Drug Interactions between itraconazole 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.

ADJUST DOSING INTERVAL: Food increases the absorption of itraconazole capsules but decreases the absorption of itraconazole oral solution. Cola beverages may increase the bioavailability of itraconazole capsules. Itraconazole capsules require an acidic gastric pH for adequate dissolution and subsequent absorption. Cola beverages help lower gastric pH and improve absorption.

GENERALLY AVOID: Grapefruit juice may impair the absorption of itraconazole capsules, resulting in decreased antifungal effects. In a small, randomized, crossover study, the administration of itraconazole capsules with double-strength grapefruit juice (compared to water) was associated with significantly decreased (43%) plasma concentrations of itraconazole and its pharmacologically active hydroxy metabolite, as well as delayed times to reach peak concentrations of both. The exact mechanism of interaction is unknown but may involve reduced absorption of itraconazole secondary to enhanced activity of intestinal P-glycoprotein drug efflux pumps and delayed gastric emptying induced by certain compounds present in grapefruits. Another study reported no pharmacokinetic changes with single-strength grapefruit juice. Whether or not these observations apply to itraconazole oral solution is unknown.

MANAGEMENT: The manufacturer recommends that the capsules be taken immediately after a full meal and the solution be taken on an empty stomach to ensure maximal absorption. Cola beverages may help increase the bioavailability of itraconazole capsules, particularly in patients with hypochlorhydria or those treated concomitantly with gastric acid suppressants. Until more information is available, it may be advisable to avoid the consumption of grapefruits and grapefruit juice during itraconazole therapy.