[Tetracyclines, sulfonamides, and metronidazole]

Tetracyclines, whether natural or semisynthetic, act by inhibiting bacterial protein synthesis. These antibiotics are bacteriostatic and have a broad spectrum of activity. In the past, tetracyclines were discredited because of the high prevalence of isolates with acquired resistance, but they are now regaining status because of the incorporation of new, more active components. Doxycycline is currently the most commonly used tetracycline and is considered an essential drug by the World Health Organization. Tigecycline, a third-generation tetracycline, has a broader spectrum of activity and is an alternative option for the treatment of complicated infections by multiresistant organisms. Sulfonamides are synthetic, broad-spectrum bacteriostatic antibiotics. Because of associated toxicity and high rates of resistance, their use is now very limited. Metronidazole is the most important member of the 5-nitroimidazole family. It has high bactericidal activity against anaerobic bacteria, some microaerophilic bacteria and protozoa, and remains very useful in the treatment of bacterial and parasitic infections.