Drug Interactions between Aspirin Buffered and Inderide LA

MONITOR: Although they are often combined in clinical practice, diuretics and beta-blockers may increase the risk of hyperglycemia and hypertriglyceridemia in some patients, especially in patients with diabetes or latent diabetes. In addition, the risk of QT interval prolongation and arrhythmias (e.g. torsades de pointes) due to sotalol may be increased by potassium-depleting diuretics.

MANAGEMENT: Monitoring of serum potassium levels, blood pressure, and blood glucose is recommended during coadministration. Patients should be advised to seek medical assistance if they experience dizziness, weakness, fainting, fast or irregular heartbeats, or loss of blood glucose control.

ADJUST DOSING INTERVAL: Concurrent administration with calcium salts may decrease the oral bioavailability of atenolol and possibly other beta-blockers. The exact mechanism of interaction is unknown. In six healthy subjects, calcium 500 mg (as lactate, carbonate, and gluconate) reduced the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of atenolol (100 mg) by 51% and 32%, respectively. The elimination half-life increased by 44%. Twelve hours after the combination, beta-blocking activity (as indicated by inhibition of exercise tachycardia) was reduced compared to that with atenolol alone. However, during a 4-week treatment in six hypertensive patients, there was no difference in blood pressure values between treatments. The investigators suggest that prolongation of the elimination half-life induced by calcium coadministration may have led to atenolol cumulation during long-term dosing, which compensated for the reduced bioavailability.

MANAGEMENT: It may help to separate the administration times of beta-blockers and calcium products by at least 2 hours. Patients should be monitored for potentially diminished beta-blocking effects following the addition of calcium therapy.

MONITOR: Concomitant use of nonsteroidal anti-inflammatory drugs (NSAIDs) and diuretics may adversely affect renal function due to NSAID inhibition of the renal synthesis of prostaglandins that help maintain renal perfusion in dehydrated states. The risk may be increased in patients on dietary sodium restriction. At the same time, hypotensive effect of the diuretics may be reduced because inhibition of prostaglandins can lead to unopposed pressor activity and, consequently, elevation in blood pressure. Natriuretic and diuretic effects may also be reduced, as NSAIDs have been reported to cause sodium and water retention, which may account for the increased risk of congestive heart failure associated with the combination. One study showed an increase in the incidence density of congestive heart failure (in patients over 55 years of age) from 9.3 per 1,000 person-years in patients on diuretics to 23.3 per 1,000 person-years in patients on both diuretic and NSAID therapy. NSAIDs may also increase the risk of hyperkalemia associated with potassium-sparing diuretics.

MANAGEMENT: In patients receiving both diuretic and NSAID therapy, management consists of avoiding dehydration and carefully monitoring the patient's renal function and blood pressure. If renal insufficiency or hyperkalemia develops, both drugs should be discontinued until the condition is corrected.

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.

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.

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.

MONITOR: Coadministration of thiazide diuretics with high dosages of calcium and/or vitamin D has been associated with reports of hypercalcemia in some patients. Thiazide diuretics inhibit the renal excretion of calcium and may also enhance responsiveness of bone and renal tubule to parathyroid hormone, thus concurrent use of large amounts of calcium or vitamin D can lead to excessively high plasma levels of calcium. Patients who are particularly susceptible include those with hyperparathyroidism, those being treated for osteoporosis, and those receiving high dosages of vitamin D for hypoparathyroidism. Metabolic alkalosis and the milk-alkali syndrome have been reported during prolonged therapy with thiazide diuretics and calcium.

MANAGEMENT: Patients receiving thiazide diuretic therapy should be cautioned against self-treatment with calcium and vitamin D supplements without first talking to their healthcare provider. Serum calcium should be monitored if thiazide diuretics are coadministered with high dosages of calcium and/or vitamin D. Patients should be advised to seek medical attention if they experience signs and symptoms of hypercalcemia such as dizziness, weakness, lethargy, headache, myalgia, anorexia, nausea, vomiting, and seizures.

MONITOR: The chronic use or abuse of laxatives may potentiate the pharmacologic effects of diuretics. Laxatives can cause significant losses of fluid and electrolytes, including sodium, potassium, magnesium and zinc, and these effects may be additive to those of diuretics.

MANAGEMENT: In general, laxatives should only be used on a short-term, intermittent basis in recommended dosages. During concomitant use with diuretics, patients should be advised to contact their physician if they experience signs and symptoms of fluid and electrolyte depletion such as dizziness, lightheadedness, dry mouth, thirst, fatigue, weakness, lethargy, muscle cramps, decreased urination, postural hypotension, and tachycardia. If maintenance of bowel regularity is required, patients should be advised to exercise and increase fiber in the diet and/or consider the use of bulk-forming laxatives.

High doses of salicylates may blunt the antihypertensive effects of beta-blockers. The proposed mechanism is inhibition of prostaglandin synthesis. Low-dose aspirin does not appear to affect blood pressure. In addition, beta-blockers may exert an antiplatelet effect, which may be additive with the effects of some salicylates. Metoprolol may also increase aspirin absorption and/or plasma concentrations of salicylates; however, the clinical significance of this effect is unknown. Data have been conflicting. Until more information is available, patients who require concomitant therapy should be monitored for altered antihypertensive response whenever a salicylate is introduced or discontinued, or when its dosage is modified.

Concurrent administration with aluminum and magnesium antacids has been shown to decrease the oral bioavailability of certain beta-blockers, although data are conflicting. The exact mechanism of interaction is unknown but may involve cation binding of beta-blockers or a reduction in the dissolution rate due to increased gastric pH. In six healthy volunteers, concomitant administration of a single dose of antacid (magnesium hydroxide-aluminum oxide 1200 mg-1800 mg) reduced the peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and 24-hour urinary excretion of sotalol (160 mg) by 27%, 21% and 9%, respectively, while administration of the antacid 2 hours after the sotalol dose produced no change. Pharmacodynamic data suggest that the negative chronotropic effect of sotalol was also reduced up to 4 hours after administration of the combination, although the lack of a placebo control might have confounded the results. In another study, concomitant administration of an aluminum hydroxide antacid in six healthy volunteers decreased atenolol (100 mg) Cmax and AUC by 37% and 33%, respectively. However, the Cmax and AUC of metoprolol (100 mg) in the same group was increased 25% and 11%, respectively, by administration of the antacid. Two other studies with aluminum hydroxide failed to find a significant effect on pharmacokinetics or pharmacodynamics of atenolol and propranolol. Based on available data, the clinical significance of this potential interaction is difficult to determine. As a precaution, patients may want to consider separating the administration times of beta-blockers and antacids or other aluminum- or magnesium-containing products by at least 2 hours.

Concurrent administration with aluminum and magnesium antacids has been shown to decrease the oral bioavailability of certain beta-blockers, although data are conflicting. The exact mechanism of interaction is unknown but may involve cation binding of beta-blockers or a reduction in the dissolution rate due to increased gastric pH. In six healthy volunteers, concomitant administration of a single dose of antacid (magnesium hydroxide-aluminum oxide 1200 mg-1800 mg) reduced the peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and 24-hour urinary excretion of sotalol (160 mg) by 27%, 21% and 9%, respectively, while administration of the antacid 2 hours after the sotalol dose produced no change. Pharmacodynamic data suggest that the negative chronotropic effect of sotalol was also reduced up to 4 hours after administration of the combination, although the lack of a placebo control might have confounded the results. In another study, concomitant administration of an aluminum hydroxide antacid in six healthy volunteers decreased atenolol (100 mg) Cmax and AUC by 37% and 33%, respectively. However, the Cmax and AUC of metoprolol (100 mg) in the same group was increased 25% and 11%, respectively, by administration of the antacid. Two other studies with aluminum hydroxide failed to find a significant effect on pharmacokinetics or pharmacodynamics of atenolol and propranolol. Based on available data, the clinical significance of this potential interaction is difficult to determine. As a precaution, patients may want to consider separating the administration times of beta-blockers and antacids or other aluminum- or magnesium-containing products by at least 2 hours.