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Editors Selection IGR 11-4

Medical treatment: Cooperation with medical therapy

Comment by Harry Quigley on:

12461 Does adjunctive glaucoma therapy affect adherence to the initial primary therapy?, Robin AL; Covert D, Ophthalmology, 2005; 112: 863-868

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Using an insurance/pharmacy database, Robin et al. (661) selected persons filling two or more prescriptions for latanoprost who then filled a prescription for an additional glaucoma medication and continued to fill two more latanoprost prescriptions. They measured the effect of the second drug addition on latanoprost refill rate, controlling the observation against persons who continued to fill latanoprost alone. Persons who filled latanoprost every 40 days when on monotherapy increased their refill rate to 47 days after addition of the second drug. This was interpreted as a potentially important decrease in 'adherence'. The authors' hypothesis was that patients "wait to refill a medication for glaucoma if they still have some left of the adjunctive medication." If true, then the size of the second medication bottle should be statistically related to the lengthening of refill time for latanoprost. It wasn't. In fact, the opposite was the true. "Stratified by fill size (Fig. 1), the increase in latanoprost refill interval was somewhat less with the 15-ml fill size for the second-line drug (4.8 &plm; 27.9 days) than with the 5- and 10-ml fill sizes (6.9 &plm; 25.7 and 8.0 &plm; 25.9 days, respectively)." Thus, the primary outcome was incompatible with the authors' explanation. A 2.5 ml bottle of latanoprost dispensing 25 microliter drops should last 50 days for bilateral therapy. We do not know what proportion of the study group was using monocular therapy in such databases. Hence, the increase in duration between refills found here falls within the needs of a patient dutifully taking drops each day. The study seems uniquely aimed at latanoprost. No data are presented on other drugs, so we cannot determine if this effect would occur with other drugs or other bottle sizes, which would have been easily carried out with this database.

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