Antihypertensive adherence may only partly explain BP variability

By Eleanor McDermid

Study findings strengthen the suggestion that visit-to-visit variability in blood pressure (BP) is at least partly accounted for by patients' adherence or otherwise to their antihypertensive medication.

However, BP variability remained associated with clinical outcomes even after accounting for medication adherence, leading the researchers to suggest that other factors may contribute to BP variability.

In a related editorial, Giuseppe Mancia (University of Milano Bicocca, Italy) says: "This may well be the case, but it is up to future studies in which adherence to treatment will be measured accurately within its usual wide range to move ahead from the present contribution and to confirm what seems at this stage just an interesting suggestion."

The analysis, which appears in Hypertension, is based on data from the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), in which patients' medication adherence was measured by self-report - considered to be of limited reliability. Mancia also notes that patients in a randomised trial setting tend to have increased motivation to adhere to medication.

"This is an important issue to address because adherence to treatment has often been shown to markedly improve cardiovascular protection already when it raises to intermediate levels (50% to 75% of the available drugs), with little further advantage when the level increases further", he says.

Of the 19,970 included ALLHAT participants, 2912 reported nonadherence (taking <80% of the study drug). Systolic BP standard deviation independent of the mean (SDIM), reflecting BP variability, was significantly higher among nonadherent than adherent participants, at 11.4 versus 10.5, equating to a difference of 0.8 after accounting for confounders including antihypertensive medication type.

And the same was true when Ian Kronish (Columbia University Medical Center, New York, USA) and team restricted the analysis to patients with no changes in their antihypertensive medication.

As expected, BP variability influenced clinical outcomes, with patients in the highest versus the lowest quintiles of SDIM having a 24% increased risk of fatal coronary heart disease or nonfatal myocardial infarction, as well as 43%, 41% and 56% increased risks of stroke, heart failure and all-cause mortality, respectively.

However, further adjustment for adherence had little or no influence on the findings, leading the team to suggest that improving patients' medication adherence will not counter the adverse influence of BP variability on outcomes.

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