Drug Interactions between amoxicillin / clarithromycin / lansoprazole and omaveloxolone

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.

GENERALLY AVOID: Coadministration with potent or moderate inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of omaveloxolone, which is primarily metabolized by the isoenzyme. When administered with itraconazole, a potent CYP450 3A4 inhibitor, omaveloxolone peak plasma concentration (Cmax) and systemic exposure (AUC) increased 3-fold and 4-fold, respectively. When administered with verapamil, a moderate CYP450 3A4 inhibitor, omaveloxolone Cmax and AUC increased approximately 1.25-fold each. Increased exposure to omaveloxolone may increase the risk of adverse reactions such as lipid abnormalities and increased aminotransferases and B-type natriuretic peptide (BNP).

MANAGEMENT: Coadministration of omaveloxolone with potent or moderate CYP450 3A4 inhibitors should be avoided. If concomitant use of a potent CYP450 3A4 inhibitor is unavoidable, reduce the omaveloxolone dose to 50 mg once daily, and if adverse reactions occur, coadministration should be discontinued. If concomitant use of a moderate CYP450 3A4 inhibitor is unavoidable, reduce the omaveloxolone dose to 100 mg once daily, and if adverse reactions occur, further reduce the dose to 50 mg once daily.

MONITOR: Omaveloxolone may decrease the plasma concentrations of drugs that are substrates of CYP450 2C8 and/or 3A4 via induction of these isoenzymes. The systemic exposure (AUC) of repaglinide, a CYP450 2C8 substrate, decreased by approximately 35%, and the AUC of midazolam, a CYP450 3A4 substrate, decreased by approximately 45%, when administered with omaveloxolone. Reduced effectiveness of the substrates may result.

MANAGEMENT: The potential for diminished pharmacologic effects of CYP450 2C8 and/or 3A4 substrates should be considered during coadministration with omaveloxolone. The prescribing information for the substrates should be consulted for any dosage adjustments that may be required.

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.