Table 2.

Risk Factors for PNR to Anti-TNF Therapy

Etiology	Risk for PNR to Anti-TNF Terapy
Drug-related factors	Low drug concentrations (pharmacoki-netics): nonimmune clearance, immu-nogenicity (development of antidrug antibodies)
	Adequate drug concentrations (pharma-codynamics): mechanistic failure
Patient-related factors	Smoking, obesity
Disease-related factors	Longstanding disease (>2 years), isolated small bowel disease, upper gastrointestinal involvement, severe intestinal infammation, hypoalbuminemia
PNR, primary nonresponse; TNF, tumor necrosis factor