Novel biological strategies in inflammatory bowel diseases

Clinical pharmacokinetics and use of infliximab

Tumor necrosis factor-alpha (TNFalpha) is a key proinflammatory cytokine involved in chronic inflammatory diseases. Infliximab, a chimeric (human-murine) monoclonal IgG1 anti-TNFalpha antibody, is used in the treatment of Crohn's disease (including fistulising disease) and rheumatoid arthritis (in combination with methotrexate) if standard treatments have failed. The indications for infliximab have recently been expanded to include ankylosing spondylitis, psoriatic arthritis, psoriasis and ulcerative colitis. The biological agent infliximab is given by multiple intravenous infusions in a dosage of 3-5 mg/kg (initially at weeks 0, 2 and 6; subsequently in intervals of 4-8 weeks). In controlled trials, clinical response rates of 20-40% have been achieved with such regimens in Crohn's disease and rheumatoid arthritis. However, the therapeutic benefits must be balanced against the risks of a variety of severe adverse events (e.g. severe infections including tuberculosis, hepatotoxicity, infusion reactions, serum sickness-like disease and lymphoma). Following single and multiple infusions of infliximab, no relevant differences in median concentration-time profiles have been observed between patients with Crohn's disease, patients with rheumatoid arthritis and patients with psoriasis. The apparent volume of distribution of the high-molecular-weight infliximab (149.1 kDa) is low (3-6L) and represents the intravascular space. The long persistence in this compartment (elimination half-life 7-12 days, mean residence time 12-17 days) is due to the very low systemic clearance of about 11-15 mL/hour (0.18-0.25 mL/minute). Elimination of infliximab is most probably accomplished through degradation by unspecific proteases. During multiple infusions (every 4-8 weeks), no accumulation was observed, and serum concentrations and the area under the plasma concentration-time curve of infliximab increased in proportion to the infused dose, indicating linear pharmacokinetics. Co-medication with methotrexate delayed the decline in the serum concentrations of infliximab. When relating serum concentrations to the clinical response in patients with rheumatoid arthritis and patients with Crohn's disease, it can be assumed that trough concentrations above 1 microg/mL could be used as a kind of therapeutic target. In the future, identification of biomarkers for (non-)response and risk factors for adverse drug reactions would be very helpful. Furthermore, combined biological, pharmacokinetic, pharmacogenomic and clinical studies have not yet been performed and are needed to optimise the therapeutic potential of infliximab, which is currently established as a rescue treatment in refractory patients.

Natalizumab: a promising treatment for Crohn's disease

A primary feature contributing to the pathology of Crohn's disease (CD) is inappropriate and persistent recruitment and migration of circulating leukocytes from the bloodstream to affected tissues and organs. These processes are mediated by interactions between alpha(4) integrin adhesion molecules expressed on leukocyte surfaces and cognate receptors on vascular endothelial cells. Natalizumab is a humanized immunoglobulin G(4) monoclonal antibody against alpha(4) integrins. Natalizumab has demonstrated efficacy in inducing and maintaining sustained remission in patients with moderately to severely active CD, including those intolerant of or unresponsive to infliximab. Maintenance therapy with natalizumab in adult patients allowed elimination of steroids in a significant number of patients and sustained patients' quality of life. Natalizumab has been well tolerated in the majority of patients. However, progressive multifocal leukoencephalopathy, a rare opportunistic infection associated with the JC polyomavirus, occurred in three natalizumab-treated patients; two multiple sclerosis patients and one CD patient. This article reviews the properties of natalizumab and addresses its potential benefits and risks in the treatment of CD.