Tsakok T, Wilson N, Dand N, et al. - In patients with psoriasis, researchers conducted this prospective observational cohort to assess the clinical utility of therapeutic drug monitoring for ustekinumab. From June 2009 to December 2017, 491 adults with psoriasis was recruited to the multicenter Biomarkers of Systemic Treatment Outcomes in Psoriasis study within the British Association of Dermatologists Biologic and Immunomodulators Register. Findings suggested an association of early serum ustekinumab levels with a subsequent 75% decline from baseline in Psoriasis Area and Severity Index score, although this connection did not hold across other Psoriasis Area and Severity Index outcomes. Drug immunogenicity seemed to be low, with antidrug antibodies identified in only 17 of 490 patients. Early serum ustekinumab levels measurement may be helpful in guiding the psoriasis treatment approach. In determining the clinical outcome, adequate drug exposure early in the treatment cycle can be particularly important.