Psoriasis is a chronic immune-mediated disease characterized by red papules and plaques with a silver scale, and it affects 0.6% to 4.8% of the world population and approximately 2.2% of the US population.1-3 Psoriasis has a significant impact on patientsâ€™ quality of life and is associated with an increased risk of cardiovascular disease, metabolic syndrome, and cancer.1 Moderate to severe psoriatic disease usually requires phototherapy or systemic therapy, including biologic agents such as tumor necrosis factor (TNF)-α inhibitors.
Although TNF-α inhibitors are effective and commonly used in treating psoriasis, drug safety is a consistent, long-term concern for physicians prescribing these drugs.4 One of the key safety concerns about TNF-α inhibitors is the risk of overall infection or serious infection, especially tuberculosis (TB). The majority of available information regarding this safety concern is from the patients with rheumatoid arthritis (RA) and Crohnâ€™s disease. Evidence from observational studies, surveillance reports, and systemic reviews and meta-analyses of randomized controlled trials suggests increased risks of infection and serious infection in patients with RA.5-10 Whether we can draw the same conclusion in the psoriatic population is uncertain. Patients with psoriasis are usually treated with monotherapy rather than concomitant immunosuppressive agents, such as methotrexate and prednisone. Patients with psoriasis also have different comorbidities and may be a generally healthier patient population than the RA population. RA itself is a risk factor for infectious diseases, whereas this is not thought to be the case for psoriasis. Therefore, infection rates in RA cannot be generalized to the psoriatic population without further investigation.
Because of the limited evidence in patients with psoriasis, it is still controversial as to whether or not TNF-α inhibitors increase the risk of infection or serious infection in treating psoriasis. This systemic review discusses the mechanism of TNF-α inhibitors and different types of serious infection associated with them,11-27 current evidence in the psoriatic population,28-38 and implications for future research.
TNF-α and TNF-α Inhibitors
TNF-α is a proinflammatory cytokine that mediates inflammation and immune functions.11 TNF-α is involved in a variety of immunological and physiologic processes, such as the recruitment of inflammatory cells to the sites of infection, cell activation, maintenance and formation of granulomas, and the induction of cytokines and adhesion molecules.11,12 TNF-α inhibitors block these processes, which results in reducing the expression of pattern-recognition receptors, decreasing the production of interferon α, increasing monocyte apoptosis, and the deterioration of granulomas.11 Overall, TNF-α inhibitors intervene in the hostâ€™s immune resistance against several infectious microorganisms such as Mycobacterium tuberculosis, Listeria monocytogenes, and Pneumocystis jiroveci. This is why there is particular concern about the increasing risk of infectionâ€”especially TBâ€”associated with the use of TNF-α inhibitors. This article focuses on the 3 most commonly used TNF-α inhibitors for treating moderate to severe psoriasis: adalimumab, etanercept, and infliximab. These 3 drugs have been approved to treat psoriasis in the United States, the European Union, and other regions.13