Telotristat ethyl (Xermelo), developed by Lexicon Pharmaceuticals, is an oral tryptophan hydroxylase inhibitor blocking peripheral conversion of tryptophan to serotonin (5-hydroxytryptamine [5-HT]). It was approved by the U.S. Food and Drug Administration (FDA) in February 2017 and by the European Commission in September 2017 for patients with carcinoid syndrome in whom diarrhea is not adequately controlled by somatostatin analogues (SSAs). Diarrhea, secondary to the release of serotonin, is the predominant gastrointestinal symptom in patients with carcinoid syndrome and has a significant impact on patients' quality of life. Telotristat is not meant for all patients with diarrhea and carcinoid syndrome. Prescribing of telotristat for patients with diarrhea refractory to SSAs requires careful consideration and an approach that involves identifying and ruling out other common causes of diarrhea in patients with carcinoid syndrome. Delineating the timing of diarrhea and whether it occurs in patients with stable disease versus cancer progression can help identify the right drug candidates for therapy.
Keywords: Carcinoid syndrome; Diarrhea; Gastrointestinal disorders; Neuroendocrine tumors; Serotonin-mediated disorders; Telotristat; Tryptophan hydroxylase inhibitors.
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