Infliximab is a biologic medication used to treat several chronic inflammatory conditions, including Crohn’s disease, ulcerative colitis, rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and severe plaque psoriasis. It works by blocking a specific protein in the body that drives inflammation, and it’s given as an intravenous infusion on a set schedule.
How Infliximab Works
Your immune system produces a signaling protein called TNF-alpha that triggers inflammation. In healthy amounts, this protein helps fight infections. But in autoimmune and inflammatory diseases, the body produces too much of it, causing the immune system to attack healthy tissue in the joints, gut lining, or skin.
Infliximab is an antibody designed to latch onto TNF-alpha and neutralize it before it can cause damage. Each infliximab molecule can bind two TNF-alpha molecules, and multiple infliximab molecules can cluster around a single TNF-alpha unit, forming large complexes that effectively shut down the inflammatory signal. This makes it particularly effective for conditions where TNF-alpha is a central driver of disease.
Crohn’s Disease and Ulcerative Colitis
Infliximab is one of the most widely used biologics for inflammatory bowel disease. It’s approved for adults and children aged 6 and older with moderately to severely active Crohn’s disease or ulcerative colitis who haven’t responded well to standard treatments like corticosteroids or immunosuppressants.
For Crohn’s disease specifically, infliximab also treats fistulizing disease, where abnormal tunnels form between the intestine and other organs or the skin surface. It can reduce the number of draining fistulas and help maintain fistula closure over time. In ulcerative colitis, it’s used to induce and maintain remission, promote healing of the intestinal lining, and help patients taper off corticosteroids. The REACH trial, a landmark pediatric study, confirmed that infliximab is effective for inducing and maintaining remission in children with moderate to severe Crohn’s disease as well.
Rheumatoid Arthritis
Infliximab is approved for moderately to severely active rheumatoid arthritis and is always used alongside methotrexate for this condition. The combination reduces joint pain and swelling, slows the structural damage that RA causes to bones and cartilage, and improves physical function. In clinical trials, about 55 to 59% of patients achieved at least a 20% improvement in symptoms by week 30. Around 30 to 34% of patients hit a higher bar of 50% symptom improvement in the same timeframe. These response rates held steady through week 54, suggesting durable benefit for patients who respond initially.
Psoriatic Arthritis and Ankylosing Spondylitis
For psoriatic arthritis, infliximab reduces joint inflammation, slows joint damage, and improves daily function. It addresses both the skin and joint components of the disease, which often occur together. For ankylosing spondylitis, a type of inflammatory arthritis that primarily affects the spine and large joints, infliximab reduces the pain and stiffness that can progressively limit mobility.
Severe Plaque Psoriasis
Infliximab is approved for adults with chronic, severe plaque psoriasis, particularly when the disease is extensive or disabling and other systemic treatments aren’t appropriate. Its efficacy in psoriasis is striking. In a phase III trial published in The Lancet, 80% of patients treated with infliximab achieved at least 75% skin clearance by week 10, and 57% achieved 90% clearance or better. At week 24, those results held, with 82% maintaining 75% clearance. Even at week 50, 61% of patients still had 75% clearance and 45% had 90% clearance, though some loss of response over time is typical.
What Treatment Looks Like
Infliximab is given through an IV infusion, typically at an infusion center or clinic. The standard schedule starts with three loading doses: the first infusion on day one, a second infusion two weeks later, and a third at six weeks. After that, maintenance infusions are given every six to eight weeks depending on the condition being treated. Each infusion takes about two hours, and you’re usually monitored for a short time afterward.
The dose is calculated based on body weight. For most conditions, including Crohn’s disease, ulcerative colitis, psoriatic arthritis, ankylosing spondylitis, and plaque psoriasis, the standard dose is 5 mg per kilogram. Rheumatoid arthritis uses a lower dose of 3 mg per kilogram. A subcutaneous (self-injection) formulation is also available for maintenance treatment of Crohn’s disease and ulcerative colitis after patients complete their initial IV infusions.
Screening Before Starting Treatment
Because infliximab suppresses part of the immune system, you’ll need specific screening tests before your first dose. Tuberculosis testing is required, typically with both a skin test and a blood test. Even a mildly positive skin test (5 mm or larger) warrants treatment for latent TB before starting infliximab, since the drug can reactivate dormant infections. A negative skin test doesn’t always rule out TB infection, so your doctor may still recommend preventive treatment if you have risk factors like living in an area where TB is common, a history of exposure, or certain chest X-ray findings. Hepatitis B screening is also standard, since infliximab can cause reactivation of the virus.
Key Safety Risks
Infliximab carries a boxed warning for serious infections and certain cancers. Pooled data from clinical trials of infliximab and similar TNF-blocking drugs show roughly double the risk of serious infections compared to placebo, with serious infections defined as those requiring hospitalization or IV antibiotics. This includes bacterial infections, tuberculosis, and invasive fungal infections. The increased infection risk applies at both standard and higher doses.
There is also a small increased risk of certain malignancies, particularly lymphoma, with TNF-blocking therapies. This risk appears more pronounced at higher doses. For most patients, the benefits of controlling a severe inflammatory disease outweigh these risks, but they’re an important part of the decision-making process.
Infusion reactions, ranging from mild symptoms like flushing and headache to more serious allergic responses, can occur during or shortly after an infusion. Your infusion center will monitor for these, and premedication with antihistamines or acetaminophen is common to reduce the likelihood.
Biosimilar Options
The original brand of infliximab, Remicade, was one of the first biologics to have biosimilars approved in the United States. Several biosimilar versions are now available, including Inflectra, Renflexis, Avsola, and Ixifi. Biosimilars are held to rigorous FDA standards showing they have no clinically meaningful differences from the original drug in terms of safety and effectiveness. They’re typically available at a lower cost, which can be a significant factor since biologic therapy is a long-term commitment for most patients.