herx noun 1verb 1forms 4 noun1 •(informal) A Jarisch-Herxheimer reaction. verb1 •(informal) To experience a Jarisch-Herxheimer reaction, a negative reaction to antibiotic treatment.When using any antimicrobial against any Lyme-like infection, most patients will herx at some stage. — 2020 formsherxed · herxing · herxes · Herxes