UTI: extended-spectrum penicillins linked to trimethoprim resistance

  • Mulder M & al.
  • Eur J Clin Microbiol Infect Dis
  • 7 Sep 2019

  • International Clinical Digest
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  • Use of extended-spectrum penicillins is associated with trimethoprim resistance in urinary tract infections (UTIs).
  • The mechanism is unclear but may be due to selection by coresistance.
  • Nitrofuran derivatives are associated with lower odds of trimethoprim resistance.

Why this matters

  • Consider coresistance when prescribing antibiotics.
  • Incorporate resistance testing into overall management for patients with recurrent UTIs.

Key results

  • 1264 patients, 80.0% (1011) women; median age, 75.3 (range, 66.5-83.3) years.
  • 31.1% (393) Escherichia coli isolates were trimethoprim-resistant.
  • 70.6% (893) participants were prescribed ≥1 beta-lactam during the study period, including sulfonamide and trimethoprim (58.9%), fluoroquinolone (39.9%), nitrofurantoin (47.7%).
  • Multivariate:
    • >3 extended-spectrum penicillin prescriptions associated with trimethoprim resistance (OR, 1.68; 95% CI, 1.10-2.55).
    • >3 trimethoprim/sulfonamide prescriptions significantly associated with trimethoprim resistance (OR, 2.22; P<.05>
    • >3 nitrofurantoin prescriptions significantly associated with lower frequency of trimethoprim resistance (OR, 0.60; P<.05>
    • Time since last extended-spectrum penicillin prescription associated with trimethoprim resistance (1-3 months; OR, 2.86; 95% CI, 1.29-6.34), except for penicillin/enzymes combinations.

Study design

  • Nested case-control study evaluating effects of prior antimicrobial drug prescriptions on trimethoprim resistance in UTI among Rotterdam (the Netherlands) patients with E coli UTI.
  • Funding: None disclosed.


  • Adherence data missing.
  • Residual confounding.
  • Inability to confirm results by genetic association.