The "Nonadherent" Patient with Asthma: Time to Revise the Paradigm

Pediatric asthma in developing countries: challenges and future directions

PURPOSE OF REVIEW

Asthma continues to be a significant health problem worldwide, and epidemiological studies in the last few decades have consistently shown a marked increase in childhood asthma prevalence. The International Study of Asthma and Allergies in Childhood (ISAAC) showed significant geographic variability in prevalence, and larger associations with morbidity and mortality in low-middle income countries (LMICs). The Global Burden of Disease estimated that 420,000 deaths occurred globally from asthma in 2016, and although asthma prevalence is higher in high-income countries, most asthma-related mortality occurs in LMICs. The general health of a population is measured, in part, by the under-5 childhood death rate, and developing countries still account for more than 80 percentage of child deaths in the world, highlighting the need for efforts to reduce disease burden in these regions.

RECENT FINDINGS

The burden of asthma is higher in developing countries and underserved populations. Despite this, LMICs still face many barriers to appropriate allergy and asthma care, resulting in significant morbidity, potentially preventable asthma deaths, and economic consequences. A 2017 survey of 112 countries participating in the Global Asthma Network found that only 26 countries (23%) had a national asthma plan for children, with a lower proportion in LMICs.

SUMMARY

The rising asthma prevalence and high asthma-related death rates in LMICs suggest that global efforts in improving asthma diagnosis and care are not reaching the most vulnerable communities. Lack of appropriate diagnosis, availability of viable treatment options, and access to specialised care still remain a challenge in many parts of the world. Though barriers to achieving better outcomes differ in specific populations, many LMICs share similar barriers relating to accessibility.

Novel Methods of Measuring Adherence Patterns Reveal Adherence Phenotypes with Distinct Asthma Outcomes

RATIONALE

Poor adherence with asthma controller medication contributes to worse symptom control and increased exacerbation risk. Adherence is often expressed as the mean proportion of prescribed doses taken over a period of 6-12 months. New metrics may capture individual day-to-day variability patterns linked with distinct clinical outcomes.

OBJECTIVES

To test the hypotheses that novel time- and dose-based adherence variability metrics offer independent value to mean adherence in identifying distinct adherence patterns, that are associated with symptom control (Asthma Control Test [ACT] score) and exacerbation risk, using electronically-recorded medication data from a 6-month cluster randomized trial examining the effect of inhaler reminders on adherence.

METHODS

Adherence metrics were calculated from the first two months (months 0-2) of the study period. In addition to mean adherence (%prescribed puffs/day taken, PTmean), we examined novel metrics including: time adherence area-under-curve (T-AUC), reflecting cumulative gaps in adherence over time, entropy (H), reflecting disorder in the ways in which a patient changed their medication dose adherence from day to day, and standard deviation of the %prescribed puffs/day taken (PTSD). Dominant metrics identified from factor analysis were included in hierarchical clustering analysis. We compared the resultant clusters in terms of outcomes over months 2-6, and exacerbation risk over the entire study period.

RESULTS

Two factors explained >65% of the total variance in adherence, primarily driven by T-AUC and H. Two main patient clusters based on their adherence metrics were identified: Cluster 1 ("high time adherence", n=75) had better T-AUC, i.e. fewer gaps between medication-taking days, than Cluster 2 ("low time adherence", n=23). Though both clusters had similar symptom control at 2 months, Cluster 1 showed less subsequent decline in ACT over months 2-6 (median(IQR) change in ACT score: 1(-1, 4) vs -2(-3.75,0.75); p=0.012), and had better symptom control at 6 months (ACT score: 20(17, 23) vs 17 (15, 20); p=0.034). There were no significant differences between the clusters in terms of proportion of exacerbators or time to exacerbation.

CONCLUSIONS

Novel metrics showed that low time adherence was associated with greater risk of decline in asthma symptom control. Adherence patterns may exhibit 'memory' relevant to future clinical status, warranting validation in a larger dataset.