What PDC is
PDC is a claims-based adherence measure defined by the Pharmacy Quality Alliance. For a drug or drug class, it divides the days a patient had medication on hand by the days in their treatment period, which runs from the first fill to the end of the measurement year. A patient needs at least two fills on different dates to be counted.
The threshold is 80% for most chronic medications. Part D Star Ratings use PDC for statins, RAS antagonists, and diabetes medications, excluding hospice and ESRD patients. Those three measures are weight 3 in the 2027 Star Ratings. CMS finalized a sociodemographic status (SDS) risk adjustment for them starting with the 2028 Star Ratings (CY2024 MA and Part D final rule, CMS-4201-F, April 12, 2023). CMS has not posted the 2028 weights. Consultant analyses from Wakely and RISE expect weight 1 for 2028 and a return to weight 3 for 2029, so treat the 2028 weight as expected, not final.
PDC moves when patients refill on time, and that usually means solving a barrier: cost, transportation, side effects, or confusion. Rivvi runs refill and adherence outreach as two-way conversations and routes clinical questions to a pharmacist by warm transfer or task. "In just 3 months with Rivvi we're already 2 to 3 points higher on medication adherence," says Jennifer Saddanathan, PharmD, Director of Care Management at Southeast Medical Group.