INFLECTRA (infliximab for Injection) Action And Clinical Pharmacology

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Mechanism of Action

Infliximab is a chimeric IgG1κ monoclonal antibody with an approximate molecular weight of 149,100 daltons. It is composed of human constant and murine variable regions. Infliximab binds specifically to human tumour necrosis factor alpha (TNFα) with an association constant of 1010 M-1. Infliximab is produced by a recombinant cell line cultured by fed-batch and is purified by a series of steps that includes measures to inactivate and remove viruses.

Infliximab neutralizes the biological activity of TNFα by binding with high affinity to the soluble and transmembrane forms of TNFα and inhibits binding of TNFα with its receptors9,10,11. Infliximab does not neutralize TNFβ (lymphotoxin α), a related cytokine that utilises the same receptors as TNFα. Biological activities attributed to TNFα include: induction of pro-inflammatory cytokines such as interleukins (IL) 1 and 6, enhancement of leukocyte migration by increasing endothelial layer permeability and expression of adhesion molecules by endothelial cells and leukocytes, activation of neutrophil and eosinophil functional activity, and induction of acute phase reactants and other liver proteins12. Cells expressing transmembrane TNFα bound by infliximab can be lysed in vitro by complement or effector cells.10 Infliximab inhibits the functional activity of TNFα in a wide variety of in vitro bioassays utilising human fibroblasts, endothelial cells, neutrophils,9 B and T lymphocytes13,14, and epithelial cells. Anti-TNFα antibodies reduce disease activity in a cotton-top tamarin colitis model15 and decrease synovitis and joint erosions in a murine model of collagen-induced arthritis. Infliximab prevents disease in transgenic mice that develop polyarthritis as a result of constitutive expression of human TNFα, and, when administered after disease onset, facilitates eroded joints to heal.



Infliximab binds to the soluble and transmembrane forms of TNFα with high affinity and blocks the interaction of TNFα with its receptors, thereby neutralising the biological activity of TNFα.9,10 Cells expressing transmembrane TNFα can be lysed in vitro by complement or effector cell-mediated mechanisms after infliximab binds.10 Infliximab inhibits the functional activity of TNFα in a wide variety of in vitro bioassays utilising human fibroblasts, endothelial cells, neutrophils,11 B and T lymphocytes,13,14 and epithelial cells.14

Infliximab specifically neutralises TNFα-induced cell cytotoxicity but not lymphotoxin α.10 Lymphotoxin α is a cytokine that shares 30% homology with TNFα and utilises the same receptors as TNFα. Species cross-reactivity of infliximab is limited to human and chimpanzee TNFα. In vivo, infliximab rapidly forms stable complexes with human TNFα, a process that parallels the loss of TNFα bioactivity.

In a transgenic mouse (Tg197) that constitutively expresses human TNFα, infliximab for injection administered twice weekly at 5 mg/kg or once weekly at 10 mg/kg prevents the development of polyarthritis by Week 10, demonstrating that infliximab for injection neutralises TNFα in vivo.


Elevated concentrations of TNFα have been found in the joints of rheumatoid arthritis patients16 in the joints of psoriatic arthritis patients, in the skin lesions of plaque psoriasis patients, and in the stools of Crohn’s disease and ulcerative colitis patients. This correlates with elevated disease activity.16 In rheumatoid arthritis, treatment with infliximab for injection reduced infiltration of inflammatory cells into inflamed areas of the joint as well as expression of molecules mediating cellular adhesion [E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1)], chemoattraction [IL-8 and monocyte chemotactic protein (MCP-1)] and tissue degradation [matrix metalloproteinase (MMP) 1 and 3].16 In Crohn’s disease, treatment reduces infiltration of inflammatory cells and TNFα production in inflamed areas of the intestine, and reduces the proportion of mononuclear cells in the lamina propria able to express TNFα and interferon y ex vivo.16 After treatment with infliximab for injection, patients with rheumatoid arthritis or Crohn’s disease exhibited decreased levels of serum IL-6 and C-reactive protein compared to baseline. Peripheral blood lymphocytes from infliximab for injection-treated patients showed no decrease in proliferative responses to in vitro mitogenic stimulation when compared to cells from untreated patients. In psoriatic arthritis, treatment with infliximab for injection resulted in a reduction in the number of T cells and blood vessels in the synovium and psoriatic skin lesions as well as a reduction of macrophages in the synovium. Infliximab for injection treatment alters the histopathological features of plaque psoriasis as demonstrated in lesional skin biopsies collected at baseline, day 3 and Week 10 following initiation of treatment. Infliximab for injection treatment reduced epidermal thickness and infiltration of inflammatory cells, downregulated the percentage of activated and cutaneous lymphocyte antigen (CLA)-positive inflammatory cells, including CD3-, CD4-, and CD8-positive lymphocytes, and upregulated the percentage of CD1a-positive epidermal Langerhans cells. In ulcerative colitis, treatment with infliximab for injection showed changes consistent with histological healing and decreased expression of pharmacodynamic markers of tissue injury and inflammation in colonic biopsies. Treatment with infliximab for injection also decreased serum levels of the proinflammatory molecules with statistically significant and consistent decreases observed for IL-2R, and ICAM-1. In patients with ankylosing spondylitis, infliximab for injection was more effective at decreasing levels of serum markers of inflammation (IL-6 and VEGF) at both weeks 2 and 24 than placebo. In addition, serum levels of markers of bone formation (bone alkaline phosphatase and osteocalcin) were increased at both weeks 2 and 24 in patients with ankylosing spondylitis treated with infliximab for injection compared with patients receiving placebo.

Siegel SA, Shealy DJ, Nakada MT, Le J, Woulfe DS, Probert L, Kollias G, Ghrayeb J, Vilcek J, Daddona PE. The mouse/human chimeric monoclonal antibody cA2 neutralizes TNF in vitro and protects transgenic mice from cachexia and TNF lethality in vivo. Cytokine 1995;7:15-25.
Beutler B. Tumour necrosis factor. The molecules and their emerging roles in medicine. Raven Press, NY, 1992.
Boussiotis VA, Nadler LM, Strominger JL, Goldfeld AE. Tumour necrosis factor α is an autocrine growth factor for normal human B cells. Proc Natl Acad Sci USA 1994;91:7007-7011.
Cope AP, Londei M, Chu NR, Cohen SBA, Elliott MJ, Brennan FM, Maini RN, Feldmann M. Chronic exposure to tumour necrosis factor (TNF) in vitro impairs the activation of T cells through the T cell receptor/CD3 complex; reversal in vivo by anti- TNF antibodies in patients with rheumatoid arthritis. J Clin Invest 1994;94:749-760.
Watkins PE, Warren BF, Stephens S, Ward P, Foulkes R. Treatment of ulcerative colitis in the cottontop tamarin using antibody to tumour necrosis factor alpha. Gut 1997;40:628-633.
Jones M, Symmons D, Finn J, Wolfe F. Does exposure to immunosuppressive therapy increase the 10 year malignancy and mortality risks in rheumatoid arthritis? A matched cohort study. Br J Rheum 1996;35:738-45.
Chu CQ, Field M, Feldmann M, et al. Localization of tumor necrosis factor α in synovial tissues and at the cartilage-pannus junction in patients with rheumatoid arthritis. Arthritis and Rheum 1991;34:1125-1132.
Plevy SE, Landers CS, Prehn J, Carramanzana NM, Deem RL, Shealy D, Targan SR. A role for TNFα and mucosal T helper-1 cytokines in the pathogenesis of Crohn’s disease. J Immunol 1997;159:6276-6282.
Lipsky PE, van der Heijde D., St. Clair EW et al. Infliximab and methotrexate in the treatment of rheumatoid arthritis. N Engl J Med 2000;343:1594-1602.


Single intravenous infusions of 1 to 20 mg/kg showed a linear relationship between the dose administered and the maximum serum concentration. The volume of distribution at steady state was independent of dose and indicated that infliximab for injection was distributed primarily within the vascular compartment. Median pharmacokinetic results for the doses of 3 mg/kg to 10 mg/kg in rheumatoid arthritis, 5 mg/kg in Crohn’s disease and 3 mg/kg to 5 mg/kg in plaque psoriasis indicate that the terminal half-life of infliximab for injection is approximately 7.7 to 10 days. The terminal half-life in ulcerative colitis trials was 12.3 to 14.7 days.


Rheumatoid Arthritis

Crohn’s Disease










3 mg/kg

10 mg/kg

5 mg/kg

10 mg/kg

Cmax (μg/mL)





AUC (μg • day/mL)





CL (mL/day/kg)





Vss (mL/kg)










Absorption: Infliximab for injection is administered intravascularly and thus has no absorption profile.

Distribution: Infliximab for injection is primarily distributed into the blood, its apparent median steady state volume of distribution of 57.2 to 80 mL/kg estimated to 4.0 to 5.60 litres in a 70 kg individual corresponds to the total blood volume.

Metabolism: It is believed that infliximab for injection is metabolized in a similar manner to other proteins in the body. It is probably hydrolysed into its component amino acids and recycled or catabolized.

Excretion: Infliximab for injection as a whole molecule was not detected in the urine after its intravenous infusion.

Following an initial dose of infliximab for injection, repeated infusions at 2 and 6 weeks resulted in predictable concentration-time profiles following each treatment. No systemic accumulation of infliximab for injection occurred upon continued repeated treatment with 3 mg/kg or 10 mg/kg at 4- or 8-week intervals in rheumatoid arthritis patients or patients with moderate or severe Crohn’s disease retreated with 4 infusions of 10 mg/kg infliximab for injection at 8-week intervals. No systemic accumulation of infliximab for injection occurred upon continued repeated treatment with 3 mg/kg or 5 mg/kg at 8-week intervals in patients with psoriatic arthritis or plaque psoriasis. The proportion of patients with rheumatoid arthritis who had undetectable infliximab for injection concentrations at 8 weeks following an infusion was approximately 25% for those receiving 3 mg/kg every 8 weeks, 15% for patients administered 3 mg/kg every 4 weeks, and 0% for patients receiving 10 mg/kg every 4 or 8 weeks. At steady state, the proportion of patients with plaque psoriasis who had undetectable infliximab for injection concentrations at 8 weeks following an infusion ranged from 71.4% to 73.1% for patients receiving 3 mg/kg every 8 weeks (EXPRESS II), and from 25.9% to 46.4% for those administered 5 mg/kg every 8 weeks (EXPRESS and EXPRESS II). The proportion of patients with psoriatic arthritis who had undetectable infliximab for injection concentrations was 15.8% at Week 38 when administered 5 mg/kg every 8 weeks (IMPACT 2). In IMPACT 2, approximately half of the patients received concomitant MTX.

Special Populations and Conditions

No major differences in clearance or volume of distribution were observed in patient subgroups defined by age. It is not known if gender differences, genetic polymorphism, renal insufficiency or hepatic insufficiency have effects on clearance or volume of distribution of infliximab for injection.

Pediatrics: Infliximab pharmacokinetic characteristics (including peak and trough concentrations) were generally similar in pediatric patients (aged 6 to 17 years) with Crohn’s disease or ulcerative colitis following the administration of 5 mg/kg infliximab for injection. Similar terminal half-life values were also observed in pediatric patients with Crohn’s disease, and adult patients with Crohn’s disease or ulcerative colitis. However, for pediatric patients with ulcerative colitis, median serum peak and steady-state trough infliximab concentrations were about 13% and 25% lower than those in adult patients with ulcerative colitis, respectively; the clinical significance of the relatively lower serum infliximab concentrations in pediatric patients is unknown (see INDICATIONS, Pediatrics, and WARNINGS AND PRECAUTIONS, Special Populations, Pediatrics).