Contraindicated drug–drug interactions associated with oral antimicrobial agents prescribed in the ambulatory care setting in the United States

Objectives: Antimicrobial agents are commonly used in ambulatory care settings. Our objective was to examine national-level patterns of contraindications between oral antibacterial or antifungal agents and patients' other oral medications in the US ambulatory care setting. Methods: This cross-sectional study included multiple year pooled data (2003–2011) from the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey (NHAMCS Outpatient Department). Visits by adults (age ≥18 years) in ambulatory settings in the United States who were prescribed oral antibacterial or antifungal agents were evaluated for potential drug–drug interaction (DDI) contraindications. Findings with relative standard error >30% or unweighted sample size <30 were not reported because these were deemed unreliable estimates. Results: From 2003 to 2011, there were 1 235 000 outpatient visits (proportion = 0.52%; 95% confidence interval (CI), 0.29–0.74) in which a patient was prescribed an antimicrobial agent associated with a contraindicated DDI. The most prevalent antimicrobials with contraindicated combination among outpatients were simultaneous use of macrolide-containing products (erythromycin or clarithromycin) with statin medication–containing products (simvastatin or lovastatin) (841 864 visits, proportion = 1.91%; 95% CI, 0.96–2.86). The next most common combination was use of fluoroquinolones with antiarrhythmic agents (amiodarone, sotalol, quinidine or procainamide) (365 622 visits, proportion = 0.19%; 95% CI, 0.06–0.32). Conclusions: Providers should be aware of potential contraindicated DDIs when prescribing antibiotics, especially macrolides and fluoroquinolones.