Expert: Charles Cusumano, FMP, PA-C - 5/9/2009

Question
I currently take atenolol 25 mg daily.  I am interested in taking calcium as well as magnesium too.

When I researched online I found an interaction between the atenolol and calcium.  This is what I got:
    "atenolol and calcium citrate (Moderate Drug-Drug)
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."

What I need to know is, if I take the atenolol at 8pm at night, and take the calcium citrate at 8 am in the morning, am I at risk for interactions?  Or would enough time have passed to make it safe?  

Answer
Hi Shawn,
Calcium blocks the absorbtion of atenolol. I wouldn’t take either calcium or magnesium unless you discuss this with your doctor first and determine a real need. Supplements such as these are not always necessary and in some cases can cause toxicity.