Dentistry and Allergies…Part Two–Local Anaesthetics


In this series of blogs, we’re not just looking at a sneeze or cough as a result of an allergic reaction…rather it’s the whole spectrum of undesirable events that may occur.

Please ‘refresh’ by reviewing the blog on Anaphylaxis that was posted on October 8th, 2013.

We will discuss local anaesthetics and possible allergic reactions to them but for the record, allergies to the local anaesthetics we use nowadays are extremely rare.

What is a Local Anaesthetic?
These are used to freeze or numb an area so that the patient can be worked on pain-free.
Local anaesthetics contain two active ingredients: the actual anaesthetic agent I.e., lidocaine and epinephrine.

Amides and Esters
Local anaesthetics contain either amides or esters.
An allergy to an amide is rare and if you are allergic to one, it doesn’t mean you’ll be allergic to another. However, an allergy to one ester usually means an allergy to all of them.

Novacaine, a type of ester, is the local anaesthetic that most people are aware of. It has not been used in dentistry for decades because it wears off quickly and is based on the ester formulation.

Fortunately, the local anaesthetics used nowadays contain amides and not esters.

The Role of Epinephrine
Local anaesthetics contain epinephrine. As seen in the blog on Anaphylaxis, epinephrine constricts blood vessels. The purpose of epinephrine in local anaesthetics is to ‘constrict’ the local blood vessels in the area so that the effect of the local anaesthetic will last longer, otherwise it will be resorbed by the blood vessels of the body much quicker.

Through the act of causing vasoconstriction (constriction of the blood vessels), epinephrine also stops the soft tissues from bleeding. If there is no epinephrine added to the local anaesthetic, then the numbing effect may only last about 5 – 10 minutes. When epinephrine is added the effects can be for about an hour.

The local anaesthetics that contain epinephrine also contain the ingredient ‘metabisulfite’ or ‘sodium bisulfite.’ These are preservatives which prevent the local anaesthetic from getting brown. The preservative is needed to keep the epinephrine fresh.

These compounds are part of the ‘sulfite’ family. And for the record, individuals that are allergic to sulpha are not necessarily allergic to bisulfites.

We will continue our discussion of sulpha allergies in the next blog…until then.

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