Lidocaine Side Effects and Toxicity

Lidocaine is a Commonly Used Local Anesthetic
Lidocaine is a Commonly Used Local Anesthetic | Source

What is Local Anesthesia?

*While the author is a physician anesthesiologist, nothing in this article is intended to represent medical advice. This hub is for informational purposes, only.

Lidocaine is an example of a local anesthetic. Local anesthetics can be injected into tissue or around nerves to cause numbing. The numbing will affect the area immediately surrounding the injection site when lidocaine is used for "local anesthesia". Regional anesthesia makes use of the class of drugs called local anesthetics (like lidocaine) to numb a larger area of the body by numbing a nerve or group of nerves that supply that area.

To review and keep the terminology straight...

  • Local anesthetics are drugs that cause numbing of tissue
  • Local anesthesia specifically refers to the numbing of an area of skin or tissue at or near the injection site of a local anesthetic
  • Regional anesthesia also utilizes the drugs that are called local anesthetics, but in a more indirect manner. The local anesthetic is injected around nerves supplying the body part to be numbed.

How do Local Anesthetics Work?

Local anesthetics are often discussed in terms of their properties. Their onset time and duration of action, as well as their safety profile, may determine which anesthetic would be useful in certain situations.

The two general classes of local anesthetics are the amides and esters based on their chemical structure. Lidocaine is an amide local anesthetic.

Lidocaine, and local anesthetics in general, work by penetrating tissue and blocking pain signals from being transmitted along nerve endings, preventing the pain signal from reaching the brain. The nerve endings have channels for the electrolyte sodium (Na channels) on them. When tissue is disturbed, the channels open and sodium enters the cell, changing the electrical charge. This electrical change becomes the pain sensation when interpreted by the brain.

The local anesthetics are sodium channel blockers. In other words, they prevent sodium from entering the nerve endings, thus, preventing pain. This is perceived as numbness.

Schematic Demonstration of Lidocaine's Action

When is it Used?

Lidocaine can be used as a cream, injection or even as a mist for the nose, mouth and throat. Lidoderm is a patch containing lidocaine, available by prescription, that is applied to the skin for various painful conditions.

Lidocaine is most commonly used for injection into skin, muscle and mucous membranes for it's local numbing. It is also used in regional anesthesia like spinals, epidurals and nerve blocks.

Its most common use is as a local anesthetic, but it has also been used for it's action on heart cells to help stop or stabilize some abnormal heart rhythms.

  • Redness at or near injection site
  • Itching at or near injection site
  • Blistering at or near injection site
  • Numbness lasting longer or spreading further than desired

Side effects and complications are more likely if you have certain medical conditions or in combination with some medications. Always tell your doctor about your medical history and medications.

Side Effects of Lidocaine?

The expected effect of lidocaine is numbness of the target tissue. There are very few side effects of lidocaine used in this way.

Side effects are those effects that accompany a medicine's use. They are expected in a certain percent of the population using the medication. They are often bothersome, but not harmful.

Complications, on the other hand, are possible, but not expected effects. Precautions are taken to prevent complications and they are often, but not always, avoidable.

Brief Description of Local Anesthesia

Complications of Use

Complications can occur for a variety of reasons. Overdose of lidocaine, injection or leakage into the wrong space or allergic reaction can lead to complications.

Allergic Reactions

Allergic reactions are rare. The amide local anesthetics like lidocaine don't have nearly the potential for, or actual incidence of, allergic reaction as local anesthetics of the ester class. It is possible, but unlikely to have a true allergic reaction to lidocaine. Sometimes, the preservative used may cause a reaction, however. Also, lidocaine may be mixed with epinephrine (adrenalin) to prolong it's duration of action. The epinephrine will increase heart rate and blood pressure, and can cause nausea and a hot flushing and feelings of anxiety. This is not an allergic reaction as many patients assume or have been told. It is an exaggerated effect of the normal response to epinephrine.

Injection or leakage into blood vessels and the circulation of lidocaine meant for other tissue can lead to overdose and signs of toxicity. This can also occur when too much lidocaine is injected anywhere in the body. The maximum safe dose of lidocaine is calculated based on body weight and perhaps age and coexisting medical conditions. It is metabolized by the liver and eliminated from the body in the urine, so if you have liver or kidney problems, be sure to tell your doctor before receiving an injection with lidocaine.

Unintended Injection

When lidocaine enters a space for which it is not meant, it can cause unwanted side effects and complications. For example, epidural medication administration requires many times the dose of medicine injected directly into the spinal fluid. If lidocaine meant for the epidural space enters the spinal fluid instead, the result is an unwanted spinal block with much more medicine than would normally be used for that purpose. In this situation, the spinal can spread and cause a "total spinal" which temporarily paralyzes breathing and affect the heart rate, conduction and blood pressure in dangerous ways. The same thing can happen with certain peripheral nerve blocks, especially an interscalene block given in the neck before shoulder surgery, since the epidural and spinal spaces are close to the injection site. For this reason, these blocks are (or should) only given by highly-trained professionals who are also certified in advanced life-saving techniques.

Lidocaine toxicity from absorption into the bloodstream is another potential complication.

What are the Signs of Toxicity?

Overdosage of lidocaine, or lidocaine absorbed into the circulation can cause toxicity with lidocaine, a serious and potentially fatal complication. The severity of the complication depends on the amount that reaches the circulation.

Signs of lidocaine toxicity include

  • Numb tongue or lips
  • Ringing in the ears
  • Bad taste in the mouth
  • Nausea
  • Sedation

More severe toxicity is manifested as seizures, respiratory and cardiac arrest and coma.

Treatment of toxicity includes supportive care - medications to stop seizures and to support the cardiovascular system are used. In addition, a lipid rescue solution is now becoming a front-line treatment to neutralize local anesthetic toxicity and minimize the complications from it.

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Comments 15 comments

Austinstar profile image

Austinstar 4 years ago from Somewhere in the universe

Thanks for this information. I use the Lidoderm patch for neuropathy in my feet. It feels like I am being tasered on the bottom of my foot sometimes. I have a damaged sciatic nerve. The patch is the only thing I have tried that actually works to stop the pain.

Would lowering the Na+ help? Or increasing the K+?

Marcy Goodfleisch profile image

Marcy Goodfleisch 4 years ago from Planet Earth

What a valuable article! Lidocaine can seem harmless to some people because it can be used topically, but it is so important to understand there are still risks. I've heard about sone of the major side effects you mention here. Excellent information!

Nettlemere profile image

Nettlemere 4 years ago from Burnley, Lancashire, UK

very useful to know understand the difference between local and regional anesthesia. And vaguely remembering esters from poorly understood chemistry lessons I'm pleased to know they have a use!

Also thought the song was a perfect match for the schematic video.

Dolphan5 profile image

Dolphan5 4 years ago from Warwick R.I

Thanks again Doc! Informative and well written.

Thumbs Up and interesting, useful.


TahoeDoc profile image

TahoeDoc 4 years ago from Lake Tahoe, California Author

Austin- Glad that patch is helping, it can be really good for that kind of pain/irritation. And nah, the body does such a good job of regulating and maintaining the sodium and potassium concentrations that would reach the site of action with flux into and out of cells, through the kidneys, etc. An alteration that would significantly affect that concentration would be physiologically dangerous.

Thanks for reading :)

@Marcy- thank you as always for your comments and insights. You are a star!

@Nettle- the video is simplistic (and NOT mine), but sometimes that is the best way to illustrate these processes at first. It gets pretty complex. Thanks for stopping by.

@Dolphan- Thank you for following along and being such a great supporter of my hubs!

Nettlemere profile image

Nettlemere 4 years ago from Burnley, Lancashire, UK

I completely agree - if it's chemistry it needs to be very straight forward for me to have 1/2 a chance of even vaguely understanding it!

TahoeDoc profile image

TahoeDoc 4 years ago from Lake Tahoe, California Author

Me too Nettlemere!

Mmargie1966 profile image

Mmargie1966 4 years ago from Gainesville, GA

Very informative, especially since I know someone who will be getting an epidural in the next 6 months.

My Mother has lidocaine patches for arthritis in her lower back. It really is helpful for her.

Thanks for sharing, Doc! Voted up and useful!

pogana 2 years ago

This article was very informative. I have a question may be someone answer can a person having normal liver enzymes used lidocaine spray 9.6 % w/w ( 7.7 mg per metered spray) 12 g occasionally ? Is it safe ?

TahoeDoc profile image

TahoeDoc 2 years ago from Lake Tahoe, California Author

What is the source of the 9.6% spray? Where on the body is it being used?

KJ 2 years ago

Very interesting article! Question for you - as a chronic back pain sufferer, I get facet injections, epidural injections and SI Joint injections. Recently I was supposed to have another epidural and the doc was unable to get to the correct spot because I had some calcification in the area he was trying to get to. He tried many spots and couldn't get through but after the unsuccessful injection I was extremely dizzy, tongue was numb, slight confusion and my heart was racing. Do you think it was lidocaine toxicity?

TahoeDoc profile image

TahoeDoc 2 years ago from Lake Tahoe, California Author

That sounds some of numbing medicine (lidocaine or bupivicaine or ropivicaine are most commonly used, I think) was absorbed into your blood stream. There may have also been some epinephrine in the mixture. Epinephrine is added to the numbing medicine to make it last longer and could contribute to the heart racing if it got into the blood stream. During difficult epidurals, blood vessels may be poked and some medicine can get in.

So, it seems as if some of the medicine probably went into the blood stream and not just around the nerves. Of course, I have to give the disclaimer that I can't make a diagnosis without having been there in case there is more to it than I can tell here.

Marie 4 weeks ago

I had a small cyst removed by my skin dr and he used xylocaine or lidocane to numb the area. That week I suffered from severe back stiffening for the first time and was bedridden for at least a week. I was curious if the anesthesia may have gone too far into other areas that may have caused my back to stiffen. My doctor assured me it wasn't related. A year later the same Doctor removed a skin growth from my thigh also using the anesthesia to numb the area. A few days later I am in severe throbbing pain in the same thigh that was injected and I cannot stand upright or walk. I tried all pain meds and was hospitalized but they assume it may be a pinched nerve. I am convinced that the anesthesia went too far as it did last time in my back. This can't be a coincidence that the same thing happened again. I am suffering from the pain and wondering how or if I can get the anesthetic out of the area it is affecting.

TahoeDoc profile image

TahoeDoc 3 weeks ago from Lake Tahoe, California Author

This cannot figure out how this would happen. The area numbed is usually small and the metabolism so quick that I can't see (or don't know of a mechanism) a relationship. Doesn't mean there isn't something I don't know but nothing I know of would do this unless you have a type of allergic reaction that is just "local" meaning to the surrounding area but not causing overall signs of allergy. That is not a medical conclusion though- just trying to think outside the box. So sorry for your troubles. :(

Jesus B 2 weeks ago

They injected lidocaine to numb my teeth for a filling. They had to inject me again when I could feel the pain. After one week, my throat was sore and I couldn't swallow without it hurting, then I had to go the the ER due to unusual heart palpitations, and lastly, I feel dizzy and light headed. Do you think all this could be related to the lidocaine due to the overdose, or am I wrong.

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