Drug Interaction Report

MONITOR: Nonsteroidal anti-inflammatory drugs (NSAIDs) may attenuate the antihypertensive effect of beta-blockers. The proposed mechanism is NSAID-induced inhibition of renal prostaglandin synthesis, which results in unopposed pressor activity producing hypertension. In addition, NSAIDs can cause fluid retention, which also affects blood pressure. Indomethacin and piroxicam have been reported to have greater attenuating effects than other NSAIDs, and indomethacin effects may be significant in patients with eclampsia.

MANAGEMENT: Patients receiving a beta-blocker who require prolonged (greater than 1 week) concomitant therapy with an NSAID should have blood pressure monitored more closely following initiation, discontinuation, or change of dosage of the NSAID. The interaction is not expected to occur with low doses (e.g., low-dose aspirin) or intermittent short-term administration of NSAIDs.

ADJUST DOSING INTERVAL: The bioavailability of metoprolol may be enhanced by food.

MANAGEMENT: Patients may be instructed to take metoprolol at the same time each day, preferably with or immediately following meals.

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.