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Therapeutic drug monitoring of amlodipine and the Z-FHL/HHL ratio: Adherence tools in patients referred for apparent treatment-resistant hypertension

E S W Jones, M Lesosky, M Blockman, S Castel, E H Decloedt, S L U Schwager, E D Sturrock, L Wiesner, B L Rayner

Abstract


Background. Non-adherence to antihypertensives is a cause of ‘pseudo-treatment-resistant’ hypertension.

Objective. To determine whether monitoring plasma amlodipine concentrations and inhibition of angiotensin-converting enzyme (ACE) can be adjunct adherence tools.

Methods. Patients 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.

Results. One 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.

Conclusions. Monitoring antihypertensive adherence by assaying plasma medication concentrations is a feasible option for evaluating true v. pseudo-resistant hypertension.

 


Authors' affiliations

E S W Jones, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

M Lesosky, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

M Blockman, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

S Castel, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

E H Decloedt, Department of Medicine, Tygerberg Hospital and Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa

S L U Schwager, Department of Integrative Biomedical Sciences, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

E D Sturrock, Department of Integrative Biomedical Sciences, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

L Wiesner, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

B L Rayner, Department of Medicine, Groote Schuur Hospital and Faculty of Health Sciences, University of Cape Town, South Africa

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Keywords

Hypertension; Adherence; Therapeutic drug monitoring; Antihypertensives; Amlodipine; ACE inhibitors

Cite this article

South African Medical Journal 2017;107(10):887-891. DOI:10.7196/SAMJ.2017.v107i10.12268

Article History

Date submitted: 2017-09-22
Date published: 2017-09-22

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