Objectives: To present our experiences of using the adjusted indirect comparison in a health technology assessment when randomised, direct comparisons between two competing interventions were unavailable.

Methods: We conducted a health technology assessment of two antiplatelet drugs, clopidogrel and modified-release dipyridamole, for the UK s National Institute for Clinical Excellence. A single randomised controlled trial (RCT) was identified for each drug versus aspirin. No trials were identified where the two drugs were directly compared. Using the methods proposed by Bucher and colleagues we undertook an indirect comparison. This method aims to overcome the potential problems associated with different prognostic characteristics between participants in the studies being compared. However, it is only valid when the magnitude of the treatment effect is consistent between the different studies.

Results: There were a number of differences between the two studies identified that limited the interpretation of the adjusted indirect comparison. A number of assumptions had to be made about the similarities of the patients in the two trials with regards to the dose of the comparator and in particular to the population under study. It was doubtful that the magnitude of the treatment effect was consistent between the two studies.

Conclusion: In the context of HTA there is a need for evidence about the relative effectiveness of competing interventions. The adjusted indirect comparison may provide useful information, which otherwise, is lacking. However, it is important that the internal validity and similarity of the trials being compared is carefully examined and that the findings are interpreted cautiously.