Sulfonamides

Sulfonamides are substances used mainly to treat urinary tract infections. Today, co-trimoxazole is the most widely used mixture.

Sulfonamides are administered orally and are well absorbed in the GIT. They are metabolised in the liver and excreted by the kidneys. We must check the patient’s pharmacological history before the administration, sulfonamides have numerous drug interactions and must not be administered to pregnant women and children under 2 months of age.

Mechanism of action
Sulfonamides competitively inhibit the synthesis of folic acid, which is a bacterial growth factor. Thus, antibiotics only act on microorganisms that synthesize their own folic acid. Their effect is bacteriostatic to bactericidal.

Spectrum of effect and indications
Sulfonamides have an antibacterial effect on both Gram-positive and Gram-negative bacteria. They are effective against streptococci, hemophilia, actinomycetes, neiseria, chlamydia.

We use sulfonamides in these diseases
 * severe diarrheal infections: typhus, paratyphoid A and B, shigellosis, traveler's diarrhea (Summary of product characteristics)
 * kidney and urinary tract infections, (SPC of the product)
 * respiratory infections – pneumonia and sinusitis, as a second-line drug
 * brucellosis, (SPC of the product)
 * nocardiosis, ulcus molle and granuloma inguinale, which have special dosages. (SPC of the product)

They can be used for prophylaxis and for treatment in pneumocystis pneumonia.

Contraindications and side effects
Side effects include gastrointestinal upset, photosensitization and skin allergies (up to Stevens-Johnson and Lyell's syndrome).


 * bone marrow depression (anemia, leukopenia, thrombocytopenia)

Sulfonamides should not be used by pregnant, lactating women or newborns. Acid urine increases the risk of crystallization in the urinary tract.

Drug interactions
Sulfonamides have numerous drug interactions - especially with warfarin, methotrexate, sulfonylureas (oral antidiabetics).

Individual Antibiotics
This group includes:


 * Sulfisoxazole is used to treat urinary tract infections.
 * Sulfathiazole is indicated for topical therapy.
 * Sulfasalazine is used to treat ulcerative colitis because it is poorly absorbed from the GI trakt.
 * Sulfamethoxazole is typically in combination with trimethoprim, specifically in a 5:1 ratio (sulfamethoxazole:trimethoprim, 5:1). Such a mixture is called cotrimoxazole (also co-trimoxazole), has a bactericidal effect, and is used to treat urinary tract infections.

Mechanism of action: synergistic action of both substances against a number of G + and G− bacteria

Pharmacokinetics: Trimethoprim is well absorbed after p.o. administration, penetrates well into body fluids and tissues, is excreted by the kidneys. Sulfamethoxazole is also well absorbed after p.o. administration, penetrates well into tissues, is excreted by the kidneys, where significant tubular reabsorption occurs. It penetrates the placenta and into the milk.

Side effects: nausea, vomiting, dizziness, headache, skin allergies, changes in blood counts.

Indications: upper and lower respiratory tract infections, ENT infections, urinary tract infections, gonorrhea and typhoid treatment. Therapy and prophylaxis of Pneumocystis carini

Contraindications: disorders of hematopoiesis and renal function

Related Articles

 * Antibiotics
 * Quinolones