How to know if i have a reaction to bactrim (sulfamethoxazole and trimethoprim)?

Bactrim (sulfamethoxazole and trimethoprim): Intolerance or true allergy to an antibiotic will usually be fairly apparent. If you have some new symptoms that began with the antibiotic, but find them mild, e.g. some mild nausea, that would be a mild intolerance. If you have severe problems, or break out in a rash, have fevers, those suggest an allergic reaction and the drug should be stopped.