TABLE 1.

Recommendations for Standardized Terminology and Definitions of Medication Adherence and Persistence for Electronic Data

Terminology for Medication Adherence or Persistence Construct	Recommended Foundational Definition	Components of Definition Requiring Study-Specific Decisions to Operationalize	Examples of Other Terms Previously Applied to the Same Construct ^*
Adherence
Primary Adherence^6,15	A new prescription was dispensed (“filled” or sold) within a defined number of days after the medication was ordered	Definition of “new prescription:” How far to look back to determine if the medication has been previously dispensed; 12 or 24 months commonly used Definition of “defined number of days:” The prescription must be dispensed within “x” days after the order was written, with “x” commonly60 or 30 days ^6,13,17	First-fill adherence¹³ Adoption³² Initiation³³
Primary Non-adherence^15- ¹⁷	Failure to have a new prescription dispensed (did not pick up the first prescription) within a defined number of days after the medication was ordered	Definition of new prescription(see Primary Adherence) Definition of “defined number of days:” The prescription must not be dispensed within “x” days after order was written, with “x” commonly 60 or 30 days^6,13,17	Dispensation delay³⁴
Secondary Adherence⁶	Adherence measured among patients with Primary Adherence) and who have the prescription refilled within a defined number of days following the end of the days’ supply of the first dispensing. Secondary adherence is usually measured over 6 or 12 months or longer^†	Definition of “prescription refill…defined number of days:” The prescription must be refilled within “x” days after exhaustion of the days’ supply of the first dispensing. Sometimes referred to as the grace period	Ongoing dispensing/use¹⁷ Implementation³¹
Adequate Secondary Adherence	Secondary adherence with either an overall a) gap in days of medication possession not exceeding 20% of the days between the date of initial dispensing and the date of the end of the measurement period (gap measures) or b) number of days of medication possession of no less than 80%of the days between the date of initial dispensing and date of the end of the measurement period (possession measures)	By convention – only rarely with supporting evidence – the following cut-points have commonly been used: Gap: CMG < 20% NPMG < 20% Possession: MPR >= 80% PDC >= 80%	Adequate adherence³⁵ Adherence³³ Ongoing adherence⁶ Compliance
Inadequate Secondary Adherence	Secondary adherence with either an overall a) gap in days of medication possession exceeding 20% of the days between the date of initial dispensing and the date of the end of the measurement period or b) number of days of medication possession of less than 80% of the days between the date of initial dispensing and the date of the end of the measurement period	By convention – only rarely with supporting evidence – the following cut-points have been used: CMG > 20% to < 60% or upper cut- point can be as high as 100% NPMG > 20% to < 60% or upper cut-point can be as high as < 100% MPR > 40% to < 80% or lower cut- point can be as low as 0%) PDC > 40% to < 80% or lower cut- point can be as low as 0%) Sometimes further subcategorized into MPR or PDC ≥ 60 – 80%, ≥ 40 – 60%, and < 40%	Partial adherence Poor adherence³⁶ Inadequate adherence Non-compliance

Persistence
Early-stage Persistence⁶	A new prescription was dispensed (Primary Adherence) and at least one refill of that prescription was dispensed over a time period consistent with (implying) current use of the drug	Definition of time period allowed or considered between the new prescription dispensing and the one refill.	Point-of-Time Persistence Early Persistence Persistence³⁷
Early-stage Non- persistence^10,38	Failure to have the new prescription refilled over a time period consistent with current use of the drug	Definition of time period allowed or considered between the new prescription dispensing and the one refill.	Early Non-persistence
Later-stage Persistence	Two or more refills (i.e., the new prescription was dispensed and at least 2 refills of that prescription were dispensed) over a time period consistent with current use of the drug. The time period can span several refills that occur over 6 months, 12 months, or longer	Definition of time periods allowed or considered between refills; can include definition of time period allowed after last refill in the measurement period	Second stage persistence⁶ Refill compliance Persistent/Persistence^31,38- ⁴³
Later-stage Non-persistence	Failure to have two or more refills over a time period consistent with current use of the drug. Can imply either that the patient has discontinued the medication or that usage is inconsistent over time	Definition of time periods allowed or considered between refills; can include definition of time period allowed after last refill in the measurement period	Second stage non- persistence Suboptimal persistence Not persistent Non-persistence^34,44

Discontinuation
Discontinuation^32,45-48	Failure to have a medication dispensing within a defined number of days after exhaustion of the days’ supply of the previous dispensing (often includes exhaustion of any stockpiled medication accumulated from previous dispensings)	Definition of “defined number of days after exhaustion of the days’ supply of the previous dispensing;” 180 days often used	Termination⁴⁰ End of therapy

The terms listed in this column are provided as examples of terminology used in the published literature. The terms and their use within the cited publication(s) can be quite different from the Recommended Foundational Definition presented here. In some cases these example terms can have been used imprecisely or were incorrectly applied in the cited publication(s).

^†

Secondary adherence can only be measured among patients who have at least early-stage persistence.