Drug Interactions between gepirone and itraconazole

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.

GENERALLY AVOID: Grapefruit and/or grapefruit juice may increase the plasma concentrations and effects of gepirone. The proposed mechanism is inhibition of CYP450 3A4 mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Inhibition of hepatic CYP450 3A4 may also contribute. The interaction has not been studied with grapefruit juice, but has been reported for other CYP450 3A4 inhibitors. For example, when subjects who were at steady state on the strong CYP450 3A4 inhibitor ketoconazole (200 mg twice daily) received a single dose of gepirone (36.3 mg), the maximum plasma concentration (Cmax) and systemic exposure (AUC) of gepirone increased by approximately 5-fold. Similarly, when subjects who were at steady state on the moderate CYP450 3A4 inhibitor verapamil (80 mg three times daily) received a single dose of gepirone (18.2 mg), the maximum plasma concentration (Cmax) and systemic exposure (AUC) of gepirone increased by approximately 2.6-fold. In general, the effects of grapefruit products are concentration-, dose-, and preparation-dependent and can vary widely among both brands and individual patients. Some preparations have demonstrated strong CYP450 3A4 inhibition, while others have demonstrated moderate inhibition.

ADJUST DOSING INTERVAL: Food enhances the bioavailability of gepirone and its major active metabolites (3'-OH-gepirone and 1-PP). The magnitude of the effect is dependent on the fat content of the meal, but the systemic exposure of gepirone and its major metabolites was consistently higher under fed conditions as compared to the fasted state. The peak plasma concentration (Cmax) of gepirone after intake of a low-fat (about 200 calorie) breakfast was 27% higher, after a medium-fat (about 500 calorie) breakfast was 55% higher, and after a high-fat (about 850 calorie) breakfast was 62% higher than the Cmax achieved in the fasted state. Likewise, the systemic exposure (AUC) of gepirone was about 14% higher after a low-fat breakfast, 22% higher after a medium-fat breakfast, and 32% to 37% higher after a high-fat breakfast when compared to the AUC achieved in the fasted state. The effect of varying amounts of fat on the AUC and Cmax of 3'-OH-gepirone and 1-PP were similar to that of gepirone.

MANAGEMENT: Coadministration of gepirone with grapefruit products should be avoided. If grapefruit juice is consumed, monitoring for adverse effects (e.g., QT prolongation, serotonin syndrome, dizziness, nausea, insomnia, abdominal pain, and/or dyspepsia) should be considered. Gepirone should be taken orally with food at the approximately the same time each day. Tablets should be swallowed whole.