Although these drugs are no longer used to treat meningitis, CSF levels are high in meningeal infections. Their antibacterial action is inhibited by pus. The sulfonamides are metabolized mainly by the liver to acetylated forms and glucuronides, both of which are therapeutically inactive. Excretion is primarily renal by glomerular filtration with minimal tubular secretion or reabsorption. When these drugs are given in pregnancy, high levels are achieved in the fetus.
Sulfonamides are loosely and reversibly bound in varying degrees to serum albumin.
Since the bound sulfonamide is inactive and nondiffusible, the degree of binding can affect antibacterial effectiveness, distribution, and excretion. The relative insolubility of most sulfonamides, especially their acetylated metabolites, may cause precipitation in the renal tubules. The more soluble analogs, such as sulfisoxazole and sulfamethoxazole, should generally be chosen, and the patient must be well hydrated. Sulfonamides should not be used in renal insufficiency. Sulfadiazine is used rarely because of crystalluria.