title: Are antibiotics related to oral combination contraceptive failures in the Netherlands? A case-crossover study.
abstract: OBJECTIVE
  To investigate whether there is an association between use of antibiotics and breakthrough pregnancy.
  
  
  METHODS
  The study was performed in a population-based prescription database (IADB.nl). We computed case-crossover odds ratios of 397 cases of defined breakthrough pregnancy comparing the use of antibiotics in the exposure window with the use of antibiotics in two control windows. We defined a control group consisting of 29 022 other pregnancies. We computed case-control odds ratios of the use of antibiotics in cases as compared with controls in the different time windows.
  
  
  RESULTS
  The case-crossover odds ratios comparing the use of antibiotics in the exposure window with both control windows were 2.21 (95%CI = 1.03-4.75) and 1.65 (95%CI = 0.78-3.48), respectively. The traditional case-control odds ratios after adjustment for age were 1.71 (95%CI = 1.09-2.66) in the exposure window, 0.81 (95%CI = 0.44-1.47) 2 months before the exposure window, and 1.04 (95%CI = 0.61-1.78) 12 months before the exposure window.
  
  
  CONCLUSIONS
  We did find a relationship between the use of antibiotics and breakthrough pregnancy in a population-based prescription database. The results did not hold for broad-spectrum antibiotics or in a sensitivity analysis. The results are partly not the same as those found in a pharmacoepidemiological study with a similar design using two US pregnancy databases. Both studies can suffer from bias and confounding, but these will be different because of the use of different databases.
authors.affiliation: Department of Occupational Health Services, 365/ArboNed, Groningen, The Netherlands. petra.koopmans@365.nl
authors.forename: Petra C
authors.initials: PC
authors.lastname: Koopmans
authors.forename: Jens H J
authors.initials: JH
authors.lastname: Bos
authors.forename: Lolkje T W
authors.initials: LT
authors.lastname: de Jong van den Berg
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000009:adverse effects*; D016022:Case-Control Studies; D003277:Contraceptives, Oral, Combined / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004347:Drug Interactions; D005260:Female; D006801:Humans; D009426:Netherlands; D016017:Odds Ratio; D011247:Pregnancy; D049168:Pregnancy, Unplanned / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D003277:Contraceptives, Oral, Combined