👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Pharmacological Therapies🔖 Free to read, print, and share
Also known as: sulfamethoxazole-trimethoprim · Bactrim · Septra · TMP-SMX · sulfa drugs
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Use this quick-reference guide to spot, treat, and prevent Sulfonamides on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
📌 Use
UTI, PCP → Bactrim (TMP-SMX)
Blocks folic acid synth
🚩 Danger
Stevens-Johnson syndrome (rash)
Crystalluria → kidney stones
Avoid pregnancy, sulfa allergy
✅ Do
Push fluids → 8 glasses/day
Sunscreen → photosensitive
🚩 Report
Any rash → stop, call provider
↓urine, sore throat, fever
📚 Sulfonamides — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Sulfonamides are bacteriostatic antibiotics, most commonly trimethoprim-sulfamethoxazole, used for UTIs, Pneumocystis pneumonia, and some MRSA skin infections. They are notable for causing severe skin reactions like Stevens-Johnson syndrome and for hyperkalemia. The key principle is high fluid intake and watching for rash and hyperkalemia.
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Key points
Understand these first
Sulfonamides are bacteriostatic and inhibit folic acid synthesis in bacteria.
They can cause Stevens-Johnson syndrome and other severe hypersensitivity skin reactions.
They cause crystalluria, so adequate fluid intake is essential.
Trimethoprim-sulfamethoxazole can cause hyperkalemia, especially with ACE inhibitors or potassium supplements.
They potentiate warfarin, sulfonylureas, and phenytoin, increasing the risk of bleeding and hypoglycemia.
They are avoided near term in pregnancy and in newborns because of kernicterus risk.
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Nursing priorities
What to do, in order
Screen for sulfa allergy before giving and assess for prior reactions.
Encourage at least 2 to 3 liters of fluid per day to prevent crystalluria.
Inspect the skin and stop the drug at the first sign of rash.
Monitor potassium and INR in at-risk patients.
Monitor blood glucose in diabetics taking sulfonylureas.
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Red flags — report now
Escalate immediately
A spreading rash, blistering, or mucosal involvement may be Stevens-Johnson syndrome - stop the drug and report immediately.
Signs of hyperkalemia such as muscle weakness or arrhythmia must be reported.
Sore throat, fever, or unusual bruising may signal blood dyscrasia and must be reported.
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Labs & values
Numbers to know
Potassium 3.5-5.0 mEq/L (watch for hyperkalemia)
INR 0.8-1.1 (rises with concurrent warfarin)
WBC 5,000-10,000/mm3 (monitor for bone marrow suppression)
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Patient teaching
What patients must know
Drink plenty of water throughout the day to protect your kidneys.
Stop the drug and call your provider at the first sign of a rash or mouth sores.
Use sunscreen because of photosensitivity.
Report fever, sore throat, or easy bruising.
❓ Sulfonamides: NCLEX FAQs
What are the priority nursing interventions for Sulfonamides?
Screen for sulfa allergy before giving and assess for prior reactions. Encourage at least 2 to 3 liters of fluid per day to prevent crystalluria. Inspect the skin and stop the drug at the first sign of rash. Monitor potassium and INR in at-risk patients.
What are the warning signs of Sulfonamides a nurse must report?
A spreading rash, blistering, or mucosal involvement may be Stevens-Johnson syndrome - stop the drug and report immediately. Signs of hyperkalemia such as muscle weakness or arrhythmia must be reported. Sore throat, fever, or unusual bruising may signal blood dyscrasia and must be reported.
What do I need to know about Sulfonamides for the NCLEX?
Sulfonamides are bacteriostatic and inhibit folic acid synthesis in bacteria. They can cause Stevens-Johnson syndrome and other severe hypersensitivity skin reactions. They cause crystalluria, so adequate fluid intake is essential. Trimethoprim-sulfamethoxazole can cause hyperkalemia, especially with ACE inhibitors or potassium supplements.
What patient teaching is important for Sulfonamides?
Drink plenty of water throughout the day to protect your kidneys. Stop the drug and call your provider at the first sign of a rash or mouth sores. Use sunscreen because of photosensitivity. Report fever, sore throat, or easy bruising.
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Quick Tip
Sulfonamides are bacteriostatic and inhibit folic acid synthesis in bacteria.