A screening question to assess risk of using antibiotics without a prescription: a diagnostic study.

Objectives: Non-prescription antibiotic use (using antibiotics without medical advice) is potentially unsafe and promotes antimicrobial resistance. We studied predictors of prior non-prescription use and whether screening for prior non-prescription antibiotic use predicted intention of future non-prescription antibiotic use.

Methods: The survey was performed from January 2020 - June 2021 in six public primary care clinics and two private emergency departments. Prior non-prescription users were respondents who reported taking oral antibiotics for symptoms without contacting a clinician. Intended use was defined by answering yes to the question, "would you use antibiotics without contacting a doctor/nurse/dentist/clinic." We examined predictors for prior non-prescription use. We also calculated the sensitivity, specificity, and positive and negative predictive value (PPV, NPV) of (a) any prior non-prescription antibiotic use and (b) prior use in the past 12 months - for future intended non-prescription use.

Results: Of 564 survey respondents, 246 (43.6%) reported non-prescription use; 91 (37.0%) of these respondents, 16.1% overall, reported doing so in the past 12 months. Approximately 63% of non-prescription antibiotic use was in those with a previous prescription of the same antibiotic for similar symptoms/illnesses. The screening characteristics of non-prescription use in the past 12 months to identify intention to use of antibiotics without a prescription in the future were: sensitivity 75.9% (95% CI: 65.3-84.6), specificity 91.4% (95% CI: 87.8-94.2), Bayes' PPV 74.5% (95% CI: 66.7-80.9), and Bayes' NPV 93.7% (95% CI: 90.5-96.1).

Conclusions: This study proposed a method to screen for future use of non-prescription antibiotics, which may have implications on antimicrobial stewardship efforts in primary care settings.