The MACH2 study: role of omeprazole in eradication of Helicobacter pylori with 1-week triple therapies

Gastroenterology. 1999 Feb;116(2):248-53. doi: 10.1016/s0016-5085(99)70119-8.


Background & aims: The role of omeprazole in triple therapy and the impact of Helicobacter pylori resistance on treatment outcome are not established. This study investigated the role of omeprazole and influence of primary H. pylori resistance on eradication and development of secondary resistance.

Methods: Patients (n = 539) with a history of duodenal ulcer and a positive H. pylori screening test result were randomized into 4 groups. OAC group received 20 mg omeprazole, 1000 mg amoxicillin, and 500 mg clarithromycin; OMC group received 20 mg omeprazole, 400 mg metronidazole, and 250 mg clarithromycin; and AC (amoxicillin, 1000 mg, and clarithromycin, 500 mg) and MC (metronidazole, 400 mg, and clarithromycin, 250 mg) groups received no omeprazole. All doses were administered twice daily for 1 week. H. pylori status was assessed before and after therapy by 13C-urea breath test. Susceptibility testing was performed at entry and in patients with persistent infection after therapy.

Results: Eradication (intention to treat [n = 514]/per protocol [n = 449]) was 94%/95% for OAC, 26%/25% for AC (P < 0.001), 87%/91% for OMC, and 69%/72% for MC (P < 0.001). Primary resistance was 27% for metronidazole, 3% for clarithromycin, and 0% for amoxicillin. Eradication in primary metronidazole-susceptible/-resistant strains was 95%/76% for OMC and 86%/43% for MC. Secondary metronidazole and clarithromycin resistance each developed in 12 patients: 8 treated with omeprazole and 16 without omeprazole.

Conclusions: Addition of omeprazole achieves high eradication rates, reduces the impact of primary resistance, and may decrease the risk of secondary resistance compared with regimens containing only two antibiotics.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amoxicillin / therapeutic use
  • Anti-Bacterial Agents / therapeutic use*
  • Clarithromycin / therapeutic use
  • Double-Blind Method
  • Drug Resistance, Microbial
  • Gastric Mucosa / drug effects*
  • Gastric Mucosa / microbiology
  • Helicobacter Infections / drug therapy*
  • Helicobacter pylori / drug effects*
  • Humans
  • Metronidazole / therapeutic use
  • Middle Aged
  • Omeprazole / therapeutic use*
  • Treatment Outcome


  • Anti-Bacterial Agents
  • Metronidazole
  • Amoxicillin
  • Clarithromycin
  • Omeprazole