The most common side effects of sulfamethoxazole/trimethoprim (generic Bactrim) include nausea, vomiting, and loss of appetite. Seek medical attention right away if you experience any of the following symptoms while taking sulfamethoxazole/trimethoprim:
- sore throat
- fever or chills
- severe diarrhea (watery or bloody stools) that may occur with or without fever and stomach cramps (may occur up to 2 months or more after your treatment)
- shortness of breath
- unusual bruising or bleeding
- yellowing of the skin or eyes
- red or purple skin discolorations
- joint or muscle pain
This is not a complete list of adverse effects. Call your health care provider if symptoms are persistent or severe.
As with all prescription medication, be sure to inform the prescribing doctor about any medical conditions you have been previously diagnosed with, as well as any medication/ supplements you are currently taking before starting treatment with sulfamethoxazole/trimethoprim. Sulfamethoxazole/trimethoprim can interact with other forms of medication and substances, causing potentially serious side effects or life-threatening allergic reactions. Drug interactions can occur with other antibiotics, blood thinners such as warfarin, certain retinoids, penicillin, and proton pump inhibitors among others.
If you have phenylketonuria (PKU), be sure to tell your doctor; sulfamethoxazole/trimethoprim chewable tablets are sweetened with aspartame, which can be extremely dangerous to patients with PKU.
Sulfonamide antibiotics can cause folate deficiencies (they prevent certain cells from creating folic acid), so be sure to talk to your doctor if you’ve ever had low folic acid levels.
In addition, let your doctor know if you are breastfeeding, pregnant or plan on becoming pregnant before starting treatment with this medication.