Octreotide is an octapeptide that mimics natural somatostatin pharmacologically, though it is a more potent inhibitor of growth hormone, glucagon, and insulin than the natural hormone. Octreotide is used in nuclear medicine imaging by labelling with indium-111 (Octreoscan) to noninvasively image neuroendocrine and other tumours expressing somatostatin receptors. More recently, it has been radiolabelled with carbon-11 as well as gallium-68, enabling imaging with positron emission tomography (PET), which provides higher resolution and sensitivity. Octreotide can also be labelled with a variety of radionuclides, such as yttrium-90 or lutetium-177, to enable peptide receptor radionuclide therapy (PRRT) for the treatment of unresectable neuroendocrine tumours. Octreotide has also been used off-label for the treatment of severe, refractory diarrhea from other causes.
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