Letter: body surface area and body muscle parameters may influence adalimumab trough levels.

Abstract

We read with great interest the publication by Lie et al.1 assessing the pharmacokinetic properties of adalimumab (ADA) and observing that body mass index (BMI) at the start of therapy may influence ADA levels at week 28. We have been interested in this topic also, so we would like to present our results and recommend them for further consideration. Some data show that BMI may influence the long-term efficacy of ADA in psoriasis,2 spondylo-arthritis3 and inflammatory bowel disease (IBD),4 but clear evidence to prove a relationship between ADA trough levels and efficacy is limited. Other data also support the fact that certain body parameters (e.g. body surface) may influence the clearance of monoclonal antibodies, particularly those that exhibit linear clearance,5 as ADA has. Our aim was to explore whether body composition influences ADA trough levels and its variability. We initiated ADA treatment (160/80/40EOW) in 18 IBD patients in our prospective study. ADA trough levels were measured at week 6 and 12. Body composition parameters, like fat-free mass index (FFMI), skeletal muscle index (SMI) and body fat mass index (BFMI) were measured by bioelectrical impedance analysis at inclusion. Similar to Lie et al., we found a stable intra-patient ADA level (8.00 ± 2.9 μg/mL and 7.73 ± 3.14 μg/mL at week 6 and 12, respectively). However, the intra-patient changes of ADA trough levels showed a negative correlation with body surface area (r = −0.682; P = 0.002) (Figure 1). Moreover, intra-patient ADA level variability correlated negatively with the parameters indicating muscle content of the patients (FFMI: r = −0.494, P = 0.045, SMI: r = −0.508, P = 0.038), but did not correlate with fat parameters (BFMI: r = −0.099, P = 0.708). These findings suggest that body surface area and body muscle parameters may influence the constancy of ADA trough levels. Results of our pilot study regarding the relationship between ADA trough levels and body composition need further confirmation in other studies. Declaration of personal and funding interests: None.