Retrospective cohort analysis of outpatient antibiotic prescribing for community-acquired pneumonia in Canadian older adults

Background — This retrospective cohort study is the first in North America to examine population-level appropriate antibiotic use for community-acquired pneumonia (CAP) in older adults, by agent, dose and duration. With the highest rates of CAP reported in the elderly populations, appropriate antibiotic use is essential to improve clinical outcomes. Given the ongoing crisis of antimicrobial resistance, understanding inappropriate antibiotic prescribing is integral to direct community stewardship efforts.

Methods — All outpatient primary care visits for CAP (aged ≥65 years) were identified using physician billing codes between January 1 2014 to December 31 2018 in British Columbia (BC) and Ontario (ON). Categories of prescribing were derived from existing literature, and constructed for clinical relevance using Canadian and international guidelines available during the study period. Categories were mutually exclusive and included: guideline adherent (first-line agent, adherent dose/duration), clinically appropriate (non-first line agent, presence of comorbidities), effective but unnecessary (first-line agent, excess dose/duration), undertreatment (first-line agent, subtherapeutic dose/duration), and not recommended (non-first line agent, absence of comorbidities). Proportions of prescribing were examined by category. Temporal trends in prescribing were examined using Poisson regression.

Results — A total of 436,441 episodes of CAP were identified, with 46% prescribed an antibiotic in BC, and 52% in Ontario. Guideline adherent prescribing was minimal for both provinces (BC: 2%; ON: 1%) however the largest magnitude of increase was reported in this category by the final study year (BC—Rate Ratio [RR]: 3.4, 95% Confidence Interval [CI]: 2.7–4.3; ON—RR: 4.62, 95% CI: 3.4–6.5). Clinically appropriate prescribing accounted for the most antibiotics issued, across all study years (BC: 61%; ON: 74%) (BC—RR: 0.8, 95% CI: 0.8–0.8; ON—RR: 0.9, 95% CI: 0.8–0.9). Excess duration of therapy was the hallmark characteristic for effective but unnecessary prescribing (BC: 92%; ON: 99%). The most common duration prescribed was 7 days, followed by 10. Not recommended prescribing was minimal in both provinces (BC: 4%; ON: 7%) and remained stable by the final study year (BC—RR: 1.1, 95% CI: 0.9–1.2; ON—RR: 0.9, 95% CI: 0.9–1.1).

Conclusion — Three quarters of antibiotic prescribing for CAP was appropriate in Ontario, but only two thirds in BC. Shortening durations—in line with evidence for 3 to 5-day treatment presents a focused target for stewardship efforts.