After applying the correction factors, the concordance improved significantly for these three ICS products. Our validation study has several strengths, including the use of a representative large population-based sample of ICS prescriptions covering patients up to 65 years of age, the possibility to selleck chemicals develop and validate correction factors for the days’ supply in an independent second large sample, and being the first study to assess the accuracy of the number of refills allowed. In the field of pharmacoepidemiology, it is important that the days’ supply recorded in prescription claims databases be valid

because we assess medication adherence by summing the days’ supply of all prescriptions filled during the study period, and this serves as a proxy of the number of days the patient took the medication. As such, the days’ supply is more important than the duration of the prescription written by the physician on the original prescription sheet. This study has also limitations that need to be mentioned. In particular, we did not include

patients aged >65 years, as the reMed database does not include them. This might reduce the external validity of our study, if prescription patterns of ICS differ with age. The post hoc age stratification (ie, 0–11 and 12–64 years) based on ICS drug monographs reduced the number of patients in the younger group. Finally, the clinical indication for the ICS prescriptions was unknown, and probably the accuracy of the days’ supply for ICS would have been better if only asthmatic patients were considered. In summary, we found that the information recorded in Québec prescription claims databases used to calculate adherence measures was accurate but only after correction. By focusing on ICS in this study, we probably explored a worst-case scenario, and it is likely that the accuracy would have been better with tablets. Conflicting possible interpretations of the days’ supply for ICS limit the accuracy as GSK-3 currently recorded. We recommend that the pharmacists

be given clearer instructions regarding what should be recorded for days-supply-PER, namely, the duration (number of days) of the ICS inhaler at the prescribed dosage be recorded, taking into consideration the maximum number of puffs per day when the dosage is variable. In addition, if the number of days of treatment stated on the original prescription does not correspond to the days’ supply, we recommend that it be recorded in a new field in the PER. The observed inaccuracies in the days’ supply may have had an impact (likely underestimation) on measures of adherence calculated in our previous studies (eg, the proportion of days covered and the proportion of prescribed days covered).