Sulfonamides

Sulfonamides

Sulfonamides were the first effective systemic antibacterialdrugs. They include:

·                 co-trimoxazole (sulfamethoxazole and trimethoprim)

·                 sulfadiazine.

Pharmacokinetics

Most sulfonamides are well absorbed and widely distributed in the body. They’re metabolized in the liver to inactive metabolites and excreted by the kidneys.

Lots and lots and lots of liquid

Because crystalluria and subsequent kidney stone formation may occur during the metabolic excretory phase, adequate fluid intake is highly recommended during sulfonamide therapy. The patient taking oral sulfonamides should take the medication with 8 oz of water and should drink plenty of fluids throughout therapy (2 to 3 L daily).

Pharmacodynamics

Sulfonamides are bacteriostatic drugs that prevent the growth of microorganisms by inhibiting folic acid production. The decreased folic acid synthesis decreases the number of bacterial nucleotides and inhibits bacterial growth.

Pharmacotherapeutics

Sulfonamides are commonly used to treat acute UTIs. With recur-rent or chronic UTIs, the infecting organism may not be suscepti-ble to sulfonamides. Therefore, the choice of therapy should be based on bacteria susceptibility tests.

Infectious behavior

Sulfonamides also are used to treat infections caused by Nocardiaasteroides and Toxoplasma gondii. Co-trimoxazole (a combina-tion of a sulfa drug and a folate antagonist) is used for a variety of other infections, such as Pneumocystis carinii (Pneumocystisjiroveci) pneumonia, acute otitis media (due to H. influenzae and S. pneumoniae), and acute exacerbations of chronic bronchitis(due to H. influenzae and S. pneumoniae). Sulfonamides exhibit a wide spectrum of activity against gram-positive and gram-nega-tive bacteria.

Drug interactions

Sulfonamides have few significant interactions.

§    They increase the hypoglycemic effects of the sulfonylureas (oral antidiabetic drugs), which may decrease blood glucose lev-els.

§    When taken with methenamine, they may lead to the develop-ment of crystals in urine.

§    Co-trimoxazole may increase the anticoagulant effect of coumarin anticoagulants.

§    Co-timoxazole and methotrexate may cause increased methotrexate levels and increase the risk of toxicity.

§    Co-trimoxazole plus cyclosporine increases the risk of kidney toxicity. (See Adverse reactions to sulfonamides.)