Aim: Many challenges exist in determining true rates of adherence to antihypertensive medications among individuals in a clinic setting. For the first time, we aimed to compare patient-reported antihypertensive adherence with objective evidence using mass spectrometry spot urinalysis in a tertiary referral clinic setting.
Methods: A prospective observational single-centre cohort study was performed in a tertiary referral hypertension clinic, encompassing antihypertensive initiation and persistence. Patients were referred with apparent treatment-resistant hypertension or for suspected secondary causes. Participants completed a self-reported assessment of antihypertensive adherence and provided a spot urine sample. The presence of antihypertensive medications and/or their respective metabolites was evaluated using high-performance liquid chromatography tandem mass spectrometry. Patients were determined to be adherent if they demonstrated both self-reported adherence and objective mass spectrometry evidence.
Results: Of all 105 eligible participants initially recruited, 73 (69.5%) met the eligibility criteria. Only 27.4% (95% confidence interval 0.2-0.4) of participants demonstrated true adherence to their self-reported antihypertensives, despite 75.3% (0.6-0.8) reporting adherence. Greatest medication adherence was achieved with angiotensin II receptor blockers (61%), with calcium-channel blockers and mineralocorticoid antagonists demonstrating least adherence (38%).
Conclusion: In patients attending a tertiary hypertension clinic, the combined use of spot urine mass spectrometry and self-reporting identifies higher rates of nonadherence when compared to either modality alone. Both techniques should be combined for more accurate detection of medication adherence.
Keywords: adherence; compliance; hypertension; prescribing; urinalysis.
© 2022 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.