Days’ Supply Pharmacy Validation


What are we studying?

How do we know how many days a prescribed opioid analgesic was supposed to be taken by a patient? It seems like a simple problem, but the implications are profound – we may mistake a low dose prescription for a high dose prescription if this number is not accurate. For example, if we just know that 30 tablets were dispensed we may not know if they were meant to be taken once a day for 30 days, or 5 times a day for 6 days. Sometimes opioids are taken “as needed for pain” (pro re nata or prn) and the number of days is not specified. How do pharmacists code days’ supply when the prescription says to take two tablets a day, but an odd number of pills is specified?

In most states, pharmacists calculate by hand the “days’ supply” (the number of days a prescription is intended for), because doctors don’t always write out the number of days. The days’ supply then gets put into a database at the pharmacy along with all the other information on a prescription (prescriber and patient names and addresses, drug dispensed, quantity, dose strength, etc.). These databases are used for research, but we don’t know how consistent the days’ supply calculations are. There is discretion at the pharmacist level and we would like to find out how consistent and accurate interpretations of doctors’ instructions are.

Why it matters

The days’ supply is a key number that allows us to calculate average daily dose for an opioid prescription. For example, if a patient receives 10 tablets of dose strength 50 milligrams of morphine each, then the total is 500 milligrams. If the days’ supply is 5 days, we divide 500 by 5 days to arrive at an average daily dose of 100 milligrams per day, which some guidelines consider to be a “high dose.” But, if the prescription is really supposed to be consumed over 10 days, the average daily dose would be 50 milligrams per day. Since days’ supply isn’t always written on the prescription, it is up to busy pharmacists to make this calculation at the moment of dispensing, interpreting the doctors instructions.


How we are studying it

The days’ supply is a key number that allows us to calculate average daily dose for an opioid prescription. We will go to dozens of pharmacies in Kentucky and review 10 randomly selected prescriptions at each, matching up what is written down on the paper prescription with what was entered into the database. This study will be completed in 2020.

How to use the results

The accuracy and consistency results will be used to inform database studies where average daily opioid dose (calculated as milligrams of morphine equivalents) is critical to evaluating changes in policies and medical practice. Results from our study can be plugged into sensitivity analyses where we estimate a range of possible outcome values based on assumptions of how accurately and consistently days’ supply is calculated. The results will be made public on this website for other researchers to calibrate their own studies.

Who is conducting the study

This study is being led by Patricia Freeman at the University of Kentucky College of Pharmacy. The data are being collected by John Brown, and analyzed as a team. This study is funded by the United States Food and Drug Administration, but is conducted by independent researchers at the University of Kentucky and the University of North Carolina at Chapel Hill.

John Brown

Nabarun Dasgupta
Epidemiologist, Factotum