Is 'class effect' relevant when assessing the benefit/risk profile of a biologic agent?

Psoriasis is a chronic, genetically predisposed skin disorder, characterised by thickened scaly plaques. Although no therapy is recognised as curative, therapies aimed at symptom control include biologic agents that are generally designed to block molecular activation of cellular pathways of a pathogenic immune response. Although biologics are often described as a class, they can be further sub-classified according to properties including structure and molecular target. For example, the two main groups of biologics for the treatment of psoriasis are those targeting cytokines and those targeting T-cells or antigen-presenting cells. Agents that inhibit cytokines can be broadly split into anti-p40 agents, which target the p40 subunit of IL-12 and IL-23 (such as ustekinumab), and anti-TNF agents. Anti-TNF agents may then be further divided into soluble receptors (etanercept) and monoclonal antibodies (adalimumab and infliximab). Even within the same subclass, agents may display variations in structure, function, route of administration and pharmacokinetics, which are reflected in their clinical profiles. For example, of the TNF antagonists, infliximab, provides a rapid onset of response, high efficacy, high peak serum concentrations, anti-granulomatous activity, potential for tuberculosis reactivation and frequent antibody formation; adalimumab provides a fast response, high efficacy, potential for tuberculosis reactivation and the possibility of antibody formation; and etanercept provides a slower response, good efficacy, rare antibody formation and is rarely linked to tuberculosis cases. This suggests that biologic agents exhibit unique properties, which appear to be more relevant than a 'class effect' in assessing risk-benefit profiles for this diverse group of drugs. With a range of agents available, studying the immunogenesis of psoriasis is likely to be useful in profiling individuals best suited to the characteristics of particular drugs. It should also be noted that because differences between agents may affect safety profiles, long-term patient registries are an important tool to assess tolerability and develop guidelines for the most effective use of these drugs.