Drug Interactions between aspirin / calcium carbonate and Zinacef

ADJUST DOSING INTERVAL: Coadministration with antacids or agents with acid-neutralizing effects may reduce the oral bioavailability of cefpodoxime proxetil and cefuroxime axetil. The proposed mechanism is a pH-dependent reduction in drug dissolution and absorption. In ten healthy volunteers, 10 mL of magnesium hydroxide-aluminum hydroxide (600 mg-900 mg) administered at 2 hours and at 15 minutes before the ingestion of cefpodoxime proxetil 200 mg led to an approximately 40% reduction in cefpodoxime peak plasma concentration (Cmax) and systemic exposure (AUC) compared to when the antibiotic was administered alone. Similar results were reported with sodium bicarbonate and aluminum hydroxide in another study. Likewise, pretreatment with ranitidine plus sodium bicarbonate decreased the Cmax and AUC of cefuroxime by over 40% in six healthy volunteers. The clinical significance of these effects is unknown, but potentially reduced antibiotic efficacy should be considered.

MANAGEMENT: Until further data are available, patients treated with cefpodoxime proxetil or cefuroxime axetil should avoid taking antacids or oral medications that contain antacids (e.g., didanosine buffered tablets or pediatric oral solution) for at least two hours before and after administration of the antibiotic.

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MONITOR: Chronic administration of antacids may reduce serum salicylate concentrations in patients receiving large doses of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to urinary alkalinization by antacids, resulting in increased renal salicylate clearance. In three children treated with large doses of aspirin for rheumatic fever, serum salicylate levels declined 30% to 70% during coadministration with a magnesium and aluminum hydroxide antacid. Other studies have found similar, albeit less dramatic results. Antacids reportedly have no effect on the oral bioavailability of aspirin in healthy adults. However, administration of antacids containing either aluminum and magnesium hydroxide or calcium carbonate two hours before aspirin dosing led to reduced absorption of aspirin in uremic patients.

MANAGEMENT: Patients treated chronically with antacids (or oral medications that contain antacids such as didanosine buffered tablets or pediatric oral solution) and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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