title: The relationship among previous antimicrobial use, antimicrobial resistance, and treatment outcomes for Helicobacter pylori infections.
abstract: BACKGROUND
  The relationship between previous antimicrobial treatments and infection with drug-resistant Helicobacter pylori is unknown.
  
  
  OBJECTIVE
  To determine whether previous use of antimicrobial agents predicts subsequent antibiotic resistance of H. pylori and whether resistance affects treatment outcome.
  
  
  METHODS
  Retrospective cohort analysis of adults recruited sequentially from a clinical practice.
  
  
  METHODS
  A referral hospital in Anchorage, Alaska.
  
  
  METHODS
  125 adults infected with H. pylori.
  
  
  METHODS
  Medical records were reviewed for antimicrobial agents prescribed in the 10 years before diagnosis with H. pylori infection. Antimicrobial susceptibility of H. pylori isolates obtained from endoscopic gastric biopsy was determined by using agar dilution. Cure was determined by using the urea breath test 2 months after antimicrobial treatment.
  
  
  RESULTS
  Among the 125 patients, 37 (30%) were found to have H. pylori isolates resistant to clarithromycin and 83 (66%) were found to have H. pylori isolates resistant to metronidazole. Resistance to clarithromycin was associated with previous use of any macrolide antibiotic (P < 0.001), and resistance to metronidazole was associated with previous use of metronidazole (P < 0.001). The odds of isolates being resistant to clarithromycin increased in relation to the number of courses of macrolides received (P < 0.001). Among 53 persons treated with clarithromycin-based regimens, treatment failed in 77% of those carrying clarithromycin-resistant H. pylori (10 of 13) and 13% of those with clarithromycin-susceptible strains (5 of 40) (relative risk, 6.2 [95% CI, 1.9 to 37.1]; P < 0.001).
  
  
  CONCLUSIONS
  Previous use of macrolides and metronidazole is associated with H. pylori resistant to these antimicrobial agents. Clarithromycin resistance is associated with a greater risk for failure with clarithromycin-based treatments.
mesh_terms: D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000009:adverse effects*; D017291:Clarithromycin / Q000009:adverse effects*; D015331:Cohort Studies; D024881:Drug Resistance, Bacterial; D005260:Female; D005500:Follow-Up Studies; D016481:Helicobacter Infections / Q000188:drug therapy* / Q000382:microbiology; D016480:Helicobacter pylori / Q000187:drug effects*; D006801:Humans; D008297:Male; D008795:Metronidazole / Q000009:adverse effects*; D008875:Middle Aged; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D000900:Anti-Bacterial Agents; D008795:Metronidazole; D017291:Clarithromycin