Drug Interaction Report

Coadministration with antacids may decrease the oral bioavailability of captopril and other angiotensin converting enzyme (ACE) inhibitors due to delayed gastric emptying and/or elevated gastric pH. In 10 healthy volunteers, 50 mL of an antacid suspension decreased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of captopril (50 mg single oral dose) by 50% and 42%, respectively, compared to administration after fasting. The relative bioavailability of captopril was 0.66 with antacid, although its hypotensive activity did not seem to be affected. Based on available data, the clinical significance of this interaction appears to be minor. As a precaution, patients may want to consider separating the administration times of ACE inhibitors and antacids or oral medications that contain antacids (e.g., didanosine buffered tablets or pediatric oral solution) by 1 to 2 hours.

ADJUST DOSING INTERVAL: Administration with food may increase the absorption of calcium. However, foods high in oxalic acid (spinach or rhubarb), or phytic acid (bran and whole grains) may decrease calcium absorption.

MANAGEMENT: Calcium may be administered with food to increase absorption. Consider withholding calcium administration for at least 2 hours before or after consuming foods high in oxalic acid or phytic acid.

ADJUST DOSING INTERVAL: Bulk-forming laxatives such as guar gum, psyllium, polycarbophil, or methylcellulose may affect the bioavailability of concomitantly administered substances due to their effect on the rate of gastrointestinal transit and gastric emptying.

MANAGEMENT: In general, oral medications should be administered at least 2 hours before or 2 hours after dosing of the bulk-forming laxative.

GENERALLY AVOID: Moderate-to-high dietary intake of potassium can cause hyperkalemia in some patients who are using angiotensin converting enzyme (ACE) inhibitors. In some cases, affected patients were using a potassium-rich salt substitute. ACE inhibitors can promote hyperkalemia through inhibition of the renin-aldosterone-angiotensin (RAA) system.

MANAGEMENT: It is recommended that patients who are taking ACE inhibitors be advised to avoid moderately high or high potassium dietary intake. Particular attention should be paid to the potassium content of salt substitutes.