Directly observed administration of anti-hypertensive medication prior to ambulatory blood pressure monitoring-a useful tool for investigating resistant hypertension

Objective: Non-adherence to anti-hypertensive medication is a well-recognized cause of apparent ‘resistant hypertension’. We investigated whether directly observed administration (DOA) of anti-hypertensive medications, immediately prior to 24-hour ambulatory blood pressure monitoring (ABPM), would help exclude ‘treatment resistance’ potentially caused by medication non-adherence. Design and method: Resistant hypertension was defined (as per UK guidelines) as a mean daytime blood pressure (BP) of 135/85 or more despite the use of three or more anti-hypertensives. All patients had 24-hour ABPM immediately after a morning clinic appointment. Patients attending our nurse-led hypertension clinic were requested in advance to not take their prescribed anti-hypertensives on the morning of their appointment, but to bring their medications with. Patients were then observed taking their medications prior to ABPM. Patients that did not follow these instructions or who had ABPM organised from a different clinic (without DOA) formed the control group. Proportions were compared with Chi-squares tests. Data analysis was performed using Microsoft EXCEL 2010. Results: From November 2018 – October 2019, 53 patients had DOA before ABPM and were compared with 136 controls (see Table 1 for characteristics of each group). In the DOA group the average daytime BP was 138/83 with 38% having BP <135/85. In the control group average daytime BP was 141/86 with 27% having BP < 135/85. In total 54 patients were taking three or more anti-hypertensive medications. Table 2 compares the characteristics of these patients that underwent DOA (n = 14) compared with those that did not (n = 40). Of these patients, 50% that underwent DOA had a mean daytime BP of <135/85 compared with 20% in the control group (p = 0.03).Conclusions: Eliminating any effect of medication non-adherence by directly observed administration of prescribed anti-hypertensives immediately prior to ABPM leads to a lower rate of ‘resistant hypertension’ diagnoses. This strategy may therefore negate the need for further treatment and/or investigation in some patients.