Drug Interaction Report

MONITOR: Coadministration with telotristat ethyl may decrease the plasma concentrations of drugs that are substrates of CYP450 3A4 and/or 2B6 isoenzymes. The proposed mechanism is accelerated clearance due to induction of CYP450 3A4 and/or 2B6 (in vitro) isoenzymes by telotristat ethyl. When the probe CYP450 3A4 substrate midazolam (3 mg) was administered orally after 5 days of treatment with telotristat ethyl 500 mg three times daily (twice the recommended dosage), mean midazolam peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by 25% and 48%, respectively, compared to administration of midazolam alone. The mean Cmax and AUC of the active metabolite, 1'-hydroxymidazolam, also decreased by 34% and 48%, respectively. This suggests induction by telotristat ethyl of the glucuronidation of 1'-hydroxymidazolam.

MANAGEMENT: When drugs that are known substrates of CYP450 3A4 and/or 2B6 are coadministered with telotristat ethyl, the possibility of a diminished therapeutic response to those drugs should be considered. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs, particularly those with a narrow therapeutic range, whenever telotristat ethyl is added to or withdrawn from therapy.

MONITOR: Grapefruit juice may increase the plasma concentrations of tofacitinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. The extent and clinical significance are unknown. Moreover, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability.

MANAGEMENT: Until more information is available, some authorities recommend avoiding consumption of grapefruit juice during tofacitinib therapy (Canada). Patients receiving tofacitinib therapy who ingest grapefruits or grapefruit juice should be monitored for adverse effects and undue fluctuations in plasma drug levels.

ADJUST DOSING INTERVAL: Food increases the systemic exposure to both telotristat ethyl and its active metabolite, telotristat. Following administration of a single 500 mg dose of telotristat ethyl (twice the recommended dose) with a high-fat meal, telotristat ethyl peak plasma concentration (Cmax) and systemic exposure (AUC) were 112% and 264% higher, respectively, compared to administration under fasted conditions. The Cmax and AUC values for telotristat were also increased by 47% and 33%, respectively. The in vitro inhibitory potency of telotristat towards tryptophan hydroxylase has been shown to be approximately 29 times higher than that of the parent drug.

MANAGEMENT: Telotristat ethyl should be administered with food.