<s>[INST] context: METRONIDAZOLE It is the prototype nitroimidazole introduced in 1959 for trichomoniasis and later found to be a highly active amoebicide. It has broad-spectrum cidal activity against protozoa, including Giardia Iamblia in addition to the above two. Many anaerobic bacteria, such as Bact. fragilis, Fusobacterium, Clostridium perfringens, Cl. difficile, Helicobacter pylori, Campylobacter, peptococci, spirochetes and anaerobic Streptococci are sensitive. Though, it does not directly inhibit the helminth Dracunculus medinensis, extraction of the worm from under the skin is facilitated. Metronidazole does not affect aerobic bacteria. Clinically significant resistance has not developed among E. histolytica, but decreased responsiveness of T. vaginalis has been observed in some areas. Anaerobic bacteria and G. Iamblia also can develop metronidazole resistance, but this is a clinical problem only in the case of H. pylori. Uses 1 . Amoebiasis: Metronidazole is a first line drug for all forms of amoebic infection. Many dosageregimens have been tried; the current recommendations are: For invasive dysentery and liver abscess-800 mg TDS (children 30- 50 mg/kg/day) for 7- 10 days. In serious cases of liver abscess 1 g may be infused i.v. slowly followed by 0.5 g every 8-12 hr till oral therapy is instituted. For mild intestinal diseas [/INST] question: Drug of choice for antibiotic associated pseudomembranous colitis is? | options: A: Oral vancomycin B: Metronidazole C: Clindamycin D: Penicillin G | answer: B </s>