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.