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.