Tumor necrosis factor (TNF) blockers, such as adalimumab (Humira®), infliximab (Remicade®), and the infliximab biosimilar infliximab-dyyb (Inflectra®), are used to treat inflammatory bowel disease (IBD; Crohn disease, ulcerative colitis) and rheumatic diseases (eg, rheumatoid arthritis, plaque psoriasis, psoriatic arthritis, ankylosing spondylitis).1-3
TNF blockers have had a major impact on the course of treatment for these conditions, but response rates vary by indication and other factors (eg, dose, smoker vs nonsmoker, etc.). While some patients respond to treatment, many others are refractory to treatment, showing either nonresponse during induction (primary failure) or response during induction followed by loss of efficacy (secondary failure).
When treatment fails, a physician may need to consider other treatment options, such as adjusting dose or dosing intervals, switching to a different TNF blocker, or switching to a non–TNF blocker. Measuring TNF blocker drug levels can help differentiate pharmacodynamic from possible pharmacokinetic conditions associated with treatment failure.