3, and 5.
It inhibits basal secretion of motilin, gastric inhibitory peptide, and pancreatic polypeptide and markedly inhibits meal-induced increases in superior mesenteric artery blood flow and portal venous blood flow. Lanreotide also significantly decreases prostaglandin E1–stimulated jejunal secretion of water, sodium, potassium, and chloride and reduces prolactin levels in acromegalic patients undergoing long-term treatment.
Pasireotide (Signifor LAR)
Pasireotide is a cyclohexapeptide somatostatin analog that binds to human somatostatin receptors 1, 2, 3, 4 and 5. It is indicated for the treatment of patients with acromegaly who have had an inadequate response to surgery and/or for whom surgery is not an option.
Antiparkinson Agents, Dopamine Agonists
Class Summary
Dopamine-receptor agonists make up another pharmacologic option. They have modest effects if used as single agents and are usually added to somatostatin analogues if complete remission has not been achieved. Cabergoline is well tolerated.
Bromocriptine (Parlodel, Cycloset)
This is the dopamine-receptor agonist that is most often used to treat GH and prolactin excess. It is safe when administered to a child for extended period.
Cabergoline
Cabergoline is a potent dopamine-receptor agonist with a prolonged duration of action. It inhibits prolactin secretion more effectively than bromocriptine.
GH-Receptor Antagonist
Class Summary
GH-receptor agonists are the newest class of drugs used to decrease excessive GH effect. It blocks GH binding to receptors, thus decreasing IGF-I, IGF binding protein 3 (IGFBP-3), and acid-labile subunit.
Pegvisomant (Somavert)
Pegvisomant is a recombinant deoxyribonucleic acid (DNA) analogue of human GH that has been structurally altered to act as a GH receptor antagonist. It selectively binds to GH receptors on cell surfaces, blocking endogenous GH binding. By interfering with GH signal transduction, it decreases levels of IGF-I, IGFBP-3, and acid-labile subunit.
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Gigantism and Acromegaly. Image shows a coauthor of this article with a statue of Robert Wadlow, who was called the Alton giant. The tallest person on record, he was 8 feet 11 inches tall at the time of his death.
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Gigantism and Acromegaly. A 12-year-old boy with McCune-Albright syndrome. His growth-hormone excess manifested as tall stature, coarse facial features, and macrocephaly.
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Gigantism and Acromegaly. Robert Wadlow, 19 years of age, with his father (postcard photo prior to 1937). Courtesy of Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Robert_Wadlow_postcard.jpg).
