Ask the Pharmacist I was just put on atenolol and my heart rate went down to 45. My physician has now prescribed Lopressor. Aren't both drugs beta blockers? Will I have the same reaction to Lopressor that I did to atenolol?
Lopressor is a brand name of the drug metoprolol. You are correct in thinking that it is a beta blocker like atenolol (brand name - Tenormin).

Beta blockers are drugs that work on the adrenergic nervous system of the body. The terms "sympathetic nervous system" and "fight or flight system” are sometimes used as well. Within the adrenergic system are alpha and beta receptors. Among other things, the beta receptors are important in the regulation of the activities of the heart and lungs.

Beta blockers are often differentiated by their selectivity. Some work at both beta-1 (heart) and beta-2 (lungs) receptors, while others work primarily at the beta-1 receptors (heart). The beta-1 selective agents are sometimes called cardioselective agents.

Both atenolol and metoprolol are beta-1 selective agents that could have profound activity in the heart. They are often used to decrease the blood pressure or the heart rate. They are sometimes used in people who have angina (heart pain brought about by exertion) or after a heart attack. Sometimes they are even used to prevent migraine headaches.

Since the drugs are sometimes used to decrease the heart rate, it is logical to think that a decreased heart rate could be a side effect of the drug. In your case, the heart rate dropped to 45 beats per minute. You did not mention the dose you were using, nor the dose of metoprolol you have been prescribed.

The metoprolol could decrease your heart rate to a level below what you and/or your physician are comfortable with. However, this type of response is usually dependent on the dose being used. My guess is that you are being started on a small dose to see how well you tolerate it. The dose will then be increased slowly to see if it will help the problem without decreasing the heart rate too much. It is quite possible that this can be done even in a patient who did not tolerate atenolol.

Good luck.

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