It is not metoprolol and bactrim that is the problematic interaction.
Amiodarone has a "serious" interaction with both components of bactrim [trimetoprim and sulfamethoxazole] and the official recommendation is to pick an alternative.
This is according to pharmacologic data bases.
I would not make light of this, and talk with your doctor immediately, before your next dose.
The interaction can increase the qt interval, which can in some cases be life threatening.
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