Effects of new drug interaction index on drug adherence in older patients with hypertension

OBJECTIVE
Hypertension is a challenging problem in the older population because of poor drug adherence (DA). We aimed to determine the DA and examine the drug interaction index (DII) on DA in older patients with hypertension.

METHODS
In this cross-sectional, observational study, we enrolled 418 eligible patients aged ≥ 65 years between 1 February 2020 and 30 September 2020 in a tertiary hospital outpatient cardiology clinic. We prepared a questionnaire to record sociodemographic characteristics, morbidities, and drugs used by the population. The Morisky Medication Adherence Scale-8 (MMAS-8) was used for DA assessment. We identified drug interactions using the Lexicomp application. We calculated the DII from a ratio of clinically relevant interaction to total interaction. Descriptive tests and multiple linear regression analyses were performed to find independent factors on DA.

RESULTS
The mean age (± standard deviation [SD]) was 72.91 (±6.47), and 272/146 were female/male in the study population. The most frequent comorbid disease was diabetes mellitus (23.5%). The percentage of patients having polypharmacy was 39.5, and the mean daily drug (±SD) use was 4.27 (±2.57). The most prescribed antihypertensive drugs were thiazide/derivates (29.8%) and angiotensin receptor blockers (24.8%). The mean MMAS-8 (±SD) was 4.55±0.98, and 321 (76.8%) participants had a poor DA. A total of 33.4% of patients had significant drug interaction. The mean DII (±SD) was 0.345±0.017. The area under the receiver operating characteristic (ROC) curve for DII was 0.616 (95% confidence interval [CI]: 0.547-0.686).

CONCLUSION
We defined a new index for drug interaction intensity. Furthermore, the DII may be a useful tool to study aspects of DA in older patients with hypertension.