Allergy to local anaesthetics
True allergies to the actual local anaesthetics used nowadays are exceedingly rare – only a few cases have been reported worldwide. Some people are allergic to preservatives in local anaesthetics. But most of the time, people complain of symptoms like heart palpitations, shaking, sweating, or feeling faint.
On this page, you can find out about
- True allergic reactions to local anaesthetics
- Other adverse reactions (heart palpitations, shaking etc.)
- Local anaesthetic overdose
“I got a bad rash or an asthmatic attack the last time I had local anaesthetic. My allergist has confirmed an allergy. What can I do now?”
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.
What are the symptoms of an allergic reaction to local anaesthetics?
Symptoms of an allergic reaction to local anaesthetics 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 anaesthetics only experience temporary itching and skin rash after receiving the injection. Anaphylactic shock is almost unheard of with local anaesthetics (though dentists have to be prepared for this possibility, so they have emergency equipment to reverse such a situation).
What causes the allergy?
Local anaesthetic cartridges contain two active ingredients: the actual anaesthetic (which ends in -caine, e. g. lidocaine) and epinephrine. They also contain preservatives.
Most people who have a genuine allergic reaction to local anaesthetics are not allergic to the actual anaesthetic agent (or “caine”). It is much more common (though still rare) to be allergic to preservatives in the local anaesthetic solution.
Why are preservatives added?
All standard local anaesthetics contain the preservative sodium bisulphite or metabisulfite. The preservative is necessary to keep the epinephrine fresh (epi quickly deteriorates and becomes useless otherwise). The standard local anaesthetic 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 anaesthetic for a good reason: it makes it work longer and more efficiently. For example, the most commonly used local anaesthetic (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 anaesthetic 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 bisulphites often know about it, because bisulphites are commonly sprayed onto fruit and vegetables to keep them looking fresh. If you have an allergy to bisulphites, let your dentist know about it!
Allergy to “Caines”
People from the U.S. often use the term “novocain”… 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:
- general anaesthesia in a hospital
- using a histamine blocker instead of an amide anaesthetic (stings and burns and is only suitable for emergency situations)
- going without local anaesthetic – 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.
- hypnosis can be used in some cases
- using a different -caine (the best option).
1. 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 anaesthetics used in dentistry today (in order of popularity) are:
- Lidocaine Hydrochloride (UK: Lignocaine) (tradenames: Xylocaine, Alphacaine, Lignospan, Octocaine)
- Articaine Hydrochloride (tradenames: Septocaine, Septanest, Astracaine, Ultracaine)
- Prilocaine Hydrochloride (tradename: Citanest)
- Mepivacaine Hydrochloride (tradenames: Carbocaine, Arestocaine, Isocaine, Polocaine, Scandonest)
- Bupivacaine Hydrochloride (tradename: Marcaine)
Luckily, there is no cross-allergenicity with amide local anaesthetics – 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 anaesthetics were esters rather than amides, and allergic reactions to these were not uncommon. They are no longer sold these days. Novocain was an ester anaesthetic, as was the very first local anaesthetic: cocaine!
Nowadays, esters are only used for topical anaesthesia (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 anaesthetic 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.
Tips for coping if you suspect a true allergic reaction:
- An allergist can test exactly which substance you are allergic to. Your dentist should request testing two or three different amide local anesthetics as well as sodium metabisulphite.
- Local anaesthetics (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 bisulphite, a local anaesthetic without epi can be used.
Other adverse reactions to local anaesthetics
“Each time I have novocaine, I get heart palpitations, start shaking and sweating, and get a bad headache. Last time, I felt as though I was going to die!”
“I am afraid of how the local anaesthetic makes me feel. My heart feels like it beating out of my chest (even without the epinephrine) and I swear, it feels like I can’t swallow and like I’m going to choke or stop breathing. It really freaks me out.”
Are heart palpitations and shaking a sign of allergy to epinephrine?
It is physically impossible to be truly allergic to epinephrine (epinephrine, or epi for short, is the same as adrenaline). Our bodies produce epinephrine all the time.
- 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
- a headache afterwards
are all signs of an adrenaline rush. It’s unlikely (but not impossible) that the epinephrine in the injection caused it. The amount of epinephrine in local anaesthetics is very small 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.
But I wasn’t even feeling nervous when it happened!
On rare occasions, the epi may be accidentally injected into a blood vessel (either a vein or an artery) instead of muscle tissue. The local anaesthetic is usually ineffective in this instance. Depositing the epi into a blood vessel can cause a very dramatic increase in heart rate – though the resulting blood plasma concentration is unlikely to exceed that produced by the body under stressful situations or when performing physical exercise 1.
While not dangerous in healthy people, such an experience can certainly be very unsettling. The good news is that the chances of it happening again are extremely slim. Also, the use of aspirating syringes has become more common in recent years, and this usually prevents the accidental injection of adrenaline-containing local anaesthetic directly into a blood vessel.
Some people do appear to react more sensitively to the injection of epinephrine than others. In this case, it’s a good idea to limit the amount of epinephrine used by either choosing a plain solution or one with minimal epi concentration.
There are two local anaesthetics which work for a reasonable amount of time even without epi:
- mepivacaine (carbocaine) and
- prilocaine without epinephrine (Tradename: Citanest Plain).
The final choice of local anaesthetic depends on the actual tooth or teeth being worked on and on the duration of the procedure. For example, Citanest Plain lasts for a duration of 1 to 1.5 hours for lower teeth (when using an inferior alveolar nerve block) which is only slightly different from Citanest with epi. However, for upper teeth, Citanest Plain only provides profound numbing for 15 minutes when given via infiltration – ok for short procedures, but not so good for something longer like root canal treatment.
Sometimes it may be more difficult to get totally numb without epi. In this case, using laughing gas or IV sedation in addition to the local anaesthetic may be helpful. From our message board:
“There have been some people who had a sensitivity to the local anaesthetic itself or the preservative used. Sometimes the dentist can try a different type or brand of anaesthetic to see if that might help. I had one patient who experienced the same after effects from anaesthetics, 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 anaesthetic might work better for you. You could then wait 20 minutes to see if you had any problems.”
Epinephrine and medical conditions
It is important that you let your dentist know if you have any medical conditions, and also to tell them what medications or drugs you’re on.
If you have high blood pressure, a prior heart attack, by-pass surgery, angina, uncontrolled diabetes, an uncontrolled thyroid disorder or if you are taking non-cardioselective beta blockers, tricyclic antidepressants or cocaine, you might benefit from the use of a solution without epinephrine.
These conditions are relative contraindications – profound anaesthesia is paramount, because causing pain during procedures could result in your body producing large amounts of epinephrine as a reaction to stress and pain, potentially resulting in a medical emergency.
Tips for Coping
Most commonly, what feels like an allergy to local anaesthetic 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.
- Distraction techniques such as listening to music can help.
- 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!
Local Anaesthetic Overdose
This may be more common than one might believe, but it is pretty much never dangerous in adults (unless it’s badly abused – see below). For example, one study cited by Local anaesthesia guru Stanley Malamed showed one particularly LA-happy general dentist using an average of 19.24 cartridges of local anaesthetic (per person!) for the removal of all 4 wisdom teeth (or wizzies, as they are called in the trade)2. Gulp. Clearly, a lot of these patients received an overdose, yet none of them experienced any adverse reactions. Which shows that local anaesthetics are extremely safe for healthy adults.
However, it’s clearly not best practice, and dentists need to be particularly careful with young children, those who have a low body weight, or those with certain medical conditions.
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 anaesthetic in one go and you experienced these symptoms, it may well 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 anaesthetics are concerned because they’ve read about deaths following local anaesthetic overdose (invariably in the US) 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 if you are concerned about an 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 anaesthetic to one quadrant, treat that area, then numb the next quadrant, and so on. This results in a lower concentration of local anaesthetic in the blood compared with giving the local all at the same time.
The information on this page has been provided by the Dental Fear Central Web Team. Last reviewed by a dental professional, Lincoln Hirst, BDS, on January 4, 2019. We welcome your feedback on our information resources.
- UK Medicines Information. What is the clinical significance of potential drug interactions with local anaesthetic preparations used in primary care dentistry? 2015. Online information available at https://www.sps.nhs.uk/wp-content/uploads/2015/10/NW-QA152.4-Local-anaesthetic-drug-interactions-.pdf
- Stanley Malamed (2004). Handbook of Local Anesthesia, Fifth Edition, p. 313. St. Louis, Missouri: Elsevier Mosby.