Background and importance The introduction of the first biological drugs has led to a new era for patients. Moreover, the recent arrival of biosimilars has guaranteed effectiveness at a more sustainable cost. We compared the recently approved biological drugs with biosimilars and older biological molecules, using a new cost effectiveness analysis approach.

Aim and objectives To compare the long term therapy cost and cost effectiveness of biological systemic therapies for treating patients with moderate to severe plaque psoriasis.

Material and methods We collected therapy costs from our internal hospital database. We reported the purchase price, including any discounts. Efficacy data, measured with the PASI index, for 12/16 weeks, was obtained from a recent meta-analysis by Sawyer et al. We calculated the long term costs by multiplying the monthly cost for a single patient, including the induction phase. Our cost effectiveness analysis was performed by a correlation analysis between efficacy and the cost of therapy for the 12/16 weeks of treatment. We calculated, for each molecule at a different PASI, a correlation index (R) to investigate if a correlation between cost and efficacy could be established.

Results Cost analysis of the first year and the first 3 years of therapy showed how the introduction of biosimilar drugs greatly lowered global expenditure. The cost/PASI ratio showed that adalimumab and infliximab biosimilars were the most convenient drugs in relation to their cost and clinical effectiveness (57€/PASI90; 112€/PASI90, respectively).

In terms of efficacy alone, a greater therapeutic result was observed for the most recently approved molecules, especially for PASI90/100. The cost/PASI ratio of these newer therapies was convenient only for PASI90 and 100 (guselkumab 41€/PASI100). Therefore, there seems to be a positive, albeit weak, correlation between the effectiveness and cost of innovative drugs, especially for PASI90/100 where R increased with increasing PASI (PASI75, R=0.22; PASI100, R=0.32).

Conclusion and relevance The introduction of biosimilar drugs in the treatment of moderate to severe psoriasis has significantly lowered costs. From the correlation analysis, we observed some linearity between cost and efficacy; a higher cost correlated with greater efficacy, especially for PASI90/100. However, it should be noted that there is still a lack of longer term studies (over 16 weeks) comparing more consistently long term therapies with drugs of different classes.

References and/or acknowledgements https://doi.org/10.1371/journal.pone.0220868

No conflict of interest.