Assuming one dose per day yields a similar estimate of medication adherence in patients with stroke: An exploratory analysis using linked registry data

Abstract

Purpose Prescribed daily dose (PDD), the number of doses prescribed to be taken per day, is used to calculate medication adherence using pharmacy claims data. PDD can be substituted by (i) one dose per day (1DD), (ii) an estimate based on the 75th percentile of days taken by patients to refill a script (PDD75) or (iii) the World Health Organization's defined daily dose (DDD). We aimed to compare these approaches for estimating the duration covered by medications and whether this affects calculated 1‐year adherence to antihypertensive medications post‐stroke. Methods We conducted a retrospective review of prospective cohort data from the ongoing Australian Stroke Clinical Registry linked with pharmacy claims data. Adherence was calculated as the proportion of days covered (PDC) for 1DD, PDD75 and DDD. Differences were assessed using Wilcoxon rank‐sum tests. Results Among 12 628 eligible patients with stroke, 10 057 (80%) were prescribed antihypertensive medications in the year after hospital discharge (78.2% aged ≥65 years, 45.2% female). Overall, the 75th percentile of patient time until next medication refill was 39 days. The greatest variations in dose regimens, estimated using person‐ and dose‐level refill times, were for beta blockers (11.4% taking two tablets/day). There were comparable levels of adherence between 1DD and the PDD75 (median PDC 91.0% vs 91.2%; P = 0.70), but adherence was slightly higher using DDD (92.3%; both P < 0.001). However, this would represent a clinically nonsignificant difference. Conclusion Adherence to antihypertensive medications shows similar estimates across standard measures of dosage in patients during the first year after an acute stroke.

Towards better reporting of the proportion of days covered method in cardiovascular medication adherence: A scoping review and new tool TEN‐SPIDERS

“…and 26 (35%) were related to secondary prevention (Table 1). 6,67–93 Lipid‐lowering medicines were the most commonly investigated cardiovascular medicine (36%). The majority of the scientific articles were observational studies (93%), conducted in Europe (31%) or the USA (47%), and included ≥10 000 individuals (52%).…”

“…Thus, researchers often replace it with the defined daily dose published by the World Health Organization or other proxy estimates of dose 98 . A common approach involves imputing a dose of 1 unit per day, which has been shown to be reliable for certain antihypertensive medications 91 . However, this approach is less reliable for drugs with variable dosages such as β blockers and warfarin and induces variability in the calculation with these agents 99 .…”

“…98 A common approach involves imputing a dose of 1 unit per day, which has been shown to be reliable for certain antihypertensive medications. 91 However, this approach is less reliable for drugs with variable dosages such as β blockers and warfarin and induces variability in the calculation with these agents. 99 Given that information on the prescribed daily dose is fundamental for accurately assessing the duration of medication exposure, custodians of administrative databases should consider collecting this information to better support research on medication use and associated outcomes.…”

Real-World Effectiveness of Lipid-Lowering Medications on Outcomes after Stroke: Potential Implications of the New-User Design

“…The numerator was adjusted to account for pre-supply or early refills of the same medication. Patients were assumed to have been prescribed a dose of one tablet of lipid-lowering medications per day, consistent with standard prescribing recommendations [17] and literature [18]. Because of the dispersion of data on PDC and to ensure reliable comparison of findings with literature, adherence was categorized as poor (PDC <80%) or good (PDC ≥80%).…”

Evaluation of adherence to antipsychotics: A real‐world data study using four different dosing assumptions

“…7 Several assumptions in recommended dosing have been assessed in the effort to overcome limitations arising from lack of information in posology in studies based on dispensing-only data. [10][11][12] However, these assumptions, often lead to inaccurate estimates of medication adherence. 13,14 Whereas linked prescription and dispensing data result in more precise adherence estimates, 14 suboptimal prescription practices can result in registries with unclear information for research purposes, such as inconsistencies in recommended dosing information.…”