BackgroundDepressive disorders place a great burden on society and rank as the fourth leading cause of burden among all diseases. (WHO 2001) Antidepressants are the first-line treatment for major depressive disorder in Norway. Escitalopram (Cipralex®) is a patented antidepressant and therefore more costly than the generic drug citalopram. Since its introduction in the Norwegian market in 2002, the market share of escitalopram has increased sharply and accounted for NOK 131 mil in 2005. The same year, sales of citalopram were NOK 43 mil. By comparing costs and effects of the two drugs, an incremental cost-effectiveness ratio will indicate whether switching to escitalopram is a cost-effective option.MethodsThe study was based on a decision analytic model (decision tree) developed in Tree Age Pro Healthcare Module program for the adult Norwegian patients with major depressive disorder. Data used in the model consisted of costs and effectiveness data for citalopram and escitalopram. Cost data included relevant costs for each of the treatments from two perspectives: the health care payer perspective and the societal one. Effectiveness data were based on clinical trials. The time perspective of the model was six months. Health consequences were measured in terms of symptom reduction and translated into the quality- adjusted life years (QALYs). In one-way sensitivity analyses on all parameters, the results were, in the societal perspective, robust for all parameters except for the probability of a good response in the escitalopram group. When lower bound (0.39) was used for good response rate in escitalopram group, results have changed so that escitalopram was not cost-effective.ResultsThe proportion of patients who had symptom reduction after six months increased by 5% (from 80% to 85%) by replacing citalopram with escitalopram. When indirect costs were taken into consideration (societal perspective), the cost per additional successfully treated patient was NOK 18 600. From the health care payer perspective, this cost was NOK 27 000. Assuming that one successful treatment is equivalent to 0.11 QALYs, the cost per QALY was NOK 169 000 and 245 000, respectively for the societal and health care perspective.ConclusionEscitalopram is a cost-effective option for treatment of major depressive disorder in Norway. This conclusion is valid for both the societal and the health care payer perspective.