Sulfonamides are derivatives of para-aminobenzenesulfonamide (sulfanilamide); the structures of selected members are shown in Figure 43-1. Most are relatively insoluble in water, but their sodium salts are readily soluble. The minimal structural prerequisites for antibacterial action are embodied in sulfanilamide itself. The sulfur must be linked directly to the benzene ring. The para-NH2 group (the N of which is designated N4) can be replaced only by moieties that can be converted in vivo to a free amino group. Substitutions in the amide NH2 group (N1) have variable effects on antibacterial activity of the molecule, but substitution of heterocyclic aromatic nuclei at N1 yields highly potent compounds.
Sulfonamides have wide antimicrobial activity, but their usefulness has diminished as resistant strains have emerged. These drugs are bacteriostatic, and host defenses are essential for eradication of the infection.
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