Allergy to LA

Management of a patient with true, documented and reproducible allergy to local anesthetics varies according to the nature of the allergy.If the allergy is limited to ester drugs( e.g procaine, propoxycaine ,benzocaine or tetracaine) the amides(eg.articaine,lidocaine,mepivacaine or prilocaine) may be used because cross-allergenicity although possible is quite rare. If the local anaesthetic allergy was actually an allergy to the paraben preservative an amide local anaesthetic may be injected if it does not contain any preservative. A statement on local anaesthetic allergy by Aldrete and Johnson concludes sayin that , a thorough evaluation of the circumstances surrounding an adverse reaction to a local anaesthetic be made before the label of allergy to drug be entered on the front of parents chart. The untoward reactions observed during the use of local anaesthetic agents are quiet frequently the result of over dosage.

Management of alleged allergy to local anaesthetics.
The most practical application to this situation is immediate consultation with a person able to test the patient for allergy to local anaesthetics.If present, pain may be managed with orally administered analgesics and infection controlled with antiobiotics, though they are temporary measures only.

A second approach might be to use general anaesthesia in place of local anaesthesia to manage dental emergency. Although general anaesthesia is highly useful and relatively safe technique when properly performed there are complications and problems associated with it not the least of which is the fact that is unavailable in most dental offices.However general anaesthesia remains a viable alternative to local anaesthesia in the management of the allergic patient provided adequate facilities and well trained personnel are available.

A third option to consider when emergency treatment is necessary and general anaesthesia is not available is the use of a histamine – blocker such as diphenhydramine as a local anaesthetic for the management of pain during treatment.Most of injectable histamine blockers possess local anaesthetic properties.Several are more potent local anaesthetics than procaine .Diphenhydramine has been the most commonly used histamine blocker in this regard. Used as a 1% solution with 1:100,000 epinephrine , diphenhydramine produces pulpal anaesthesia of up to 30 minutes duration.But its unwanted side effect during intra oral administration is burning or stinging sensation.Concurrent administration of N2O-02 along with diphenhyramine minimizes discomfort.Another unwanted result is posoperative tissue swelling and soreness.For these reasons the use of diphenhydramine as a local anaesthetic is usually limited to those circumstances in which (1) there is a questionable history of local anaesthetic allergy (2)the patient has a dental emergency requiring immediate physical intervention (3)general anaesthesia is not a reasonable alternative.It must be kept in mind that allergy may develop to any drug including histamine blockers.The patient must be questioned about prior exposure to histamine blockers or other drugs before they are used.