The effect of pharmacist intervention on medication adherence measured with proportion of days covered: a systematic review and meta-analysis.

Introduction: Pharmacist-led interventions improve medication outcomes, but existing evidence on adherence remains limited by heterogeneous tools and qualitative outcomes. The proportion of days covered (PDC) offers a quantifiable measure of adherence, with recommended threshold (PDC ≥ 80%) supporting evidence-based optimization of pharmacy services in chronic care management. However, studies using PDC to evaluate pharmacist interventions versus usual care show heterogeneity.

Aim: This study aimed to systematically review and meta-analyze the effect of pharmacist-led interventions versus usual care using standardized PDC-based outcomes, and synthesize quantifiable evidence for pharmacy practice.

Method: Five databases were searched from inception to March 2024. Eligible studies included randomized controlled trials (RCTs) or non-randomized studies evaluating pharmacist-led interventions versus usual care with adherence measured by PDC. Two reviewers independently screened studies and extracted data. RCTs were assessed using Cochrane risk of bias 2.0 and non-randomized studies with the Newcastle-Ottawa Scale. Meta-analyses were conducted using random-effects models (I² ≥ 40%) to pool mean differences (MD) for continuous outcomes (mean PDC) and risk ratios (RR) for binary outcomes (PDC ≥ 80%). Subgroup analyses explored variability by region, sample size, baseline adherence, publication year, PDC calculation method, intervention duration, and delivery modality. Sensitivity analyses were conducted restricting to RCTs or excluding low-quality studies.

Results: Twenty-nine studies were included in the analysis. Quality appraisal identified 54.5% of non-randomized studies as high quality, and the majority of RCTs were rated as low risk or some concerns. Pharmacist-led interventions significantly enhanced adherence versus usual care, with a pooled MD of 0.08 (95% CI 0.04-0.12) for mean PDC and an RR of 1.09 (95% CI 1.06-1.13) for adherence rate. Greater effects were observed for lipid-lowering (MD = 0.08, 0.04-0.11) and hypotensive medications (MD = 0.06, 0.03-0.10) than for antidiabetics (MD = 0.02, 0.01-0.03), for 6-month (MD = 0.12, 0.07-0.17) versus 12-month interventions (MD = 0.03, 0.01-0.06), and for telephone-based delivery (RR = 1.16, 1.06-1.28) versus multifaceted counterparts (RR = 1.12, 1.01-1.25). High heterogeneity was observed across pooled analyses. Sensitivity analyses confirmed the robustness of results.

Conclusion: Pharmacist-led interventions enhance medication adherence in mean PDC and adherence rate. These consistent effects across different durations and delivery methods show their adaptability and scalability in clinical settings, highlighting their value in real-world pharmacy practice.