Pharmacotherapeutic group: Somatostatin and analogues, ATC code: H01CB02
Mechanism of action
Octreotide is a synthetic octapeptide derivative of naturally occurring somatostatin with similar pharmacological effects, but with a considerably prolonged duration of action. It inhibits pathologically increased secretion of growth hormone (GH) and of peptides and serotonin produced within the GEP endocrine system.
In animals, octreotide is a more potent inhibitor of GH, glucagon and insulin release than somatostatin is, with greater selectivity for GH and glucagon suppression.
In healthy subjects octreotide, like somatostatin, has been shown to inhibit:
• Release of GH stimulated by arginine, exercise- and insulin-induced hypoglycaemia,
• Post-prandial release of insulin, glucagon, gastrin, other peptides of the GEP endocrine system, and arginine-stimulated release of insulin and glucagon,
• thyrotropin-releasing hormone (TRH)-stimulated release of thyroid-stimulating hormone (TSH).
Unlike somatostatin, octreotide inhibits GH secretion preferentially over insulin and its administration is not followed by rebound hypersecretion of hormones (i.e. GH in patients with acromegaly).
In patients with acromegaly, Olatuton, a galenical formulation of octreotide suitable for repeated administration at intervals of 4 weeks, delivers consistent and therapeutic octreotide serum concentrations thus consistently lowering GH and normalising IGF 1 serum concentrations in the majority of patients. In most patients, octreotide prolonged-release injection markedly reduces the clinical symptoms of the disease, such as headache, perspiration, paraesthesia, fatigue, osteoarthralgia and carpal tunnel syndrome. In previously untreated acromegaly patients with GH-secreting pituitary adenoma, octreotide prolonged-release injection treatment resulted in a tumour volume reduction of >20% in a significant proportion (50%) of patients.
In individual patients with GH-secreting pituitary adenoma, octreotide prolonged-release injection was reported to lead to shrinkage of the tumour (prior to surgery). However, surgery should not be delayed.
For patients with functional tumours of the gastro-entero-pancreatic endocrine system, treatment with Olatuton provides continuous control of symptoms related to the underlying disease. The effect of octreotide in different types of gastro-entero-pancreatic tumours are as follows:
Carcinoid tumours
Administration of octreotide may result in improvement of symptoms, particularly of flushing and diarrhoea. In many cases, this is accompanied by a fall in plasma serotonin and reduced urinary excretion of 5 hydroxyindole acetic acid.
VIPomas
The biochemical characteristic of these tumours is overproduction of vasoactive intestinal peptide (VIP). In most cases, administration of octreotide results in alleviation of the severe secretory diarrhoea typical of the condition, with consequent improvement in quality of life. This is accompanied by an improvement in associated electrolyte abnormalities, e.g. hypokalaemia, enabling enteral and parenteral fluid and electrolyte supplementation to be withdrawn. In some patients, computed tomography scanning suggests a slowing or arrest of progression of the tumour, or even tumour shrinkage, particularly of hepatic metastases. Clinical improvement is usually accompanied by a reduction in plasma VIP levels, which may fall into the normal reference range.
Glucagonomas
Administration of octreotide results in most cases in substantial improvement of the necrolytic migratory rash which is characteristic of the condition. The effect of octreotide on the state of mild diabetes mellitus which frequently occurs is not marked and, in general, does not result in a reduction of requirements for insulin or oral hypoglycaemic agents. Octreotide produces improvement of diarrhoea, and hence weight gain, in those patients affected. Although administration of octreotide often leads to an immediate reduction in plasma glucagon levels, this decrease is generally not maintained over a prolonged period of administration, despite continued symptomatic improvement.
Gastrinomas/Zollinger-Ellison syndrome
Therapy with proton pump inhibitors or H2 receptor blocking agents generally controls gastric acid hypersecretion. However, diarrhoea, which is also a prominent symptom, may not be adequately alleviated by proton pump inhibitors or H2 receptor blocking agents. Olatuton can help to further reduce gastric acid hypersecretion and improve symptoms, including diarrhoea, as it provides suppression of elevated gastrin levels, in some patients.
Insulinomas
Administration of octreotide produces a fall in circulating immunoreactive insulin. In patients with operable tumours, octreotide may help to restore and maintain normoglycemia pre-operatively. In patients with inoperative benign or malignant tumours, glycaemic control may be improved even without concomitant sustained reduction in circulating insulin levels.
Advanced neuroendocrine tumours of the midgut or of unknown primary origin where non-midgut sites of origin have been excluded
A Phase III, randomised, double-blind, placebo-controlled study (PROMID) demonstrated that octreotide prolonged-release injection inhibits tumour growth in patients with advanced neuroendocrine tumours of the midgut. 85 patients were randomised to receive octreotide prolonged-release injection 30 mg every 4 weeks (n=42) or placebo (n=43) for 18 months, or until tumour progression or death.
Main inclusion criteria were: treatment naïve; histologically confirmed; locally inoperable or metastatic well-differentiated; functionally active or inactive neuroendocrine tumours/carcinomas; with primary tumour located in the midgut or unknown origin believed to be of midgut origin if a primary within the pancreas, chest, or elsewhere was excluded.
The primary endpoint was time to tumour progression or tumour-related death (TTP).
In the intent-to-treat analysis population (ITT) (all randomised patients), 26 and 41 progressions or tumour-related deaths were seen in the octreotide prolonged-release injection and placebo groups, respectively (HR = 0.32; 95% CI, 0.19 to 0.55; p-value =.000015).
In the conservative ITT (cITT) analysis population in which 3 patients were censored at randomization, 26 and 40 progressions or tumour-related deaths were observed in the octreotide prolonged-release injection and placebo groups, respectively (HR=0.34; 95% CI, 0.20 to 0.59; p-value =.000072; Fig 1). Median time to tumour progression was 14.3 months (95% CI, 11.0 to 28.8 months) in the octreotide prolonged-release injection group and 6.0 months (95% CI, 3.7 to 9.4 months) in the placebo group.
In the per-protocol analysis population (PP) in which additional patients were censored at end study therapy, tumour progression or tumour-related death was observed in 19 and 38 octreotide prolonged-release injection and placebo recipients, respectively (HR = 0.24; 95% CI, 0.13 to 0.45; p-value =.0000036).
Figure 1 Kaplan-Meier estimates of TTP comparing octreotide prolonged-release injection with placebo (conservative ITT population)

Table 3 TTP results by analysis populations
| | TTP Events | Median TTP months [95% C.I.] | HR [95% C.I.] p-value* |
| | octreotide prolonged-release injection | Placebo | octreotide prolonged-release injection | Placebo |
| ITT | 26 | 41 | NR | NR | 0.32 [95% CI, 0.19 to 0.55] P=0.000015 |
| cITT | 26 | 40 | 14.3 [95% CI, 11.0 to 28.8] | 6.0 [95% CI, 3.7 to 9.4] | 0.34 [95% CI, 0.20 to 0.59] P=0.000072 |
| PP | 19 | 38 | NR | NR | 0.24 [95% CI, 0.13 to 0.45] P=0.0000036 |
| NR=not reported; HR=hazard ratio; TTP=time to tumour progression; ITT=intention to treat; cITT=conservative ITT; PP=per protocol *Logrank test stratified by functional activity |
Treatment effect was similar in patients with functionally active (HR = 0.23; 95% CI, 0.09 to 0.57) and inactive tumours (HR = 0.25; 95% CI, 0.10 to 0.59).
After 6 months of treatment, stable disease was observed in 67% of patients in the octreotide prolonged-release injection group and 37% of patients in the placebo group.
Based on the significant clinical benefit of octreotide prolonged-release injection observed in this pre-planned interim analysis the recruitment was stopped.
The safety of octreotide prolonged-release injection in this trial was consistent with its established safety profile.
Treatment of TSH-secreting pituitary adenomas
Octreotide prolonged-release injection, one i.m. injection every 4 weeks, has been shown to suppress elevated thyroid hormones, to normalise TSH and to improve the clinical signs and symptoms of hyperthyroidism in patients with TSH-secreting adenomas. Treatment effect of octreotide prolonged-release injection reached statistical significance as compared to baseline after 28 days and treatment benefit continued for up to 6 months.