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Effectiveness and Cost-Effectiveness of Diabetes Prevention Among Adherent Participants
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Effectiveness and Cost-Effectiveness of Diabetes Prevention Among Adherent Participants

William H. Herman, MD, MPH; Sharon L. Edelstein, ScM; Robert E. Ratner, MD; Maria G. Montez, RN, MSHP; Ronald T. Ackermann, MD, MPH; Trevor J. Orchard, MD; Mary A. Foulkes, PhD; Ping Zhang, PhD; Christopher D. Saudek, MD†; and Morton B. Brown, PhD; The Diabetes Prevention Program Research Group
Over 10 years, among adherent participants, lifestyle intervention and metformin were effective and cost-effective for diabetes prevention compared with placebo.
Outcomes. We assessed outcomes for adherent participants as both incident diabetes and quality-adjusted life-years (QALYs).13 QALYs measure length of life adjusted for quality of life as assessed by the health utility score. By convention, health utility scores are placed on a continuum where perfect health is assigned a value of 1.0 and health judged equivalent to death is assigned a value of 0.0. We assessed health utilities annually using the Self-Administered Quality of Well-Being Index.14 Mathematically, QALYs are calculated as the sum of the product of the number of years of life and the quality of life, measured in health utilities, in each of those years.

Perspective. For the primary analysis, we followed the recommendations of the Panel on Cost-Effectiveness in Health in Medicine13 and took the perspective of a health system. Thus, we included only direct medical costs of the interventions and non-intervention–related medical care in our basecase analysis. We included direct nonmedical costs excluding participant time in a sensitivity analysis from a modified societal perspective and direct nonmedical costs including participant time in a sensitivity analysis from a full societal perspective. These sensitivity analyses assessed the impact of covering the cost of the interventions implemented by the study participants on society as a whole.

Analyses. The analyses of lifestyle and metformin were conducted for participants who adhered to the lifestyle intervention (as assessed by weight loss) and who regularly took metformin (as assessed by pill counts). The analyses of placebo were conducted for all participants randomized to the placebo group. For the DPP group lifestyle analysis, we estimated what the costs of lifestyle would have been during the 3 years of DPP if the 16-session core curriculum and monthly follow-up visits with the case managers had been conducted as closed-group sessions with 10 participants. We assumed that outcomes for DPP group lifestyle would have been the same as observed for the lifestyle intervention as originally implemented. We excluded from the analyses the costs of the research component of the DPP/DPPOS. All costs were expressed as year 2010 US dollars. Analyses were performed with a 10-year time horizon. Data on resource utilization were aggregated using SAS (SAS Institute, Cary, North Carolina). The aggregated resource utilization data were then multiplied by the unit cost and by the probability that a participant was followed during the time period. The latter analyses and the tables and figures were generated using Excel (Microsoft Inc, Redmond, Washington). Initial analyses were performed without discounting. Subsequently, where noted, both costs and health outcomes were converted to net present value using a 3% discount rate.

RESULTS

At 10 years, the cumulative incidence of diabetes was 52.4% among participants originally randomized to the minimal intervention arm that included placebo medication and standard lifestyle recommendations (ie, the “placebo” group). The incidence of diabetes was 41.5% among metformin participants who regularly took metformin, and 26.5% among lifestyle participants who achieved and maintained a 5% reduction in initial body weight (Figure 1). Compared with placebo, the absolute risk reduction at 10 years was 25.9% with lifestyle and 10.9% with metformin. The relative risk reduction was 49.4% with lifestyle compared with placebo and 20.8% with metformin compared with placebo. Due largely to the reduced incidence of diabetes, quality of life, as assessed by health utility scores, was better among adherent lifestyle and  adherent metformin participants than placebo participants. At 10 years, the mean undiscounted cumulative QALYsaccrued were 6.80 for lifestyle, 6.74 for metformin, and 6.67 for placebo participants. Compared with placebo participants, adherent lifestyle participants accrued 0.13 more QALY (ie, years of perfect health) over 10 years and adherent metformin participants accrued 0.07 more QALY.

The annual undiscounted per capita direct medical costs of lifestyle, DPP group lifestyle, metformin, and placebo over 10 years for adherent participants are summarized in Table 1 and Figure 2a. The costs of lifestyle ($3801) are $1578, or over 70%, greater than the costs of offering lifestyle in a group format ($2223) in DPP years 1 to 3 (DPP group lifestyle) because of the difference in resource utilization between an individual- and group-implemented intervention. The per capita costs of lifestyle were substantially lower during DPPOS than during DPP because of the change from an individual- to a group-implemented intervention, less frequent intervention sessions, and lower session attendance. The costs of placebo were slightly higher during DPPOS than during DPP because placebo participants engaged in the group lifestyle intervention.

The cumulative undiscounted per participant cost of the lifestyle intervention ($4810) was substantially greater than the estimated cost of the DPP group lifestyle intervention ($3232), the metformin intervention ($2934), or the placebo intervention ($768) (Figure 2b). Over 10 years, the cumulative undiscounted per capita incremental direct medical costs of the interventions were greater for adherent participants in lifestyle ($4042), group lifestyle ($2464), and metformin ($2166) compared with placebo.

The cumulative undiscounted per capita direct medical costs of non–intervention-related medical care by intervention group and year following randomization for adherent participants are shown in Table 2 and Figure 2c. These are the costs of medical care received outside the DPP/DPPOS. The cumulative direct medical costs of non–intervention-related medical care ($23,218 to $27,468 per person over 10 years) were substantially greater than the costs of the interventions ($768 to $4810 per person over 10 years). Among all groups, the costs of non–intervention-related medical care increased over time. Over 10 years, the cumulative, per capita non–intervention-related direct medical costs were $4250 greater for placebo participants compared with adherent lifestyle participants and $3251 greater for placebo participants compared with adherent metformin participants.

By year 10, cumulative undiscounted per participant total direct medical costs of the DPP/DPPOS interventions and medical care received outside the DPP/DPPOS were higher for placebo ($28,236) than for lifestyle ($28,027), DPP group lifestyle ($26,449), or metformin ($27,150) (Figure 2d). Thus, when both intervention- and non–intervention-related medical costs were considered, all 3 interventions saved money relative to the placebo intervention.

Cumulative, 10-year, diet-, physical activity-, transportation-,and time-related costs were similar across treatment groups ($147,704 for lifestyle, $146,999 for metformin, and $147,043 for placebo). Although adherent lifestyle participants spent more time exercising, the adjusted value of the time they spent exercising was not greater than for either metformin or placebo because of their greater enjoyment of leisure time physical activity and the lower opportunity cost.

Table 3 summarizes the differences in costs and QALYs and the incremental cost-effectiveness ratios of lifestyle, DPP group lifestyle, and metformin versus placebo and for lifestyle compared with metformin. From the health system perspective and without discounting, the total direct medical costs for the lifestyle, DPP group lifestyle, and metformin participants were less than for placebo participants and the interventions were more effective as assessed by QALYs gained. In other words, all 3 interventions were cost saving compared with placebo. With discounting and compared with metformin, lifestyle cost $2004 more but produced an additional 0.06 QALY over 10 years. From a health system perspective, with both costs and health outcomes discounted at 3% per year, the cost of lifestyle compared with placebo was $19,988 per QALY gained, the cost of DPP group lifestyle compared with placebo was $9688 per QALY gained, and the cost of metformin compared with placebo was $20,183 per QALY gained. The cost of lifestyle compared with metformin was $19,662 per QALY gained.

Without discounting, from both a modified societal perspective (excluding participant time) and a full societal perspective (including participant time), lifestyle cost <$5000 per QALY gained and both DPP group lifestyle and metformin were cost saving compared with placebo. Compared with metformin, lifestyle cost <$35,000 per QALY gained.

DISCUSSION

In this 10-year analysis of the combined Diabetes Prevention Program/Diabetes Prevention Program Outcomes Study, the cumulative incidence of diabetes was 26.5% among lifestyle participants who adhered to the lifestyle intervention, 41.5% among metformin participants who adhered to metformin, and 52.4% among placebo participants. Compared with placebo, lifestyle reduced the absolute risk of diabetes by 25.9% and metformin reduced the absolute risk of diabetes by 10.9%. The relative risk reduction associated with lifestyle was 49.4% and that associated with metformin was 20.8%. In our previous intent-to-treat analysis, the risk of diabetes at 10 years was 42% with lifestyle and 47% with metformin and 52% with placebo.2 It is not surprising that lifestyle and metformin were substantially more effective among participants who adhered to the interventions.

The benefit of metformin as assessed by QALYs gained was also greater in this analysis than in the intent-to-treat analysis. In this analysis, lifestyle participants accrued 6.80 QALYs over 10 years, metformin participants accrued 6.74 QALYs, and placebo participants accrued 6.67 QALYs. In the intent-to-treat analysis, lifestyle participants accrued a similar number of QALYs (6.81 QALYs) but metformin participants accrued fewer QALYs (6.69 QALYs).2 The lower QALYs gained in the intent-to-treat analysis of metformin participants may have been related to adverse events experienced by some metformin participants who subsequently were unable to remain adherent to therapy.

The cumulative undiscounted per capita direct medical costs of the DPP/DPPOS lifestyle and metformin interventions were higher in participants who were adherent to treatment than in participants in the intent-to-treat analysis.2 Lifestyle was approximately 5% more expensive ($4810 vs $4601), group lifestyle was 7% more expensive ($3232 vs $3023), and metformin was 28% more expensive ($2934 vs $2300). This likely reflects the greater adherence of participants to their interventions and greater resource utilization, especially in the case of metformin participants.

Undiscounted per capita direct medical costs of care outside the DPP/DPPOS were lower in lifestyle and metformin participants who were adherent to their randomized treatment assignments compared with intent-to-treat participants.2 This could, in part, reflect the substantially lower incidence of diabetes among participants adherent to the lifestyle and metformin interventions. The undiscounted per capita 10-year cumulative direct medical costs of care outside DPPOS were 5% lower for adherent lifestyle participants than intent-to-treat lifestyle participants ($23,218 vs $24,563) and 5% lower for adherent metformin participants than intent-to-treat metformin participants ($24,217 vs $25,615).2

 
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