You’re on a GI block, you see Crohn/UC, and the stem drops infliximab or adalimumab—your brain should immediately jump to: anti–TNF-α monoclonal antibodies, used for moderate–severe IBD, with big infectious risk (TB!) and a few classic Step traps.
The 5‑Second Rule (Infliximab/Adalimumab in IBD)
If it’s IBD + “-mab” (infliximab/adalimumab), think: “Block TNF → calm inflammation, but wake up TB.”
One-liner: Anti–TNF-α mAbs used for Crohn/UC; screen for latent TB/HBV first because blocking TNF impairs granuloma maintenance → reactivation infections.
Visual / Mnemonic Device
“TNF = The ‘Necrosis Fire’ in the gut”
Picture a campfire (TNF-α) burning a hole through the intestinal wall.
- Inflixi/Adali = fire extinguishers that calm the blaze → ↓ inflammation and mucosal damage
- But that same fire was also keeping a “TB cave” sealed shut (granulomas)
- Extinguish it → the cave opens → TB reactivates
Mnemonic: “Before you block TNF, check T.B. (and B)”
- T = TB testing (IGRA/PPD + chest imaging if indicated)
- B = Hepatitis B screening (risk of reactivation with biologics)
What They Are (Mechanism)
| Drug | Class | Target | High-yield mechanism |
|---|---|---|---|
| Infliximab | Chimeric monoclonal antibody | TNF-α | Neutralizes TNF-α → ↓ inflammatory signaling, leukocyte recruitment, cytokines |
| Adalimumab | Fully human monoclonal antibody | TNF-α | Same concept; “human” tends to be less immunogenic than chimeric |
Key concept: TNF-α is important for granuloma formation/maintenance → blocking it increases risk of reactivating latent intracellular infections (esp. TB).
When to Use in IBD (USMLE framing)
Crohn disease
- Moderate–severe Crohn or fistulizing Crohn: anti-TNF agents are classic
- Often used when:
- Steroids can’t be tapered (steroid-dependent)
- Disease is refractory to conventional therapy
- Significant fistulas/perianal disease
Ulcerative colitis
- Moderate–severe UC (especially steroid-refractory/dependent)
- Biologics are escalation therapy to induce/maintain remission
Step buzzword clue: “Biologic started; symptoms improve; later develops fever/cough/night sweats” → think TB reactivation.
Must-Know Adverse Effects (the ones NBME loves)
1) Serious infections (highest yield)
- Reactivation of TB (classically tested)
- Other opportunistic infections:
- Histoplasma (Ohio/Mississippi River valleys)
- Listeria
- Other intracellular pathogens
Why TB? TNF is critical for containing TB in granulomas.
2) Hepatitis B reactivation
- Screen HBsAg and anti-HBc (institution-dependent protocols vary, but Step concept is “screen for HBV before immunosuppression”)
3) Demyelinating disease
- Can worsen MS-like syndromes (avoid in demyelinating disease history)
4) Heart failure exacerbation
- Can worsen NYHA class III/IV CHF (classic test association)
5) Infusion/injection reactions
- Infliximab (IV): infusion reactions (fever, chills, hypotension, urticaria)
- Adalimumab (SC): injection-site reactions
6) Malignancy risk (testable but less “slam dunk”)
- Slightly increased risk of lymphoma and non-melanoma skin cancers (especially when combined with other immunosuppressants)
Pre-Treatment Checklist (Rapid-fire)
Before infliximab/adalimumab, do the “don’t get burned” checklist:
- TB screening (IGRA or PPD; add CXR if positive/clinical concern)
- HBV screening
- Update vaccines:
- Avoid live vaccines during biologic therapy (and typically avoid starting biologics immediately after live vaccines per guidelines)
- Look for active infection (hold therapy if serious infection)
Quick Clinical Vignettes (5-second pattern recognition)
- Crohn + perianal fistulas + starting infliximab → appropriate escalation therapy
- On infliximab + chronic cough + night sweats + weight loss → TB reactivation
- On adalimumab + new neurologic symptoms (optic neuritis/weakness) → possible demyelination
- On anti-TNF + worsening edema/orthopnea → CHF exacerbation
Tiny Step 1 Immunology Tie-In (Why granulomas fail)
Granulomas are a “wall-off” immune strategy against intracellular pathogens.
- TNF-α (from macrophages/T cells) helps:
- Recruit/activate immune cells
- Maintain granuloma structure
- Block TNF-α → granuloma integrity weakens → latent bugs escape
Your Shareable 5‑Second Summary Card
Infliximab/Adalimumab = anti–TNF-α mAbs for moderate–severe Crohn/UC (esp fistulas).
Big risk: serious infections—reactivate TB (and HBV) → screen before starting.
Other classic traps: infusion/injection reactions, demyelination, CHF worsening, lymphoma risk.
Frequently Asked Questions
Why do infliximab and adalimumab reactivate TB?
They can reactivate latent TB because they block TNF-α, which is essential for granuloma formation and maintenance. Granulomas help contain intracellular pathogens such as Mycobacterium tuberculosis. When TNF-α is neutralized, granuloma integrity weakens, latent organisms can escape, and patients are at risk for serious reactivation infection, making TB the classic infectious complication tested with anti-TNF therapy.
What do you need to check before starting infliximab or adalimumab for IBD?
You should screen for latent TB and hepatitis B before starting infliximab or adalimumab. TB testing is done with IGRA or PPD, with chest imaging if indicated, because anti-TNF therapy can impair granuloma maintenance and reactivate latent infection. Hepatitis B screening is also important because biologic immunosuppression can lead to HBV reactivation. Active serious infection should also prompt holding therapy.
When are infliximab and adalimumab used in Crohn disease or ulcerative colitis?
Infliximab and adalimumab are used for moderate to severe inflammatory bowel disease. In Crohn disease, they are classic choices for moderate to severe or fistulizing disease, especially when patients are steroid-dependent, refractory to conventional therapy, or have significant perianal disease. In ulcerative colitis, they are escalation therapy for moderate to severe disease, particularly when it is steroid-refractory or steroid-dependent.
How do you tell infliximab from adalimumab on side effects and route?
Infliximab is given intravenously and is associated with infusion reactions, while adalimumab is given subcutaneously and more often causes injection-site reactions. Infliximab is a chimeric monoclonal antibody, whereas adalimumab is fully human. Both target TNF-α and share the same major infectious risks, but route and reaction type are useful exam clues.
What classic adverse effects of anti-TNF drugs are high-yield besides infection?
Besides serious infections, the classic high-yield adverse effects are hepatitis B reactivation, demyelinating disease, heart failure worsening, infusion or injection reactions, and a slight increase in malignancy risk. Anti-TNF drugs can worsen MS-like syndromes, so a history of demyelinating disease is a concern. They can also exacerbate advanced congestive heart failure, particularly NYHA class III or IV disease.