Background Loss of response of TNFα inhibitors (TNFi) over time resulting in discontinuing of this therapy is a major issue in RA, but underlying reasons for this remains unknown. A few studies suggest the influence of BMI on serum levels of subcutaneous TNFi. However, there is no available data on the possible influence of BMI on infliximab (IFX) serum levels, which is intravenously administred and adjusteing the dose according to patient weight.
Objectives To determine the possible influence of BMI on serum IFX levels in patients with RA.
Methods Retrospective observational study incluiding 72 patients with RA treated with infliximab, at 3 mg/kg dose in a standard regimen, in our department between 2000 and 2015. Serum IFX levels were determined by ELISA in 3 visits: i)2 weeks, ii)six months and iii)one year after treatment onset. BMI (kg/m2) was classified in four categories: underweight (<18,5), normal (≥18,5- <25), overweight (≥25- <30) and obesity (≥30). Descriptive analysis was used to compare drug levels between these four groups at each visit. To analyse the relationship between BMI and IFX drug levels, generalized estimation equation models adjusted for age, gender and concomitant treatment were employed.
Results Characteristics of patients included in the study when initiating IFX therapy were: 88% female, median (range) age 52 (21–82) years, 71% RF+, 79% ACPA+, disease duration 10,4 (1,0–39,0) years, 79% with concomitant methotrexate and 57% with other DMARDs. Median (range) BMI was 25,5 (16,7–40,2) kg/m2. According to BMI, patients with underweight, normal, overweight and obesity were 2 (2,7%), 35 (48,6%), 23 (31,9%) and 12 (16,7%), respectively. Median (range) IFX serum levels, in ng/ml, for each of the four BMI categories,and for each of the visits, are presented in Table 1.
In the longitudinal analysis, an inverse statistically significant relationship between BMI and drug serum levels was observed: β: -441,7; 95%CI (-829,7 to -53,8). This relationship remained despite of adjusting the model for potential confounders: β: -457,3; 95%CI (-858,8 to -55,8).
Conclusions BMI influences serum IFX levels in patients with RA treated with infliximab. Higher BMI values are associated with lower serum drug levels.
Acknowledgement Unrestricted grants from Pfizer
Disclosure of Interest None declared