Drug Interactions between Prevpac and Qtern

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.

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ADJUST DOSE: Coadministration with potent inhibitors of CYP450 3A4 may significantly alter the plasma concentrations of saxagliptin and its pharmacologically active metabolite, both of which are substrates of the isoenzyme. In one study, administration of a single 100 mg dose of saxagliptin in combination with the potent inhibitor ketoconazole (200 mg every 12 hours at steady state) resulted in increases to saxagliptin peak plasma concentration (Cmax) by 62% and systemic exposure (AUC) by 2.5-fold. These changes were accompanied by corresponding decreases in the Cmax and AUC of the active metabolite by 95% and 88%, respectively. The pharmacokinetics of ketoconazole were not significantly affected, with Cmax and AUC decreasing by just 16% and 13%, respectively. In another study, saxagliptin Cmax increased by 2.4-fold and AUC increased by 3.7-fold during coadministration of a single 20 mg dose of saxagliptin with ketoconazole (200 mg every 12 hours at steady state), while Cmax and AUC of the active metabolite decreased by 96% and 90%, respectively. However, some authorities suggest that these pharmacokinetic effects on saxagliptin and its metabolite are not clinically meaningful.

MANAGEMENT: Some authorities advise against using saxagliptin in combination with potent CYP450 3A4 inhibitors. Other authorities recommend that the dosage of saxagliptin should be limited to 2.5 mg once daily when used with potent CYP450 3A4 inhibitors such as itraconazole, ketoconazole, voriconazole, nefazodone, delavirdine, protease inhibitors, and ketolide and certain macrolide antibiotics.

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MONITOR: Concomitant use of insulin and other antidiabetic agents with clarithromycin may cause significant hypoglycemia. There have been rare reports of hypoglycemia in patients treated with clarithromycin, some of whom were taking oral hypoglycemic agents or insulin. The exact mechanism of interaction has not been established. With certain hypoglycemic drugs such as nateglinide, pioglitazone, repaglinide and rosiglitazone, inhibition of the CYP450 3A4 isoenzyme by clarithromycin may be involved.

MANAGEMENT: Caution is advised if clarithromycin is prescribed to patients receiving antidiabetic agents. Patients should be advised to regularly monitor their blood sugar and counseled on how to recognize and treat hypoglycemia, which may include symptoms such as headache, dizziness, drowsiness, nervousness, confusion, tremor, hunger, weakness, perspiration, palpitation, and tachycardia.

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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.

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