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Objective A 1-year semi-Markov model was constructed to simulate the cost-effectiveness of atypical and typical antipsychotic treatments for schizophrenia. Methods The core model comprised nine 6-week cycles and includes events such as survival, response, adverse events, and compliance. The nature, duration, intensity, and timing of adverse events were incorporated. Compliance was modeled as a function of health state, time, and adverse events. Three first-line treatments were considered (risperidone, olanzapine, and haloperidol oral) and the transition probabilities of switching between five different therapies (haloperidol oral, haloperidol depot, risperidone, olanzapine and clozapine) were included. Effectiveness was modeled based on a modified method of TWiST (time without symptoms and toxicity). The direct costs of utilization of medical resources are taken into account, including five different patient care settings, consultations, neuroleptic medication, laboratory tests, and treatment of side-effects. Results This paper reports the methodology used to construct the model and the results obtained when it was applied to the treatment of patients with schizophrenia in the Belgian health care system. Conclusions Over the study period, risperidone and olanzapine were more cost-effective than haloperidol and of the two major atypical drugs, risperidone was the more cost-effective.

Lyme disease produces a diverse clinical picture that can include serious and potentially debilitating cardiac, neurologic, joint, and skin involvement. It is characterized in three stages--early localized (stage I), early disseminated (stage II), and late disseminated (stage III)--and medical management is highly dependent on the stage at which the patient presents and the physician's awareness of available treatment options. This study was conducted to establish the medical and economic burden of Lyme disease in the overall US population, which included determining its endemicity in high-risk states and counties, describing current treatment patterns, measuring direct and indirect costs, and defining the cost burden by age group (18 years andor =18 years of age). Medical, epidemiologic, and economic data were collected, and an algorithm was developed representing the natural course of Lyme disease and the progress of health states over time following medical intervention. Using an annual mean incidence of 4.73 cases of Lyme disease per 100,000 population in the decision analysis model yielded an expected national expenditure of $2.5 billion (1996 dollars) over 5 years for therapeutic interventions to prevent 55,626 cases of Lyme disease sequelae. This estimate included both direct medical and indirect costs. However, there is evidence of considerable variation in incidence within states. Our findings support development of vaccination strategies for specific target groups.