Sulfonamides

Summary

Sulfonamides, also called sulfa drugs, are easily recognized because they start with “sulfa-”. Sulfonamides are antibiotics that treat a wide variety of bacterial infections. Sulfa allergies are quite common, and it’s important to remember that there is a cross-sensitivity between other sulfa-derivative drugs like sulfonylureas and thiazide diuretics. One side effect is crystalluria, so it’s important that the patient stays well-hydrated to avoid kidney damage. Sulfonamides can also cause photosensitivity, so advise the patient to wear sunscreen and avoid direct sunlight. Sulfonamides may cause a folate deficiency, so there’s a chance that the patient will also be prescribed a folic acid supplementation. Sulfonamides are teratogenic and should not be taken by pregnant women.

Key Points

• Sulfonamides
  • Key Drugs (Sulfa-)
    • Do not confuse with sulfonylureas - drug class used to treat type II diabetes (e.g. glipizide, glyburide). They are also a sulfa- derivative, but are used for a different purpose.
    • Sulfamethoxazole (SMX)
      • Often combined with another antibacterial agent, trimethoprim (TMP) into TMP-SMX, commonly known as Bactrim
    • Sulfadiazine
    • Sulfasalazine (SSZ) - used as an auto-immune drug
  • Mechanism
    • Antibiotic
      • Inhibit synthesis of folic acid, an essential component of bacterial growth
      • Bacteriostatic
  • Clinical Use
    • Bacterial Infections
      • Urinary tract infections
      • Ear infections
      • Meningococcal meningitis
      • E. coli
      • MRSA
      • Used as an alternative for patients allergic to penicillin
  • Side Effects and Adverse Reactions
    • Hypersensitivity/Allergy
      • Cross-allergenicity with other sulfa drugs (e.g. sulfonylureas and thiazide diuretics)
    • Crystalluria
      • Crystallization in the urine
      • Can cause kidney injury
      • Increase fluid intake to maintain adequate urine output
        • Ideally, patient should be consuming at least 2,000 mL/day
        • Increased hydration reduces the risk of crystal formation
    • Photosensitivity
      • Avoid direct sunlight, wear sunscreen and protective clothing during sun exposure
      • May escalate into Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis
        • If rash presents, patient should stop taking medication and it should be reported immediately to the provider
    • Folate deficiency
      • Folic acid supplementation may be needed
    • Teratogenic
      • Should be avoided in pregnancy
      • Can cause neural tube defects and infantile kernicterus, especially if taken in the 3rd trimester
    • Red-orange discoloration of body fluids
    • Anemia, agranulocytosis, low platelet count
      • Due to a reduction in folic acid
      • Report bruising, bleeding, petechial rash
    • Hemolysis is especially common in G6PD deficiency
    • Superinfection
      • e.g. C. difficile overgrowth
    • GI disturbances
      • Nausea, vomiting, anorexia