Non-adherence to antihypertensive medications is related to pill burden in apparent treatment resistant hypertensive individuals

Objective: Non-adherence to medication is present in ≥50% of patients with apparent treatment resistant hypertension. We examined the factors associated with non-adherence as detected by an LC-MS/MS based urine antihypertensive drug assay. Methods: All urine antihypertensive test results, carried out for uncontrolled hypertension (BP persistently >140/90 mmHg) between January 2015 and December 2016 at a single toxicology laboratory were analysed. Drugs detected were compared to the antihypertensive drugs prescribed. Patients were classified as adherent (all drugs detected), partially non-adherent (≥1 prescribed drugs detected) or completely non-adherent (no drugs detected). Demographic and clinical parameters were compared between the adherent and non-adherent groups. Binary logistic regression analysis was performed to determine association between non-adherence and demographic and clinical factors. Results: Data on 300 patients from 9 hypertension centres across the UK were analysed. The median age was 59 years, 47% female, 71% Caucasian , median clinic BP was 176/95 mmHg and the median number of antihypertensive drugs prescribed was four. One hundred and sixty-six (55%) were non-adherent to prescribed medication with 20% of these being completely non-adherent. Non-adherence to antihypertensive medication was independently associated with younger age, female gender, number of antihypertensive drugs prescribed, total number of all medications prescribed (total pill burden) and prescription of a calcium channel blocker. Conclusion: This LC-MS/MS urine analysis-based study suggests the majority of patients with apparent treatment resistant hypertension are non-adherent to prescribed treatment. Factors that are associated with non-adherence, particularly pill burden, should be taken into account while treating these patients.