Accuracy of a provincial prescription database for assessing medication adherence in heart failure patients.
BACKGROUND
British Columbia's central prescription database, PharmaNet, is often used for both clinical and research applications. However, PharmaNet details prescription transactions, not actual medication consumption, resulting in many potential sources of inaccuracy when the information is assumed to reflect population or individual drug utilization.


OBJECTIVE
To assess the accuracy of PharmaNet for adherence assessment in patients with heart failure who are taking beta-blockers.


METHODS
A 6-month prospective, longitudinal assessment of adherence to the prescribed beta-blocker regimen was carried out using both PharmaNet data and the Medication Event Monitoring System (MEMS) for each patient enrolled. The limit of agreement between the 2 adherence assessment methods was assessed using the Bland-Altman approach.


RESULTS
Fifteen of 58 patients initially enrolled in the study were excluded, most due to misuse of MEMS or failure to return the MEMS vial despite thorough follow-up. For the 43 patients included in the final analysis, mean +/- SD adherence was 97.8 +/- 11.8% when assessed by PharmaNet and 97.1 +/- 7.3% when MEMS was used. However, the limit of agreement, reported as the mean of the differences +/- 2SD, was 6.8 +/- 18.5%, indicating a moderate-to-high level of agreement between the 2 methods when the confidence interval is taken into consideration.


CONCLUSIONS
These results suggest that PharmaNet data accurately reflect medication adherence for most patients. The MEMS system proved unreliable in several cases, illustrating the difficulty of identifying a gold standard for adherence assessment.
Dahri
Karen
K
CSU Pharmaceutical Sciences, Vancouver Coastal Health, Vancouver, British Columbia, Canada. Karen.Dahri@vch.ca
Shalansky
Stephen J
SJ
Jang
Linda
L
Jung
Leon
L
Ignaszewski
Andrew P
AP
Clark
Catherine
C
D000368:Aged; D001955:British Columbia / Q000453:epidemiology; D016208:Databases, Factual / Q000592:standards*; D016903:Drug Monitoring / Q000592:standards; D011307:Drug Prescriptions; D005260:Female; D006333:Heart Failure / Q000188:drug therapy* / Q000453:epidemiology; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010349:Patient Compliance; D011446:Prospective Studies; D015203:Reproducibility of Results