INTRODUCTION
Psoriasis is a chronic immunological cutaneous disorder that affects 2-3% of the general population.1 The most common subtype, plaque psoriasis, is characterized by erythematous plaques with silvery scales and affects 80-90% of patients with psoriasis.2 Up to 30% of psoriasis patients may develop psoriatic arthritis, an inflammatory and progressive arthritis that may lead to debilitating deformations.3 Psoriasis and psoriatic arthritis have a significant negative impact on patients’ quality of life, both physically and psychologically.Some of the systemic treatments for psoriasis include retinoids, cyclosporin A, methotrexate, and phototherapy, used as monotherapy or in combination. However, many of these treatments are limited by their efficacy and their adverse effects.4 In addition, until recently, there have been few treatment options for psoriatic arthritis, and traditional disease-modifying antirheumatic drugs have shown limited efficacy.5The precise pathogenesis of psoriasis and psoriatic arthritis remain unclear. They are thought to be multifactorial, with contributions from genetic susceptibility, immune dysregulation, and environmental factors. The majority of genes that have been associated with psoriatic disease relate to components of the cascade of cutaneous inflammation. Cytokines involved in the pathogenesis of psoriasis and psoriatic arthritis include tumor necrosis factor (TNF)-α, interleukin (IL)-12, IL-17, IL-22, and IL-23. Elevated levels of these cytokines are found in psoriatic plaques as well as in the synovial fluid of patients with psoriatic arthritis.6Advancements in understanding the pathogenesis of psoriasis and psoriatic arthritis have led to the development of targeted therapies. The introduction of new biologic agents targeting TNF-α, IL-12, IL-23, and IL-17 has greatly improved the treatment of psoriasis and psoriatic arthritis. Biologic therapies administered via subcutaneous injection for the treatment of psoriatic disease include etanercept (anti-TNF-α), adalimumab (anti-TNF-α), certolizumab pegol (anti-TNF-α), ustekinumab (anti-IL-12/23), secukinumab (anti-IL-17), and ixekizumab (anti-IL-17).Efficacy and safety of these biologic agents have been well documented.4,7-9 Injection site reactions (ISRs) have been documented in clinical trials with many of these therapies, and are reported to be the most common adverse event of etanercept, adalimumab, and ixekizumab.10 In this paper, we will review the literature on injection site reactions with the major biologic agents used in psoriasis and psoriatic arthritis.EtanerceptEtanercept is a soluble TNF receptor fusion protein. It inhibits binding of both TNF-α and TNF-β to cell surface TNF receptors, rendering TNF biologically inactive and thus preventing TNF-mediated cellular responses. Etanercept is indicated for the treatment of plaque psoriasis, psoriatic arthritis, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis, and ankylosing spondylitis.In clinical trials for any indication, 20 to 49% of patients treated with etanercept developed ISRs.11 ISRs were reported in 13 to 18% of patients with moderate-to-severe plaque psoriasis,12 and in 36% of patients with psoriatic arthritis.13 All ISRs were characterized as mild to moderate, consisting of erythema,
