The Impact of Adherence and Exacerbation Frequency on Health Care Utilization and Associated Direct Costs in Severe Asthma

Determining the optimal threshold for medication adherence in adult asthma patients: an analysis of British Columbia administrative health database in Canada

OBJECTIVE

This study investigated the association between varying cutoffs for Medication Adherence (MA) among physician-diagnosed asthma patients and subsequent association with asthma exacerbation.

METHODS

We linked four administrative health databases obtained from the Population Data in British Columbia. Index cases were physician-diagnosed asthma patients between January 1, 1998, to December 31, 1999, aged 18 years and older. Patients were prospectively assessed in the follow-up period from January 1, 2000, to December 31, 2018, to identify asthma exacerbation. Two proxy measures were used to assess MA: the proportion of days covered (PDC) and the medication possession ratio (MPR). Using the generalized estimating equation (GEE) logistic regression adjusted for patient covariates, the outcome of "asthma exacerbation" was modeled against varying MA cutoffs; excellent '≥0.90'; very good '0.80-0.89'; good '0.70-0.799'; moderate '0.6-0.699'; mild '0.50-0.599' compared to poor '<0.50' for both PDC and MPR.

RESULTS

The sample included 68,211 physician-diagnosed asthma patients with a mean age of 48.2 years and 59.3% females. The adjusted odds ratios (OR) and 95% confidence interval (CI) at the various cutoff for PDC-levels predicting asthma exacerbation events were: Excellent MA [OR = 0.84, 95% (0.82-0.86), very good MA [OR: 0.86, (0.83, 0.89), good MA [0.91, (0.88-0.94)]; moderate MA [0.93, (0.90-0.96)]; mild MA [0.95, (0.92-0.98)]; compared to poor MA level. Threshold levels for both the PDC and MPR measure greater than 0.80 provided optimal threshold associated with over 15% reduced likelihood of experiencing asthma exacerbations.

CONCLUSION

Intervention aimed at improving asthma exacerbation events in adult asthma patients should encourage increased medication adherence threshold level greater than 0.80.

Supplemental data for this article is available online at at www.tandfonline.com/ijas .

Measuring Medication Adherence in a Population-Based Asthma Administrative Pharmacy Database: A Systematic Review and Meta-Analysis

Background

Limited studies have systematically reviewed the literature to identify and compare the various database methods and optimal thresholds for measuring medication adherence specific to adolescents and adults with asthma. In the present study, we aim to identify the methods and optimal thresholds for measuring medication adherence in population-based pharmacy databases.

Methods

We searched PubMed, Embase, International Pharmaceutical Abstracts (IPA), Web of Science, Google Scholar, and grey literature from January 1, 1998, to March 16, 2021. Two independent reviewers screened the studies, extracted the data, and assessed the quality of the studies. A quantitative knowledge synthesis was employed.

Results

Thirty-eight (38) retrospective cohort studies were eligible. This review identified 20 methods for measuring medication adherence in adolescent and adult asthma administrative health records. Two measures namely the medication possession ratio (MPR) and proportion of days covered (PDC) were commonly reported in 87% of the literature included in this study. From the meta-analysis, asthma patients who achieved adherence threshold of "0.75-1.00" [OR: 0.56, 95% CI: 0.41 to 0.77] and ">0.5" [OR: 0.71, 95% CI: 0.54 to 0.94] were less likely to experience asthma exacerbation.

Conclusion

Despite their limitations, the PDC and the MPR still remain the most common measures for assessing adherence in asthma pharmacy claim databases. The evidence synthesis showed that an adherence threshold of at least 0.75 is optimal for classifying adherent and non-adherent asthma patients.