How does infliximab work in ulcerative colitis and Crohn's disease?

How Infliximab Works in Ulcerative Colitis and Crohn's Disease

Infliximab is a chimeric monoclonal antibody that binds with high affinity to tumor necrosis factor-alpha (TNF-α), neutralizing both its soluble and membrane-bound forms, thereby blocking the inflammatory cascade that drives intestinal inflammation in UC and CD 1.

Mechanism of Action

Infliximab works through multiple anti-inflammatory pathways:

Primary mechanism: The drug binds to soluble TNF-α, preventing it from binding to cellular TNF receptors and triggering downstream inflammatory signaling 1. This interrupts the pro-inflammatory cytokine cascade that perpetuates mucosal inflammation in both UC and CD.

Secondary mechanisms include:

• Induction of apoptosis: Infliximab binds to membrane-bound TNF-α on inflammatory cells (particularly activated T-cells and macrophages), triggering programmed cell death of these inflammatory cells 2

• Reduction of inflammatory cell infiltration: In CD, treatment reduces infiltration of inflammatory cells and TNF-α production in inflamed intestinal areas, and decreases the proportion of lamina propria mononuclear cells expressing TNF-α and interferon 1

• Decreased expression of adhesion molecules: Treatment reduces expression of E-selectin, ICAM-1, and VCAM-1, which mediate cellular adhesion and inflammatory cell recruitment 1

• Reduced chemokine production: Decreases IL-8 and monocyte chemotactic protein (MCP-1), limiting further inflammatory cell recruitment 1

• Systemic anti-inflammatory effects: Patients exhibit decreased serum IL-6 and C-reactive protein levels compared to baseline 1

Clinical Efficacy in Crohn's Disease

For CD, infliximab is strongly recommended for both induction and maintenance therapy in moderate-to-severe disease 3. The 2024 ECCO guidelines provide strong recommendations (100% consensus) for:

• Infliximab as induction therapy (moderate-quality evidence)
• Infliximab as maintenance therapy (low-quality evidence, but strong recommendation based on extensive real-world experience)

Key efficacy data:

• Standard dosing (5 mg/kg) achieved 81% clinical response at Week 12 versus 16% with placebo 3
• At 44 weeks, infliximab maintenance therapy achieved clinical remission in 39-45% of responders versus placebo 3
• Mucosal healing occurred in significantly more patients on infliximab (RR: 7.00) 3

Clinical Efficacy in Ulcerative Colitis

Infliximab demonstrates robust efficacy in moderate-to-severe UC, particularly when used as combination therapy with immunomodulators 4. The ACT 1 and 2 trials established its effectiveness:

• Clinical response at 8 weeks: 61-69% with infliximab versus 29-37% with placebo (p<0.001) 2
• Significantly reduced need for colectomy: 29% versus 67% with placebo (p=0.017) 2

Combination Therapy Strategy

Combination therapy with thiopurines is strongly recommended for CD, particularly during the first 6-12 months 3, 5, 3. The SONIC trial demonstrated:

• Clinical remission at Week 26: 64% higher with combination therapy versus infliximab monotherapy (RR: 1.64) 3
• Mucosal healing: 82% higher with combination therapy (RR: 1.82) 3
• Lower rates of serious adverse events with combination therapy (RR: 0.56) 3

The mechanism behind improved combination therapy efficacy is enhanced pharmacokinetics - thiopurines reduce immunogenicity and antibody formation against infliximab, maintaining therapeutic drug levels 3, 5.

For UC, combination therapy with immunomodulators is conditionally recommended 4, though the evidence is less robust than in CD. The benefit must be balanced against increased risk of adverse events, particularly in patients with more moderate disease.

Dosing and Administration

Standard dosing regimen 3, 1:

• Induction: 5 mg/kg IV at weeks 0,2, and 6
• Maintenance: 5 mg/kg IV every 8 weeks

The induction schedule at weeks 0,2, and 6 was established by the landmark ACCENT I trial and results in predictable concentration-time profiles 3.

Important Clinical Considerations

Immunogenicity is a major limitation: Development of anti-drug antibodies increases infliximab clearance and can lead to loss of response 5. The PANTS cohort showed 26-28% immunogenicity rates at week 54, but concomitant immunomodulator use reduced immunogenicity risk by 63% (HR=0.37, p<0.0001) 5.

After achieving long-term remission (>12 months) on combination therapy, de-escalation to infliximab monotherapy with withdrawal of thiopurines is suggested 3, though caution is warranted in patients with prior immunogenicity.

Therapeutic drug monitoring is valuable 5 - patients with adequate trough levels (>3.8 μg/mL for infliximab) and low/absent antibodies respond better to dose optimization, while those with high-titer antibodies require switching to alternative therapy.

The median terminal half-life is 7.7-9.5 days, with no systemic accumulation during maintenance dosing 1.