The facts about allergies to local anesthetics


By Mary-Ann Shearer

True allergies to local anesthetics used nowadays are exceedingly rare – only a few cases have been reported worldwide. Some people are allergic to preservatives in local anesthetics. But most of the time, people complain of things like heart palpitations, shaking, sweating, or feeling faint, which are not the symptoms of a true allergy.

What is an allergy?

An allergy is a hypersensitive state which is acquired through exposure to an “allergen”. People can be allergic to lots of different things.

Symptoms of an allergic reaction to local anesthetics include

  • skin reactions (rashes, itching, edema or hives)
  • asthma-like attacks
  • in the most extreme cases, anaphylactic shock

Not all allergic reactions are dangerous. Most people who are allergic to local anesthetics only experience temporary itching and skin rash after receiving the injection. Anaphylactic shock is almost unheard of with local anesthetics (though dentists have to be prepared for this possibility, so they have emergency equipment to reverse such a situation).

What causes the allergies to local anesthetics?

Local anesthetic cartridges contain two active ingredients: the actual anesthetic (which ends in -caine, e. g. lidocaine) and epinephrine. Most people who have a genuine allergic reaction to local anesthetics are not allergic to the actual anesthetic agent (or “caine”). It is much more common (though still rare) to be allergic to preservatives in the local anesthetic solution.

Why are preservatives added?

All standard local anesthetics contain the preservative sodium bisulfite or metabisulfite. The preservative is necessary to keep the epinephrine fresh (epi quickly deteriorates and becomes useless otherwise). The standard local anesthetic cartridges (called lidocaine in the U.S. and lignocaine in the U.K.) have epi added.

Why use epinephrine in the first place?

Epinephrine is added to the local anesthetic for a good reason: it makes it work longer and more efficiently. For example, the most commonly used local anesthetic (lidocaine 2% with 1:100,000 epi) numbs the tooth for one hour, but without the epi, it only numbs the tooth for 5-10 minutes. Epinephrine also acts as a “vasoconstrictor”: it stops soft tissues from bleeding.

Allergy to Preservatives

If an allergy test shows that you are allergic to the preservative, a local anesthetic without epinephrine can be used. Because the usual local (lidocaine) doesn’t numb for very long without epi, mepivacaine (also known as carbocaine) or prilocaine without epi can be used. People who are allergic to bisulfites often know about it, because bisulfites are commonly sprayed onto fruit and vegetables to keep them looking fresh. If you have an allergy to bisulfites, let your dentist know about it!

Allergy to “Caines”

People from the U.S. often use the term “novacaine”, “novocain”, “novacaine” or a variation thereof when talking about local anesthetics… even though novocaine has not been used in dentistry for decades (both because it wears off too quickly and because allergies to novocain and other ester-based -caines are relatively common). All the -caines used for local anaesthesia these days are amides rather than esters. Virtually nobody is allergic to amide caines. But there are some documented cases, so if you’re among them, what can you do?

There are a few possibilities:

  1. general anaesthesia in a hospital
  2. using a histamine blocker instead of an amide anesthetic (stings and burns and is only suitable for emergency situations)
  3. going without local anesthetic – a possibility for minor work if you don’t mind the potential pain factor. If it’s anything more than that, research would suggest that the work you have done will be much less successful and will fail sooner.
  4. hypnosis can be used in some cases
  5. using a different -caine (the best option).
  6. and 2. should only be used in acute emergency situations, if there really is no time to have an allergy test done. Otherwise, an allergy test will show which of the -caines are safe for you.

The 5 local anesthetics used in dentistry today are:

  • Lidocaine Hydrochloride (UK: Lignocaine) (tradenames: Xylocaine, Alphacaine, Lignospan, Octocaine)
  • Mepivacaine Hydrochloride (tradenames: Carbocaine, Arestocaine, Isocaine, Polocaine, Scandonest)
  • Prilocaine Hydrochloride (tradename: Citanest)
  • Articaine Hydrochloride (tradenames: Septocaine, Septanest, Astracaine, Ultracaine)
  • Bupivacaine Hydrochloride (tradename: Marcaine)

Luckily, there is no cross-allergenicity with amide local anesthetics – meaning that someone may be allergic to lidocaine and mepivacaine, but not to articaine, for example.

Allergies in the Past

In the past, some local anesthetics were esters rather than amides, and allergic reactions to these were not uncommon. They are no longer sold these days. Novocain was an ester anesthetic, as was the very first local anesthetic: cocaine! Nowadays, esters are only used for topical anesthesia (numbing gels) in dentistry. Because they don’t enter the blood-stream, they can’t produce dangerous reactions. Another ingredient which is no longer used in local anesthetic cartridges is methylparaben. Allergy to methylparaben has increased over the years, because it is used in drugs, cosmetics and foods. It is still used in multiple-dose vials in hospitals, but it is no longer used at the dentist’s.

Allergy to Epinephrine

It is physically impossible to be allergic to epinephrine (epinephrine is the same as adrenaline). Our bodies produce epinephrine all the time. If you were allergic to it, you’d be long dead before reading this page, never mind seeing a dentist…

Symptoms like:

  • a racing heart
  • shaking uncontrollably
  • breaking out in a cold sweat
  • not being able to breathe properly (breathing rapidly/hyperventilating), leading to dizziness, lightheadedness and tingling in fingers, toes and lips

are all signs of an adrenaline rush – but it’s unlikely that the epinephrine in the injection caused it. The amount of epi in local anesthetics is tiny compared to the amount your body naturally pumps out. The reason your body produces adrenaline is to prepare you for a fight-or-flight situation, and an increase in heart rate and blood pressure mean that you can run faster! If you do decide to do a runner, please let your dentist know first… that way, they’ll be able to remove any sharp objects between you and the door  .

On very rare occasions, the epi may be accidentally injected into a vein instead of muscle tissue (the local anesthetic is usually ineffective in this instance). This can cause a very dramatic increase in heart rate. While not dangerous, such an experience can certainly be unsettling, but the chances of it happening again are extremely slim. Also, the use of aspirating syringes has become more common in recent years, and this prevents the accidental injection of adrenaline containing local directly into a vein.

Some people do appear to react more sensitively to the epi in injections than others. It is possible to use a local anesthetic without epi. However, not all dentists will stock this – so if you’re concerned, it’s best to ask.

Mepivacaine (carbocaine) and prilocaine work for a reasonable amount of time even without the epi and can be used instead. But it may be more difficult to achieve profound numbness without epi. In this case, using laughing gas or IV sedation in addition to the local anesthetic may be helpful.

From our message board:

“There have been some people who had a sensitivity to the local anesthetic itself or the preservative used. Sometimes the dentist can try a different type or brand of anesthetic to see if that might help. I had one patient who experienced the same after effects from anesthetics, but we tried Carbocaine with no epinephrine, and she found that one worked great for her. You could see if the dentist could try a little of that instead.

One idea might be to visit the dentist and have some nitrous oxide. The dentist could give you a very small amount (eg. 0.4 mL or quarter carpule) of Carbocaine infiltration to see whether that causes you any problems. You wouldn’t even have to have any work done. It could be just a visit to see if a different anesthetic might work better for you. You could then wait 20 minutes to see if you had any problems.”

Local Anesthetic Overdose

This may be more common than one might believe, but it is pretty much never dangerous (unless it’s badly abused – see below). For example, one study cited by Malamed (2002) showed one particularly LA-happy general dentist using an average of 19.24 cartridges of local anesthetic (per person!) for the removal of all 4 wisdom teeth (or wizzies, as they are called in the trade). Gulp . Clearly, a lot of these patients received an overdose, yet none of them experienced any adverse reactions. Which shows that local anesthetics are extremely safe for healthy adults.

However, it’s clearly not best practice and dentists need to be careful not to give an overdose. This is particularly true for young children, who have a low body weight.

The symptoms of a mild to moderate overdose can be similar to those of anxiety – lightheadedness and dizziness, nervousness, numbness, inability to focus, tinnitus, elevated heart rate, sweating, etc.
In the vast majority of adults, anxiety is a far more likely culprit than overdose. But if you have had a lot of cartridges of local anesthetic in one go and you experienced these symptoms, it might have been an overdose.

In most cases of overdose, the reaction is mild and short-lived, and requires no treatment. Some people with a fear of local anesthetics are concerned because they’ve read about deaths following local anesthetic overdose on the internet. What isn’t reported is that the few serious incidents which have occurred involved very bizarre circumstances:

“Heard of a case in the USA where the “dentist” (and I use the word very loosely) injected 20 carts to a patient who was having problems during an IV, because he wanted to get some adrenaline in!!! Patient died, dentist convicted of manslaughter.”

Tips for Coping

Most commonly, the “allergy” turns out to be an adrenaline rush. Here are a few tips for coping:

  • If you feel anxious about injections or upcoming treatment, talk to your dentist about it. Most dentists will be extra gentle with you if they know about your fears, and do their best to calm and reassure you (both before and while they administer the local).
  • Perhaps just understanding what is happening and knowing that an adrenaline rush is not dangerous, but a natural reaction, will make injections easier for you. The sensation is unpleasant, but not dangerous.
  • Your dentist may be able to offer you laughing gas, IV sedation, or anti-anxiety medications.
  • Rescue Remedy (a natural anti-anxiety remedy available in pharmacies and Natural Health stores) might also work for you, as can distraction techniques such as listening to a IPod.
  • Some dentists tell their patients beforehand that the injection contains adrenaline and that they will feel an increase in heart rate, which is not dangerous. This can actually be helpful, because it prepares people for the possibility that they’ll feel their heart beat faster. Better still, one can attribute any adrenaline rush to the drug, rather than to anxiety. For these reasons, some people find knowing about the adrenaline in the injection helpful. Unfortunately, this technique can also backfire and make people panic instead!

If you suspect a true allergic reaction:

  • Consult with an allergist. They can test exactly which substance you are allergic to.
  • Local anesthetics (caines) should be tested without the epinephrine. Preservatives should be tested separately.
  • If it turns out that you really are allergic to a -caine, an allergist can help you find out which of the -caines you can tolerate.
  • If it turns out that you are allergic to sodium bisulfite, a local anesthetic without epi can be used.

If you are concerned about a local anesthetic overdose:

  • An overdose is only really a concern when you are having a lot of dental work done in one go, especially when it’s in all 4 quarters of your mouth (upper and lower left and right).

Let your dentist know about your concern and discuss the options. For example, if there is a pressing reason to numb all 4 quarters during the same appointment, your dentist can administer local anesthetic to one quadrant, treat that area, then numb the next quadrant, and so on. This results in a lower concentration of local anesthetic in the blood compared with giving the local all at the same time.


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