Brief Answer:
it may or may not be...please see the detailed answer below...

Detailed Answer:
Hello and Welcome to 'Ask A Doctor' service...
I've gone through your query in details...
I can understand your concerns...

Well, please note, although both of them lowers the blood pressure as well as controlling heart rate, to some extent their effects are not similar...

Metoprolol is a relatively newer generation bet blocker and known for its specific effects on the heart on short-term while Atenolol's effects are a bit on the long-term compared to this (however both do reduce the blood pressure quite well)...

However, every individual's bodily response is different. So, in your case, since you've run out of the Metoprolol, I'd recommend not to use Atenolol for more than a dose or two and seek out for a refill of the same (Metoprolol) at the earliest (you can even get it from your nearest urgent care also)...

Let me know if I can assist you further...

Take Care
Kind Regards

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