Part III of this monograph deals with the direct healthcare costs of drug-related HCV infection. However, contributions to this part do have a broader reach than this description suggests. Postma et al. present estimates of drug-related costs due to HCV infection in conjunction with such estimates for two other important drug use transmissible infections: HBV and HIV. Wong et al. present a full pharmaco- economic evaluation for antiretroviral combination therapy for HCV. Both contributions have in common that the focus is on direct healthcare costs, in contrast to Part IV in which wider cost categories are considered.
In pharmaco-economics, several classifications are used for expressing the
consequences of disease on resource utilisation: direct (for example, hospital care) versus indirect costs of production losses, medical (healthcare) versus non-medical costs (for example, those related to care by family and friends) and patient-related versus general programme costs. These classifications have been widely used to address the economic impact of the HIV/AIDS epidemic (Postma, 1998). Direct healthcare costs considered in this part are all patient related; i.e. the patient is the cost driver. General programme costs (such as those of detoxification facilities), indirect costs of production losses, and non-medical costs are considered in Part IV. Furthermore, pharmaco-economics deploys various methods for economic evaluation. Three major areas distinguished are: cost-of-illness studies, cost- effectiveness analyses and cost-utility analyses (Postma, in press). The contribution by Postma et al. is a cost-of-illness assessment, whereas that by Wong et al. integrates the approaches of cost-effectiveness and cost–utility analyses. The former contribution therefore touches on two crucial discussions in cost-of-illness assessments — the usefulness of these types of studies in general, and the development of guidelines for appropriate costing. The latter study considers central issues in cost-effectiveness and cost–utility — such as discounting of health gains in terms of life years and quality of life gained.
Cost of illness in IDUs has been investigated for HIV in several instances, for example in the framework of the EU concerted action on multinational AIDS scenarios (Postma, 1998). To enhance the relevance of cost-of-illness assessments, several projects have been undertaken to develop guidelines for a generic
approach. Again, some of this work has been centred around the topic of HIV economics, for example in the framework of an EU project (Tolley and Gyldmark, 1993). The current estimate by Postma et al. in this part reflects an update of a
billion for drug-related HCV costs in France, Germany, Italy, Portugal, Spain and the UK (1999 price level). Extrapolated to the whole of the EU, and taken together with the costs of drug-related HBV and HIV, these costs reflect approximately 0.5 % of total EU healthcare expenditures.
Cost-of-illness studies have encountered criticism in the scientific literature
(Drummond, 1992). It has been argued that: (i) its usefulness for decision-making is limited; (ii) exact costing may be done using various methods; and (iii) it may be arbitrary where to draw the line with respect to the inclusion and exclusion of various cost sectors. (i) Plain assessment of cost figures may be of limited importance, in particular if the investigator neglects to put these figures into the appropriate perspective. However, putting figures into perspective (for example, by expressing them as a percentage of total healthcare expenditures) helps decision- makers to understand the relative impacts of different problems. Furthermore, we note that cost-of-illness studies are often a prerequisite for further analyses using the cost-effectiveness or cost-utility designs. (ii) Development of guidelines on how to measure and value costs may be helpful to enhance the comparability and validity of applied studies and designs. Guidelines are developed for both cost-of- illness and cost-effectiveness studies (Tolley and Gyldmark, 1993; Single et al., 1996; Hjelmgren et al., 2001). (iii) Especially with respect to cost assessments in drug users, the cost-of-illness design has been criticised regarding the choice of which cost categories to include and which to exclude (Uhl, 1998). Indeed, such a choice may sometimes seem arbitrary to the outsider and may merely reflect a consensus of those debating on the design of such studies. For example, one category that often raises debate refers to the direct medical costs in life years gained. Similarly, the total costs of drug use may be greatly inflated by the costs of police enforcement or imprisonment, which follow from arbitrary societal decisions regarding drug policy.
Wong et al. combine the cost-of-illness design with cost-effectiveness and cost–utility analyses of antiviral combination therapy. The specific combination therapy considered consists of interferon alpha 2b and ribavirin, a combination that has recently proved to double the beneficial effects of classical interferon treatment in randomised clinical trials. They deploy a previously published and validated Markov model to estimate the lifetime direct medical costs of HCV infection (Wong et al., 1998). The model was adapted to include combination therapy and allow for relapse into drug use and reinfection with HCV.
The analysis by Wong et al. allows the expression of the cost-effectiveness of combination therapy as a variety of outcomes: US dollars per life year gained, per