Routine urinary detection of antihypertensive drugs for systematic evaluation of adherence to treatment in hypertensive patients

Background: Nonadherence to antihypertensive therapy is an important cause of poor blood pressure control. However, to date, few effective and accurate tools exist to routinely evaluate drug nonadherence. Methods: In this observational study, performed under conditions of routine clinical practice, we included 174 patients (aged 67 +/- 11 years) with treated essential hypertension who attended the outpatient hypertension clinic of a university hospital. Adherence to antihypertensive treatment was measured by using ultraperformance liquid chromatography-tandem mass spectrometry in spot urine at the time of clinical appointment and blood pressure measurement. Patients were also asked to report their adherence using a validated questionnaire (four-item Morisky Medication Adherence Scale). Results: The prevalence of directly measured nonadherence by urine drug detection was approximately 10%. Compared with adherent patients, those who did not adhere to their treatment (n = 15) had a higher number of antihypertensive pills and drugs (P = 0.02), cotreatment with cardiovascular drugs (P < 0.05), and total concurrent medications and pills (P < 0.01). After adjustment for age, SBP and DBP were higher in nonadherent than adherent group (SBP: 146 +/- 18 vs. 131 +/- 14, respectively, P < 0.01; and DBP: 77 +/- 15 vs. 73 +/- 9, respectively, P < 0.01). There was no significant association between four-item Morisky Medication Adherence Scale score and directly measured nonadherence. A longitudinal analysis, performed in a subpopulation of 105 patients after a median follow-up of 11 months, showed that the adherence status remained unchanged in 88% of patients. Conclusion: These results indicate a good adherence to antihypertensive drugs in patients attending the outpatient clinics of a university hospital. They suggest that urine detection of antihypertensive drugs by ultraperformance liquid chromatography-tandem mass spectrometry is an accurate and practical tool for directly monitoring adherence. This direct information is not overlapping with self-report questionnaire.