Telotristat is a new medication for the treatment of carcinoid syndrome diarrhoea. Carcinoid syndrome is a condition that develops in around 10% of people with a carcinoid tumour. Carcinoid tumours develop from enterochromaffin cells, the most common type of neuroendocrine cell in the gastrointestinal tract. Tumours derived from these cells can produce large amounts of vasoactive substances, including serotonin and histamine. This may contribute to symptoms of carcinoid syndrome such as severe diarrhoea, bronchoconstriction, flushing, and abdominal cramps.

Telotristat inhibits peripheral tryptophan hydroxylase, an enzyme involved in the biosynthesis of serotonin. Consequently, serotonin levels decrease and symptoms of carcinoid syndrome are alleviated. Telotristat is designed not to cross the blood-brain barrier, and studies demonstrate no significant change in brain serotonin levels at the recommended dose. However, patients should be advised to report any symptoms of depression or altered mood to their doctor.

Telotristat is an oral medication that should be taken with food. It is indicated for use in combination with a somatostatin analogue such as octreotide or lanreotide. Short-acting octreotide causes a significant reduction in systemic exposure to telotristat and its active metabolite and should be administered at least 30 minutes after a telotristat dose.


  1. Aluri V, Dillon JS. Biochemical testing in neuroendocrine tumors. Endocrinol Metab Clin North Am. 2017; 46(3): 669-77.
  2. Kulke MH, O’Dorisio T, Phan A, Bergsland E, Law L, Banks P, et al. Telotristat etiprate, a novel serotonin synthesis inhibitor, in patients with carcinoid syndrome and diarrhea not adequately controlled by octreotide. Endocr Relat Cancer. 2014; 21(5): 705-14.
  3. Xermelo® (telotristat ethyl (as telotristat etiprate)) Australian approved product information. Glen Waverley: Ipsen. Approved September 2018.

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