Accuracy of patient interviews and estimates by clinical staff in determining medication compliance

In research, as well as in daily practice, patient interviews and estimates by clinical staff are used to determine patients' adherence to drug regimens. The present study was undertaken to evaluate the accuracy of these methods in determining medication compliance among patients treated with pilocarpine to prevent visual loss from glaucoma. This was done by comparisons with objective and detailed information on self-medication behaviour obtained with a recording medication monitor. Results indicated that estimates by clinical staff were not useful in determining medication compliance. Patient interviews indentified 7 out of 16 patients who missed doses at least once a week. However, underreporting of missed doses was a major problem in determining medication compliance by interview. Of 73 patients interviewed, only 4% reported two or more missed doses during the past 7 days, whereas monitor records showed that 33% of the patients missed at least 2 doses, and 16% missed at least 6 doses, during the past week.