The growth hormone (GH) axis spans four anatomical levels, each offering a distinct pharmacological target. At the hypothalamus, growth hormone-releasing hormone (GHRH) drives GH secretion while somatostatin suppresses it; in the stomach and hypothalamus, ghrelin provides a third regulatory input via the GH secretagogue receptor (GHSR). At the pituitary, GH is stored in somatotrophs and released in pulses; in the liver and peripheral tissues, GH drives insulin-like growth factor-1 (IGF-1) synthesis; and at target cells, IGF-1 mediates most of the growth-promoting, anabolic, and metabolic effects of the axis. Pharmacological agents acting at each level are now in clinical use: somatostatin receptor analogs (SSAs) suppress both GH and downstream secretory effects; GHRH analogs and secretagogues stimulate the axis for diagnostic and therapeutic purposes; GH replacement (somatropin) restores GH deficiency states; and pegvisomant blocks the GH receptor at the post-pituitary level, providing IGF-1 suppression independent of tumor GH output. This module covers the clinical pharmacology of each drug class in depth, with an emphasis on receptor selectivity, pharmacokinetics, metabolic adverse effects, drug interactions, and the practical framework for monitoring in acromegaly, GH deficiency, and HIV-associated lipodystrophy.
Growth hormone-releasing hormone (GHRH) is a 44-amino acid peptide synthesized in the arcuate nucleus of the hypothalamus and released in pulses into the hypothalamo-hypophyseal portal circulation. GHRH binds to a seven-transmembrane G protein-coupled receptor (GHRH-R) on pituitary somatotrophs, coupling to Gs and activating adenylyl cyclase; the resulting rise in cyclic AMP (cAMP) and protein kinase A (PKA) activation stimulates growth hormone (GH) gene transcription, GH biosynthesis, and GH exocytosis. The magnitude of each GH pulse is proportional to the amplitude of the preceding GHRH pulse and is gated by concomitant somatostatin tone. Individual GH pulses are brief and of high amplitude, particularly during slow-wave sleep stages 3 and 4, when somatostatin withdrawal and maximal GHRH release coincide; the nocturnal sleep burst accounts for the largest fraction of daily GH secretion in adolescents and adults.1
Somatostatin (somatotropin release-inhibiting factor, SRIF) is a cyclic tetradecapeptide (somatostatin-14) and its N-terminally extended form (somatostatin-28) produced by hypothalamic periventricular neurons, pancreatic delta cells, and D cells of the gastrointestinal tract. Somatostatin acts on five receptor subtypes designated SSTR1 through SSTR5 (somatostatin receptors 1 through 5, SSTR1–SSTR5), all of which are seven-transmembrane GPCRs (G protein-coupled receptors) that signal through Gi/Go, reducing cAMP, inhibiting voltage-gated calcium channels, and activating inwardly rectifying potassium channels. Pituitary somatotrophs predominantly express SSTR2 (somatostatin receptor subtype 2) and SSTR5; SSTR2 is the principal mediator of GH suppression by hypothalamic somatostatin, and SSAs are designed to leverage this receptor distribution. Pancreatic beta cells and delta cells express SSTR2 and SSTR5, making them targets of somatostatin-mediated insulin and glucagon suppression; this is the mechanistic basis for the hyperglycemia associated with somatostatin receptor analog (SSA) therapy.2
Ghrelin is an acylated 28-amino acid peptide produced primarily by oxyntic cells of the gastric fundus and to a lesser extent by hypothalamic neurons. Acylation of the serine-3 residue with an octanoyl group by ghrelin O-acyltransferase (GOAT) is obligatory for biological activity at the growth hormone secretagogue receptor type 1a (GHSR-1a). Ghrelin signaling through GHSR-1a couples to Gq/11 and activates phospholipase C beta (PLC-beta), IP3 (inositol trisphosphate), DAG (diacylglycerol), and protein kinase C (PKC), ultimately mobilizing calcium and potentiating GH release. Ghrelin acts synergistically with GHRH to amplify GH pulse amplitude: neither alone produces the full pulsatile response. Beyond GH regulation, ghrelin promotes positive energy balance through hypothalamic orexigenic circuits. Macimorelin, a synthetic GHSR-1a agonist used diagnostically, mimics ghrelin's GH-stimulating action and is discussed in Section 3.3
IGF-1 (insulin-like growth factor-1, also called somatomedin C) is produced predominantly by the liver under GH stimulation and circulates bound to IGF-binding protein-3 (IGFBP-3) in a ternary complex that extends its half-life from minutes to approximately 12 to 15 hours. IGF-1 mediates most of the growth-promoting effects of GH at peripheral tissues: it drives linear growth at epiphyseal growth plates, promotes protein synthesis in muscle, inhibits lipolysis in adipose tissue, and has insulin-like effects on glucose metabolism. IGF-1 provides long-loop negative feedback to both the hypothalamus (stimulating somatostatin release, suppressing GHRH release) and the pituitary (directly suppressing somatotroph GH output). The serum IGF-1 concentration, reflecting integrated 24-hour GH secretion, is the preferred clinical monitoring marker for both GH excess (acromegaly) and GH deficiency, and it is the primary endpoint used to assess response to SSAs and pegvisomant.4
Acromegaly results from autonomous GH hypersecretion, almost always from a pituitary somatotroph adenoma. Excess GH drives supraphysiological IGF-1, producing progressive soft tissue and skeletal changes, insulin resistance, cardiovascular disease, and sleep apnea. Diagnosis requires failure of GH suppression below 1 ng/mL (or below 0.4 ng/mL by ultrasensitive assay) after a 75 g oral glucose tolerance test, combined with elevated age- and sex-adjusted serum IGF-1.6 First-line treatment is transsphenoidal surgery; pharmacotherapy (SSAs, pegvisomant, dopamine agonists) is used for residual or recurrent disease and for pre-surgical tumor control.
Octreotide is a synthetic octapeptide analog of somatostatin with a 200-fold longer plasma half-life than native somatostatin-14 (approximately 1.5 to 2 hours vs. 1 to 3 minutes for native somatostatin). Octreotide has high binding affinity for SSTR2 (the principal pituitary growth hormone (GH)-suppressing receptor) and SSTR5 (somatostatin receptor subtype 5), and moderate affinity for SSTR3 (subtype 3); it has negligible affinity for SSTR1 (subtype 1) and SSTR4 (subtype 4). This SSTR2 and SSTR5-selective profile produces potent GH and insulin-like growth factor-1 (IGF-1) suppression in acromegaly while also suppressing insulin and glucagon secretion from pancreatic SSTR2-expressing cells. Subcutaneous (SC) octreotide administered three times daily achieves GH normalization in approximately 50 to 60% of acromegaly patients and IGF-1 normalization in 30 to 50% when used as monotherapy after surgical failure. A long-acting release (LAR) depot formulation of octreotide (Sandostatin LAR) consists of microspheres of poly(lactic-co-glycolic acid) (PLGA) polymer encapsulating octreotide for intramuscular (IM) injection; the 20 mg, 30 mg, and 40 mg doses are given every 28 days, with a lag of approximately 14 days before therapeutic plasma concentrations are reached from the first injection, during which SC octreotide bridging is used.5
Lanreotide is a cyclic octapeptide somatostatin analog (SSA) with receptor affinity comparable to octreotide at SSTR2 and SSTR5, with slightly higher SSTR2 affinity in some binding assays. Its key pharmacological distinction from octreotide lies in the formulation: Lanreotide Autogel (Somatuline Depot) is a high-viscosity aqueous gel delivered by deep subcutaneous injection using a pre-filled syringe; the gel depot releases lanreotide by diffusion over approximately 28 days, achieving stable plasma concentrations without the 14-day loading period required by octreotide LAR microspheres. Available as 60 mg, 90 mg, and 120 mg SC injections every 4 weeks, with an extended dosing interval option of every 6 or 8 weeks for patients achieving biochemical control. After SC injection, lanreotide is distributed primarily to the plasma and liver, with minimal central nervous system (CNS) penetration. Elimination is predominantly fecal (biliary excretion) with less than 5% renal excretion of unchanged drug, making dose adjustment unnecessary in renal impairment. Both octreotide LAR and lanreotide Autogel achieve equivalent rates of GH and IGF-1 normalization in head-to-head comparator studies in acromegaly.5
Pasireotide is a cyclohexapeptide SSA with a distinctly different receptor binding profile from octreotide and lanreotide: it binds with high affinity to SSTR1, SSTR2, SSTR3, and SSTR5, and is designated a pan-SSTR agonist (pan-somatostatin receptor agonist). SSTR5 affinity is approximately 40-fold higher for pasireotide than for octreotide; this SSTR1 and SSTR5 activity provides additive GH and corticotropin (ACTH) suppression beyond what SSTR2-selective agents alone can achieve. In the PAOLA (Pasireotide vs. Octreotide LAR Acromegaly) trial, pasireotide LAR 40 mg and 60 mg monthly produced biochemical control (normal GH and IGF-1) in 31 to 38% of patients incompletely controlled by octreotide or lanreotide, compared with 19% for a switch to the alternative SSTR2-selective agent, demonstrating clinically meaningful efficacy in the medically refractory population.7
The metabolic liability of pasireotide is substantially greater than that of octreotide and lanreotide. Hyperglycemia occurs in approximately 57 to 73% of pasireotide-treated patients, compared with 10 to 20% for SSTR2-selective agents, owing to pasireotide's high SSTR5 affinity and consequent profound suppression of both insulin and incretin hormone (glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP)) secretion from pancreatic and intestinal cells. The hyperglycemia is predominantly driven by reduced insulin secretion rather than increased insulin resistance, so metformin and sodium-glucose cotransporter-2 (SGLT2) inhibitors have limited efficacy; dipeptidyl peptidase-4 (DPP-4) inhibitors are also largely ineffective because pasireotide suppresses the incretin response that DPP-4 inhibitors depend on to work. GLP-1 receptor agonists and insulin are the preferred agents for managing pasireotide-induced hyperglycemia, because they restore insulin secretory drive independently of the suppressed endogenous pathways.8
Pasireotide suppresses insulin secretion (SSTR5) and incretin release (GLP-1, GIP). DPP-4 inhibitors work by enhancing incretin action — ineffective when incretins are suppressed at source. Metformin reduces hepatic glucose output but does not restore insulin secretion. SGLT2 inhibitors reduce glycosuria but do not address the secretory defect. First-line: GLP-1 receptor agonist (exenatide, liraglutide) or insulin. Monitor fasting glucose and HbA1c at baseline, at 1–3 months, and every 6 months thereafter. Pasireotide-induced hyperglycemia is reversible on drug discontinuation but may require treatment for the full duration of therapy.
Sermorelin (GHRH 1-29 NH2) is a synthetic analog comprising the biologically active N-terminal 29 amino acids of native GHRH. Administered as a subcutaneous (SC) injection, sermorelin stimulates pituitary somatotroph GHRH receptor (GHRH-R), releasing endogenous growth hormone (GH) in a physiological pulsatile pattern that preserves the normal negative feedback relationship between GH and insulin-like growth factor-1 (IGF-1). Because sermorelin acts upstream of the pituitary rather than replacing GH directly, it requires an intact pituitary somatotroph pool; it is therefore ineffective in patients with primary pituitary disease or radiation-induced somatotroph destruction. Sermorelin has a plasma half-life of approximately 10 to 20 minutes owing to rapid proteolytic cleavage; it is given by daily SC injection. Its primary use has been as a diagnostic provocative agent for GH secretory reserve in children with suspected GH deficiency, and to a lesser degree as a therapeutic stimulant in patients with partial hypothalamic GH deficiency. It has largely been supplanted in the adult GH deficiency population by direct somatropin replacement, which is more predictable and better characterized in terms of dose-response.11
Tesamorelin (TH9507) is a synthetic analog of GHRH in which the full 44-amino acid sequence of native GHRH is stabilized by conjugation with a trans-3-hexenoic acid group at the N-terminus, protecting the molecule from dipeptidyl peptidase-4 (DPP-4) cleavage. Tesamorelin is approved by the U.S. Food and Drug Administration (FDA) for the reduction of excess visceral adipose tissue (VAT) in human immunodeficiency virus (HIV)-infected patients with antiretroviral therapy-associated lipodystrophy, a condition characterized by excessive central fat accumulation driven in part by suppressed endogenous GH pulsatility from increased somatostatin tone. In the pivotal trials, tesamorelin 2 mg SC daily reduced trunk fat measured by dual-energy X-ray absorptiometry (DEXA) and computed tomography (CT) by approximately 15 to 20% over 26 weeks, with concurrent improvements in lipid profiles. Like sermorelin, tesamorelin stimulates endogenous GH release rather than replacing it, preserving pulsatile secretion and negative feedback; as a consequence, IGF-1 rises modestly and glucose metabolism may worsen in patients with pre-existing insulin resistance. Tesamorelin is contraindicated in active malignancy owing to the growth-promoting effects of IGF-1 elevation.10
Macimorelin (Macrilen) is an orally bioavailable, small molecule ghrelin receptor (GHSR-1a) agonist approved for the diagnosis of adult GH deficiency.9 In the standard stimulation test protocol, a single oral dose of macimorelin 0.5 mg/kg (maximum 40 mg) is administered after an overnight fast; peak GH is measured at 30, 45, 60, and 90 minutes, with a GH peak below 2.8 ng/mL (using liquid chromatography-tandem mass spectrometry immunoassay) establishing the diagnosis of GH deficiency in adults. The sensitivity and specificity of macimorelin are comparable to those of insulin tolerance testing (ITT), which has been the historical gold standard but carries significant hypoglycemia risk; macimorelin therefore offers a safer and more practical diagnostic alternative. Macimorelin has a plasma half-life of approximately 4 hours; it is metabolized by CYP3A4 (cytochrome P450 3A4) and is a moderate inhibitor of P-glycoprotein (P-gp). Strong CYP3A4 inducers reduce macimorelin exposure and may produce a falsely low GH peak, increasing the rate of false-positive GH deficiency diagnoses; these agents should be discontinued before testing. QT interval (QT) prolongation has been reported with macimorelin; a baseline electrocardiogram (ECG) is recommended, and the test should be avoided if QTc exceeds 500 milliseconds.11
Insulin tolerance testing (ITT): induces hypoglycemia (glucose <40 mg/dL) as the stimulus; peak GH <3 ng/mL = GH deficiency. Contraindicated in seizure disorders, cardiovascular disease, age >55 years. Macimorelin test: oral, no hypoglycemia risk; GH peak <2.8 ng/mL = GH deficiency; comparable sensitivity and specificity to ITT. Interference: avoid strong CYP3A4 inducers (rifampin, carbamazepine) and QT-prolonging agents before testing. Baseline ECG required. Test must be performed at a center with appropriate endocrine assay capability; the cutoff value is assay-method dependent.
Somatropin is recombinant human GH (rhGH), a 191-amino acid single-chain polypeptide produced by recombinant deoxyribonucleic acid (DNA) technology in Escherichia coli or mammalian cell systems. Because GH is a peptide hormone susceptible to enzymatic degradation in the gastrointestinal tract, all approved somatropin formulations are administered parenterally, nearly exclusively by daily subcutaneous (SC) injection. Following SC injection, somatropin is absorbed with bioavailability of approximately 70 to 90%, reaching peak plasma concentrations within 3 to 5 hours; the plasma elimination half-life is approximately 2 to 4 hours, and total body clearance occurs primarily through hepatic and renal catabolism. Although the circulating half-life is short, GH exerts sustained biological effects through insulin-like growth factor-1 (IGF-1) induction, which has a half-life of 12 to 15 hours in circulation, providing the pharmacodynamic basis for once-daily dosing. A long-acting somatropin formulation (somatrogon, once-weekly SC dosing) is approved in some markets and is discussed in the context of convenience and adherence but does not materially change the clinical monitoring approach.12
Dosing of somatropin in adult GH deficiency follows a weight-independent titration approach in adults, in contrast to the weight-based dosing used in pediatric growth failure. In adults, starting doses are low (0.2 to 0.3 mg SC daily in younger patients; 0.1 to 0.2 mg SC daily in older patients and those with diabetes or impaired glucose tolerance) and are titrated upward by 0.1 to 0.2 mg increments every 4 to 8 weeks based on serum IGF-1 response, clinical response, and tolerability. The therapeutic target is an IGF-1 concentration in the age- and sex-adjusted normal range (typically the upper half of normal), which correlates with symptom improvement including enhanced body composition, energy, and quality of life. Pediatric dosing for growth failure is weight-based (0.025 to 0.05 mg/kg/day SC) and adjusted by linear growth velocity and bone age rather than IGF-1 alone. The clinical benefits of GH replacement in adult GH deficiency include normalization of body composition (reduced truncal fat, increased lean muscle mass), improved lipid profile (reduced LDL cholesterol), increased bone mineral density (BMD) with long-term use, and improved exercise capacity and quality of life.121313
The adverse effect profile of somatropin is dominated by fluid retention, which is the most common and dose-related early adverse effect: GH promotes sodium retention via renal tubular effects and increases body water, producing peripheral edema, carpal tunnel syndrome (median nerve compression from synovial swelling), arthralgias, and myalgias. These effects are generally dose-dependent and resolve with dose reduction; titrating doses slowly in older patients minimizes their frequency. Glucose intolerance and worsening of pre-existing diabetes mellitus are important metabolic adverse effects of somatropin, because GH is a counter-regulatory hormone that reduces insulin sensitivity and promotes hepatic glucose output; patients with pre-existing type 2 diabetes may require adjustment of antidiabetic therapy during GH replacement. In pediatric patients, GH replacement has been associated with a small but measurable increase in the risk of leukemia and intracranial tumor recurrence in those with a prior history of malignancy, and somatropin is contraindicated in active malignancy and in patients with acute critical illness (associated with increased mortality in two pivotal studies).12
Somatropin has two clinically important drug interactions mediated by its induction of cytochrome P450 (CYP450) enzyme expression. GH replacement significantly increases the activity of CYP3A4 (cytochrome P450 3A4) and CYP2C19 (cytochrome P450 2C19), leading to accelerated metabolism of drugs that are CYP3A4 substrates. The most important clinical consequence is reduction in plasma concentrations of glucocorticoids: GH replacement accelerates the conversion of cortisol to inactive cortisone and increases the peripheral clearance of synthetic glucocorticoids (prednisone, hydrocortisone) by CYP3A4 induction, unmasking previously subclinical central adrenal insufficiency or rendering previous glucocorticoid replacement doses inadequate. This interaction can precipitate adrenal crisis in patients with unrecognized hypopituitarism or marginal adrenal reserve who begin GH replacement. The second major interaction is acceleration of cyclosporine metabolism, reducing plasma cyclosporine levels and risking organ rejection in transplant patients. Dose monitoring of glucocorticoids and cyclosporine is mandatory when initiating somatropin replacement.12
Panhypopituitary patients on GH replacement frequently have concurrent central adrenal insufficiency. GH accelerates cortisol clearance via CYP3A4 induction; initiating GH in a patient on a borderline hydrocortisone replacement dose may unmask insufficiency. Before starting GH replacement: assess the hypothalamic-pituitary-adrenal (HPA) axis; ensure glucocorticoid replacement is adequate. After starting: watch for fatigue, nausea, weight loss, or hypotension in the first weeks. Adjust hydrocortisone dose upward by 20–30% if needed. This interaction does not apply to physiological-range hydrocortisone in patients with normal adrenal function.
Pegvisomant (Somavert) is a genetically engineered growth hormone (GH) receptor (GHR) antagonist, structurally derived from native GH but modified with specific amino acid substitutions that prevent receptor dimerization and signal transduction while preserving high-affinity GHR binding. Native GH activates its receptor by binding a single GHR molecule, inducing dimerization of two GHR subunits and initiating downstream JAK2-STAT5 (Janus kinase 2, signal transducer and activator of transcription 5) signaling. Pegvisomant competes with endogenous GH for GHR binding but, once bound, prevents productive receptor dimerization and JAK2-STAT5 activation, acting as a functional antagonist. The molecule is PEGylated (conjugated with polyethylene glycol chains) to reduce immunogenicity and extend its half-life; the elimination half-life of pegvisomant is approximately 6 days, enabling once-daily or every-other-day subcutaneous (SC) dosing. Unlike SSAs, which suppress GH secretion from the pituitary, pegvisomant acts entirely peripherally at the receptor level: pituitary GH secretion is not suppressed and typically rises further during pegvisomant therapy (due to loss of insulin-like growth factor-1 (IGF-1) negative feedback on the pituitary), meaning serum GH is not a useful monitoring marker and cannot be used to assess adequacy of treatment.1415
Because pegvisomant does not suppress pituitary GH output, serum IGF-1 is the sole reliable monitoring marker for treatment response and dose titration. The starting dose is 40 to 80 mg SC daily (or loading dose 80 mg SC on day 1 followed by 10 to 20 mg SC daily), and doses are adjusted based on monthly IGF-1 measurements during the titration phase, with a target IGF-1 in the age- and sex-adjusted normal range. IGF-1 normalization is achieved in 90 to 97% of patients treated with pegvisomant at therapeutic doses, making it the most effective single agent for IGF-1 normalization in acromegaly, substantially higher than the 30 to 50% normalization rates achieved with SSAs. The principal limitation of pegvisomant monotherapy is that it does not reduce pituitary tumor volume; this contrasts with SSAs, which can produce tumor shrinkage of 20 to 50% in some patients and are preferred when tumor mass effect (visual field compromise, headache) requires treatment. In patients with inadequate IGF-1 control on somatostatin receptor analog (SSA) monotherapy, combination of SSA plus pegvisomant achieves superior biochemical control compared with either agent alone, while the SSA component may continue to modestly limit tumor growth.15
Hepatotoxicity is the most important safety concern with pegvisomant. Clinically significant elevations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) have been reported in approximately 5 to 8% of patients, with rare cases of serious hepatotoxicity necessitating drug discontinuation. The mechanism is not fully established but may involve GH-related changes in hepatic lipid metabolism or immune-mediated injury. Liver function tests (ALT, AST, bilirubin) must be measured at baseline and every 6 months during therapy; any AST or ALT elevation exceeding three times the upper limit of normal (ULN) requires more frequent monitoring, and an elevation exceeding five times the ULN requires drug discontinuation pending investigation. Patients with pre-existing liver disease or alcohol use should be monitored more frequently. In clinical practice, the hepatotoxicity signal from pegvisomant is distinguished from liver enzyme elevations caused by the underlying acromegaly itself (uncontrolled GH excess promotes hepatic steatosis), and normalization of IGF-1 with pegvisomant therapy often improves baseline liver enzyme elevations in patients with acromegaly-related hepatic steatosis.15
SSA monitoring: serum GH (target <1 ng/mL random, or <0.4 ng/mL nadir on OGTT) AND serum IGF-1 (age/sex-adjusted normal range). Pegvisomant monitoring: serum IGF-1 ONLY — serum GH is not informative and should not be used. GH rises during pegvisomant therapy due to loss of negative feedback; measuring GH will show apparent worsening but does not indicate treatment failure. Liver function tests: baseline then every 6 months. Tumor imaging: pituitary MRI (magnetic resonance imaging) annually during pegvisomant therapy, because tumor growth is not prevented by this agent.
The most clinically significant drug interaction common to all somatostatin analogs is suppression of insulin and glucagon secretion, which alters glycemic responses to antidiabetic agents. In diabetic patients receiving SSAs, insulin requirements may decrease (from reduced glucose counter-regulation by glucagon) or increase (from reduced insulin secretion); the net glycemic effect in any individual patient is unpredictable, requiring glucose monitoring in the first weeks of somatostatin receptor analog (SSA) initiation or dose escalation. SSAs also reduce the absorption of cyclosporine from the gastrointestinal tract by inhibiting intestinal motility and secretion; cyclosporine levels should be monitored after initiation of SSAs in transplant recipients, as reduced absorption may precipitate rejection. All SSAs inhibit gallbladder contractility by suppressing cholecystokinin (CCK) release; symptomatic cholelithiasis develops in approximately 20 to 30% of patients on long-term SSA therapy, though only 1 to 2% develop acute cholecystitis requiring cholecystectomy. Ursodeoxycholic acid prophylaxis is not routinely recommended unless the patient has additional biliary risk factors.5
The interaction between somatropin (GH replacement) and glucocorticoids is bidirectional and clinically important in both directions. As described in Section 4, GH replacement induces CYP3A4 (cytochrome P450 3A4), increasing glucocorticoid clearance and potentially unmasking adrenal insufficiency. In the opposite direction, glucocorticoids suppress insulin-like growth factor-1 (IGF-1) production at the hepatic level and blunt the anabolic response to GH replacement; patients on pharmacological glucocorticoid doses for inflammatory conditions may show attenuated IGF-1 responses to somatropin and should not have their GH dose escalated purely on the basis of a low IGF-1 without accounting for glucocorticoid effect. Estrogen replacement and oral contraceptives reduce hepatic IGF-1 production (through first-pass portal estrogen suppression of GH receptor signaling in the liver); women on oral estrogen require higher somatropin doses to achieve equivalent IGF-1 responses compared with women on transdermal estrogen or men, a pharmacodynamic sex difference with direct dose-adjustment implications.12
SSA dose optimization in acromegaly follows a structured titration protocol. First-generation SSAs (octreotide LAR, lanreotide Autogel) are started at the lowest available dose and uptitrated every 3 months based on random serum GH (target below 1 ng/mL, or ideally below 0.4 ng/mL on a sensitive assay) and age- and sex-adjusted IGF-1 (target in the normal range).16 If full-dose first-generation SSA (octreotide LAR 40 mg or lanreotide 120 mg every 28 days) fails to normalize both GH and IGF-1, three options exist: switch to pasireotide LAR (pan-SSTR agonist, higher efficacy but greater hyperglycemia risk); add pegvisomant to the SSA for combination biochemical control; or add a dopamine agonist (cabergoline) to the SSA if tumor expresses dopamine D2 (dopamine receptor subtype 2) receptors (more commonly in mixed somatotroph-lactotroph tumors). Cabergoline monotherapy achieves IGF-1 normalization in only about 10 to 15% of acromegaly patients but is a useful adjunct, particularly when serum prolactin is also elevated.1617
The monitoring framework for GH deficiency replacement encompasses both efficacy and safety domains. Efficacy monitoring: serum IGF-1 every 6 to 12 months once stable dose achieved, targeting the upper half of the age- and sex-adjusted normal range; body composition assessment (lean mass, fat mass) by dual-energy X-ray absorptiometry (DEXA) at baseline and every 1 to 2 years; lipid panel at baseline and annually; bone mineral density (BMD) by DEXA at baseline and every 2 years. Safety monitoring: fasting glucose and HbA1c (hemoglobin A1c) at baseline and annually (more frequently if pre-existing diabetes or glucose intolerance); assessment for carpal tunnel syndrome and peripheral edema at each visit; thyroid function tests (somatropin may accelerate conversion of thyroxine (T4) to triiodothyronine (T3), occasionally unmasking secondary hypothyroidism in hypopituitary patients); annual review for clinical features of pituitary tumor recurrence (visual fields, headache pattern). In pediatric patients receiving somatropin for growth failure, additional monitoring includes height velocity, bone age, and scoliosis assessment, with dose adjustment every 3 to 6 months based on growth response.1213
Step 1: Transsphenoidal surgery (first-line for all resectable tumors). Step 2 (residual/recurrent disease): first-generation SSA — octreotide LAR or lanreotide Autogel, uptitrate to maximum dose over 6–12 months. Step 3 (inadequate SSA control): (a) switch to pasireotide LAR if GH/IGF-1 both remain elevated and hyperglycemia risk is acceptable; (b) add pegvisomant to SSA for combined biochemical control when IGF-1 alone remains elevated; (c) add cabergoline to SSA if prolactin co-secretion or mild IGF-1 elevation. Step 4 (pegvisomant monotherapy): use when SSAs are not tolerated or are ineffective; monitor IGF-1 only, not GH; pituitary MRI annually. Radiotherapy: reserved for aggressive or multiple drug-refractory tumors; effect on GH/IGF-1 may take years.
Giustina A, Veldhuis JD. Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human. Endocr Rev. 1998;19(6):717–797.
doi:10.1210/edrv.19.6.0353Patel YC. Somatostatin and its receptor family. Front Neuroendocrinol. 1999;20(3):157–198.
doi:10.1006/frne.1999.0183Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656–660.
doi:10.1038/45230Melmed S. Acromegaly pathogenesis and treatment. J Clin Invest. 2009;119(11):3189–3202.
doi:10.1172/JCI39375Freda PU. Somatostatin analogs in acromegaly. J Clin Endocrinol Metab. 2002;87(7):3013–3018.
doi:10.1210/jcem.87.7.8665Carmichael JD, Bonert VS, Mirocha JM, Melmed S. The utility of oral glucose tolerance testing for diagnosis and assessment of treatment outcomes in 166 patients with acromegaly. J Clin Endocrinol Metab. 2009;94(2):523–527.
doi:10.1210/jc.2008-1371Gadelha MR, Bronstein MD, Brue T, et al; PAOLA study investigators. Pasireotide versus continued treatment with octreotide or lanreotide in patients with inadequately controlled acromegaly (PAOLA): a randomised, phase 3 trial. Lancet Diabetes Endocrinol. 2014;2(11):875–884.
doi:10.1016/S2213-8587(14)70169-XHenry RR, Ciaraldi TP, Armstrong D, Burke P, Ligueros-Saylan M, Mudaliar S. Hyperglycemia associated with pasireotide: results from a mechanistic study in healthy volunteers. J Clin Endocrinol Metab. 2013;98(8):3446–3453.
doi:10.1210/jc.2013-1771Walker RF, Codd EE, Barone FC, et al. Oral activity of the growth hormone secretagogue SM-130686. Eur J Endocrinol. 2003;148(3):379–384.
doi:10.1530/eje.0.1480379Falutz J, Allas S, Blot K, et al. Metabolic effects of a growth hormone-releasing factor in patients with HIV. N Engl J Med. 2007;357(23):2359–2370.
doi:10.1056/NEJMoa072375Yuen KCJ, Biller BMK, Radovick S, et al. American Association of Clinical Endocrinologists and American College of Endocrinology guidelines for management of growth hormone deficiency in adults and patients transitioning from pediatric to adult care. Endocr Pract. 2019;25(Suppl 2):1–44.
doi:10.4158/GL-2019-0405Molitch ME, Clemmons DR, Malozowski S, Merriam GR, Vance ML; Endocrine Society. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(6):1587–1609.
doi:10.1210/jc.2011-0179Salomon F, Cuneo RC, Hesp R, Sönksen PH. The effects of treatment with recombinant human growth hormone on body composition and metabolism in adults with growth hormone deficiency. N Engl J Med. 1989;321(26):1797–1803.
doi:10.1056/NEJM198912283212605Trainer PJ, Drake WM, Katznelson L, et al. Treatment of acromegaly with the growth hormone-receptor antagonist pegvisomant. N Engl J Med. 2000;342(16):1171–1177.
doi:10.1056/NEJM200004203421604van der Lely AJ, Hutson RK, Trainer PJ, et al. Long-term treatment of acromegaly with pegvisomant, a growth hormone receptor antagonist. Lancet. 2001;358(9295):1754–1759.
doi:10.1016/S0140-6736(01)06844-1Giustina A, Chanson P, Bronstein MD, et al; Acromegaly Consensus Group. A consensus on criteria for cure of acromegaly. J Clin Endocrinol Metab. 2010;95(7):3141–3148.
doi:10.1210/jc.2009-2670Abs R, Verhelst J, Maiter D, et al. Cabergoline in the treatment of acromegaly: a study in 64 patients. J Clin Endocrinol Metab. 1998;83(2):374–378.
doi:10.1210/jcem.83.2.4556