<s>[INST] context: Erythromycin is not effective against H pylori The agents used with the greatest frequency include amoxicillin, metronidazole, and tetracycline, clarithromycin, and bismuth compounds. Multiple drugs have been evaluated in the therapy of H. pylori. No single agent is effective in eradicating the organism. Combination therapy for 14 days provides the greatest efficacy. A shoer course administration (7-10 days), although attractive, has not proved as successful as the 14-days regimens. Regimens Recommended for Eradication of H pylori Infection Drug Dose Triple Therapy 1. Bismuth subsalicylate plus Metronidazole plus Tetracycline 2 tablets qid 250 mg qid 500 mg qid 2. Ranitidine bismuth citrate plus Tetracycline plus Clarithromycin or metronidazole 400 mg qid 500 mg qid 500 mg qid 3. Omeprazole(Lansoprazole) plus Clarithromycin plus Metronidazole or Amoxicillin 20 mg bid (30 mg bid) 250/500 mg bid 500mg bid (1 g bid) Quadruple Therapy Omeprazole(Lansoprazole) plus Bismuth subsalicylate Metronidazole Tetracycline 20 mg (30 mg ) daily 2 tablets qid 250 mg qid 500 mg qid Two anti-H pylori regimens are available in prepackaged formulation (14 days):- Prevpac (Lansoprazole, Clarithromycin, and Amoxicillin ---- Twice per day Helidac (bismuth subsalicylate, tetracycline, and metronidazole)------Constituents are taken four times per day with an antisecretory agent (PPI or H2blocker) [/INST] question: Which drug is not effective against H pylori? | options: A: Colloidal bismuth B: Metronidazole C: Amoxycilline D: Erythromycin | answer: D </s>