Identifying poor adherence to antihypertensive medications in patients with resistant hypertension

Poor adherence (compliance) to antihypertensive medications is a major contributor to morbidity and mortality in patients with hypertension. Estimates in the literature of the extent of poor adherence in patients with hypertension vary between around 20% and 80%, so it is difficult to be sure of the proportion of patients affected. Good adherence to antihypertensive medications is important. In addition to achieving better blood pressure control and thus reducing adverse hypertension-related outcomes, good adherence prevents unnecessary treatment escalation, additional appointments, investigations for secondary causes and even potentially invasive interventions. In a recent issue of BJCP, Avataneo et al. report a study that used therapeutic drug monitoring to define antihypertensive medication adherence profiles in patients with suspected resistant hypertension referred to a hypertension unit in Turin, Italy [1]. A liquid chromatography–tandem mass spectrometry approach was used to quantify a panel of ten different antihypertensive drugs in human plasma. Of the 50 patients considered to have apparent resistant hypertension who underwent therapeutic drug monitoring, 24% were found to be only partly adherent and 18% totally non-adherent to the antihypertensive medications they had been prescribed. The team also attempted to identify predictors of poor adherence and look at associations between self-reported adherence (albeit using a nonvalidated questionnaire), physician opinion of adherence and results of the therapeutic drug monitoring. No association was found with self-reported adherence, while physicians were often able to identify non-adherence. Interestingly, all nine patients found to be totally non-adherent according to results of therapeutic drug monitoring self-reported that they were fully adherent. Factors found to be associated with nonadherence included higher blood pressures, higher heart rate, previous coronary artery disease or stroke and previous invasive treatments including renal denervation and baroreceptor stimulation. The authors concluded that there was a high prevalence of poor adherence in this patient group and expressed the need for caution in use of invasive treatments in patients with resistant hypertension without first addressing adherence. They suggested that there was a need for validation of the use of therapeutic drug monitoring in a wider cohort of patients to inform whether it should become routine clinical practice. This was a relatively small study andmeasured a relatively small panel of antihypertensive drugs, but it adds to our knowledge of the extent of non-adherence in this important group of patients with resistant hypertension and some of the possible predictors of non-adherence in such patients. Resistant hypertension is a difficult problem, and while recent clinical trials such as PATHWAY-2 have highlighted effective treatment options in this scenario [2], identifying which patients have true resistant hypertension is important before additional therapies or other interventions are British Journal of Clinical Pharmacology Br J Clin Pharmacol (2019) 85 5–7 5