Non-adherence should be addressed first

EDITOR—Nuesch et al showed in their study that electronic monitoring of patient's adherence had no significant effect on ambulatory blood pressure.1 Because non-adherence was not more prevalent among patients with resistance to antihypertensive treatment, they concluded that other factors independent of a patient's willingness to adhere are more relevant in explaining failure of treatment in most patients. These results should, however, be interpreted with caution because of possible selection and differential measurement bias that may have occurred in the study.

Patients who accepted inclusion in the study and were therefore monitored for blood pressure and adherence may adhere more to antihypertensive treatments than the general population. We have no information about how many eligible patients refused to participate. Furthermore, after 28 days of study and on the basis of the results of ambulatory blood pressure, more patients became responsive to treatment than became non-responsive (χ²=2.9, P<0.09)—14/49 (28.6%) v 8/54 (14.8%), respectively. It is important to note that the patients were all following a stable treatment regimen. The only interventions were to monitor blood pressure and adherence, which are both recommended to encourage the patients to take the prescribed medication regularly. Therefore, to explain this clinically relevant difference, I believe that the impact of electronic measurement on adherence to treatment was stronger among patients with uncontrolled blood pressure at the entry to the study than among other patients (control group). Considering that adherence was improved in the non-responder group (differential bias) during the study, it is not surprising that the prevalence of non-adherence was similar among responding and non-responding patients before the study.

Reclassification of patients according to the second measure of blood pressure would not have led to a different conclusion. But, as Nuesch et al discussed, interventions to help patients to follow their regimen that improve …