Sulfonamides

Anti-Infectives

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Examples

trimethoprim-sulfamethoxazole (TMP-SMX, Bactrim)sulfasalazine

Prefix / Suffix: sulfa-

Physiology

Bacteria synthesize folic acid, which is essential for DNA synthesis. Humans get folate from diet.

Mechanism of Action

They inhibit folic acid synthesis in bacteria, blocking DNA synthesis (bacteriostatic).

Indications

UTIs
Pneumocystis pneumonia (PCP)
Otitis media
Traveler's diarrhea

Side Effects / Adverse Effects

Allergic reactions including Stevens-Johnson syndrome (severe skin reaction)
Crystalluria (kidney stones)
Photosensitivity
Hyperkalemia
Blood dyscrasias (anemia, neutropenia)

Contraindications

Sulfa allergy
Pregnancy (especially near term — kernicterus risk)
G6PD deficiency (hemolytic anemia)

Nursing Considerations

Always ask about sulfa allergy before giving
Encourage increased fluid intake — at least 2–3 L/day (prevents crystalluria)
Monitor for rash — stop drug if it appears (Stevens-Johnson risk)
Use sunscreen (photosensitivity)
Monitor CBC and potassium with long-term use

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Disclaimer: PharmPal Nurse is for education only and is not medical advice. Do not use it to diagnose, treat, prescribe, or make patient-care decisions; always verify with current drug references, your instructor, facility policy, and a licensed provider. In emergencies, call local emergency services.