Octreotide. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in conditions associated with excessive peptide secretion.

Octreotide is an analogue of somatostatin. Like endogenous somatostatin, it exerts a potent inhibitory effect on the release of anterior pituitary growth hormone and thyroid-stimulating hormone, and peptides of the gastroenteropancreatic endocrine system, while overcoming some of the shortcomings of exogenously administered somatostatin, namely a short duration of action, a need for intravenous administration and postinfusion rebound hypersecretion of hormone. Clinical studies have shown that octreotide is effective in the treatment of acromegaly and thyrotrophinomas. In comparative trials octreotide was significantly superior to bromocriptine in patients with acromegaly. Octreotide also appears to provide a significant advantage over existing therapies in the management of the carcinoid syndrome and offers considerable therapeutic potential in reversing carcinoid crises which may be life-threatening. Trials in patients with tumours producing vasoactive intestinal peptide demonstrated that octreotide may be an effective first-line choice for this condition, which has usually metastasised and become refractory to traditional symptomatic therapy. In limited studies in patients with high-output secretory diarrhoea, including cryptosporidium-related diarrhoea associated with AIDS and in patients with small bowel fistulas, octreotide has been shown to be effective in reducing stool/fistula output. However, well-designed clinical trials are still required to confirm its long term usefulness in these disorders. Similarly, although the use of octreotide in other conditions such as neonatal hypoglycaemia caused by nesidioblastosis, reactive pancreatitis, insulin-dependent diabetes mellitus, postprandial hypotension and the dumping syndrome has provided encouraging preliminary results, more studies are needed to clarify the place of octreotide in their treatment. Overall, octreotide appears to be well tolerated with the most frequently reported reactions being pain at the site of injection and gastrointestinal symptoms such as abdominal cramps, nausea, bloating, flatulence, diarrhoea and steatorrhoea. These adverse effects usually abate with time. Additionally, octreotide, like endogenous somatostatin, may also result in cholelithiasis, presumably by altering fat absorption and possibly by decreasing motility of the gallbladder. Thus, octreotide represents a new departure from traditional therapies in the treatment of various pathophysiological states associated with excessive peptide production and secretion. It offers a significant advantage over existing therapies in the medical management of patients with acromegaly, thyrotrophinomas, the carcinoid syndrome, tumours producing vasoactive intestinal peptide and severe secretory diarrhoea in whom conventional management options have either become exhausted or have provided suboptimal symptomatic relief.