OBJECTIVES

: The DPP examined 3 interventions, placebo (PBO), metformin (MET) and individual lifestyle (ILS) for diabetes prevention. A 3 year trial of these interventions added to a baseline lifestyle advice found that the two active interventions were effective, with ILS being more effective. A trial-based CEA indicated both were cost-effective. The original CEA erred in 2 ways – it failed to correctly calculate QALYs and it compared all interventions to a common, placebo, alternative. Our work corrected these errors, otherwise using the original CEA data for the societal perspective and a generic MET (MET25) as calculate in the original CEA.

METHODS

: The original CEA failed to gather baseline utilities and took utility measures at the end of each year, assigning that utility to the entire year. Correct methods would average utilities over a given time period, using beginning and end measures. Without baseline measures this cannot be done, but we show results under the assumption that baseline values were equal across treatment arms (arguably reasonable given the randomized allocation).

RESULTS

: If baseline utilities are equal, they drop out of any difference calculation between interventions. There remains a QALY difference, but is related to the terminal year utility differences. Both MET25 and ILS are on the CE frontier. Without the QALY correction, ILS is cost-effective if WTP is higher than $55K. With corrected QALYs, the ICER increases, so that it is possible that ILS is not CE and that MET is (if WTP is less than $68K).

CONCLUSIONS

: The 3 year DPP CEA concluded that both ILS and MET were cost-effective. We have shown this likely to be false, based on original data. Only by correcting the original work’s QALY calculation is there (a modest) chance that there is a role for (generic) MET in diabetes prevention from a societal perspective.