Drug Interaction Report

MONITOR: Certain medications may decrease chemotaxis and cause false-negative results with Indium In-111-labeled leukocyte studies.

MANAGEMENT: Clinicians should be aware of possible diagnostic interference in patients who are on long-term antibiotic treatment, corticosteroids, interleukin-2, parenteral nutrition, or high doses or supratherapeutic concentrations of lidocaine or procainamide.

Grapefruit juice may delay the gastrointestinal absorption of clarithromycin but does not appear to affect the overall extent of absorption or inhibit the metabolism of clarithromycin. The mechanism of interaction is unknown but may be related to competition for intestinal CYP450 3A4 and/or absorptive sites. In an open-label, randomized, crossover study consisting of 12 healthy subjects, coadministration with grapefruit juice increased the time to reach peak plasma concentration (Tmax) of both clarithromycin and 14-hydroxyclarithromycin (the active metabolite) by 80% and 104%, respectively, compared to water. Other pharmacokinetic parameters were not significantly altered. This interaction is unlikely to be of clinical significance.