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.