LAUSR

Background: Antihypertensive medication nonadherence is believed to be a prevalent issue but is very difficult to accurately assess. As a result, using a variety methods, nonadherence rates ranging from 3-86% have been suggested. To clarify this problem among hypertensive patients attending a CVD outpatient clinic, we utilized high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) to assess antihypertensive medication adherence and identify trends by sex and drug class Methods: Plasma was obtained from patients with either drug-controlled or drug resistant hypertension (RHTN) and analyzed via HPLC-MS for antihypertensive drugs which were categorized by drug class as: beta blockers, aldosterone antagonists, thiazide diuretics, ACE inhibitor/ARBs, or calcium antagonists. Clinic blood pressure (BP) measurements, sex, and prescription regimens were extracted from patient medical records at or near the time of plasma collection. “Adherence” or “nonadherence” was determined by comparison of the patient’s prescribed drug regimen and the presence/absence of prescribed drug(s) in their plasma. Results: Among 76 patients (47 women, mean age 63 ± SD 10), and 53% (43 of 76) white. Overall, nonadherence was confirmed in 29% (22 of 76). RHTN was more frequently identified in women than men (55%, 26 of 47 vs 38% 11 of 29) and nonadherence was higher in women than men (34%, 16 of 47 vs 21%, 6 of 29). As expected, BP in those who were fully adherent to prescribed antihypertensive drugs was significantly lower than in those who were nonadherent with one or more medications (129/75 vs 145/83 mm Hg, p=0.0015). Overall, ACE inhibitors or ARBs were associated with the least nonadherence. Among women, nonadherence was highest for aldosterone antagonists, whereas among men, nonadherence was highest for thiazide diuretics. Nonadherence appeared among those with RHTN (38%, 14 of 37) and those with controlled HTN (21%, 8 of 39). Conclusion: We observed nonadherence was more frequent among older women in a cohort of HTN and RHTN patients based on HPLC-MS confirmed drug levels. Nonadherence was variable based on drug class but lowest with angiotensin II active agents, which, if validated, should be considered when optimizing antihypertensive prescribing.