Sulfonamides
Sulfonamides were the first effective systemic
antibacterialdrugs. They include:
·
co-trimoxazole (sulfamethoxazole and trimethoprim)
·
sulfadiazine.
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.
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).
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.
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.
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.
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.)
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