Trimethoprim is a safe, effective, and inexpensive treatment for cystitis. However, at least 25% of bacteria isolated from urine samples in general practice are now resistant to trimethoprim in the laboratory. The relationship between laboratory resistance and clinical outcome is complex. Cephalexin appears to be more active than trimethoprim in the laboratory but has been consistently less effective in clinical trials. There is little point in collecting data about the prevalence of drug resistance in urinary bacteria unless it is linked to evidence about the impact of resistance on clinical outcomes. Pragmatic clinical trials are required to provide practices with clear thresholds for managing their antibiotic policies; for example, 'Change from trimethoprim to drug X when the probability of trimethoprim resistance reaches Y%.' Prescribers should be aware that trimethoprim resistance is most likely to occur in patients who have been exposed to trimethoprim or other antibiotics in the previous six months, and that the risk increases with age. This information could be used to stratify women according to risk of infection by trimethoprim-resistant bacteria. Health education leaflets are an effective method for reducing the frequency of recurrent cystitis. Symptomatic treatment can control symptoms and allow time for microbiological investigation. Both of these strategies may help to reduce unnecessary prescribing of antibiotics in general and quinolones in particular.
- Drug-resistant bacteria
- Urinary bacteria