Abstract
Background/Aims: Prior studies suggest that patients with a drug benefit cap decrease their treatment adherence and have poorer outcomes compared to patients with no limit. We examined differences in drug choice, adherence, and burden between patients who exceeded their cap and those that did not, focusing on subjects using a drug from at least one of five widely used therapeutic drug classes.
Methods: All subjects were continuously enrolled members of Kaiser Permanente Northern California (KPNC) in 2003, had a $1,000 annual drug benefit cap, Medicare insurance, and were 65 years and older. We identified the five therapeutic drug classes most frequently used by these subjects in 2003 (anti-lipemics, beta adrenergic blockers, angiotensin converting enzyme inhibitors, narcotic analgesic combinations, and anti-ulcer drugs) and limited our analyses to patients with at least one dispensing from one of these classes in 2002. We assessed the mean number of study classes used and other prescriptions dispensed. We used logistic regression models to examine the association between exceeding the benefit cap and adherence and generic use within each class, adjusting for patient characteristics and drug burden. We also examined cost differences between drugs dispensed and the least expensive drug within the class.
Results: Of the 97,922 subjects taking at least one of the study drugs, 15,926 (16%) exceeded the $1000 benefit cap in 2003. We found that subjects who exceed the benefit cap had a greater overall drug burden than patients who did not exceed the cap (2.4 vs. 1.8 study classes used; 25.1 vs. 11.8 dispensing of other drugs). After adjustment, patients who exceeded the cap were more likely to be adherent to their drug treatment regimen, but less likely to be a generic user compared to patients who did not exceed the cap, (e.g., anti-lipemics: 74% vs. 69% adherent, OR=1.3, 95% CI: 1.2–1.4; 56% vs. 84% generic users, OR=0.30, 95% CI: 0.28–0.31). In all study classes, patients who exceeded the cap predominantly received a drug that was not the least expensive option within the class (e.g., 83% received a higher cost anti-lipemic, mean annual difference overall = $286).
Conclusions: Drug choice, adherence, and burden all are strongly associated with overall drug expenditures as expected. Many patients who exceed their available drug benefits, however, are not on the least expensive drug regimens available to them.
- Received September 11, 2008.
