Octrea Mechanism of Action

Pharmacotherapeutic group: Antigrowth hormones. ATC code: H01BC02.
Pharmacology: Pharmacodynamics: Mechanism of action: Octreotide is a synthetic octapeptide analogue of naturally occurring somatostatin (growth hormone [somatropin] release inhibiting factor). Its pharmacological effects are similar to somatostatin by inhibiting some anterior pituitary hormones release (i.e. GH, IGF-1), inhibiting serotonin release, and the secretion of gastrin, vasoactive intestinal peptide (VIP), insulin, glucagon, secretin, motilin and pancreatic polypeptide hormones related to GEP.
Also suppresses LH response to GnRH, secretion of thyroid-stimulating hormone (TSH) and decreases splanchnic blood flow. Octreotide has longer plasma half-life and duration of action as compared to endogenous somatostatin.
Because of its inhibitory effects on the secretion of serotonin and various gastroenteropancreatic peptides (e.g. gastrin, VIP, insulin, glucagon, secretin, motilin, pancreatic polypeptide), administration of octreotide may result in improvement of symptoms associated with metastatic carcinoid tumors, particularly flushing and diarrhea associated with carcinoid syndrome, watery diarrhea associated with VIP-secreting tumors.
In patients with VIPomas, the biochemical characteristic is overproduction of vasoactive intestinal peptide (VIP). Therapy with octreotide results in decreasing plasma VIP level, stool volume, and electrolyte loss (e.g. hypokalemia), with consequent improvement in quality of life.
In patients with acromegaly, octreotide consistently decreases GH and normalizes IGF-1 plasma levels in the majority of patients.
Pharmacokinetics: Absorption: Octreotide is rapidly and completely absorbed from the injection site (s.c.). Peak plasma concentration is reached about 25 to 40 minutes after dosing, and is distributed to body tissues.
Distribution: The volume of distribution is 0.27 L/kg, the total body clearance 160 mL/min. Plasma protein binding is approximately 65%. The distribution into the blood cell was negligible.
Elimination: The half-life after subcutaneous administration is 1.7 to 1.9 hours; prolonged in elderly patients; liver cirrhosis; renal impairment. Renal impairment did not affect the total exposure (AUC) to octreotide. Most of the peptide is eliminated via the feces, while approximately 32% of the dose is excreted unchanged into the urine.