What Is Bactrim?
Bactrim® (sulfamethoxazole-trimethoprim) is an antibiotic that treats bacterial infections, including urinary tract infections, ear infections, bronchitis, traveler’s diarrhea, and certain types of pneumonia. It combines two medicines that work together to stop bacteria from growing.
Who Should Not Take Bactrim
Tell your doctor if you:
- Are allergic to sulfa drugs or any antibiotics
- Are pregnant (especially the last 3 months) or breastfeeding
- Have severe kidney or liver disease
- Have low blood counts or anemia
- Take blood thinners (warfarin)
- Have G6PD deficiency
How to Take Bactrim
- Timing: Take every 12 hours (twice daily) at the same time each day.
- With food: Can be taken with or without food. Take with food if it upsets your stomach.
- Complete course: Finish ALL medication, even if you feel better after a few days.
- Fluids: This is important: drink a full, standard glass of water (8 oz) with each dose, and 8–10 glasses daily. Not doing so can cause kidney problems and painful urine crystals in the long term.
Most Common Side Effects
- Nausea, vomiting, loss of appetite
- Diarrhea
- Dizziness or headache
- Mild skin rash
Stop Taking and Seek Emergency Care If You Develop
- Severe skin rash, blistering, or peeling skin
- Hives, itching, or swelling of the face/throat
- Difficulty breathing or swallowing
- Fever with sore throat or mouth sores
- Unusual bruising or bleeding
- Severe diarrhea (watery or bloody)
- Yellowing of skin or eyes (jaundice)
- Dark urine or pale stools
- Severe fatigue or weakness
What to Avoid While Taking Bactrim
- Prolonged sun exposure or tanning beds. Bactrim makes your skin more sensitive to sunlight. Use sunscreen (SPF 30+), wear protective clothing, and avoid tanning beds while taking this medication and for several days after finishing.
- Alcohol (may worsen side effects)
- Excessive potassium (avoid salt substitutes with potassium)
- Also avoid multivitamins high in potassium or other potassium supplements
Missed Dose
Take the missed dose as soon as you remember. If it’s almost time for your next dose, skip the missed dose. Do NOT double the dose.
When to Contact Your Doctor
Call your healthcare provider if you experience:
- Any new or worsening symptoms
- Symptoms not improving after 2–3 days
- New fever or persistent fever
- Persistent nausea, vomiting, or diarrhea
- Signs of low blood sugar (shaking, sweating, confusion) if diabetic
- Increased bruising or bleeding
- Joint pain or muscle aches
Special Considerations
For diabetics: Bactrim can cause low blood sugar. Monitor your blood glucose more frequently and report any unusual readings to your doctor.
For those on blood thinners: Bactrim increases the effect of warfarin. Your doctor may need to check your INR/bleeding times more often.
Birth control: Bactrim may reduce the effectiveness of hormonal contraceptives. Use additional barrier methods during treatment.
Have questions about Bactrim, or want me to take a look at what’s going on? You can book online or call the office at 423-528-8833. This page is for general education, not a substitute for a personal exam.