Drug Interactions between amoxicillin / clarithromycin / lansoprazole and rifabutin

GENERALLY AVOID: The coadministration of clarithromycin and rifabutin at normally recommended dosages has been reported to have resulted in significantly altered pharmacokinetics for both drugs. In a study of 34 clinically stable subjects with advanced HIV infection (CD4 less than 200 cells/mm3), the addition of rifabutin in patients stabilized on clarithromycin therapy slowly decreased the clarithromycin area under the plasma concentration-time curve (AUC) and C(max) up to an average of 44% and 41%, respectively, at the end of 4 weeks of combination therapy. In patients stabilized on rifabutin therapy, the addition of clarithromycin significantly increased rifabutin AUC and C(max) after the first dose. After 4 weeks, average increases of 99% and 69%, respectively, were reported. This bidirectional interaction is consistent with rifabutin's cumulative inducing effect over time on the CYP450 enzymatic pathway as well as clarithromycin's immediate inhibiting effect on the pathway. In the study, the combination was tolerated by more than 90% of the patients. However, 66% of them experienced gastrointestinal problems including nausea, vomiting and diarrhea. An increased incidence of uveitis has also been reported with this combination. In addition, the combination of clarithromycin and rifampin 600 mg/day (with multiple other drugs) decreased clarithromycin serum levels by approximately 90%. Other macrolide antibiotics may interact in a similar manner with rifamycins.

MANAGEMENT: Some experts recommend that this combination be avoided since it may result in decreased efficacy of the macrolide and increased rifamycin toxicity (e.g, neutropenia, uveitis).

Switch to consumer interaction data

MONITOR: Coadministration with clarithromycin may increase the plasma concentrations of lansoprazole. The proposed mechanism is clarithromycin inhibition of intestinal (first-pass) and hepatic metabolism of lansoprazole via CYP450 3A4. Although lansoprazole is primarily metabolized by CYP450 2C19 in the liver, 3A4-mediated metabolism is the predominant pathway in individuals who are 2C19-deficient (approximately 3% to 5% of the Caucasian and 17% to 20% of the Asian population). Additionally, inhibition of P-glycoprotein intestinal efflux transporter by clarithromycin may also contribute to the interaction, resulting in increased bioavailability of lansoprazole. In 18 healthy volunteers--six each of homozygous extensive metabolizers (EMs), heterozygous EMs, and poor metabolizers (PMs) of CYP450 2C19--clarithromycin (400 mg orally twice a day for 6 days) increased the peak plasma concentration (Cmax) of a single 60 mg oral dose of lansoprazole by 1.47, 1.71- and 1.52-fold, respectively, and area under the concentration-time curve (AUC) by 1.55-, 1.74- and 1.80-fold, respectively, in each of these groups compared to placebo. The AUC ratio of lansoprazole to lansoprazole sulphone, which is considered an index of CYP450 3A4 activity, was significantly increased by clarithromycin in all three groups. However, elimination half-life of lansoprazole was prolonged by 1.54-fold only in PMs. Mild diarrhea was reported in two subjects and mild abdominal disturbance in six subjects during clarithromycin coadministration. These side effects continued until day 6 and ameliorated the day after discontinuation of clarithromycin, whereas no adverse events were reported during placebo administration or after lansoprazole plus placebo. In another study, clarithromycin induced dose-dependent increases in the plasma concentration of lansoprazole in a group of 20 patients receiving treatment for H. pylori eradication. Mean 3-hour plasma lansoprazole concentration was 385 ng/mL for the control subjects who received lansoprazole 30 mg and amoxicillin 750 mg twice a day for 7 days; 696 ng/mL for patients coadministered clarithromycin 200 mg twice a day; and 947 ng/mL for patients coadministered clarithromycin 400 mg twice a day.

MANAGEMENT: Although lansoprazole is generally well tolerated, caution may be advised during coadministration with clarithromycin, particularly if higher dosages of one or both drugs are used. Dosage adjustment may be necessary in patients who experience excessive adverse effects of lansoprazole.

Switch to consumer interaction data

Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

Switch to consumer interaction data