<prompt> Drug of choice for anaerobic infection isAmphotericin BMetronidazoleAminoglycosideMacrolide  <response>: Ans. is b i.e., Metronidazole Metronidazole is a prototype nitroimidazole which has broad spectrum cidal activity against the anaerobic micro-organisms including giardia lamblia. It doesnt affect the aerobic bacteria. It is selectively toxic to anaerobic and micro-aerophilic micro-organisms. In anerobic conditions, it produces highly cytotoxic nitro radical which is attenuated in aerobic environment. It also induces mutagenesis and cause radiosensitization. Aminoglycosides are active only against aerobes. Amphotericin B is an anti-fungal agent. 