Acute Generalized Exanthematous Pustulosis Following the Administration of Cephalexin: A Case Report and Review of the Literature.

Acute generalized exanthematous pustulosis (AGEP) is a severe cutaneous reaction characterized by the sudden onset of numerous sterile, non-follicular pustules on an erythematous and edematous background, usually associated with fever. AGEP is commonly triggered by medications, including antibiotics, anticancer agents, and hydroxychloroquine, but infections and vaccinations, such as parvovirus B19 and COVID-19 vaccines, have also been implicated. We report a case of AGEP which developed two days after the administration of cephalexin. The pathological findings of subcorneal pustules and European Severe Cutaneous Adverse Reactions (EuroSCAR) score of 9 confirmed the diagnosis of AGEP. To date, only six cases of cephalexin-induced AGEP have been reported. Among these, five cases involved patients without underlying conditions, while one case occurred in a patient with pustular psoriasis undergoing treatment. Although all six cases were diagnosed based on clinical and histopathological findings, our case is the only one in which the EuroSCAR score has been used for definitive diagnosis. Interestingly, viral infections have been suggested as potential triggers for AGEP. In the present case, the patient had pre-existing cold symptoms before taking cephalexin, raising the possibility that a viral infection contributed to AGEP onset. Viral infections are known to induce CD4+ and CD8+ T-cell activation, which in combination with drug exposure may lead to excessive infiltration of inflammatory T-cells into the skin, resulting in increased production of cytokines such as interleukin (IL)-8 and IL-36. This mechanism could explain why AGEP may develop more readily in the presence of a viral infection. Further accumulation of cases and research is needed to clarify the underlying mechanisms.