Pharmacy & Therapeutics - September 2008 - (Page 536)

Copays and Oral Antidiabetic Drugs Table 2 Study Population Characteristics Drug Class Total No. Age Mean ± SD, years Median Sex Male, No. (%) Female, No. (%) DCI Mean ± SD Median Unique medication count Mean ± SD Median Comorbidities, n (%) Hypertension Dyslipidemia Ischemic heart disease Provider specialty Family/general practice Internal medicine Endocrinology/metabolism Geographic region of health plan Southeastern Western Central Mid-Atlantic 18,658 53 ± 12 Biguanides 8,437 (45.2%) 52.2 ± 11.3 52 4,237 (49.8%) 4,200 (50.2%) 1.2 ± 1.0 1.0 1.3 ± 0.5 1.0 11,735 (62.9%) 8,953 (48.0%) 2,008 (10.8%) 7,106 (38.1%) 6,793 (36.4%) 779 (4.2%) 12,708 3,350 1,970 630 (68.1%) (18.0%) (10.6%) (3.4%) 5,135 (60.9%) 3,970 (47.1%) 738 (8.8%) 3,227 (38.3%) 2,944 (34.9%) 426 (5.1%) 5,762 2,054 313 308 (68.2%) (24.3%) (3.7%) (3.7%) Sulfonylureas 4,938 (26.5%) 54.9 ± 12.6 55 2,051 (41.5%) 2,887 (58.5%) 1.4 ± 1.3 1.0 1.3 ± 0.6 1.0 3,051 (61.8%) 2,084 (42.2%) 631 (12.8%) 1,813 (36.7%) 1,798 (36.4%) 147 (3.0%) 3,420 959 379 180 (69.3%) (19.4%) (7.7%) (3.7%) TZDs 4,754 (25.5%) 54.0 ± 11.3 54 2,056 (43.3%) 2,698 (56.8%) 1.5 ± 1.2 1.0 1.2 ± 0.5 1.0 Others 529 (2.8%) 55.8 ± 12.4 56 259 (49.0%) 270 (51.0%) 1.7 ± 1.5 1.0 1.4 ± 0.7 1.0 8,603 (46.1%) 10,055 (53.9%) 1.3 ± 1.2 3,188 (67.1%) 361 (68.2%) 2,601 (54.7%) 298 (56.3%) 547 (11.5%) 92 (17.4%) 1,895 (39.9%) 171 (32.3%) 1,835 (38.6%) 216 (40.8%) 167 (3.5%) 39 (7.4%) 3,177 1,139 319 119 (66.8%) 349 (66.0%) (24.0%) 119 (22.5%) (3.1%) 38 (7.2%) (2.5%) 23 (4.4%) DCI = Deyo–Charlson Comorbidity Index; SD = standard deviation; TZDs = thiazolidinediones. In Drug Classes, “Other” includes meglitinide analogues and alpha-glucosidase inhibitors. disease (11%). Obesity and the common diabetic complications (nephropathy, neuropathy, and retinopathy) occurred in fewer than 5% of the overall population. Other vascular comorbidities were similarly uncommon. Fewer than 1% of the population needed an amputation. In general, the frequency of comorbidities was similar for the different OAD drug classes, as were provider type and health plan geographic region. Copayments Table 4 shows the copay distribution for each 30-day supply of OAD by drug class. The lowest median copay was observed for metformin ($10), the most frequently received OAD. The median copays for sulfonylureas ($13) and TZDs ($20) were higher. The least frequently prescribed drug class (other) was associated with the highest mean copay ($26) and the highest median copay ($25). Treatment Patterns Initial treatment failed for 13,091 patients (70%). Most of the patients (60%) discontinued therapy, whereas 5% of patients added, and 5% switched to, a new class of OADs. Overall, the mean time to treatment failure was 189 days. Table 3 shows the type of the time to treatment failure and copay levels for the total study population. The percentage of patients who discontinued treatment increased from 55% in the group with a copay under $10 to 67% in the group with a copay of $30 or more. Mean and median time to treatment failure decreased for patients in consecutively higher copay level categories. The mean MPR in the overall population was 0.57. As shown in Table 3, lower mean MPRs were observed with higher copay levels. The mean MPR decreased from 0.58 in the group with a copay of less than $10 to 0.52 for patients with a copay of $20 or more (P < 0.001). Multivariate Analyses A Cox proportional hazards model evaluating the impact of copay on treatment failure (discontinuing or switching from the index OAD) showed that for every $10 increase in copay, OAD therapy was 26% more likely to fail (95% confidence inter val [CI], 22.3%–29.8%). We also conducted analyses according to OAD therapeutic class; regardless of drug class, for every $10 increase in copay, OAD treatment was more likely to fail. The increase in the tendency for treatment failure ranged from 10.4% with TZDs to 27.8% with sulfonylureas (Table 5). The generalized linear model, used to estimate the effects of index copay amount on the MPR, showed that for every $10 increase in index copay, the MPR decreased by 1.5% (95% CI, 1.2%–1.9%) after our adjustments for age, sex, index drug continued on page 539 536 P&T® • September 2008 • Vol. 33 No. 9

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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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