Chemical formula: C₄₉H₆₆N₁₀O₁₀S₂ Molecular mass: 1,019.25 g/mol PubChem compound: 448601
It inhibits pathologically increased secretion of growth hormone (GH) and of peptides and serotonin produced within the GEP endocrine system.
Octreotide is a synthetic octapeptide derivative of naturally occurring somatostatin with similar pharmacological effects, but with a considerably prolonged duration of action.
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 has been shown to inhibit
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 acromegalic patients octreotide lowers plasma levels of GH and IGF-1. A GH reduction by 50% or more occurs in up to 90% patients, and a reduction of serum GH to <5 ng/mL can be achieved in about half of the cases. In most patients octreotide markedly reduces the clinical symptoms of the disease, such as headache, skin and soft tissue swelling, hyperhidrosis, arthralgia, paraesthesia. In patients with a large pituitary adenoma, octreotide treatment may result in some shrinkage of the tumour mass.
In patients with functional tumours of the GEP endocrine system, octreotide, because of its diverse endocrine effects, modifies a number of clinical features. Clinical improvement and symptomatic benefit occur in patients who still have symptoms related to their tumours despite previous therapies, which may include surgery, hepatic artery embolization, and various chemotherapies, e.g. streptozocin and 5-fluorouracil.
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.
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abnormalities, e.g. hypokalaemia, enabling enteral and parenteral fluid and electrolyte supplementation to be withdrawn.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.
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.
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. Octreotide can help to further reduce gastric acid hypersecretion and improve symptoms, including diarrhoea, as it provides suppression of elevated gastrin levels, in some patients.
Administration of octreotide produces a fall in circulating immunoreactive insulin, which may, however, be of short duration (about 2 hours). In patients with operable tumours octreotide may help to restore and maintain normoglycaemia pre-operatively. In patients with inoperable benign or malignant tumours, glycaemic control may be improved without concomitant sustained reduction in circulating insulin levels.
For patients undergoing pancreatic surgery, the peri- and post-operative administration of octreotide reduces the incidence of typical postoperative complications (e.g. pancreatic fistula, abscess and subsequent sepsis, postoperative acute pancreatitis).
In patients presenting with bleeding gastro-oesophageal varices due to underlying cirrhosis, octreotide administration in combination with specific treatment (e.g. sclerotherapy) is associated with better control of bleeding and early re-bleeding, reduced transfusion requirements, and improved 5-day survival. While the precise mode of action of octreotide is not fully elucidated, it is postulated that octreotide reduces splanchnic blood flow through inhibition of vaso-active hormones (e.g. VIP, glucagon).
The treatment effects of octreotide were prospectively observed in 21 patients and pooled with series of 37 published cases. Among 42 patients with evaluable biochemical data, there were 81% of patients (n=34) with satisfactory results (at least 50% reduction of TSH and substantial reduction of thyroid hormones), whereas 67% (n=28) had normalisations of TSH and thyroid hormones. In these patients, the response was maintained throughout the duration of treatment (up to 61 months, mean, 15.7 months).
Regarding clinical symptoms, a clear improvement was reported in 19 out of 32 patients with clinical hyperthyroidism. Tumour volume reduction greater than 20% was observed in 11 cases (41%) with a decrease greater than 50% in 4 cases (15%). The earliest reduction was reported after 14 days of treatment.
After s.c. injection, octreotide is rapidly and completely absorbed. Peak plasma concentrations are reached within 30 minutes.
The volume of distribution is 0.27 L/kg and the total body clearance 160 mL/min. Plasma protein binding amounts to 65%. The amount of octreotide bound to blood cells is negligible.
The elimination half-life after s.c. administration is 100 minutes. After i.v. injection, the elimination is biphasic, with half-lives of 10 and 90 minutes. Most of the peptide is eliminated via the faeces, while approximately 32% is excreted unchanged into the urine.
Impaired renal function did not affect the total exposure (AUC) to octreotide administered as s.c. injection.
The elimination capacity may be reduced in patients with liver cirrhosis, but not in patients with fatty liver disease.
After single i.m. injections of octreotide, the serum octreotide concentration reaches a transient initial peak within 1 hour after administration, followed by a progressive decrease to a low undetectable octreotide level within 24 hours. After this initial peak on day 1, octreotide remains at sub-therapeutic levels in the majority of the patients for the following 7 days. Thereafter, octreotide concentrations increase again, and reach plateau concentrations around day 14 and remain relatively constant during the following 3 to 4 weeks. The peak level during day 1 is lower than levels during the plateau phase and no more than 0.5% of the total drug release occurs during day 1. After about day 42, the octreotide concentration decreases slowly, concomitant with the terminal degradation phase of the polymer matrix of the dosage form.
In patients with acromegaly, plateau octreotide concentrations after single doses of 10 mg, 20 mg and 30 mg octreotide amount to 358 ng/L, 926 ng/L, and 1,710 ng/L, respectively. Steady-state octreotide serum concentrations, reached after 3 injections at 4 week intervals, are higher by a factor of approximately 1.6 to 1.8 and amount to 1,557 ng/L and 2,384 ng/L after multiple injections of 20 mg and 30 mg octreotide, respectively.
In patients with carcinoid tumours, the mean (and median) steady-state serum concentrations of octreotide after multiple injections of 10 mg, 20 mg and 30 mg of octreotide given at 4 week intervals also increased linearly with dose and were 1,231 (894) ng/L, 2,620 (2,270) ng/L and 3,928 (3,010) ng/L, respectively.
No accumulation of octreotide beyond that expected from overlapping release profiles occurred over a duration of up to 28 monthly injections of octreotide.
The pharmacokinetic profile of octreotide after injection of octreotide reflects the release profile from the polymer matrix and its biodegradation. Once released into the systemic circulation, octreotide distributes according to its known pharmacokinetic properties, as described for s.c. administration. The volume of distribution of octreotide at steady-state is 0.27 L/kg and the total body clearance is 160 mL/min. Plasma protein binding amounts to 65% and essentially no drug is bound to blood cells.
Pharmacokinetic data with limited blood sampling in pediatric patients with hypothalamic obesity, aged 7–17 years, receiving octreotide 40 mg once monthly, showed mean octreotide trough plasma concentrations of 1,395 ng/L after the first injection and of 2,973 ng/L at steady state. A high inter-subject variability is observed.
Steady-state trough octreotide concentrations were not correlated with age and BMI, but moderately correlated with body weight (52.3–133 kg) and was significantly different between male and female patients, i.e. about 17% higher for female patients.
Acute and repeated dose toxicology, genotoxicity, carcinogenicity and reproductive toxicology studies in animals revealed no specific safety concerns for humans.
Reproduction studies in animals revealed no evidence of teratogenic, embryo/foetal or other reproduction effects due to octreotide at parental doses of up to 1 mg/kg/day. Some retardation of physiological growth was noted in the offspring of rats which was transient and attributable to GH inhibition brought about by excessive pharmacodynamic activity.
No specific studies were conducted in juvenile rats. In the pre- and post-natal developmental studies, reduced growth and maturation was observed in the F1 offspring of dams given octreotide during the entire pregnancy and lactation period. Delayed descent of the testes was observed for male F1 offsprings, but fertility of the affected F1 male pups remained normal. Thus, the abovementioned observations were transient and considered to be the consequence of GH inhibition.
In rats receiving octreotide acetate at daily doses up to 1.25 mg/kg body weight, fibrosarcomas were observed, predominantly in a number of male animals, at the s.c. injection site after 52, 104 and 113/116 weeks. Local tumours also occurred in the control rats, however development of these tumours was attributed to disordered fibroplasia produced by sustained irritant effects at the injection sites, enhanced by the acidic lactic acid/mannitol vehicle. This non-specific tissue reaction appeared to be particular to rats. Neoplastic lesions were not observed either in mice receiving daily s.c. injections of octreotide at doses up to 2 mg/kg for 98 weeks, or in dogs treated with daily s.c. doses of the drug for 52 weeks.
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