The Jarisch-Herxheimer reaction is commonly seen in the first 24 hours of treatment and is characterized by low-grade fever, chills, headache, myalgias, malaise, and skin lesions (new or worsening of preexisting).
WHY? Thought to be due to cytokine release in response to endotoxins released by the dying microorganisms. May be seen following the treatment of spirochetal illnesses ( eg, Lyme disease, Syphilis, Leptospirosis).
*Typically treated with antipyretics.
FARMER TW. JARISCH-HERXHEIMER REACTION IN EARLY SYPHILIS. JAMA. 1948;138(7):480-485. doi:10.1001/jama.1948.02900070012003
Pound MW, May DB. Proposed mechanisms and preventative options of Jarisch-Herxheimer reactions. J Clin Pharm Ther 2005;30:291-295.