Sulfonamides (Bactrim/Septra) (TMP/SMX)


  • Sulfonamides are Folic Acid Antagonists
  • TMP/SMX (1:5) Ratio
  • Bactrim Tablet= (SMZ=400mg/TMP=80mg)
  • Covers: wide spectrum, Gram+, most Gram-
  • Shortage of IV formulation in U.S. so use PO if possible
  • Used for: Community-acquired MRSA skin infections, UTI’s, Nocardiosis, Pneumonia, Sinusitis, Listeria infections, Salmonella infections, Traveler’s diarrhea, acute bronchitis, otitis media and more
  • Sulfamethoxazole is combined with Trimethoprim (TMP/SMX) for its synergistic effect
  • Sulfonamide allergy (Sulfa allergy) is common
  • TMP/SMX should be used with caution in patients with impaired renal or liver function & patients with chronic folate deficiency
  • Do not use in pregnant women because TMP/SMX may interfere with folic acid metabolism
  • Patients should be instructed to drink one 8-ounce glass of water with each dose several times a day to prevent crystalluria
  • Patients should avoid prolonged exposure to sunlight because photosensitivity may occur
  • Sulfonamides increase INR in patients on Coumadin (Do not use with Coumadin)
  • Sulfonamides remain a valuable low cost agent for patients


Side Effects

  • Crystalline aggregates in urine
  • Hepatitis
  • Photosensitivity
  • Bone Marrow Toxicity (Hemolytic Anemia)
  • Steven-Johnson Syndrome (SJS)
  • Increases serum creatinine levels
  • Rash, GI irritation
  • hyperkalemia
  • hyperglycemia
  • increases the effects of Coumadin & Phenytoin
  • can cause hemolysis in glucose-6-phosphate dehydrogenase (G6PD)


Adult Dosage

Sulfonamides (Bactrim/Septra) (TMP/SMX)

  • 1tab PO BID (DS, 160mg TMP/800mg SMX)
  • For Travelers’ diarrhea 1tab PO BID DS x 5 days
  • For Pneumocystis prophylaxis 1tab PO Daily
  • Avoid use with coumadin
  • Use renal dosage in renal dysfunction

Peds Dosage

Sulfonamides (Bactrim/Septra) (TMP/SMX)

  • 1ml/kg/day sup PO divided two times per day (up to 20ml PO BID)
  • A poor option for otitis media & sinusitis due to high pneumococcus & H influenza resistance rates
  • Not effective for streptococcal pharyngitis
  • unapproved for community acquired MRSA skin infections in children



♦These dosages are a guide only & must be rechecked♦

This information was obtained from Tarascan Pocket Pharmacopoeia 2014 Deluxe Lab-Coat Edition p. 89-90♦