| Pharmacotherapeutic group: 8.1.3. Antigrowth Hormones. ATC code: H01CB02Octreotide is a synthetic octapeptide analog of naturally occurring somatostatin with similar pharmacological effects, but with a longer duration of action. It inhibits pathologically increased secretion of growth hormone (GH) and of peptides and serotonin produced within the gastroenteropancreatic (GEP) endocrine system, stomach, intestine and pancreas (for example, gastrin, insulin and glucagon). Octreotide gives symptomatic relief of the symptoms caused by functional tumours of the gastroenteropancreatic (GEP) endocrine system (stomach, intestine and pancreas) in patients whose symptoms have not been relieved by other forms of treatment such as surgery, hepatic artery embolisation or chemotherapy. The effect of Octreotide on tumour size, rate of growth or on the formation of metastases has not yet been clearly documented. In healthy volunteers Octreotide has been shown to inhibit the release of GH stimulated by arginine, exercise and insulin-induced hypoglycaemia, and thyrotropin-releasing hormone (TRH)-stimulated release of thyroid-stimulating hormone (TSH).Unlike somatostatin, Octreotide inhibits growth hormone (GH) and glucagon preferentially over insulin. Discontinuation of treatment is not followed by a rebound effect with hypersecretion of hormones.In patients with carcinoid tumours, Octreotide may result in relief 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 (5-HIAA). In patients with VIPomas, the biochemical characteristic is overproduction of vasoactive intestinal peptide (VIP). In most cases, Octreotide alleviates 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, such as hypokalaemia. The need for administration of fluids and electrolytes is reduced. In some patients, computer tomography scanning reveals 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. In glucagonomas, administration of Octreotide results in most cases in substantial improvement of the necrolytic migratory rash which is characteristic of this condition. The effect of Octreotide on the moderate 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 affected patients. 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. In patients with acromegaly, Octreotide reduces GH and IGF-1 plasma levels. A GH reduction by around 50% or more occurs in over 90% of patients, and a reduction of plasma GH to < 5 ng/ml can be achieved in about half of the cases. In most patients, Octreotide significantly reduces clinical symptoms such as headache, swelling of skin and soft tissues, hyperhidrosis, arthralgia and paraesthesia. In patients with large volume pituitary adenomas, Octreotide may lead to shrinkage of the tumour mass. For patients undergoing pancreatic surgery, the peri- and post-operative administration of Octreotide generally reduces the incidence of typical post-operative complications (e.g. pancreatic fistula, abscess and subsequent sepsis, post-operative acute pancreatitis). | |