Archives for September 2014

Novocaine Allergy Part III – True Amide Allergies

This is the third installment in the Novocaine Allergy series. Part I talked about reactions to certain older style dental anesthetics which are basically not used any more in dentistry. Part II talked about allergic and sensitivity reactions to preservatives and other components found in some local anesthetics.

This now leaves us with what I call true allergies.  I use the term true to indicate it is a real allergic reaction to a dental local anesthetic – as opposed to an adverse reaction or other phenomenon. I stress this distinction because allergic reactions to modern local anesthetics are extremely rare.

Lidocaine – A Modern Dental Local Anesthetic

lidocaine local anesthetic with epinephrine used at the dentist

Lidocaine with Epinephrine is the most common formulation in the U.S.

Lidocaine was first synthesized in 1943 and became widely available in the United States in 1948. Lidocaine was based on a new chemical structure of local anesthetics called amides. This class is chemically different than the previous ones such as novocaine and cocaine.

Immediately after its introduction, lidocaine took off in popularity for many reasons. One of the reasons is because lidocaine did not cause allergic reactions the way older anesthetics did. Because of this, the older class of anesthetics – novocaine included – were phased out – and by the 1980s basically no dentists in the United States were using novocaine anymore.

Allergic to Lidocaine?

True allergies to lidocaine and other amide based anesthetics are exceedingly rare. There is conflicting evidence on the prevalence of these reactions to lidocaine and other anesthetics. A prominent 2009 article in the journal Anesthesiology says “allergic reactions to amide local anesthetics remain anecdotal.” A 2013 article published out of Saudi Arabia documents a case study of a true lidocaine allergy in a 12 year old. According to this 2002 paper, an individual with an allergy to one amide does not mean he/she will react to others. Any Google search will yield thousands of results – some from prominent medical journals with sterling reputations – and others from individuals posting their experiences and assumptions.

lidocaine and articaine both amide type local anesthetics

Most experts agree that in the cases of true allergies to lidocaine, other local anesthetics such as articaine can be used (assuming proper testing first).

The current consensus in the dental community is that true allergies to amide based local anesthetics are possible but very rare. As a patient, you have much better odds of being struck by lightning than experiencing an allergic reaction to lidocaine!

If you are injected with a local anesthetic and are allergic, what would happen? You would likely exhibit all the classic signs of an immediate type reaction: generalized swelling, itching, urticaria (hives), possible respiratory difficulty, and many other signs.

But remember, only a qualified allergist can diagnose you with an allergy.  Neither I nor any internet site can tell you definitively.

Events where you think you are allergic but are not!

I’ve witnessed firsthand hundreds of incidents where a patient thinks he or she is allergic when in reality something else is occurring. These incidents include:

photo of epinephrine which is used at the dentist in local anesthesia

A racing heart does not mean you are allergic to epinephrine!

  • A racing heartbeat (tachycardia) occurring immediately after a dental local anesthetic is administered does not mean you are allergic to either the local anesthetic or the epinephrine in it. This is a dental myth I busted here.
  • If you start to feel faint and break out in a cold sweat and nearly pass out immediately after an injection, this is most likely vasovagal syncope (and not an immediate allergic reaction).
  • If you do exhibit signs of an allergic reaction, you are far more likely to be reacting to a preservative in the local anesthetic than you are to the actual local anesthetic. The most common culprits are methlyparaben and metabisulfite.

Dental Treatment with a Documented Amide Allergy

If you are one of the rare individuals with an amide allergy confirmed by an allergist and you need dental treatment, what are your options?

  • Get the dental treatment done without any local anesthetic. I do this periodically for my own patients who don’t like the feeling of being numb. But this would only work for minor procedures, not for major ones such as extractions or root canals.
  • Have the allergist test to see your response to other amide local anesthetics. Many papers in the literature talk about individuals reacting to one amide but not another.
  • Benadryl (diphenhydramine) can be used as a local anesthetic when injected. While not as effective as amides, it can offer some degree of local anesthesia. But check with your dentist – very few dentists are prepared to do this and would need advance notice.
  • As a last resort, the dental procedures can be done under general anesthesia.

Final Thoughts and a Disclaimer

While true allergies are rare, they can and do occur. But don’t assume. An adverse or unexpected reaction does not mean you are allergic!

And as mentioned in both the sidebar and footer of this website, this article is for informational use only and is not intended for medical advice. Please consult your physician if you believe you have an allergy and always discuss this with your dentist prior to having any dental treatment performed.