Usefulness and correlation with clinical response of serum ustekinumab levels measured at 6 weeks versus 12 weeks

Background: Monitoring serum drug levels has been proposed as a useful tool for improving and personalizing the management of psoriasis. However, in the case of ustekinumab the usefulness of such monitoring was not demonstrated when drug levels were measured at week 12. Objectives: To evaluate the correlation of serum ustekinumab levels measured at weeks 6 and 12 with clinical response. Methods: In a prospective cohort study, we enrolled patients with psoriasis treated with ustekinumab 45 mg every 12 weeks for at least 24 weeks. We measured serum ustekinumab levels at weeks 6 and 12 in each patient. Using the absolute PASI score, response to treatment was defined as optimal (3 and 5). Results: About 54 serum samples from 27 patients were analyzed. No correlation was found between serum drug levels and absolute PASI at week 12. At week 6, an inverse linear correlation was found (p = .0001). Moreover, serum levels at week 6 were higher in patients with optimal, excellent and appropriate responses than in patients with an inappropriate response. Conclusions: Assessment of ustekinumab serum levels at week 6 could provide useful information in routine clinical practice.