MODELING THE COST-EFFECTIVENESS OF ANTIDEPRESSANT TREATMENT IN PRIMARY-CARE

The aim of this study was to estimate the cost effectiveness of nefazo done compared with imipramine or fluoxetine in treating women with maj or depressive disorder. Clinical decision analysis and a Markov state- transition model were used to estimate the lifetime health outcomes an d medical costs of 3 antidepressant treatments. The model, which repre sents ideal primary care practice, compares treatment with nefazodone to treatment with either imipramine or fluoxetine. The economic analys is was based on the healthcare system of the Canadian province of Onta rio, and considered only direct medical costs, Health outcomes were ex pressed as quality-adjusted life years (QALYs) and costs were in 1993 Canadian dollars ($Can; $Can1 = $US0.75, September 1995). Incremental cost-utility ratios were calculated comparing the relative lifetime di scounted medical costs and QALYs associated with nefazodone with those of imipramine or fluoxetine. Data for constructing the model and esti mating necessary parameters were derived from the medical literature, clinical trial data, and physician judgement. Data included informatio n on: Ontario primary care physicians' clinical management of major de pression; medical resource use and costs; probabilities of recurrence of depression; suicide rates; compliance rates; and health utilities. Estimates of utilities for depression-related hypothetical health stat es were obtained from patients with major depression (n = 70). Medical costs and QALYs were discounted to present value using a 5% rate. Sen sitivity analyses tested the assumptions of the model by varying the d iscount rate, depression recurrence rates, compliance rates, and the d uration of the model. The base case analysis found that nefazodone tre atment costs $Can1447 less per patient than imipramine treatment (disc ounted lifetime medical costs were $Can50 664 vs $Can52 111) and incre ases the number of QALYs by 0.72 (13.90 vs 13.18). Nefazodone treatmen t costs $Can14 less than fluoxetine treatment (estimated discounted li fetime medical costs were $Can50 664 vs $Can50 678) and produces sligh tly more QALYs (13.90 vs 13.79). In the sensitivity analyses, the cost -effectiveness ratios comparing nefazodone with imipramine ranged from cost saving to $Can17 326 per QALY gained. The cost-effectiveness rat ios comparing nefazodone with fluoxetine ranged from cost saving to $C an7327 per QALY gained. The model was most sensitive to assumptions ab out treatment compliance rates and recurrence rates. The findings sugg est that nefazodone may be a cost-effective treatment for major depres sion compared with imipramine or fluoxetine. The basic findings and co nclusions do not change even after modifying model parameters within r easonable ranges.