Novocaine Allergy Part I – The Esters

This will be the first of a three part series covering the various types of allergies associated with dental local anesthetics. Why write this? Well, some of the most frequently used search terms that cause people to arrive at this site are some combination of “allergy” and “novocaine.”

Needle used for novocaine injection at the dentist

People love to Google what they hate. And people hate the “novocaine” shot!

Over the years, I’ve observed that many of my own patients as well as readers and commenters on this blog think they may be allergic to the local anesthetic used at the dentist. This is not surprising given that over 1 million local anesthetic injections are administered each year in dental offices in the United States. With this level of frequency, adverse events are bound to happen, some of which may be interpreted as allergies.

The three parts are:

  1. The Esters
  2. Methylparaben and Sulfites
  3. True amide allergies

The titles of the three parts may appear cryptic, weird, or just plain boring. But this is how it needs to be organized. We’ll start with a brief history of local anesthetics.

Cocaine and Procaine

Coca leaves to make cocaine - a local anesthetic

If you crush these up you get dentistry’s first local anesthetic!

As I wrote about previously in the post Cocaine and Dentistry, cocaine was the first local anesthetic used in dentistry. Cocaine was first used in a dental procedure as an injectable local anesthetic in 1884. While it was a very effective anesthetic, there were unwanted side effects (euphoria, cardiovascular stimulation, addiction, etc.).

In 1905, another anesthetic was synthesized called procaine. It had all the anesthetic properties of cocaine but none of the undesirable side effects. Because of this, it was very quickly adopted, and a brand name version of procaine – novocaine – was launched.

What the Heck is an Ester?

Ester functional group seen in cocaine and novocaine

Chemical symbol of an ester (courtesy wikipedia)

An ester is a term from organic chemistry that describes a specific part of a molecule. I will not describe that portion in detail because it is so boring it will make 99.9% of you hit the back button on your browser!

The diagram here is not that important. What is important is that cocaine, procaine (brand name novocaine), and many other dental local anesthetics are considered “ester type anesthetics.” They are given this name for two reasons. First, there’s the obvious reason: they all contain an ester group. The second reason is to differentiate them from another family of local anesthetics called “amide type anesthetics.”

Allergies to Ester Based Anesthetics

Now we actually get to what everyone wants to know. And that is to begin talking about allergic reactions to dental local anesthetics. We begin with ester based local anesthetics because at one point these were the only local anesthetics available. I’ve organized the points in bullet format for easy reading:

  • When ester based local anesthetics are injected into the body, they are metabolized into a chemical called para-aminobenzoic acid (also called PABA).
  • PABA is known to cause allergic reactions in some people. So, back when novocaine was actually being commonly used (from 1905 to the mid 1950s), patients frequently experienced true novocaine allergies.
  • Because of the documented allergic reactions to PABA (caused by injections of ester based local anesthetics), ester based injectable dental local anesthetics are no longer used in the United States.
  • What is used instead? You guessed it – amide type anesthetics.
  • Ester based local anesthetics are only used in dentistry in the U.S. as topical anesthetics (also known as numbing jelly). The most common one is benzocaine.
topical benzocaine - an ester local anesthetic still used

Topical Benzocaine is still used in the U.S. routinely.

Other ester based local anesthetics besides procaine and benzocaine include tetracaine, chloroprocaine, propoxycaine, and cocaine. But note these are no longer used in dentistry in the United States.

So, to summarize, true novocaine allergies exist, but they do not occur anymore because novocaine is no longer used.

But what about allergies from other sources? What does a true allergy look like clinically? When my heart races at the dentist does that mean I’m having an allergic reaction?

These and other subjects will be covered in Parts 2 and 3…