Delayed urticaria due to bupivacaine: A new presentation of local anesthetic allergy

Local anesthetics (LA) consist of a lipophilic aromatic ring connected to a hydrophilic amine group. The linking chain is used to classify the agents as ester or amide: ester-type, which are derivatives of para-aminobenzoic acid, including cocaine, benzocaine, procaine, proparacaine and tetracaine; and amide-type, including aminoacylamides (bupivacaine, lidocaine, prilocaine, mepivacaine), aminoalkilamides (procainamide) and quinolone derivative (dibucaine). LA have been widely used to relieve pain in surgical, obstetric, dental and ophthalmic procedures. They provide complete but temporary analgesia, because of their interaction with neural voltage-gated sodium channels, blocking the production and conduction of nerve impulses in sensory fibres. Adverse reactions related to LA can be broadly defined as either systemic or local. Systemic non-allergic adverse reactions are much more frequent than true allergy. These systemic responses comprise vasovagal or psychomotor reactions, dose-related toxic responses and, in some cases, side effects from added epinephrine in commercially-available solutions. In this context, true allergic manifestations to LA are very scarce, with a rate around 1%,1 and they can be classified as either immediate or delayed allergic reactions. Regarding allergic reactions to LA, we present a 54-year-old female whowas subjected to a bowel resection due to a colon adenocarcinoma. An analgesic treatment with oral analgesics (metamizole and dexketoprofen) and continuous epidural analgesia with bupivacaine 0.5% and fentanyl was started after this gastrointestinal surgery, developing a generalized urticaria two days later. Then, both continuous epidural and oral analgesia were stopped. Skin lesions disappeared without residual lesions in a few days, after treatment with oral antihistamines and topical corticosteroids. Our patient had previously used metamizole, dexketoprofen and LA with good tolerance, but LA composition was unknown. An allergic workup was started eight weeks later. After obtaining informed consent, both skin prick test (SPT) and intradermal test (IDT) were performed, using a commercial presentation named Bupivacaina 0.5%TM (Braun, Barcelona, Spain), containing bupivacaine hydrochloride 5 mg/ml, sodium chloride and sodium hydroxide. SPT was madewith the undiluted commercial drug, meanwhile a 1:10 dilution in saline solution was used for IDT. Readings were