Assessment of adherence to treatment in patients with resistant hypertension using toxicological serum analysis. A subgroup evaluation of the RESIST-POL study

INTRODUCTION: Nonadherence to antihypertensive therapy is one of the main causes of resistant hypertension. OBJECTIVES: The aim of our study was to evaluate adherence to therapy in patients with resistant hypertension by determining serum antihypertensive drug levels with the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). PATIENTS AND METHODS: The study included 36 patients with primary resistant hypertension selected from the RESIST-POL study (23 men and 13 women; mean age, 52.5 ±9.1 years; range, 22-67 years; mean number of antihypertensive drugs, 5.3 ±1.4), who met all 3 inclusion criteria: use of ≥4 antihypertensive drugs; average daytime ambulatory systolic blood pressure ≥140 mmHg; one of the clinical features suggesting nonadherence. All patients had their serum drug levels assessed using LC-MS/MS. Patients in whom the serum level of at least 1 drug was below the limit of quantification for the method used were regarded as nonadherent. RESULTS: Of all study patients, nonadherence was observed in 31 patients (86.1%), and none of the prescribed drugs was detected (complete nonadherence) in 5 patients (13.9%). In 26 patients (72.2%), at least 1 of the prescribed drugs could not be detected (partial nonadherence). CONCLUSIONS: In our study, we documented a surprisingly low adherence to antihypertensive treatment in patients with resistant hypertension. Our results suggest that, particularly in those patients, the analysis of serum antihypertensive drug levels using LC-MS/MS might allow to avoid a comprehensive and costly diagnostic work-up including biochemical and imaging studies.