Assessing medication adherence by pill count and electronic monitoring in the African American Study of Kidney Disease and hypertension (AASK) pilot study

The Medication Event Monitoring System (MEMS), an electronic monitor which records the date and time of bottle cap openings, and pill counts were used to assess patterns of adherence for the primary antihypertensive drug in the African American Study of Kidney Disease and Hypertension Pilot Study (AASK). Blacks with hypertension and moderately reduced renal function were randomized to one of two levels of blood pressure control and to one of three antihypertensive drug regimens: primary therapy with a calcium channel blocker, an angiotension converting enzyme inhibitor, or a beta-blocker. Of the 94 participants in AASK, 91 had MEMS recordings and pill counts for 313 regularly scheduled monthly follow-up visits. The average length of follow-up was 4.6 months. An acceptable level of adherence by pill count was achieved if 80% to 100% of the prescribed pills were not returned to the clinic. Adherence by MEMS to a once-a-day drug dosing schedule was acceptable if 80% of the time intervals between MEMS openings were within 24 +/- 6 h. Acceptable adherence by pill count was observed at 68% of the follow-up visits; MEMS indicated nonadherence at 47% of those visits. Blood pressure was within goal in 50% of the participants who were adherent by both pill count and MEMS throughout their follow-up visits, and only 14% of the participants who were identified nonadherent by one or both methods. These findings suggest that electronic monitoring is a useful adjunct to pill counts in assessing adherence to antihypertensive drugs. Feedback of electronically collected information on dosing intervals to participants and staff may enhance adherence.