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The vast majority of people will do fine if a single extra dose of metoprolol is taken. The potential concern would be for someone that is already having a heart rate that is on the low end of normal, as the extra dose may be sufficient to cause the heart rate to lower further. Many people do not check their heart rate before taking the pill, so we usually are guided by the current status of the patient.
If she or you can monitor her heart rate or pulse, then there would only be a concern if the heart rate drops below 50. If the heart rate cannot be monitored, then she should only be concerned if she develops any lightheadedness or dizziness. It also would be reasonable for her to be drinking plenty of fluids to assure that she is staying hydrated.
If I can provide any clarification, please let me know.
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