FIGURE 2.

Comparison of common approaches for establishing active medications at a fixed time point.

In the above diagram, grey bars represent days supplied by medication fills in hypothetical refill patterns for three medications prescribed to a patient. The index gap (IG) is the period between the last day supplied by the most recent fill and the index date. Medication A has an index gap of 0 days, medication B has an index gap of 70 days, and medication C has an index gap of 10 days. Two common approaches to establishing an active medication list are demonstrated as follows:

1. Fixed look-back period approach: Defines active medications as those for which any fill occurred during a specified period prior to the index date. Using a fixed look-back period of 30 days would classify medications A and C as active, while using a fixed look-back period of 90 days would classify medications A, B, and C as active.

2. Medication-on-hand approach: Also termed legend duration approach. Defines active medications as those for which the most recent refill date provided sufficient supply to last through the study index date. Using this approach, only medication A would be classified as active. An allowable index gap may be added to the medication-on-hand approach, and would define active medications as those for which the most recent refill provided sufficient supply to last through the study index date including a grace period, which can be defined either as a fixed number of days or as a given percentage of the duration of the most recent fill. Using an allowable index gap of 14 days would classify medications A and C as active.