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Sulphonamides


   Sulfonamides are a group of man-made (synthetic) medicines that contain the sulfonamide chemical group. They are also called sulfa drugs (sometimes spelled as sulpha drugs or sulphonamides). 
Sulfanilamide was the first sulfonamide developed in 1906, although it was not used as an antimicrobial until the late 1930s. Several thousand other substances have since been developed from sulfanilamide.
Sulfonamide antimicrobials work by interfering with the synthesis of folic acid in bacteria, which is essential for nucleic acid formation and ultimately DNA and RNA.
 People obtain folic acid from their diet but bacteria need to synthesize it. When used alone, sulfonamides antibiotics are bacteriostatic (stop bacteria from reproducing but don't necessarily kill them); however, in combination with trimethoprim (co-trimoxazole), which acts at a different enzyme in the pathway of folic acid synthesis, sulfonamides tend to be bactericidal (kill bacteria). Many sulphonamides are rapidly excreted and very soluble in urine so they are used to treat infections of the urinary tract.
Not all sulfonamides have antibacterial activity. Thiazide diuretics, furosemide, acetazolamide, sulfonylureas and some COX-2 inhibitors are also sulfonamides.

What are the side effects of sulfonamides?

Sulfonamides may cause:
  • dizziness,
  • headache,
  • lethargy,
  • diarrhea,
  • anorexia,
  • nausea,
  • vomiting, and
  • serious skin rashes.
Sulfonamides should be stopped at the first appearance of a skin rash before the rash becomes severe.
Serious rashes include:
  • Stevens-Johnson syndrome, which includes symptoms like:
    • aching joints,
    • aching muscles,
    • redness,
    • blistering, and
    • peeling of the skin
  • Toxic epidermal necrolysis, which includes symptoms like:
    • difficulty in swallowing,
    • peeling,
    • redness,
    • loosening, and
    • blistering of the skin.
Sulfonamides also may cause sensitivity to the sun that leads to extensive sunburn after exposure to sunlight (photosensitivity). Patients receiving sulfonamides should avoid excessive exposure to sunlight and should wear sunscreen.
Other rare side effects include liver damage, low white blood cell count (leucopenia), low platelet count(thrombocytopenia), and anemia. Formation of urinary crystals which may damage the kidney and may cause blood. Adequate hydration is needed to prevent the formation of urinary crystals.
Examples of sulfonamides include:
  • sulfamethoxazole/trimethoprim (Bactrim, Bactrim DS, Septra, Septra DS)
  • sulfasalazine (Azulfidine, Sulfazine)
  • sulfisoxazole (Truxazole)

What drugs interact with sulfonamides?



Sulfonamides can increase the blood-thinning effects of warfarin (Coumadin), possibly leading to abnormal bleeding.
The increased metabolism (break-down and elimination) of cyclosporine by the liver caused by sulfonamides (reduces the effectiveness of cyclosporine and can add to the kidney damage caused by cyclosporine.
All sulfonamides can crystallize in the urine when the urine is acidic. Since methenamine (Hiprex, Urex, Mandelamine) causes acidic urine, it should not be used with sulfonamides.
Blood levels of digoxin may increase blood levels of digoxin (Lanoxin) and possibly lead to serious toxic effects.
Anemia, due to a reduction in folic acid, can occur in persons receiving sulfonamides in combination with divalproex, valproic acid (Depakote, Depakote ER, Depakene, Depacon, Stavzor), methotrexate(Rheumatrex, Trexall), pyrimethamine, triamterene, or trimetrexate.
Increased blood levels of potassium may occur when sulfamethoxazole/trimethoprim is combined with angiotensin converting enzyme (ACE) inhibitors.


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