Biologics in Psoriasis; a Step towards Individualized Treatment

Psoriasis is a chronic immune-mediated skin disease with a prevalence of 2 to 3% in the Caucasian population. Since there is a better understanding of the pathogenesis of psoriasis, specific targeted therapies have been developed. The biologics have dramatically changed the management and outlook of patients with psoriasis. However, there are some difficulties with the treatment of biologics in psoriasis. One problem is that biologic monotherapy appears to loose efficacy over time which results in reduced drug survival. Another problem is that a proportion of patients with stable low disease activity on long-term maintenance treatment with biologics may be overtreated. We believe that a more individualized treatment of biologics is necessary to overcome these problems. In addition, monitoring of biologic trough concentrations (therapeutic drug monitoring, TDM) could be an useful tool to optimize individualized treatment of biologics. As result of individualized treatment, it hopefully will lead to an extended drug survival and an increase of the quality of life and treatment satisfaction. TDM of biologics can be used as tool for individualized treatment of biologics and increase drug adherence. First, evaluation of conditions for TDM is warranted before implementation of TDM in psoriasis.

Current literature shows that the evidence is scarce for individualized treatment strategies of biologics in psoriasis, and we hope that this thesis will be a good start. Our final conclusions are as follows:
Combination therapies (part I):
- Combination therapy of biologics with MTX may increase the drug survival. Therefore combination therapy of adalimumab with MTX is currently being investigated in a RCT.
- Combination therapy of etanercept with fumarates results in a higher efficacy in psoriasis patients, but may be inferior to the novel IL-12 and IL-23 and IL-17 inhibitors.
Biologic dosing interval prolongations (part II):
- In patients with sustained remission biologic dosing interval prolongations should be considered, as cost reductions are substantial.
Conditions for therapeutic drug monitoring (TDM) (part III):
- Harmonization of assays for measurement of biologics is warranted to compare data on biologic trough concentrations.
- The intra-patient variability of etanercept concentrations complicates TDM and should also be investigated for other biologics.

The explored strategies in this thesis are just the first steps towards individualized treatment. More studies are needed for implementation of individualized treatment of biologics in psoriasis.