Background: Pharmacoepidemiologic studies utilize the days’ supply field in prescription (Rx) claims to classify exposures and outcomes; however, data on the accuracy of days’ supply are lacking. In the United States, days’ supply is calculated at the time of Rx filling. Pharmacists’ interpretation may influence days’ supply calculations leading to variability.
Objectives: The objectives of this study are to assess consistency of pharmacists’ calculation of days’ supply for opioid Rxs and identify factors pharmacists consider when calculating days’ supply for a given Rx.
Methods: A cross-sectional survey was designed to collect information from Kentucky-licensed pharmacists about opioid analgesic dispensing practices and days’ supply calculations. The survey was distributed electronically via email through the Kentucky Board of Pharmacy. Responses were collected anonymously over a 4-week period in December 2019. Inclusion criterion was experience dispensing opioid analgesics; other questions were voluntary. For days’ supply calculations, pharmacists saw 2 hypothetical opioid Rxs and calculated days’ supply. Additional questions examined factors influencing days’ supply and pharmacists’ perception of the importance of accuracy.
Results: Of 753 responses, 643 were eligible. For hydrocodone tablets, 19.4% (n=347) of pharmacists assigned inaccurate days’ supply, ranging from 7 days to 90 days. Common mistakes were 40 and 45 days instead of the correct 30. For morphine solution, days’ supply was inaccurate in 10.0% (n=351), ranging from 2 to 90 days. Common mistakes were 10 and 15 days instead of the correct 7. Most reported considerations when assigning days’ supply were instructions from the prescriber on intended duration (75.5%), third-party payer restrictions (48.4%) and familiarity with practitioners prescribing habits (45.3%). Most pharmacists perceived that accurate days’ supply are important to determine when medication is due to be filled/refilled (89.8%) and to support safe medication use for patients (80.8%), although fewer perceive accuracy as important for calculating morphine milligram equivalents (61.8%) and assessment of doctor shopping in the state prescription drug monitoring program (63.7%).
Conclusions: Between 10-20% of pharmacists inaccurately assigned days’ supply values to opioid analgesic Rx. While most believe accuracy in days’ supply is important to dispensing decisions, fewer consider it important for other activities such as surveillance monitoring. The estimated error rate from the survey will be used to inform the design of a validation study using stratification-sampled pharmacy records.