Pharmacy & Therapeutics - September 2008 - (Page 539)

Copays and Oral Antidiabetic Drugs continued from page 536 Table 3 Treatment Patterns Copay Level Variable Total <$10 4,028 1,377 176 2,230 220 22 3 (34.2%) (4.4%) (55.4%) (5.5%) (0.5%) (0.1%) $10 – <$20 6,954 2,242 375 3,943 344 45 5 (32.2%) (5.4%) (56.7%) (4.9%) (0.6%) (0.1%) $20 – <$30 5,491 1,419 241 3,570 231 27 3 (25.8%) (4.4%) (65.0%) (4.2%) (0.5%) (0.1%) ≥$30 2,185 529 84 1,464 103 5 0 (24.2%) (3.8%) (67.0%) (4.7%) (0.2%) (0.0%) No. Treatment failure type No change 5,567 (29.8%) Add 876 (4.7%) Discontinue 11,207 (60.1%) Switch, different* 898 (4.8%) Switch, same* 99 (0.5%) Switch, both* 11 (0.1%) Time to treatment failure Mean days ± SD 189.3 ± 135.1 Median days 140 Medication Possession ratio Mean ± SD 0.57 ± 0.34 200.56 ± 137.98 173 0.58 ± 0.34 196.44 ± 136.29 153 0.57 ± 0.33 179.18 ± 131.63 122 0.52 ± 0.34 170.9 ± 131.10 108 0.52 ± 0.33 SD = standard deviation. * “Different” indicates a switch to a new drug within a different class; “same” indicates a switch to a new drug within the same class; and “both” indicates that both types of switches occurred simultaneously. group, provider’s specialty, geographic region, health insurance type, pre-index DCI, number of unique medications, and post-index insulin use. To assess the effect of the MPR on outcomes, we analyzed the subpopulation of 2,272 patients who had both baseline and post-index HbA1c measurements and who either discontinued OADs (n = 1,059 patients) or continued them (n = 1,213 patients). The mean baseline HbA1c was 8.10% ± 2.16%, and the mean post-index HbA1c concentration was 7% ± 1.66%. The mean MPR in this subpopulation was 68% ± 31%. The generalized linear model showed that for every 10% increase in the MPR, the absolute change in post-index HbA1c was a decrease of 0.12% ± 0.01% (P < 0.0001). We studied a large sample of patients from a wide geographic range of health plans who were just starting OADs as monotherapy. In contrast to monotherapy, regimens with multiple OADs have been associated with lower adherence6 and less glycemic control.21 The cohort consisted primarily of patients who received metformin, sulfonylureas, or TZDs; these findings are in accordance with previously reported trends indicating the increase in use of metformin and TZDs after their introduction and the corresponding decreased use of sulfonylureas.22,23 TZDs, the newest of these OADs, were associated with the highest mean copay, as expected, because they were available only as branded products. Most patients experienced treatment failure, usually in the form of discontinuing therapy. Each higher copay category DISCUSSION corresponded with a higher percentage of patients who discontinued OAD treatment. Along with the decrease in the In our study, an increased copayment for oral antidiabetic time to treatment failure observed with each increase in copay agents was a statistically significant predictor of treatment failcategory, patients who paid more for their medications were ure among patients with type-2 diabetes who received at least more likely to stop treatment. one OAD. This effect was observed overall and by drug class Mean copay levels were similar for metformin and sulfor OADs. To a lesser extent, the copay predicted a decrease fonylureas and were each $10 less than for TZDs. Correspondin adherence; overall, however, adherence was poor regardless ingly, MPRs were similar for metformin and sulfonylureas, of copay level. However, increased adherence was associated whereas the mean MPR was lower for patients taking TZDs. with improved HbA1c levels. As expected, mean MPR decreased Table 4 Copay Distribution by Drug Class with increase in copay category. An earlier study by Dailey et al. Biguanides Sulfonylureas TZDs Other had shown similar results but lower adherence rates than our study, alNo. 8,437 4,938 4,754 529 though the Dailey study was perCopay formed in older patients (mean age, Mean ± SD $14.81 ± 100.22 $14.12 ± 7.92 $24.43 ± 16.71 $25.76 ± 14.35 61 years).6 Furthermore, our model 25th percentile $7.00 $8.96 $20.00 $15.00 showed a statistically significant 50th percentile $10.00 $13.36 $20.00 $25.00 higher probability of treatment fail75th percentile $20.00 $20.00 $25.00 $30.00 ure with higher copays for OADs. SD = standard deviation; TZDs = thiazolidinediones. Models analyzing each class of Copay is given per 30 days’ supply. OADs in our study showed that for Vol. 33 No. 9 • September 2008 • P&T® 539

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Pharmacy & Therapeutics - September 2008 Contents Editorial Medication Errors Prescription: Washington New Drugs/Drug News/New Medical Devices Drug Forecast Effect of Prescription Copays on Adherence and Treatment Failure with Oral Antidiabetic Medications Vaccine Declinations Present New Challenges for Public Health Universal Health Care in America Digestive Disease Week and American Diabetes Association Pharmaceutical Approval Update

Pharmacy & Therapeutics - September 2008

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