Telotristat ethyl

Pronunciation: tel-OH-tri-stat-ETH-il
Brand name: Xermelo
Dosage form: tablet (250mg)
Drug class: Miscellaneous GI agents

Medically reviewed by Melisa Puckey, BPharm. Last updated on Apr 29, 2025.

What is telotristat ethyl?

Telotristat ethyl (Xermelo) tablets are a prescription medicine used to treat carcinoid syndrome diarrhea in adults. Telotristat ethyl targets the underlying cause of carcinoid syndrome diarrhea, which is high serotonin levels produced by carcinoid tumors.

Telotristat ethyl works by blocking tryptophan hydroxylase, a key enzyme that helps make serotonin. By blocking tryptophan hydroxylase, serotonin levels decrease and diarrhea symptoms improve. Telotristat ethyl mechanism of action is as a tryptophan hydroxylase inhibitor, it is not chemotherapy.

Telotristat ethyl brand name is Xermelo. Telotristat ethyl tablets are taken three times a day.

Telotristat ethyl is used with medications such as octreotide (Sandostatin), a somatostatin analog (SSA), when the SSA has not effectively controlled diarrhea on its own.  Telotristat ethyl reduces how much serotonin is made, and octreotide blocks the amount of serotonin released, so together they improve carcinoid syndrome diarrhea symptoms.

Telotristat ethyl FDA approval was granted for the indication of carcinoid syndrome diarrhea when used in combination with a somatostatin analog (SSA) therapy, such as octreotide. It can be used in adults whose carcinoid syndrome diarrhea has not been controlled by somatostatin analog therapy.

What is carcinoid syndrome diarrhea?

Carcinoid syndrome diarrhea is caused by carcinoid tumors releasing too much serotonin into the bloodstream. Excess serotonin stimulates the gut, speeding up movement through the intestines and preventing water and electrolyte absorption, which leads to frequent watery diarrhea. Carcinoid syndrome is a rare condition that affects people with metastatic neuroendocrine tumors (mNETs).

Clinical trials: How effective is telotristat ethyl?

Phase III Study Results

A placebo-controlled phase III study (TELESTAR) evaluated telotristat ethyl in 135 carcinoid syndrome patients who experienced 4 or more bowel movements (BM) per day despite taking somatostatin analog therapy. Telotristat dose was three times daily.

Key Findings (12-Week Double-Blind Study):

BM Frequency Reduction:

• Telotristat ethyl 250 mg: 1.7 fewer bowel movements per day 
• Telotristat ethyl 500 mg: 2.1 fewer bowel movements per day 
• Placebo group: 0.9 fewer bowel movements per day 

Urinary 5-HIAA Reduction:

• Both telotristat ethyl dosages significantly lowered 5-hydroxyindole acetic acid (5-HIAA) levels (a marker of serotonin production), confirming the drug's effectiveness.

Conclusion: The study demonstrated that telotristat ethyl effectively reduces diarrhea symptoms in patients with carcinoid syndrome when SSAs alone are insufficient.

Telotristat ethyl side effects

Common telotristat side effects:

• Nausea (13%)
• Loss of appetite (7%)
• Gas (7%)
• Headache (11%)
• Depressed mood (9%)
• Swelling in hands or feet (7%)
• Fever (7%)
• Increased GGT levels (9%)

These common side effects occurred in 5% or more of patients taking Telotristat 250 mg three times a day in the double-blind, placebo-controlled clinical trial of 90 patients with metastatic neuroendocrine tumors and carcinoid syndrome diarrhea.

Serious telotristat side effects

• Signs of an allergic reaction (hives, difficulty breathing, swelling of the face, lips, tongue, or throat)
• Severe constipation
• Severe or worsening stomach pain

This is not a comprehensive list of side effects. Consult your doctor for medical advice, or report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

Warnings 

Use only as directed by your doctor. Tell your doctor about any medications, allergies, or pre-existing conditions.

Discontinue use if you experience severe constipation or persistent abdominal pain.

Before taking this medicine

Tell your doctor if you have ever had liver disease or if you are pregnant or breastfeeding.

This medication is not approved for individuals under 18 years old.

Telotristat ethyl dosing information

Usual telotristat ethyl adult dose: 250 mg tablet orally 3 times a day with food.

Telotristat ethyl (Xermelo) comes in a monthly case that contains 4 weekly boxes; 1 box of 7 daily doses for use each week. Keep each tablet in the package until you are ready to take a dose.

Short-acting Octreotide is usually given at least 30 minutes after taking this medicine.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

This medicine is only part of a complete treatment program that may also include other medications. Do not change your doses or medication schedule without your doctor's advice.

Available as Xermelo 250mg tablets.

Missed Dose

If you miss a dose, skip it and take the next dose at the regular time. Do not double the dose to make up for a missed one.

Overdose

In case of overdose, seek emergency medical help or call the Poison Help Line at 1-800-222-1222.

Drug interactions

Sometimes it is not safe to use certain medications at the same time. Some drugs can affect your blood levels of other drugs you take, which may increase side effects or make the medications less effective.

CYP3A4 substrates, such as midazolam, may have reduced effectiveness when taken with telotristat ethyl.

Always inform your doctor about all medications you are taking, including:

• Prescription drugs
• Over-the-counter medicines
• Vitamins and supplements
• Herbal products

You can use the Drug Interaction Checker or consult your healthcare provider to verify potential interactions.

Telotristat Ethyl Package Insert 

HCPs and patients often use the Telotristat Ethyl Package Insert (PI) - Xermelo brand - for more detailed information about this medicine. The Telotristat Ethyl Package Insert (prescribing information) contains more comprehensive information on Indications and Usage, Dosage and Administration, Clinical Pharmacology, Clinical Studies, Drug Interaction, and more. Discuss any medical questions you have with your HCP (health care professional). This is not all the information you need to know about this medicine for safe and effective use, and it does not take the place of talking to your doctor about your treatment.

The Package Insert is sometimes called Prescribing Information (PI) or FDA label.

Storage

• Store at 25°C (77°F).
• Permitted temperature excursions: 15°C to 30°C (59°F to 86°F).

Ingredients

Active ingredient: 250 mg of telotristat ethyl (free base), equivalent to 328 mg telotristat etiprate.

Inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, hydroxypropyl cellulose, lactose anhydrous, macrogol/PEG, magnesium stearate, polyvinyl alcohol (partially hydrolyzed), talc, and titanium dioxide.

Company

Telotristat ethyl (Xermelo) by Lexicon Pharmaceuticals, Inc., located in The Woodlands, TX 77381.

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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