Anti-TNF (anti-tumor necrosis factor) biologics were the first approved targeted therapies for IBD (inflammatory bowel disease) and remain the most widely used advanced therapies in clinical practice. They act by neutralizing soluble and membrane-bound TNF-alpha, a central pro-inflammatory cytokine in both UC (ulcerative colitis) and CD (Crohn's disease). Their efficacy is well established across clinical trial programs, but the safety profile including infection risk, immunogenicity, and infusion reactions requires systematic management.
Infliximab is a chimeric (25% murine, 75% human) IgG1 monoclonal antibody (mAb (monoclonal antibody)) that binds soluble and transmembrane TNF-alpha with high affinity. Transmembrane TNF binding is believed to contribute to infliximab's efficacy in fistulizing CD through activation of reverse signaling and induction of T-cell apoptosis in the lamina propria.1 Infliximab is administered by IV (intravenous) infusion at 5 mg/kg at weeks 0, 2, and 6 (induction) followed by every-8-week maintenance infusions. Its chimeric structure makes it more immunogenic than fully human anti-TNF agents, and the formation of ADA (anti-drug antibodies) against the murine component is the primary mechanism of secondary loss of response. IV administration allows rapid therapeutic serum concentrations but requires an infusion center visit. Infliximab biosimilars (including CT-P13, SB2, and others) are available in most markets and have demonstrated equivalent efficacy and safety to the reference product in switching studies; biosimilar substitution is now standard practice in many health systems.3
Adalimumab is a fully human IgG1 mAb that neutralizes soluble and transmembrane TNF-alpha; it has the same pharmacological mechanism as infliximab but a lower immunogenicity due to its fully human structure. It is administered SC (subcutaneously) at 160 mg at week 0, 80 mg at week 2, then 40 mg every 2 weeks for maintenance. The SC route provides convenience for patients but requires self-injection, which may be a barrier for some. Adalimumab is approved for both CD and UC and for several extraintestinal manifestations of IBD including ankylosing spondylitis and psoriasis. Biosimilars are widely available.2 Certolizumab pegol is a PEGylated (polyethylene glycol-conjugated) Fab' fragment of a humanized anti-TNF antibody that lacks the Fc (fragment crystallizable) region; the absence of the Fc region means it cannot fix complement, induce antibody-dependent cellular cytotoxicity (ADCC (antibody-dependent cellular cytotoxicity)), or cross the placenta via neonatal Fc receptor, making it the preferred anti-TNF agent in the third trimester of pregnancy when anti-TNF therapy must be continued. It is approved for CD but not UC in most markets. Golimumab is a fully human IgG1 anti-TNF mAb approved specifically for UC; it is SC-administered on a monthly maintenance schedule after induction, which may improve adherence compared with every-2-week regimens.4
All anti-TNF agents carry a class-wide safety profile defined by immunosuppression-related risks. Serious bacterial infections, most commonly pneumonia, septic arthritis, and intra-abdominal infections, occur at approximately 2- to 3-fold higher rates than in biologic-naive IBD patients and require prompt investigation and treatment.5 Reactivation of latent TB (tuberculosis) is the most important infectious adverse effect; TNF-alpha is essential for the maintenance of granuloma integrity, and its neutralization releases viable mycobacteria from quiescent granulomas. All patients must be screened for latent TB with TST (tuberculin skin test) and/or IGRA (interferon-gamma release assay) and chest X-ray before starting any anti-TNF agent; latent TB must be treated with isoniazid for at least 4 weeks (ideally 4 to 8 weeks) before initiating anti-TNF therapy. Reactivation of hepatitis B virus (HBV (hepatitis B virus)) is a second serious risk; all patients must be screened for HBV serology (HBsAg (hepatitis B surface antigen), anti-HBc (antibody to hepatitis B core antigen), anti-HBs (antibody to hepatitis B surface antigen)) before starting biologics; HBsAg-positive patients require antiviral prophylaxis throughout biologic therapy and for 6 to 12 months after stopping.5
Combining anti-TNF biologics with AZA (azathioprine) or 6-MP (6-mercaptopurine) reduces the formation of ADA (anti-drug antibodies) against the biologic, increasing trough drug concentrations and improving long-term clinical outcomes. This combination benefit was demonstrated for infliximab in the SONIC (Study of Biologic and Immunomodulator Naive Patients in Crohn's Disease) trial and for adalimumab in the DIAMOND (Double Blind Investigation of Adalimumab in a New Long-Term Efficacy study) trial. However, combination immunosuppression increases the risk of opportunistic infections and also rare but serious HSTCL (hepatosplenic T-cell lymphoma), which has been reported almost exclusively in young males on long-term combination anti-TNF plus thiopurine therapy. For patients who have been on thiopurine monotherapy for more than 2 years without response escalation, the decision to add a biologic while maintaining the thiopurine requires assessment of individual lymphoma risk (age, sex, thiopurine duration) against the immunogenicity reduction benefit. After 2 years of combination therapy, many clinicians and guidelines support consideration of withdrawing the immunomodulator while continuing the biologic, particularly in patients who are in deep remission.6
Latent TB: TST (tuberculin skin test) and/or IGRA (interferon-gamma release assay) + chest X-ray. Treat latent TB with isoniazid ≥4 weeks before starting anti-TNF. Hepatitis B: HBsAg, anti-HBc, anti-HBs. HBsAg-positive patients require antiviral prophylaxis. Hepatitis C: screening. HIV (human immunodeficiency virus): consider screening given immunosuppression. Varicella immunity: vaccinate if non-immune before starting (live vaccine contraindicated during biologic therapy). Document and update all vaccinations; all live vaccines are contraindicated once biologics are started.
JAK (Janus kinase) inhibitors are small molecule oral immunosuppressants that block intracellular JAK (Janus kinase)-STAT (signal transducer and activator of transcription) signaling downstream of multiple cytokine receptors simultaneously. The JAK family comprises four members, JAK1 (Janus kinase 1), JAK2 (Janus kinase 2), JAK3 (Janus kinase 3), and TYK2 (tyrosine kinase 2), which pair in various combinations to transduce signals from cytokines including IL-6 (interleukin-6), IL-12 (interleukin-12), IL-23 (interleukin-23), and the common gamma chain cytokines (IL-2 (interleukin-2), IL-4 (interleukin-4), IL-7 (interleukin-7), IL-15 (interleukin-15), IL-21 (interleukin-21)) that drive T-cell differentiation and IBD (inflammatory bowel disease) mucosal inflammation.7 Unlike biologics, JAK inhibitors are small molecules with oral bioavailability, rapid onset of action (days rather than weeks for initial response), and no immunogenicity, as they are not proteins recognized by the immune system.
Tofacitinib is a pan-JAK inhibitor with relative selectivity for JAK1 and JAK3 over JAK2; it is approved for moderate to severe UC (ulcerative colitis) at 10 mg twice daily for induction (8 weeks) and 5 mg twice daily for maintenance (or 10 mg twice daily in patients at higher risk of loss of response). In the OCTAVE (Oral Clinical Trials for Tofacitinib in Ulcerative Colitis) trials, tofacitinib produced significantly higher rates of clinical remission and mucosal healing compared with placebo at weeks 8 and 52.8 Upadacitinib is a selective JAK1 inhibitor approved for both UC (ulcerative colitis) and CD (Crohn's disease) at 45 mg once daily for induction and 15 or 30 mg once daily for maintenance. JAK1 selectivity was designed to reduce JAK2-mediated adverse effects (anemia from erythropoietin signaling disruption, neutropenia) while preserving efficacy through JAK1/JAK3 (Janus kinase 1/3)-dependent cytokine pathway blockade. In the U-ACHIEVE (UC) and U-EXCEED (CD) trial programs, upadacitinib demonstrated superior induction and maintenance outcomes compared with placebo and, in some analyses, numerically higher remission rates than adalimumab.9
The cardiovascular and thromboembolic safety profile of JAK inhibitors requires careful risk stratification before prescribing. The FDA (U.S. Food and Drug Administration) issued a class-wide black box warning for JAK inhibitors in 2022 based on the ORAL (Ongoing Long-term Impact of Tofacitinib) Surveillance trial, a post-marketing safety study comparing tofacitinib with TNF (tumor necrosis factor) inhibitors in rheumatoid arthritis patients. In patients aged 50 years or older with at least one additional cardiovascular risk factor, tofacitinib was associated with an increased incidence of major adverse cardiovascular events (MACE (major adverse cardiovascular events)) including myocardial infarction, stroke, and cardiovascular death, and also increased risk of malignancy (particularly lung cancer) and venous thromboembolism (VTE (venous thromboembolism)) compared with anti-TNF therapy.10 The FDA black box warning now applies to all approved JAK inhibitors including upadacitinib and filgotinib, stating that JAK inhibitors should be used in patients who have had an inadequate response to, or are intolerant of, one or more TNF inhibitors, and should be avoided in patients with known MACE risk factors, active malignancy, and thromboembolism history unless no adequate alternatives exist.10
Despite the cardiovascular safety signal, JAK inhibitors offer distinct practical advantages over biologics in selected patients. The oral route eliminates the need for injection or infusion visits. The rapid onset of action makes them useful for patients with acutely active disease where a faster response is needed than a new biologic can reliably provide. The absence of immunogenicity means JAK inhibitors do not develop primary or secondary anti-drug antibody resistance, a significant advantage in patients who have lost response to multiple biologics. Herpes zoster reactivation is a recognized adverse effect of JAK inhibitor therapy, occurring at higher rates than with biologics or conventional immunomodulators; recombinant zoster vaccine (Shingrix) should be administered before or as early as possible after starting JAK inhibitor therapy. Lipid changes (mild increase in LDL (low-density lipoprotein) cholesterol) occur with JAK inhibitors and should be monitored; management follows standard cardiovascular risk reduction principles.7
The 2022 FDA (U.S. Food and Drug Administration) black box warning for all JAK (Janus kinase) inhibitors states: increased risk of MACE (major adverse cardiovascular events), VTE (venous thromboembolism), malignancy including lymphoma, and serious infections compared with TNF (tumor necrosis factor) inhibitors, particularly in patients aged ≥50 with cardiovascular risk factors. Use only after inadequate response or intolerance to one or more TNF inhibitors. Screen for cardiovascular risk factors, active malignancy, and thromboembolism history before prescribing. Do not use in patients with active serious infection.
VDZ (vedolizumab) is a humanized IgG1 mAb (monoclonal antibody) that selectively blocks the alpha4beta7 (alpha-4-beta-7) integrin on gut-homing lymphocytes, preventing their interaction with MAdCAM-1 (mucosal addressin cell adhesion molecule-1) on the intestinal vascular endothelium and blocking lymphocyte trafficking to the GI (gastrointestinal) mucosa.11 Because alpha4beta7 integrin is predominantly expressed on gut-homing memory T cells rather than systemic lymphocytes, vedolizumab's immunosuppressive effect is compartmentalized to the gut. This gut-selective mechanism produces a systemic infection and malignancy risk profile that is substantially more favorable than systemic biologics; large registry and post-marketing data show no increase in serious systemic infections compared with baseline IBD (inflammatory bowel disease) rates, making vedolizumab the preferred biologic in patients with higher infection risk, including elderly patients, those with prior serious infections, and those with comorbidities limiting systemic immunosuppression.11 Vedolizumab is approved for both moderate to severe UC (ulcerative colitis) and CD (Crohn's disease). It is administered IV (intravenously) at 300 mg at weeks 0, 2, and 6 (induction) then every 8 weeks for maintenance, or alternatively SC (subcutaneous) at 108 mg every 2 weeks for maintenance after IV induction. The onset of action is slower than anti-TNF agents, particularly in CD, where weeks 10 to 14 may be required to see meaningful clinical response; this slower onset limits its use in acute severe disease.
UST (ustekinumab) is a fully human IgG1 mAb that binds the p40 subunit shared by IL-12 (interleukin-12) and IL-23 (interleukin-23), two cytokines that drive Th1 (T helper 1) and Th17 (T helper 17) cell differentiation and activation, respectively. IL-12 drives IFN-gamma (interferon-gamma) production by Th1 cells; IL-23 maintains and amplifies Th17 cells, which produce IL-17 (interleukin-17) and IL-22 (interleukin-22), key mediators of mucosal inflammation in IBD and of several extraintestinal manifestations.12 Ustekinumab was originally developed for psoriasis and psoriatic arthritis, and its approval in CD and UC reflects the shared IL-12 (interleukin-12)/IL-23 (interleukin-23) pathobiology across inflammatory conditions. It is administered as a weight-based single IV induction dose (approximately 6 mg/kg), followed by 90 mg SC every 8 or 12 weeks for maintenance. Ustekinumab has an excellent safety profile across its indications; it does not carry the cardiovascular risk signal of JAK (Janus kinase) inhibitors and has a more favorable infection profile than anti-TNF agents, with no increased risk of TB (tuberculosis) reactivation or serious opportunistic infections demonstrated in the clinical trial and post-marketing programs. It is approved for both CD and UC.
RZB (risankizumab) is a humanized IgG1 mAb that selectively blocks the IL-23 p19 (interleukin-23 p19) subunit, inhibiting only IL-23 without affecting IL-12. This selective IL-23 blockade is based on the observation that the Th17 pathway driven by IL-23, rather than the Th1 pathway driven by IL-12, is the dominant pathological mechanism in both CD and UC, making selective p19 blockade pharmacologically sufficient while preserving IL-12-dependent protective immunity including antiviral and antimycobacterial responses.13 Risankizumab is approved for moderate to severe CD and UC; induction dosing is 600 mg IV at weeks 0, 4, and 8, followed by 360 mg SC every 8 weeks for maintenance. The ADVANCE (A Study to Evaluate the Efficacy and Safety of Risankizumab) and MOTIVATE (A Study to Evaluate the Efficacy and Safety of Risankizumab as Induction Therapy) induction trials established risankizumab's superiority over placebo for CD induction, and the INSPIRE (A Study to Evaluate the Efficacy and Safety of Risankizumab as Maintenance Therapy) trial demonstrated maintenance efficacy. Safety data from the CD program show a favorable profile, with no unexpected infection or malignancy signals. Selective IL-23 inhibitors as a class (including mirikizumab, also approved for UC) represent an evolution toward more precisely targeted cytokine blockade compared with dual IL-12 (interleukin-12)/IL-23 (interleukin-23) p40 inhibition.
Vedolizumab blocks alpha4beta7 (alpha-4-beta-7) integrin on gut-homing lymphocytes, preventing their migration to intestinal mucosa. Because this integrin is expressed predominantly on gut-homing rather than systemic lymphocytes, systemic immune surveillance is largely preserved. In practice: vedolizumab does not require latent TB screening (no increase in TB reactivation), does not increase systemic serious infection rates, and does not require dose modification in elderly patients on clinical grounds alone. This profile makes it the preferred biologic for patients at elevated infectious risk. The trade-off is slower onset of action than anti-TNF agents, particularly in CD.
TDM (therapeutic drug monitoring) of biologic agents measures serum trough drug concentrations and ADA (anti-drug antibody) levels to guide dose optimization and loss-of-response management. Trough concentrations are measured immediately before the next scheduled dose, at the time of lowest serum drug levels; trough levels correlate with clinical, endoscopic, and histological remission outcomes, and maintaining adequate trough levels is the primary pharmacokinetic goal of TDM-guided dosing.14 For IFX (infliximab) maintenance therapy, trough concentrations of 3 to 7 mcg/mL are associated with clinical remission; for ADA (adalimumab), trough concentrations of 5 to 12 mcg/mL are targeted. These ranges are not absolute and should be interpreted alongside clinical and inflammatory biomarker data, including CRP (C-reactive protein) and fecal calprotectin levels.
Primary non-response, defined as failure to achieve a meaningful response within 8 to 14 weeks of starting a biologic at standard induction doses, affects approximately 10 to 30% of patients depending on the agent and the disease. Primary non-response to anti-TNF agents indicates that TNF (tumor necrosis factor) is not the dominant driver of inflammation in that patient; in this context, switching to a biologic with a different mechanism (vedolizumab, ustekinumab, or a JAK inhibitor) is the appropriate strategy rather than optimizing the anti-TNF dose. Secondary loss of response, defined as loss of clinical response after an initial period of successful maintenance, is the more common clinical problem, affecting approximately 40 to 50% of anti-TNF-treated patients over 5 years of follow-up. Secondary loss of response is most commonly caused by one of three pharmacokinetic and immunological mechanisms: low trough concentration with low or absent ADA (pharmacokinetic failure, also called drug clearance; managed by dose escalation or shortening the dosing interval), low trough concentration with high ADA (immunogenic failure; managed by switching to a different anti-TNF agent or a different class biologic), or adequate trough concentration despite loss of response (pharmacodynamic failure or disease mechanism shift; managed by switching to a different biologic class).14
Proactive TDM (therapeutic drug monitoring), in which trough concentrations are measured at regular intervals in all patients regardless of clinical symptoms, has been compared with reactive TDM (measuring only when loss of response is clinically apparent) in several RCT (randomized controlled trial) programs. The TAILORIX (Tofacitinib Dose Optimization With Infliximab) and PANTS (Prospective Evaluation of Anti-TNF Therapy in Patients with Crohn's Disease) study data suggest that proactive TDM during the first year of anti-TNF therapy detects subtherapeutic trough concentrations early enough to prevent immunogenicity development, potentially reducing the rate of ADA formation and secondary loss of response over time. Current guidelines increasingly support proactive TDM at specific time points, including at the end of induction (weeks 14 to 16) and after dose changes, rather than waiting for clinical deterioration before measuring drug levels.15
The practical positioning of advanced IBD (inflammatory bowel disease) therapies depends on disease type (UC vs. CD), disease location and behavior, prior treatment history, comorbidities, and patient preference regarding route of administration. For both UC and CD, the principle of treat-to-target now guides management: the treatment goal is transmural (histological for UC, transmural imaging for CD) remission, not just symptom control. For moderate to severe UC requiring advanced therapy, anti-TNF agents, vedolizumab, and ustekinumab are all appropriate first-line biologic options; JAK inhibitors are second-line after inadequate anti-TNF response. Tofacitinib is approved specifically for UC; upadacitinib is approved for both UC and CD. For moderate to severe CD, anti-TNF agents remain the most commonly used first-line biologics, but vedolizumab (with its favorable infection profile), ustekinumab, and risankizumab are approved alternatives. The choice between gut-selective biologics and systemic biologics depends heavily on individual patient risk factors for infection, extraintestinal manifestations (anti-TNF or ustekinumab preferred when significant extraintestinal disease is present), and availability.16
When a patient loses response to an anti-TNF biologic, measure serum trough drug concentration and ADA (anti-drug antibody) level before deciding on next therapy. Low trough + low ADA (pharmacokinetic failure): dose-escalate or shorten interval. Low trough + high ADA (immunogenic failure): switch to a different anti-TNF agent or switch biologic class. Adequate trough + loss of response (pharmacodynamic failure): switch biologic class — do not dose-escalate. Adding AZA (azathioprine) to a patient who is already ADA-positive does not reliably reverse established immunogenicity; class switch is preferred in this scenario.
UC (moderate to severe), first advanced therapy: Anti-TNF (infliximab or adalimumab), vedolizumab, or ustekinumab — all guideline-recommended first-line options. Tofacitinib or upadacitinib are alternatives if oral therapy is preferred, after TNF inhibitor consideration.
CD (moderate to severe), first advanced therapy: Anti-TNF (infliximab or adalimumab), vedolizumab, ustekinumab, or risankizumab. Anti-TNF preferred when rapid response is needed or extraintestinal manifestations are prominent. Vedolizumab preferred in elderly or high-infection-risk patients.
After anti-TNF failure: If primary non-response or pharmacodynamic failure — switch biologic class (vedolizumab, ustekinumab, JAK inhibitor for UC). If immunogenic failure with high ADA — switch to different anti-TNF or different class. Use TDM (therapeutic drug monitoring) to distinguish these mechanisms.
Pregnancy: Certolizumab pegol preferred (no placental transfer). Vedolizumab and ustekinumab may be continued in pregnancy if benefit outweighs risk. Infliximab and adalimumab transfer across placenta in third trimester; delay infant live vaccines until 6 months of age if mother received anti-TNF after 22 weeks.
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