Table 2.

Serum drug levels (ng/mL) at 6 months based on rheumatoid factor (RF) levels at baseline (n = 161 patients).

	Serum drug levels ng/mL [median (IQR)] at 6 months after starting TNFi a		p
	Baseline RF levels ≤203 IU/mL	Baseline RF levels >203 IU/mL
Infliximab n = 85	376 [0–2,076]	0 [0–1,057]	0.09
Adalimumab n = 44	4,570 [1,104–7,572]	751 [53–2,401]	0.02
Certolizumab n = 32	33,000 [20,000–46,000]	32,000 [13,000–39,000]	0.6

TNFi, tumor necrosis factor alpha inhibitor; RF, rheumatoid factor. IFX, infliximab; ADL, adalimumab; CZP, certolizumab pegol; RF, rheumatoid factor.

^aNo serum sample was available to measure drug levels in 7 patients.