Injection site reactions with the use of biological agents

Injection site reactions (ISRs) are a local phenomenon defined as a constellation of symptoms, including swelling, erythema, pruritus, and pain around the site of injection. This article reviews the different aspects of ISRs, including their epidemiology and pathogenesis, and provides practical guidance to diagnose and treat such reactions. More focus is given to food and drug administration (FDA)-approved biological agents and biosimilars, which are licensed mainly for the treatment of dermatological conditions, including psoriasis, atopic dermatitis, and chronic urticaria. ISRs are major complications of all FDA-approved self-injectable biological agents, both in adults and children, with studies showing an incidence rate of 0.5-40%. The article emphasizes that ISRs are not correlated with drug efficacy or development of antidrug antibodies. Therefore, misunderstanding of the pathophysiology of the ISRs, most of them not being allergic or immunogenic reactions, might result in unnecessary discontinuation of the treatment. Almost all local reactions to subcutaneously administered biological agents can be prevented by changing the injection techniques, patient education, and training.