Cost-effectiveness Analysis of Isavuconazole Versus Voriconazole for the Treatment of Patients with Possible Invasive Aspergillosis in Sweden

Background: Voriconazole is well established as standard treatment for invasive aspergillosis (IA). In 2017, isavuconazole, a new antifungal from the azole class, with a broader pathogen spectrum, was introduced in Sweden. A model has therefore been developed to compare the cost-effectiveness of isavuconazole and voriconazole in the treatment of possible IA in adults in Sweden.

Methods: The cost-effectiveness of isavuconazole versus voriconazole was evaluated using a decision-tree model. Patients with possible IA entered the model, with 6% assumed to actually have mucormycosis. It was also assumed that pathogen information would become available during the course of treatment for only 50% of patients, with differential diagnosis unavailable for the remainder. Patients who were considered unresponsive to first-line treatment were switched to second-line treatment with liposomal amphotericin-B. Data and clinical definitions included in the model were taken from the published randomised clinical trial comparing isavuconazole with voriconazole for the treatment of IA and other filamentous fungi (SECURE) and the single-arm, open-label trial and case-control analysis of isavuconazole for the treatment of mucormycosis (VITAL). A probabilistic sensitivity analysis was used to estimate the combined parameter uncertainty, and a deterministic sensitivity analysis and a scenario analysis were performed to test the robustness of the model assumptions. The model followed a Swedish healthcare payer perspective, therefore only considering direct medical costs.

Results: The base case analysis showed that isavuconazole resulted in an incremental cost-effectiveness ratio (ICER) of 174,890 Swedish krona (SEK) per additional quality adjusted life-year (QALY) gained. This was mainly due to the efficacy of isavuconazole against IA and mucormycosis, as opposed to voriconazole, which is only effective against IA. Sensitivity and scenario analyses of the data showed that the average ICER consistently fell below the willingness to pay (WTP) threshold of 1,000,000 SEK. The probability of isavuconazole being cost-effective at a WTP of 170,000 SEK per QALY gained was 50% and at a WTP of 500,000 SEK per QALY gained was 100%.

Conclusions: This model suggests that the treatment of possible IA with isavuconazole is cost-effective compared with treatment with voriconazole from a Swedish healthcare payer perspective.