Therapeutic Drug Monitoring and the Challenge of Conducting Trials to Improve Antihypertensive Medication Adherence

Low adherence to antihypertensive medication is common and associated with uncontrolled blood pressure (BP), adverse cardiovascular outcomes, and premature mortality. 1A meta-analysis of 161 studies estimated a prevalence of nonadherence to antihypertensive medication between 27% and 40%. 2 Another meta-analysis, published in the American Journal of Hypertension, estimated that 37% of patients with apparent treatment-resistant hypertension have nonadherence to antihypertensive medication. 3t has been recognized for several decades that nonadherence to antihypertensive medication is a barrier to achieving BP control.In 1980, the second Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High BP guideline emphasized the importance of long-term adherence to antihypertensive medication as a means to achieve BP control. 4The most recent US guideline, the 2017 American College of Cardiology/American Heart Association BP guideline, recommends follow-up evaluation of adherence for adults initiating or adjusting their antihypertensive drug regimen. 5igh-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a type of therapeutic drug monitoring that provides highly sensitive and specific detection of all commonly prescribed antihypertensive medications or their metabolites in urine or serum samples. 6It is considered a valuable diagnostic test given its ease of use and ability to assess adherence objectively.In an observational study, therapeutic drug monitoring was associated with improved medication adherence and lower BP. 7This makes sense as sharing the results from therapeutic drug monitoring with patients may lead to a transparent conversation between them and their healthcare providers, which can be used to identify barriers to high antihypertensive medication adherence.Building a relationship, empowering patients and having strategies to overcome barriers to high antihypertensive medication adherence can enhance patient-provider communication and address obstacles to medication adherence. 8However, data are needed from randomized trials testing if therapeutic drug monitoring can improve adherence and lower BP.