Background In rheumatoid arthritis the concentration-effect relationship of adalimumab has been investigated. However, in psoriatic arthritis (PsA) there is a lack of knowledge about the pharmacodynamics and pharmacokinetics of adalimumab.
Objectives To investigate the relationship between serum adalimumab trough concentrations and clinical response in PsA patients after 28 weeks of treatment, using a concentration-effect curve.
Methods In this prospective cohort study 103 consecutive patients diagnosed with PsA were included and treated with 40 mg adalimumab subcutaneously every other week. Adalimumab concentrations at 28 weeks of treatment were measured in serum trough samples, using an enzyme linked immunosorbent assay (ELISA). Clinical response was defined as a change in disease activity score in 28 joints (ΔDAS28) between baseline and week 28. All patients were sorted from low to high adalimumab concentration (mg/L). Each dot represents 10 patients (the last dot represents 13 patients) and their mean adalimumab trough concentration and mean ΔDAS28.
Results At 28 weeks of treatment serum trough concentrations ranged from 0.0 to 18.8 mg/L, with a mean of 7.2 mg/L. Concentrations of approximately 1.0 mg/L already showed reasonable efficacy. Adalimumab concentrations of 5-8 mg/L appear most optimal. (see figure 1) Concentrations above 8 mg/L appear to have no additional benefit. In 48 (47%) patients adalimumab concentrations exceeded 8 mg/L. Furthermore 36 (35%) patients had adalimumab concentration below 5 mg/L.
Conclusions Adalimumab concentrations of 5-8 mg/L appear necessary for achieving the most optimal clinical benefit. A substantial group of PsA patients that uses adalimumab are not able to profit from this optimal clinical benefit. This study, in patients with PsA, confirms the results that have been found in RA patients.
Pouw MF et al. Key findings towards optimising adalimumab treatment: the concentration-effect curve. Ann Rheum Dis. 2013 [Epub ahead of print].
Disclosure of Interest E. Vogelzang: None declared, E. Kneepkens: None declared, M. Nurmohamed: None declared, A. van Kuijk: None declared, T. Rispens Speakers bureau: Pfizer and Abbvie, G. Wolbink Grant/research support: Pfizer, Speakers bureau: Pfizer and Amgen, C. Krieckaert Speakers bureau: Pfizer and Abbvie