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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.

The possibility of monitoring serum drug levels has opened the door to optimising biologic therapy. To consolidate this advance, it is imperative to demonstrate an adequate correlation between serum drug levels and clinical course.To investigate whether a correlation exists between adalimumab levels and clinical response measured as absolute PASI.In a prospective cohort study, we enrolled 51 patients with psoriasis treated with adalimumab for at least 16 s. Patients received approved doses of adalimumab, but after 52 s the dosing interval could be modified according to clinical criteria. Excellent response was defined as PASI ≤3, appropriate response as PASI3 and ≤5 and inappropriate response as PASI 5. Correlations were calculated using Spearman's correlation test.A total of 92 serum samples from 51 patients were analysed. Significant differences were found in serum trough levels between patients achieving an excellent response (6.46 μg/mL), versus an appropriate (2.5 μg/mL) and an inappropriate response (2 μg/mL). The therapeutic range for adalimumab serum levels was from 3.30 to 7.30 μg/mL.We found an adequate correlation between drug serum levels and PASI scores. Monitoring of absolute PASI and serum levels can provide a personalised and cost-effective evaluation.