ANTIBIOTIC COMPLIANCE FOR VESICOURETERAL REFLUX2000

REPLY BY AUTHORS

One of the original works on compliance with anti-biotic prophylaxis in the vesicoureteral reflux popu-lation was by Hensle et al (reference 12 in article). Itdrew our attention to the fact that our patients arenot unique and compliance with antibiotic prophy-laxis is likely poor, as it is with other chronic med-ication treatments. Thus we used a national phar-macy claims database to estimate compliance withantibiotic prophylaxis and verify whether compli-ance rates were as poor as defined by Hensle et al.To clarify, the medication possession ratio is theamount of medication prescribed during the obser-vation period divided by the number of days in theobservation period (reference 9 in article). For exam-ple, a MPR of 50% means that a patient had enoughmedication to last them 50% of the year, or approx-imately 183 days of medication during a 365-dayperiod. We and Hensle et al defined compliance withantibiotic prophylaxis as a MPR of 80% or greater,as this is a common cut point used in the complianceliterature (reference 9 in article). In other words,patients who have a medication for 80% or greater ofthe designated period (292 or more days of medica-tion during a 365-day period) are defined as compli-ant with the medication. Therefore, when we say thecompliance rate is 40% this means that 40% of thepopulation had a MPR of 80% or greater.

Although both studies showed poor compliance,there is a major difference in the compliance rate.

Hensle et al demonstrated an average MPR of 40%

but a compliance rate of 17%. Thus, on averagepatients had enough medication to last them 40% ofthe year but only 17% had enough medication to lastat least 80% of the year. On the other hand, ourstudy demonstrated an average MPR of 69% (onaverage patients had enough medication to lastthem 69% of the year) and a compliance rate of 40%(40% of the population had enough medication tolast them at least 80% of the year).

We agree that the 19% hospitalization rate ap-pears high. However, this rate does not representhospitalizations solely for UTI and likely the per-centage of hospitalizations for UTI alone is lower.Nonetheless, one of the greatest challenges withrandomized controlled trials is external validity asthese trials often are not completely representativeof the general population. It is possible that thepatients enrolled in the Australian trial werehealthier overall and less susceptible to hospitaliza-tion, especially considering that only 576 underwentrandomization of an initial 9,482 who were assessedfor eligibility (reference 1 in comment).

We agree that compliance with antibiotic prophy-laxis is less than optimal. Whether compliance(MPR 80% or greater) is 17%, 40% or somewhere inbetween, the important message is that it is not100%. This must be factored in not only when we areanalyzing the outcomes of clinical studies, but also

when we are deciding how to treat our patients.