© 2016 The Authors. Clinical and Translational Science published by Wiley Periodicals, Inc. on behalf of American Society for Clinical Pharmacology and Therapeutics Systemic inflammation has been linked to suppressed CYP3A(4) activity. We determined 4$β$-hydroxycholesterol (4$β$OHC), an endogenous CYP3A4 metabolite, in patients with rheumatoid arthritis (RA) before and after treatment with biological disease-modifying antirheumatic drugs (bDMARDs). The 4$β$OHC was compared in 41 patients before and 2–5 months after initiating TNF$α$ inhibitors (n = 31), IL-6 inhibitors (n = 5), or B-cell inhibitors (n = 5). Correlations between 4$β$OHC and inflammatory markers (C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)) were also tested before and after bDMARDs. 4$β$OHC did not differ following bDMARD treatment (P = 0.6), nor in patients who started with IL-6 inhibitors (median 51.6 vs. 50.6 nmol/L). The 4$β$OHC and CRP/ESR did not correlate before treatment (P textgreater 0.5), but correlated significantly after bDMARDs (CRP = Spearman r -0.40; P textless 0.01; ESR = r -0.34; P = 0.028) suggesting that mainly non-CYP3A4-suppressive cytokines were reduced during treatment. Thus, this study does not support a generally regained CYP3A4 phenotype in patients with RA following initiation of bDMARDs.