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Sulfamethoxazole/trimethoprim

Brand: Bactrim (Septra discontinued)

Sulfonamide antibioticUsed for: UTI, MRSA infectionsAnti-Infectives

No boxed warning on the current FDA label.

Caution
Severe skin reactions including Stevens-Johnson syndrome; high potassium; contraindicated with sulfonamide allergy.
Pregnancy
Avoid in the first trimester (folate antagonist) and near term (newborn kernicterus).

Common side effects

  • Rash and photosensitivity
  • Nausea
  • Elevated potassium
  • Rarely, severe skin reactions

Key interactions

  • Raises warfarin's effect sharply: INR can climb
  • Raises methotrexate levels
  • Additive potassium rise with ACE inhibitors

Counseling points

  • Drink plenty of fluid
  • Use sun protection
  • Report any new rash immediately
  • The DS tablet is 800 mg/160 mg
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