Bromide as marker for drug adherence in hypertensive patients

AIMS Adherence to antihypertensive medication is essential for adequate long-term control of blood pressure (BP). This study investigated different methods of measuring adherence in hypertensive patients. METHODS Patients were included if BP was insufficiently controlled on monotherapy. After a placebo period patients were treated with trandolapril 2 mg/verapamil SR 180 mg (TV). BP was determined using a mercury sphygmomanometer and ambulatory BP monitoring. Adherence was measured by capsule counting, electronic registration of pill-box openings and by measuring serum bromide concentrations. Potassium bromide was added to each TV capsule. RESULTS Thirty patients participated in the study. Treatment with TV significantly lowered office BP and ambulatory BP. Results for electronic monitoring and adherence based on bromide measurements were comparable. Adherence was slightly higher when assessed by capsule counting. CONCLUSIONS Measuring serum bromide concentrations may be suitable for assessment of adherence to drug therapy giving comparable results to electronic monitoring. Using capsule counting, electronic monitoring and measurement of bromide concentrations, nonadherent patients were identified.