PHARMACOEPIDEMIOLOGY AND PRESCRIPTION Physicians’ and pharmacies’ overview of patients’ medication. An analysis of fidelity coefficients

Background It is essential that pharmacies and prescribers have an overview of each patient’s medication in order to prevent drug interactions, unintentional co-prescribing, unnecessary polypharmacy and underprescribing. We have assessed this overview by measuring the ‘fidelity coefficient’, a measure of the extent to which a drug user has a preference for one prescriber or one pharmacy. Methods and setting Data for all prescriptions issued for the population in Southern Denmark (population 1.2 million) in 2009 was extracted from the Odense University Pharmacoepidemiological Database (OPED). Analysis of the extracted data was then limited to persons with at least ten prescriptions within the year, resulting in 8,246,064 prescriptions issued to 283,388 individuals. For each individual, we identified the most used prescriber and calculated the proportion of all prescriptions accounted for by that prescriber (FCpresc). The individual user’s most frequented pharmacy was also identified and the FCpharm calculated in a similar fashion. Results The average FCPresc and average FCPharm were 0.883 (standard deviation 0.158) and 0.927 (0.139), respectively. The estimated difference was 0.0446 (95% confidence interval 0.0439–0.0453). Among the factors associated with a high FCpresc and high FCpharm were older age, male gender and a high volume of prescriptions. The major drug classes that were most often prescribed by a non-main prescriber were beta-lactams, antidepressants and opioids. Similarly, the major drug classes associated with use of non-main pharmacy were beta-lactams, antidepressants and inhaled beta-agonists. Conclusion Based on this analysis, both prescribers and pharmacies generally have an equal potential for maintaining an excellent overview of their patients’ medication, but the pharmacies account for a slightly higher proportion of patients.