Telotristat for Treating Carcinoid Syndrome Diarrhoea in Adults

Carcinoid syndrome (CS) is a constellation of symptoms caused by hormonesecreting neuroendocrine tumours (NETs). The most troublesome symptom for many patients is profuse, watery diarrhoea, which can lead to dehydration, electrolyte imbalance, and a marked reduction in quality of life. While somatostatin analogues (SSAs) such as octreotide and lanreotide control hormone secretion in many patients, a substantial proportion remain symptomatic. Telotristat (Telotristat ethyl) is the first oral therapy specifically designed to reduce serotonin production, addressing diarrhoea that persists despite optimal SSA therapy.

How Telotristat Works

Telotristat is a peripheral inhibitor of the enzyme tryptophan hydroxylase (TPH), the ratelimiting step in serotonin synthesis. By blocking TPH, telotristat markedly reduces the amount of serotonin released into the bloodstream from NET cells. Because most of the drugs activity is confined to the gut and does not cross the bloodbrain barrier, central serotonin pathways remain largely unaffected, minimizing central nervous system sideeffects.

Indications & Patient Selection

Telotristat is approved for adult patients with CS who have:

• 4 bowel movements per day despite stable, maximally tolerated SSA therapy.
• Documented elevation of urinary 5hydroxyindoleacetic acid (5HIAA) or plasma serotonin.
• No contraindications to oral medication (e.g., severe hepatic impairment).

It is not a substitute for SSA therapy; rather, it is used in combination with an SSA.

Dosage & Administration

Capsules should be swallowed whole; crushing may affect absorption. If a dose is missed, take it as soon as remembered if it is still the same day; otherwise, skip and resume the regular schedule.

Clinical Efficacy

Two pivotal Phase III trials (the TELESTAR and TELECAST studies) evaluated telotristat in patients with CSrelated diarrhoea.

• TELESTAR enrolled 135 patients with 4 bowel movements/day despite SSA therapy. After 12 weeks, the mean reduction in daily bowel movements was 1.7 in the 500mg threetimesdaily group vs 0.9 in the placebo group (p<0.001). 44% of patients achieved a 30% reduction versus 20% on placebo.
• TELECAST focused on patients with <4 bowel movements/day but persistent symptoms. A statistically significant reduction in stool frequency (0.5vs0.2 per day) and improvement in qualityoflife scores were observed.

Both studies demonstrated reductions in urinary 5HIAA, correlating with the clinical benefit.

Safety Profile

Overall, telotristat is well tolerated. The most common adverse events (AEs) reported in >5% of patients include:

• Depression or mood changes (approximately 69%).
• Nausea (57%).
• Abdominal pain or cramping (5%).

Because serotonin also plays a role in platelet function, routine monitoring of platelet counts is advised, though clinically significant thrombocytopenia is rare.

Patients with a history of major depressive disorder should be monitored closely; abrupt onset or worsening depression warrants evaluation.

Drug Interactions

Telotristat is metabolised primarily by hepatic glucuronidation (UGT1A9, UGT2B7). Significant drugdrug interactions are uncommon, but the following should be considered:

• Strong UGT inhibitors (e.g., atazanavir) may increase telotristat exposure.
• Concomitant serotonergic agents (SSRIs, MAOinhibitors) do not appear to increase serotonin syndrome risk because telotristat works peripherally, but clinicians should remain vigilant.

Monitoring & FollowUp

Key parameters to assess before and during treatment include:

• Baseline urinary 5HIAA or plasma serotonin.
• Frequency of bowel movements (patient diary).
• Depression screening (PHQ9 or equivalent).
• Liver function tests every 36 months (telotristat is hepatically cleared).

Clinical response is usually evident within 24 weeks. If there is no meaningful reduction in stool frequency after 8 weeks at the highest tolerated dose, discontinuation may be considered.

Special Populations

Renal impairment: No dose adjustment is required for mildtomoderate renal dysfunction. Data are limited in severe renal failure; use with caution.

Hepatic impairment: Not recommended for patients with ChildPugh Class C disease. For Class B, start at the lowest dose and monitor liver enzymes closely.

Pregnancy & lactation: Animal studies show no teratogenicity, but human data are lacking. Telotristat should be avoided unless the potential benefit outweighs the risk.

Practical Tips for Clinicians

1. Confirm that the patient is on a stable dose of an SSA for at least 4 weeks before adding telotristat.
2. Use a stool diary to establish baseline frequency and to track treatment response.
3. Educate patients to take the medication with meals to improve absorption and reduce gastrointestinal upset.
4. Schedule a followup visit at 4 weeks to assess efficacy and tolerability; adjust dose if needed.
5. Maintain open communication about mood changes; involve mentalhealth professionals when appropriate.

Patient Perspective

John, a 58yearold with metastatic midgut NET, described his experience:

Before telotristat I was going to the bathroom every two to three hours, even at night. It ruined my sleep and made me anxious about leaving the house. After a month on telotristat, my stools dropped to about onetwo a day, and I finally feel like I have a normal life again. The only thing I had to watch for was feeling a bit down, which my doctor helped me manage.

Key Takeaways

• Telotristat is the first oral, peripheral TPH inhibitor approved for CSrelated diarrhoea in adults.
• It is used in addition to, not instead of, somatostatin analogues.
• Clinical trials demonstrate a meaningful reduction in bowel movements and serotonin biomarkers.
• Common side effects are mild; mood monitoring is essential.
• Regular assessment of stool frequency, 5HIAA, liver function, and depression scores guides safe longterm use.

For more detailed prescribing information, refer to the FDA drug label or the manufacturers product monograph.