Long term adherence to prescribed cardiovascular medications in patients after percutaneous coronary intervention

Background Optimal long-term medication adherence is a crucial part of secondary prevention in patients after percutaneous coronary intervention (PCI) to achieve guideline-based treatment goals. Therapeutic drug monitoring (TDM) provides an objective method of assessing adherence to prescribed medications. Although patients generally respond positively to TDM when it is delivered within a supportive and autonomy-respecting clinician–patient relationship, the extent of non-adherence that persists is underexplored. Purpose To quantify adherence to prescribed cardiovascular medications using TDM 12 months after PCI. Methods A sub-sample of 500 patients from the prospective multicentre cohort CONCARDPCI were invited to undergo TDM of a range of cardiovascular medications 12 months after hospital discharge. The panel comprised 21 antihypertensive agents or metabolites, 3 direct oral anticoagulants (DOACs), and 2 statins. Serum samples were analysed utilizing ultra-high performance liquid chromatography coupled with tandem mass spectrometry. Sampling was done at the time of inclusion, permitting spontaneous sampling irrespective of timing of drug intake. Medication adherence was dichotomized as either full or suboptimal adherence. Results from the TDM analyses were compared to self-reported medication adherence utilizing the Medication Adherence Report Scale (MARS-5). To assess representativeness of the sample, it was compared with the full CONCARDPCI data (n=1970) on selected background variables (e.g. age, sex, polypharmacy, number of comorbidities, and education). Results In all, 167 patients consented to TDM and provided spontaneous blood samples and an updated medication list. The TDM sample was similar to the CONCARDPCI cohort except for age (median age 65.5 vs 67.2 for CONCARDPCI and TDM sample respectively, p=0.043). The number of concomitant measurable medications ranged from 1 to 5 (median 2). Non-adherence to one or more prescribed medications was identified in 19 patients (12%). Of these, 13 had MARS-5 scores of ≥24, indicating high medication adherence. In 15 patients (9%), cardiovascular medications not documented in the patients’ medication lists were detected. Adherence to DOACs, calcium channel blockers, and doxazosin was 100%. For beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, and diuretics, adherence ranged from 90% to 100%. Non-adherence to atorvastatin however was 12%. Conclusions Long-term adherence to prescribed cardiovascular medications, especially statins, was suboptimal. Non-adherence and the presence of undocumented medications persisted even among patients who consented to TDM, indicating that TDM is superior to self-reported medication adherence. This supports the clinical value of TDM in identifying discrepancies in medication use and supporting patient-centred adherence-improvement strategies.