Constraints on antidepressant prescribing and principles of cost-effective antidepressant use. Part 2: Cost-effectiveness analyses.

Cost-effectiveness studies are a useful tool in drug-choice decisions. They are appropriate when alternative therapies have different levels of effectiveness, as with antidepressants. The calculation of cost effectiveness is similar to that used by some authors to determine whether a drug should be included in a formulary, so it clearly has immediate practical application and potential acceptability. However, the actual acceptability of cost-effectiveness studies has been hampered by a lack of conformity over study objectives, methodology and use of available data, and this significantly affects results. Studies that focus on the same location and setting, and conducted at the same time, frequently provide different results in their conclusions, depending on the assumptions and viewpoints, and the effects of sampling error. For example, dosage can affect purchase price calculations, but also compliance and efficacy, which are important considerations. Moreover, conclusions based on cost disadvantages of new drugs are not appropriate for planning for the future, since a drug's market price tends to fall with time and increasing demand. Appropriate use of outcome measures is important, and treatment failures, as well as successes, should be considered. Cost-effectiveness analysis has been used to demonstrate an important point: even when the appropriate use of antidepressants and specialty care increases medical costs, it improves value for money. A variety of drugs for one indication should be available to the prescriber, as the most cost-effective one may differ between patient subpopulations. Many costs of morbidity, adverse effects and secondary effects of antidepressants remain to be properly quantified, but are likely to have an important influence on cost effectiveness. These costs are likely to be higher for tricyclic antidepressants than the newer reversible inhibitors of monoamine oxidase and selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors. Costing in some areas of health is relatively straightforward. Depression is among the most difficult areas to cost because of its gradation in severity, its chronic and recurrent nature, and its subtle effects on working capacity. Quantification of differences resulting from the use of different drugs has many pitfalls. Until now, each cost analysis of depression has differed from the last, and most have placed excessive reliance on poorly substantiated and hypothetical assumptions. More in-depth studies are required to define the most cost-effective policies for recommendation to healthcare decision-makers and antidepressant drug prescribers. Compliance, adverse effects, and safety in overdose are important factors. The impact of indirect costs also needs to be addressed.