Drug Interactions between alvimopan and levomethadyl acetate

GENERALLY AVOID: The concurrent use of levomethadyl acetate and alcohol may result in additive CNS and respiratory depression, hypotension, sedation, or coma. Grapefruit juice may increase the plasma concentrations of orally administered drugs which are substrates of the CYP450 3A4 isoenzyme, such as levomethadyl acetate. 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: Patients who are known to abuse alcohol should be warned of the risk of potentially fatal overdose if these substances are taken concurrently. Patients who regularly consume grapefruits and grapefruit juice should be monitored for adverse effects and altered plasma concentrations of levomethadyl acetate. A 12-lead ECG should be performed before initiating therapy, 12 to 14 days after initiating therapy, and periodically thereafter. Patients should be advised to immediately seek medical attention if they experience palpitations, dizziness, lightheadedness, fainting, or seizures. Grapefruits and grapefruit juice should be avoided if an interaction is suspected. Orange juice is not expected to interact.

Coadministration with a high-fat meal may decrease the rate and extent of alvimopan absorption. According to the product labeling, alvimopan peak plasma concentration (Cmax) and systemic exposure (AUC) were decreased by approximately 38% and 21%, respectively, and the time to reach peak plasma concentration (Tmax) was prolonged by approximately 1 hour when taken with a high-fat meal. The clinical significance is unknown. In postoperative ileus clinical trials, the preoperative dose of alvimopan was administered in a fasting state, and subsequent doses were given without regard to meals.