Drug Interactions between amoxicillin / clarithromycin / lansoprazole and imatinib

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

MONITOR: Imatinib is a substrate of the CYP450 3A4 isoenzyme as well as a potent competitive inhibitor of the CYP450 2C9, 2D6 and 3A4 isoenzymes. Some drugs that are known inhibitors of CYP450 3A4 are also metabolized by one or more of the isoenzymes inhibited by imatinib. Theoretically, coadministration of imatinib with those drugs may result in mutually elevated plasma drug concentrations due to competitive and noncompetitive inhibition of CYP450 activities.

MANAGEMENT: The possibility of prolonged and/or increased pharmacologic effects of imatinib, including serious adverse effects such as edema, hematologic toxicity and immunosuppression, should be considered during concomitant therapy, particularly with potent CYP450 3A4 inhibitors such as ketoconazole, itraconazole, ritonavir, nefazodone, and erythromycin. In addition, clinical and laboratory monitoring for potentially increased pharmacologic effects of coadministered medications is recommended, especially those with a narrow therapeutic range.

Switch to consumer interaction data

MONITOR: Theoretically, coadministration with imatinib may increase the plasma concentrations of lansoprazole. The proposed mechanism is imatinib inhibition of lansoprazole metabolism via CYP450 2C9 and 3A4. There has also been a reported case of a patient with gastrointestinal stromal tumors who developed severe cutaneous adverse reactions during treatment with imatinib and lansoprazole. The patient had been receiving imatinib 400 mg/day alone for two months without incident. Ten days after lansoprazole 15 mg/day was added for dyspepsia, the patient exhibited bilateral palpebral edema with hyperemic conjunctivae and labial edema. The drugs were immediately withdrawn and were restarted five days later, whereupon the symptoms reappeared promptly within 24 hours. The patient was treated with a piperazine antihistamine but subsequently developed mucocutaneous lesions that led to her hospitalization with a diagnosis of Stevens-Johnson syndrome. The patient recovered following discontinuation of the drugs and treatment with methylprednisolone and desloratadine for 30 days. A reintroduction of imatinib at 300 mg/day, along with methylprednisolone and desloratadine, resulted in a third episode of cutaneous adverse reactions when the patient failed to inform her physicians that she had taken a dose of lansoprazole the day before. The drugs were withdrawn and the patient once again recovered. The mechanism of this potential interaction is unknown, but involvement of CYP450 3A4 metabolism is suspected.

MANAGEMENT: Until more data are available, caution is advised if imatinib must be used in combination with 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