Purpose: To determine with electronic monitoring an objective measurement of adherence in two populations of subjects: those using once-daily prostaglandin analogs as sole ocular hypotensive therapy (one-drug group) and those requiring an adjunctive medicine to the prostaglandin analog (two-drug group). Design: Single-site, open-label, nonrandomized, parallel design of 60 days. Methods: Sixty-two consecutive adult subjects with a diagnosis of open-angle glaucoma (OAG) or ocular hypertension: 31 were taking one drug and 31 were taking two drugs. An electronic event medication monitoring device was used to record each bottle opening. The main outcome measures were dosing errors (number of under-adherence or over-adherence events) and coverage (proportion of pharmacologic duration covered by dosing) relative to the ophthalmologist-prescribed regimen. Results: Adherence to the prostaglandins once daily was good in both groups by all measures (≤10% of subjects with more than five dosing errors and mean coverage of 97.2% ± 6.1%). Adherence to the second medication in the two-drug group was poorer (37% of subjects with more than five dosing errors and mean coverage of 85.6% ± 12.6%). For the subjects using β-adrenoceptor antagonists, 24.8% ± 18.4% of doses were taken at less than 10-hour intervals (over-adherence). Conclusions: The incorporation of a time component in electronic monitoring provides more information than prescription refill rate or other methods. We found that more complex dosing regimens result in poorer adherence, although once-daily drugs in a complex dosing regimen were found to have good adherence.
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