Octreotide is a synthetic octapeptide somatostatin analog with a plasma half-life of approximately 1.5 to 2 hours from subcutaneous injection, compared to 1 to 3 minutes for native somatostatin. It binds selectively to somatostatin receptor subtype 2 and somatostatin receptor subtype 5 (with moderate affinity for somatostatin receptor subtype 3), producing potent growth hormone and insulin-like growth factor-1 suppression in acromegaly. Subcutaneous octreotide three times daily achieves growth hormone normalization in approximately 50 to 60% of acromegaly patients. The long-acting release depot formulation (Sandostatin long-acting release) uses poly(lactic-co-glycolic acid) microspheres for intramuscular injection every 28 days, available in 20, 30, and 40 milligram doses. A bridging period of approximately 14 days with subcutaneous octreotide is needed after the first long-acting release injection while therapeutic plasma concentrations are being established from the microsphere depot.

Lanreotide has comparable receptor affinity to octreotide at somatostatin receptor subtype 2 and somatostatin receptor subtype 5. Its key distinction is the formulation: Lanreotide Autogel (Somatuline Depot) is a high-viscosity aqueous gel delivered by deep subcutaneous injection from a pre-filled syringe, forming a depot that releases lanreotide over approximately 28 days without the 14-day loading period required by octreotide long-acting release. Available in 60, 90, and 120 milligram doses every 4 weeks, with extended dosing intervals of every 6 or 8 weeks possible for patients achieving biochemical control. Elimination is predominantly fecal (biliary excretion), with less than 5% renal excretion, making dose adjustment unnecessary in renal impairment. Octreotide long-acting release and lanreotide Autogel achieve equivalent rates of growth hormone and insulin-like growth factor-1 normalization in head-to-head comparisons.

Pasireotide is a pan-somatostatin receptor agonist with high affinity for somatostatin receptor subtypes 1, 2, 3, and 5 — with somatostatin receptor subtype 5 affinity approximately 40-fold higher than octreotide. This broader receptor profile provides additive growth hormone and adrenocorticotropic hormone suppression beyond what somatostatin receptor subtype 2-selective agents alone can achieve. In the PAOLA trial, pasireotide long-acting release 40 and 60 milligrams monthly produced biochemical control (normal growth hormone and insulin-like growth factor-1) in 31 to 38% of patients with inadequate control on first-generation somatostatin analogs, compared to 19% for switching to the alternative first-generation agent. Pasireotide is also approved for Cushing disease, where corticotroph adenomas predominantly express somatostatin receptor subtype 5.

The metabolic liability of pasireotide substantially exceeds that of octreotide and lanreotide. Hyperglycemia occurs in approximately 57 to 73% of pasireotide-treated patients versus 10 to 20% with somatostatin receptor subtype 2-selective agents. The mechanism is profound somatostatin receptor subtype 5-mediated suppression of both insulin secretion and incretin hormone (glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide) release from pancreatic and intestinal cells. Because the hyperglycemia is driven by reduced insulin secretion rather than increased insulin resistance, dipeptidyl peptidase-4 inhibitors are largely ineffective (they depend on intact incretin responses) and metformin has limited efficacy. Glucagon-like peptide-1 receptor agonists and insulin are the preferred agents for managing pasireotide-induced hyperglycemia.

Somatropin is recombinant human growth hormone, a 191-amino acid polypeptide produced by recombinant deoxyribonucleic acid technology. All approved formulations are administered parenterally — nearly exclusively by daily subcutaneous injection — because growth hormone is a peptide that undergoes gastrointestinal hydrolysis. Subcutaneous bioavailability is approximately 70 to 90%, with peak plasma concentrations at 3 to 5 hours and a plasma elimination half-life of approximately 2 to 4 hours. Growth hormone exerts sustained biological effects through insulin-like growth factor-1 induction (half-life 12 to 15 hours in circulation), providing the pharmacodynamic basis for once-daily dosing despite the short growth hormone half-life.

Adult growth hormone deficiency dosing follows weight-independent titration: starting doses of 0.2 to 0.3 milligrams subcutaneously daily in younger adults and 0.1 to 0.2 milligrams daily in older patients or those with diabetes, titrated upward by 0.1 to 0.2 milligram increments every 4 to 8 weeks based on serum insulin-like growth factor-1 response and tolerability. The therapeutic target is insulin-like growth factor-1 in the upper half of the age- and sex-adjusted normal range. Pediatric dosing for growth failure is weight-based (0.025 to 0.05 milligrams per kilogram per day subcutaneously), adjusted by linear growth velocity and bone age.

The most common and dose-related early adverse effect is fluid retention: growth hormone promotes sodium retention via renal tubular effects, producing peripheral edema, carpal tunnel syndrome (median nerve compression from synovial swelling), arthralgias, and myalgias. These are generally dose-dependent and resolve with dose reduction. Glucose intolerance and worsening of pre-existing diabetes mellitus are important metabolic adverse effects, because growth hormone is a counter-regulatory hormone that reduces insulin sensitivity and promotes hepatic glucose output. Somatropin is contraindicated in active malignancy and in patients with acute critical illness (associated with increased mortality in pivotal studies).

Somatropin has two clinically important drug interactions mediated by its induction of cytochrome P450 enzyme expression. First, growth hormone replacement significantly increases cytochrome P450 3A4 and cytochrome P450 2C19 activity, accelerating glucocorticoid metabolism. This can unmask previously subclinical central adrenal insufficiency or render existing glucocorticoid replacement doses inadequate in panhypopituitary patients — potentially precipitating adrenal crisis. Before starting growth hormone replacement, the hypothalamic-pituitary-adrenal axis should be assessed and glucocorticoid replacement confirmed as adequate. Second, somatropin accelerates cyclosporine metabolism by cytochrome P450 3A4 induction, reducing cyclosporine plasma levels and risking organ rejection in transplant patients. Monitoring of glucocorticoid adequacy and cyclosporine levels is mandatory when initiating somatropin.

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 unpredictably. In diabetic patients receiving somatostatin analogs, glucose monitoring in the first weeks of initiation or dose escalation is essential. Somatostatin analogs also reduce cyclosporine absorption from the gastrointestinal tract by inhibiting intestinal motility and secretion; cyclosporine levels should be monitored after somatostatin analog initiation in transplant recipients. All somatostatin analogs inhibit gallbladder contractility by suppressing cholecystokinin release; symptomatic cholelithiasis develops in approximately 20 to 30% of patients on long-term therapy, though only 1 to 2% require cholecystectomy.

The interaction between somatropin and glucocorticoids is bidirectional. Growth hormone replacement induces cytochrome P450 3A4, increasing glucocorticoid clearance and potentially unmasking adrenal insufficiency as described in Section 4. In the opposite direction, pharmacological glucocorticoid doses suppress insulin-like growth factor-1 production at the hepatic level and blunt the anabolic response to growth hormone replacement, so patients on anti-inflammatory glucocorticoid doses may show attenuated insulin-like growth factor-1 responses to somatropin. Additionally, women on oral estrogen require higher somatropin doses than women on transdermal estrogen or men, because oral (but not transdermal) estrogen undergoes first-pass hepatic metabolism that reduces growth hormone receptor signaling and insulin-like growth factor-1 production.

Transsphenoidal surgery is first-line for all resectable tumors. For residual or recurrent disease, first-generation somatostatin analogs (octreotide long-acting release or lanreotide Autogel) are started at the lowest available dose and uptitrated every 3 months based on random serum growth hormone (target below 1 nanogram per milliliter) and age- and sex-adjusted insulin-like growth factor-1. If full-dose first-generation somatostatin analog fails to normalize both markers, three options exist: switch to pasireotide long-acting release (superior efficacy but greater hyperglycemia risk); add pegvisomant to the somatostatin analog for combined biochemical control when insulin-like growth factor-1 alone remains elevated; or add cabergoline to the somatostatin analog if serum prolactin is also elevated (suggesting co-secreting tumor with dopamine type 2 receptor expression, where cabergoline monotherapy achieves insulin-like growth factor-1 normalization in approximately 10 to 15% of acromegaly patients). Radiotherapy is reserved for aggressive or multiple drug-refractory tumors; its effect on growth hormone and insulin-like growth factor-1 may take years.