• endodontic flare-up;
  • symptomatic apical periodontitis;
  • antihistamine

Abstract Endodontic flare-ups often occur within 24 h of root canal debridement, during which time a small amount of antigen in the form of necrotic pulp tissue and bacteria within the root canal, may be inadvertently extruded through the apical foramen. Subsequently, preformed mediators such as histamine are released into the tissue, causing symptoms of pain and swelling. The IgE-mast cell mechanism conceivably plays an important role in this development. A rationale for using local injection of Benadryl® prior to canal debridement of infected teeth is given, along with an indication of a lack of adverse reactions and side effects following such treatment.