• E S W Jones, M Lesosky, M Blockman, S Castel, E H Decloedt, S L U Schwager, E D Sturrock, L Wiesner, and B L Rayner.
• Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa. eswjones@gmail.com.
• S. Afr. Med. J. 2017 Sep 22; 107 (10): 887-891.

BackgroundNon-adherence to antihypertensives is a cause of 'pseudo-treatment-resistant' hypertension.ObjectiveTo determine whether monitoring plasma amlodipine concentrations and inhibition of angiotensin-converting enzyme (ACE) can be adjunct adherence tools.MethodsPatients with hypertension who were prescribed enalapril and amlodipine were enrolled. Blood pressures (BPs) were monitored and an adherence questionnaire was completed. Steady-state amlodipine was assayed using liquid chromatography-mass spectrometry and degree of ACE inhibition using the Z-FHL/HHL (z-phenylalanine-histidine-leucine/hippuryl-histidine-leucine) ratio.ResultsOne hundred patients (mean (standard deviation) age 50.5 (12) years, 46% male) were enrolled. Based on plasma assays, 26/97 patients (26.8%) were unsuppressed by enalapril and 20/100 (20%) were sub-therapeutic for amlodipine. There were significant BP differences based on plasma levels of the medication: 21/20 mmHg lower in the group with suppressed ACE and 26/20 mmHg in the group with steady-state amlodipine concentrations.ConclusionsMonitoring antihypertensive adherence by assaying plasma medication concentrations is a feasible option for evaluating true v. pseudo-resistant hypertension.

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