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Clinician’s Corner: Sulfonamides

Sulfonamide mechanism:

  • Sulfa drugs block the formation of folic acid that bacteria need to survive. Humans however get their folic acid from food sources.

Most common Drugs & dosage of this class

Septra SS, Septra DS, Bactrim SS, Bactrim DS are most commonly used.

5:1 ratio SMX to TMP

  • Double strength: 800mg sulfamethoxazole +160mg trimethoprim
  • Single strength: 400mg sulfamethoxazole + 80mg
  • Suspension: 200mg sulfamethoxazole + 40mg per teaspoonful

Sulfa drugs are used for:

  • Urinary Tract Infections caused by E.coli.
  • Certain pneumonias in HIV patients (PCP pneumonia
  • Also, for post-transplant antibiotic prevention of PCP pneumonia
  • Methicillin resistant Staph aureus (Community acquired MRSA)
  • Upper Respiratory Infections, Acute bronchitis
  • Second line treatment for ear infections
  • Lice- the combination of topical permethrin (Nix®) and oral (TMP/SMX) was a better second line treatment for head lice infestation than was Nix alone. Monitor for adverse effects

Warnings/Precautions: sulfonamides cause more allergic reactions than the other antibiotics.

About 3%- 4% of patients develop allergic reactions to sulfonamide antibiotics, also popularly known as “sulfa” antibiotics.

  • Might see cross-over allergies to certain diuretics, diabetes pills like Glipizide, arthritis treatments like celecoxib (Celebrex) and others. Be sure to tell your Thompson Pharmacist is you have had a SEVERE allergic reaction to sulfa antibiotics.  It is rare to see such cross-over allergy, but it is best to be informed to watch out for signs and symptoms of allergy reactions.

Pregnancy Category-C:

  • Avoid in the first trimester of pregnancy since trimethoprim is a folic acid antagonist, and may have an association with folate-sensitive birth defects
  • Avoid at term. Can cause jaundice, anemia and liver issues. Both sulfa and trimethoprim easily cross placenta. Premature infants and infants with hyperbilirubinemia.

Glucose-phosphate dehydrogenase deficiency: Any patient with G-6-PD (glucose-6- phosphate dehydrogenase) deficiency is at increased risk for adverse effects.  Inform your Thompson Pharmacist if you have been diagnosed with G6PD deficiency.  It is more commonly seen in patients from Middle East descent.

Side effects:

Increase sunburn (wear sunscreen!)

GI upset including Nausea, Vomiting, Diarrhea

Crystal formation in kidney, especially if dehydrated— encourage patient to drink plenty of fluids.

Drug Interactions: (Sulfa drugs)

Warfarin: may prolong prothrombin time—significant drug interaction (increasing warfarin effect)

Potassium: may cause elevated potassium (hyperkalemia):

Drug Monitoring:

Watch for blood cell changes.

Don’t take if you have G-6-PD deficiency

Watch for allergic reactions

Adjust dose for significantly reduced kidney function.

Patient Education:

Take full course of therapy.  Drink large glass of water with each dose.

Your Thompson Pharmacist wants you to get the most out of your antibiotic therapy.  Sulfa drugs have been around almost 90 years and we have a lot of experience with them.  Allergic problems are rare but can be devastating.  Be sure to share any information with your Thompson Pharmacist to monitor for drug interactions with sulfa drugs.  Go Ahead and ASK…at Thompson Pharmacy It’s ALL for YOU!!