In the metformin model, QALYs, life-years and costs were 13.20, 22.58, and $10,066 with metformin plus insulin and 13.33, 22.58 and $11,396 with metformin plus saxagliptin. The incremental cost per QALY gained with metformin plus saxagliptin was $9,966 over metformin plus insulin. When using life-years, metformin plus saxagliptin was dominated by metformin plus insulin, which was similarly effective but cheaper.
In the sulphonylurea model, QALYs, life-years and costs were 13.18, 22.53 and $10,406 with sulphonylurea plus insulin and 13.32, 22.53 and $11,688 with sulphonylurea plus saxagliptin. The incremental cost per QALY gained with sulphonylurea plus saxagliptin was $8,953 over sulphonylurea plus insulin. Incremental cost per life-year gained was $852,127.
At a threshold of $36,300 per QALY gained, the probability of saxagliptin strategies being cost-effective was 74% in the metformin model and 76% in the sulphonylurea model. The most influential inputs were disutilities, weight gain, assumptions related to a second-line therapy, HbA1c at baseline, patient age and dose of insulin in second-line treatment. The incremental cost per QALY did not exceed $18,150 in any of the simulations.