INTRODUCTION
Local anesthetics are classified according to their chemical structure. The two main groups are the "ester type anesthetics", which are all derivatives of para-aminobenzoic acid (i.e. procaine, benzocaine, tetracaine) and the "amides" which include the aminoacylamides (lidocaine,prilocaine,mepivacaine), aminoalkilamides (i.e. procainamide) and the quinoline derivative dibucaine.
Contact dermatitis due to ester type anesthetics are well know,but allergic reactions to the amide group are rare.
CASE REPORT
A 54-year-old woman started a course of dental treatment in September 2002. Forty eight hours after local anesthesia with Scandinibsa (mepivacaine 2 %, ClNa, NaOH, water) she developed swelling of the soft tissues over the left zygoma and an eczematous eruption of her left cheek. She was treated with oral and topical steroids,clearing the lesions in seven days. One month later, 24 hours after the use of lidocaine (lidocaine 2 %, ClNa, NaOH, water) for a new dental surgery a similar acute dermatitis ocurred. She had previously undergone dental anesthesia with lidocaine and mepivacaine without incident.
Patch tests with the European Standar series were negative. Patch tests with the following local anesthetics were also performed: lidocaine (2 % aq), mepivacaine (2 % aq), bupivacaine (0.5 % aq), prilocaine (5 % aq),and articaine (4 % aq). They were evaluated at 48 h and 96 h according the recommendations of I.R.C.G. Positive reactions were observed to lidocaine (+ + +), mepivacaine (+ + +), bupivacaine (+ +), and prilocaine (+ +) at days 2 and 4,but negative to articaine. Tests in ten controls were negative.
DISCUSSION
This case demostrates delayed-type hypersensitivity to lidocaine and mepivacaine with cross reaction to other aminoacylderivatives (prilocaine, bupivacaine) but not with articaine. Anesthetics used were preservative-free so allergy to preservatives was excluded.
Altough contact allergy to amide local anaesthetics is uncommon, there are some publications about it1-4. We have found cross reactivity between the members of the group (there was no evidence that prilocaine or bupivacaine were previously used in this patient) as previous reports1-4.
It is interesting that there has not been reaction to articaine. This may be explained by its different chemical structure: all aminoacylamides have a methylated phenyl ring with the exception of articaine, wich has a substituted thiophen ring. Bircher et al5 describe a similar case of tolerance to aricaine in a patient with delayed hypersesitivity to local amide anestethics.
When allergy to an amide local anesthetic is suspected, we suggest testing other members of the group as well, including articaine.
