Poor adherence to antihypertensive medication is one of the major problems in the treatment of hypertension. Electronic monitoring is currently considered to be the gold standard for assessing adherence, but it may trigger patients to open the pill bottle without taking medication or to take out more than prescribed.

In adjunct to electronic monitoring, pill count could be a valuable tool for exploring adherence patterns, and their effects on blood pressure reduction.

Among a total of 228 patients with mild-to-moderate hypertension, adherence to treatment was measured by means of both the Medication Event Monitoring System (MEMS) and pill count. Patients were followed-up for seven visits over a period of 1 year.

At each visit to the physician's office, patient's adherence was assessed by both methods.

Adherence is defined as the percentage of days with correct dosing; median adherence according to MEMS was lower than median adherence according to pill count (91.6 vs. 96.1; P < 0.001).

Both methods agreed in defining patients as adherent in 107 (47%) and nonadherent in 33 (14%) patients. Thirty-one (14%) patients were adherent only by MEMS and 59 (25%) patients only by pill count. At the end of the study, patients in the four categories reached comparable blood pressure values and reductions.

Pill count could be a useful adjunct to electronic monitoring in assessing adherence patterns. Although deviant intake behavior occurred frequently, the effect on achieved blood pressure and blood pressure reduction was not remarkable.

American Journal of Hypertension 2010; doi:10.1038/ajh.2009.207

Insufficient adherence to antihypertensive medication remains a challenging and poorly understood phenomenon.¹ The World Health Organization estimated that half of the patients suffering from hypertension do not comply with the prescribed drug regimen.²

Recently, a longitudinal study also demonstrated that after 1 year of treatment almost 50% of a large group of hypertensive patients discontinued treatment.³ In contrast, results of clinical trials show much better figures for adherence,^4,5,6,7,8 suggesting that the degree of adherence found in clinical trials does not represent a “real-life” situation.

A factor that complicates the interpretation of adherence data is the method of measurement and its unit of definition. Presently, electronic monitoring by means of a Medication Event Monitoring System (MEMS) is considered to be the gold standard.^{5,9,10,11,12,13}

Other methods, such as patient self-reports, pharmacy refilling data, and pill counts are easy to perform but lack reliability.^10,13

Several studies show that pill counts overestimate adherence to medication,^11,14,15 whereas pharmacy refilling data only give information about the collection of the medication by the patient.¹⁶

Theoretically, the use of MEMS could trigger the patient to open the MEMS container each day without taking medication from it. As a result, adherence would appear to be sufficient, yet the outcome variable, e.g., effect on blood pressure control, will be disappointing.

On the other hand, patients could open the pill bottle less than prescribed and spare up extra doses while ingesting the medication at the correct time (pocket dosing).

This behavior will lead to an underestimation of adherence determined by MEMS, even though blood pressure may at times be better controlled.

So far, not much information is available with respect to these different behavioral patterns in relation to achieved blood pressure.

This prompted us to investigate adherence patterns in more detail by comparing and matching MEMS data with pill count data and by assessing the effect on blood pressure reduction in patients with mild-to-moderate hypertension.

Hein A.W. van Onzenoort^1,2, Willem J. Verberk^2,3, Alfons G.H. Kessels⁴, Abraham A. Kroon^2,5, Cees Neef⁶, Paul-Hugo M. van der Kuy⁷ and Peter W. de Leeuw^2,5

• ^{1Department of Clinical Pharmacy, University Medical Center St Radboud, Nijmegen, The Netherlands}
• ^{2Department of Internal Medicine, University Hospital Maastricht, Maastricht, The Netherlands}
• ^{3Microlife, Widnau, Switzerland}
• ^{4Department of Clinical Epidemiology and Medical Technology Assessment, University Hospital Maastricht, Maastricht, The Netherlands}
• ^{5Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands}
• ^{6Department of Clinical Pharmacy and Toxicology, University Hospital Maastricht, Maastricht, The Netherlands}
• ^{7Department of Clinical Pharmacy and Toxicology, Orbis Medisch Centrum, Sittard, The Netherlands}
• ^{Correspondence: Peter W. de Leeuw,} (p.deleeuw@intmed.unimaas.nl)