<prompt> Which drug is not effective against H. pylori:Colloidal BismuthMetronidazoleAmoxicillinErythromycin  <response>: Answer is D Erythromycin: The most successful are the Triple and Quadruple multi-drug regimens: Name Drug 1 Drug 2 Drug 3 Drug 4 OCA Omeprazole 20 mg BD Clarithromycin 500 mg BD Amoxicillin 1g BD OCM Omeprazole 20 mg BD Clarithromycin 500 mg BD Metronidazole 500 mg BD OBTM Omeprazole 20 mg BD Bismuth Subsalicylate 2 tabs QID Tetracycline 500 mg Q1D Metronidazole 