Objectives: Interferon beta-1b has recently become available for the treatment of secondary progressive multiple sclerosis (SPMS). This study aims at estimating the cost-effectiveness of this new treatment that has been shown in a clinical trial to reduce the progression of the disease. Effectiveness is measured as the number of quality-adjusted life-years (QALYs) gained from the reduction in progression. Because the clinical trial period will only capture part of the treatment's effect in terms of QALYs gained, since benefits achieved during the trial will have an effect beyond it, the cost-effectiveness analysis involves modeling over the longer term using complementary data.

Methods: A Markov model with states based on disability expressed by EDSS scores was used. Transition probabilities were calculated directly from clinical trial data for the first 3 years and then extrapolated to 10 years. Mean costs and utilities for each Markov state were calculated from a population-based cross-sectional study in Sweden.

Results: The incremental cost per QALY is SEK 342,700 (US $39,250;US $1 = SEK 8.73, March 10, 2000) when all costs (direct, informal care, and indirect) are included (discounted 3%). When indirect costs are excluded, the cost per QALY is SEK 542,000 ($62,100).

Conclusions: Cost-effectiveness analysis in SPMS requires that the effect of treatment beyond clinical trials be included. Also, analysis should be done from a societal perspective, since many of the costs occur outside the healthcare system. The cost-utility ratios estimated in this analysis are at or below the mean threshold value indicated in a recent survey of health economists ($60,000).