Drug Interactions between I-L-X and Omeclamox-Pak

MONITOR: Inhibitors of the proton pump (PPIs or potassium-competitive acid blockers [PCABs]) may impair the gastrointestinal absorption of nonheme iron, a process that is dependent on an acidic environment. The interaction was suspected in two patients with iron deficiency anemia due to gastrointestinal blood loss that were unresponsive to oral iron replacement therapy, even after the bleeding had apparently stopped. Both patients had been on omeprazole for six months while being treated with ferrous sulfate. An iron-loading test was performed on one of the patients and indicated iron malabsorption. Within two months after discontinuation of omeprazole, notable improvements in hemoglobin level and mean corpuscular volume (MCV) were observed in both patients, and iron absorption was significantly increased in the patient who underwent absorption testing. In a case review of patients with hereditary hemochromatosis treated at one institution, investigators observed a reduced requirement for maintenance phlebotomy in seven patients following initiation of PPI therapy (mean 2.5 L blood removed/year before PPI therapy vs. 0.5 L/year during PPI therapy), presumably due to reduced tissue iron accumulation stemming from impaired absorption of dietary nonheme iron. Mean annual phlebotomy requirement during PPI therapy in these patients was also lower than that in controls who had never taken a PPI (mean 2.3 L blood removed/year). The same group of investigators also studied iron absorption in 14 patients fed an iron-loaded meal before and after PPI therapy for one week. PPI therapy was associated with a 51% reduction in area under the serum iron concentration-time curve (AUC 0 to 4 hours); a 55% reduction in maximum increase of serum iron following ingestion of iron-loaded meal; and a 46% reduction in percent recovery of administered iron at peak serum iron concentration. Interestingly, the interaction has not been reported in healthy, iron-replete individuals. In a study of 109 patients with Zollinger-Ellison syndrome who had not undergone gastric resection, omeprazole treatment for an average of 5.7 years did not significantly decrease body iron stores or cause iron deficiency compared to H2-receptor antagonist therapy or no gastric acid-suppressant treatment. It is possible that the interaction may not affect people with healthy iron stores because of compensation by dietary heme iron, which typically comprises only a small fraction of dietary iron but whose absorption is not dependent on gastrointestinal pH. In contrast, dietary heme iron alone may not be sufficient to restore normal iron balance in patients with anemia or those with defective regulatory mechanisms of iron absorption.

MANAGEMENT: Patients with iron deficiency may not respond adequately to oral iron replacement therapy during coadministration of PPIs or PCABs. If an interaction is suspected after ruling out other causes, it may be appropriate to discontinue the PPI or PCAB or consider administering iron parenterally.

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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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Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.

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