Design and assessment of cost-effectiveness studies in AIDS populations.

Cost-effectiveness (CE) ratios are indicators of comparative efficiency of competing drugs. Unfortunately, they are subject to variations, depending on factors such as the study population chosen, the comparison treatment selected, and the economic analysis methods employed. CE ratios tend to be unfavorably skewed in the case of chronic illnesses, such as HIV disease, because management of AIDS patients is costly and complex. Routine AIDS therapy requires expensive drugs, treatment is directed at many disease stages and severities, and gain in patient survival is relatively short. Variations in disease stage, co-morbidities, and antiviral drug use produce variations in both the risk of opportunistic infections (OIs) and the routine costs of OI prophylaxis and thus affect the CE ratio. Routine therapy for AIDS varies among and even within communities. Overall, these factors translate to a widening gap between trial results (efficacy) and community outcomes (effectiveness). This article discusses these concerns and reviews methodologic issues that must be considered by decision-makers using CE analyses to describe a therapy's value.