Comparative Cost Effectiveness of Metformin Monotherapy and Metformin/dipeptidylpeptidase4 Inhibitor Combination Therapy in Drug Naïve Type 2 Diabetes Patients at Kenyatta National Hospital

Abstract

Introduction The combination of metformin and Dipeptidyl Peptidase 4 inhibitors has superior health outcomes as compared to metformin alone. However, the cost may be prohibitive and the combination is being considered as a replacement of metformin alone as first line therapy for management of Type 2 diabetes. The comparative cost effectiveness of either treatment is unknown. Objectives To compare the cost effectiveness of changing the first line therapy in the treatment of Type 2 diabetes mellitus from metformin monotherapy to dual therapy of metformin and Dipeptidyl Peptidase 4 inhibitors in drug naïve patients. Methodology The study was divided into three parts. The first part was a local and international price survey on the prices of metformin and Dipeptidyl Peptidase 4 inhibitors. The second part, a key informant interview with staff at Kenyatta National Hospital to identify the key resource input required in the management of diabetic nephropathy and lastly a Markov chain model is developed to obtain the long term cost and effectiveness of treating type 2 diabetes patients on either metformin monotherapy or metformin/Dipeptidyl Peptidase 4 inhibitor dual therapies. The design was a predictive model based cost effectiveness study. The comparator interventions were metformin monotherapy and metformin/Dipeptidyl Peptidase 4 inhibitor dual therapy. Costing was done from the perspective of the provider and only health care costs were considered. The time horizon was 25 years. A macro-ingredient approach was considered for costing. Effectiveness data was obtained from literature and the measures of effectiveness was the life expectancy and time to development of diabetic nephropathy. A sensitivity analysis was used to determine how variation in the costs of the different therapies affected the overall cost effectiveness ratio. 10 Results The factors affecting the price of metformin andDipeptidyl Peptidase inhibitors were found to be the pack size of the drug (P<0.05) and the country of importation of the drug (P<0.05). The median local price of the daily defined dose of metformin was KShKSh22.8 (International United States Dollar (IUD) 0.48). The median price ratio of the international median price and the local median price of metformin 500mg tablets and 850mg was 1.3 and 8.4 respectively. The median local price of a daily defined dose of Dipeptidyl Peptidase 4 inhibitors was KShKSh 58 (IUD1.22) while that of Fixed Dose Combination of metformin and Dipeptidyl Peptidase 4 inhibitors was KShKSh122 (IUD 2.58). The annual cost of dialysis treatment, with the perspective of the health provider, at Kenyatta National Hospital was found to be KShKSh 1,871,640 (IUD 39,678). The annual cost of treating microalbuminuria and macroalbuminuria was KShKSh 174,360 (IUD 3696) and KShKSh 251,160 (IUD 5324) respectively. The crude life expectancy of drug naïve diabetic patients taking metformin was 21 years. Those taking Fixed Dose Combination of metformin/Dipeptidyl Peptidase 4 inhibitors had a crude life expectancy of 23 years. The incremental cost effectiveness ratio of Fixed Dose Combination of metformin/Dipeptidyl Peptidase 4 inhibitors compared with metformin monotherapy in drug naïve diabetes patients was found to be 336,698 (IUD 7138) per person per year. CONCLUSION It is more cost effective to treat drug naïve type 2 diabetes patients with dual therapy of metformin and Dipeptidyl Peptidase inhibitors as compared to metformin monotherapy.