The purpose of this study is to evaluate the effects of steady-state telotristat ethyl on the pharmacokinetics (PK) of single-dose fexofenadine in healthy subjects.

Inclusion Criteria:

• Healthy adult subjects aged ≥18 to ≤55 years of age at screening
• Body mass index ≥18.0 to ≤32.0 kg/m^2
• Acceptable vital signs at Screening: Systolic blood pressure = 90-140 mm Hg, Diastolic blood pressure = 50-90 mm Hg, Heart rate = 40-100 beats per minute
• Willingness to adhere to the restrictions outlined in the protocol
• Able to comprehend and sign the Informed Consent Form

Exclusion Criteria:

• Presence of any clinically significant physical, laboratory, or ECG finding that may interfere with the study in the opinion of the Investigator
• Use of any medications, herbal tea, energy drink, herbal products, or supplements within 14 days of Day 1
• Receipt of any investigational agent or study drug within 30 days or 5 half-lives prior to Screening
• Receipt of any protein- or antibody-based therapeutic agent within 3 months of Screening
• Prior exposure to telotristat etiprate
• Use of tobacco, smoking cessation products, or nicotine products within 3 months prior to Screening
• History of major surgery within 6 months prior to Screening
• History of any GI surgery that may induce malabsorption
• History of any serious adverse reaction or hypersensitivity to any component of fexofenadine
• History of renal disease, or significantly abnormal glomerular filtration rate (<90 mL/min as calculated using the Cockcroft-Gault equation) at Screening
• History of hepatic disease, or significantly abnormal liver function tests at Screening
• History of any clinically significant psychiatric, renal, hepatic, pancreatic, cardiovascular, neurological, endocrinologic, hematological, or GI abnormality
• History of any active infection within 14 days prior to first dosing
• History of alcohol or substance abuse within 2 years prior to Screening
• Positive hepatitis panel (including hepatitis B surface antigen and hepatitis C virus antibody) or positive human immunodeficiency virus antibody screens
• Concurrent conditions that could interfere with safety and/or tolerability measurements
• Donation or loss of >500 mL of blood or blood product within 3 months prior to Screening
• Women who are breastfeeding or are planning to become pregnant during the study
• Positive serum pregnancy test (females only)
• Positive urine screen for selected drugs of abuse and cotinine
• Consumption of alcohol within 48 hours prior to study start
• Consumption of caffeine- and/or xanthine-containing products within 72 hours of study start
• Consumption of grapefruit, Seville oranges, and grapefruit- or Seville orange-containing products within 72 hours prior to study start
• Unable or unwilling to communicate or cooperate with the Investigator for any reason
• Use of any drugs or substances that are known to be substrates, inducers, or inhibitors of CYP3A4 within 30 days prior to the first dose