The ideal topical anesthetic would have high efficacy with minimal systemic absorption. These agents are used for a variety of applications, ranging from venipuncture in children, 9 to skin graft harvesting, 10 , 11 to laser treatments such as facial rejuvenation and hair removal in adults.
Although these topical lidocaine-containing compounds are considered safe, they have been poorly studied. There is some systemic absorption of lidocaine, and in rare cases, this has led to severe cardiac and neurological side effects and, in extreme cases, death. Local anesthetics LA can be split into two classes: amides eg, lidocaine, prilocaine and esters eg, benzocaine and tetracaine. The basic chemical structure of local anesthetics consists of a lipophilic group and intermediate bond which is either an ester or an amide and a hydrophilic group.
All local anesthetics are weak bases; inflammation causes an acidic environment that in turn causes more of the LA to be ionized, leading to a slower onset of action. Amides are metabolized in the liver by the P cytochrome pathway more slowly than esters, which are metabolized in the plasma by cholinesterases. Therefore, because they are metabolized more slowly, amides can be more toxic than esters.
Lidocaine amide has a relative potency of four, whereas tetracaine ester has a relative potency of The higher the pH, the longer-acting the LA: lidocaine pH 7. Many clinicians use a combination of local anesthetics. Indeed, three of the five drugs that were used in this study contain more than one type of local anesthetic. The effect of the different anesthetics is additive. Our results showed that the OTC products were associated with greater levels of lidocaine in the bloodstream than the prescription preparations.
The literature relating to lidocaine toxicity is largely centered on its intravenous use for cardiac arrhythmias. Clinical symptoms of lidocaine toxicity include lightheadedness, paraesthesia, nausea, and vomiting, which can progress to seizures, arrhythmias, and cardiorespiratory depression.
The doses that were used in this study and the application of occlusive dressings were all within the manufacturer guidelines. Allergy rarely occurs with amides but can occur with esters such as benzocaine because, when metabolized, it forms p-aminobenzoic acid PABA , which has been associated with allergic reactions.
Other studies support our findings, particularly with EMLA, showing that it can cause minor skin irritations. It has already been shown that the prilocaine component of generic topical anesthetic, which resembles the same composition as EMLA, can cause contact sensitivity.
For these reasons, our study highlights the need for caution with unsupervised patient use of these drugs. Even when a test patch is offered, as in this study, skin reactions may not be evident until the drug is actually applied to the face.
This study compared five different lidocaine-containing topical anesthetics and demonstrated that absorption of the drug through the facial skin varies from individual to individual. This has previously been demonstrated by our group in topical anesthetic and liposuction studies. Lidocaine is metabolized in the liver via the P cytochrome pathway, and its breakdown products, including MEGX, are excreted via the kidneys.
As a result, patients who have liver or kidney problems will have a reduced capacity for lidocaine metabolism and therefore will have greater circulating levels of the drug.
In addition, patients who have broken areas on the skin prior to drug application will also have greater absorption of the drug, as the barrier to drug absorption is the stratum corneum the outermost layer of the skin.
The results of this study highlighted the effect of the drug- delivery vehicle on the absorption through the skin. One of the drugs had an alcohol-based composition, the second was a liposomal drug-delivery system, and the third was an emollient-based product. Alcohols act as skin penetration enhancers by removing lipid from the stratum corneum and therefore increasing its permeability.
This is because the drug exists in a eutectic mixture with 2. This means that at room temperature, lidocaine and prilocaine exist as a liquid rather than a solid, and absorption is therefore enhanced. This is further facilitated by the addition of an occlusive dressing. LET had the least absorption of all five drugs, with only one participant in this group having any detectable levels in the bloodstream. This is probably attributable to the fact that this drug contains epinephrine, which is a known vasoconstrictor.
Two of the local anesthetic mixtures in this study were compounded in the pharmacy. Recently, the US Food and Drug Administration FDA has issued warnings to five companies with regard to their practice of mass-producing compounded products. These drugs should be administered under the guidance of a healthcare professional, who can give the patient clear instructions for use.
This study and previous studies by this group have demonstrated that although topical anesthetics are safe, there can be considerable systemic absorption of lidocaine- containing topical anesthetics. We would therefore advise patient and physician caution, particularly with OTC lidocaine preparations, which our results showed to have the greatest systemic absorptions. This study focused on lidocaine and its metabolites because the drug has well-documented guidelines for toxicity and the serum drug levels at which symptoms occur.
It is also the most potent of the active drugs in the topical anesthetics. Esters such as benzocaine and tetracaine are less well-researched in the literature but have less potency than amides due to their method of metabolism. For future studies, levels of benzocaine, tetracaine, and prilocaine could be measured in the serum to give an indication of their relative contribution.
Occlusive dressings enhance penetration of the drug, and the length of time over which the occlusive dressing is applied will influence drug absorption. Added to this, participants in all study groups still had detectable levels of lidocaine and MEGX in their serum at eight hours, which has ramifications for repeat applications.
Ideally, these drugs should be used under the supervision of a healthcare professional, so that patients do not apply large amounts of the drug to large surface areas under occlusive dressings, all factors that result in enhanced absorption. Although these products are packaged with instructions on maximum recommended surface areas for application, maximum dosage, and the need for occlusion, it is still prudent for the healthcare professional to be familiar with warning signs of lidocaine toxicity.
Systemic drug absorption following topical application will be influenced by several factors, but again, our study demonstrates that it also is dependent on individual patient physiology.
Skin of the face would most likely have an increased absorption profile compared with skin on the leg or abdomen. Further studies would need to be carried out to compare these areas before recommendations can be made on specific drugs and their doses.
It is well known that disruption of the stratum corneum leads to enhanced drug absorption. Several clinical studies show that disruption of the stratum corneum by laser pretreatment, followed by topical application of anesthetic, can lead to a faster onset of anesthesia. Our next step is to examine the safety profile of laser pretreatment as a method to facilitate faster anesthesia in a clinical model, for procedures such as laser facial resurfacing. Topical anesthetics are safe, but systemic absorption in some individuals can reach unpredictably high levels.
The type of drug-delivery system, occlusive dressings, and individual patient factors such as liver function can affect systemic absorption, metabolism, and excretion of lidocaine. Our data show that OTC products have the greatest level of systemic absorption and can persist in the bloodstream at eight hours postapplication. Therefore, we recommend that topical anesthetics—even OTC formulations—be used under the supervision of a healthcare professional to avoid adverse toxic effects and, in rare cases, death.
The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article. Systemic toxicity from topically applied lidocaine in conjunction with fractional photothermolysis. Arch Dermatol ; : - Google Scholar. EMLA-induced methemoglobinemia and systemic topical anesthetic toxicity. J Emerg Med ; 26 : 85 - Are one or two dangerous?
Lidocaine and topical anesthetic exposures in children. J Emerg Med ; 37 : 32 - Lidocaine toxicity misinterpreted as a stroke. West J Emerg Med ; 10 : - Topical anesthetics update: EMLA and beyond. Dermatol Surg ; 27 : - Comparative study of the efficacy of four topical anesthetics. Dermatol Surg ; 25 : - Aesthetic Surg J ; 30 : - An intra-individual quantitative assessment of acute laser injury patterns in facial versus abdominal skin.
Lasers Surg Med ; 43 : 99 - Split skin grafting using topical local anaesthesia EMLA : a comparison with infiltrated anaesthesia. Br J Plast Surg ; 41 : - Scand J Plast Reconstr Surg ; 19 : - Efficacy of erbium: yttrium-aluminum-garnet laser-assisted delivery of topical anesthetic. J Am Acad Dermatol ; 47 : - Lidocaine skin creams such as EMLA and Nulbia may not be suitable for people with porphyria, methaemoglobinaemia or G6PD deficiency because they contain a combination of local anaesthetics.
A doctor or nurse will usually give you a prescription for the lidocaine cream or the cream itself ahead of your appointment. Always follow the instructions that come with your cream. If you're having a drip fitted or having blood taken, put the lidocaine cream on 1 hour beforehand. For minor surgery, your doctor may tell you to use the cream more than 1 hour before the procedure.
If the procedure is delayed and the numbing effects of the cream have worn off, ask your doctor or nurse for advice before using any more cream. If you're having a cosmetic procedure and have bought lidocaine from a pharmacy to numb the area, tell the person doing the procedure before it starts.
It will help them to know that the area has been numbed and you will not feel as much pain. The amount you use depends on the procedure you're having and the type of lidocaine cream you're using.
They may tell you to use a whole tube of cream on each area of your skin, more than 1 tube, or only part of a tube. Do not use the cream on your eyes, ears, nose or the inside of your mouth, or on your genitals or bottom anus — unless your doctor tells you to. If you forget to use the cream, or you put it on less than 1 hour beforehand, tell the person who is going to do the procedure.
They may want to delay it. Using more than the recommended amount can cause side effects. This can also happen if you put the cream on a large area of skin, or use it for longer than recommended. If you've been prescribed lidocaine, you're unlikely to use too much cream, as a doctor or nurse will usually give you the amount you need for a one-off procedure.
Lidocaine skin cream is generally very safe. Many people do not have any side effects at all, or only mild ones, when using the cream. It's extremely rare to have an allergic reaction anaphylaxis to a lidocaine.
These are not all the side effects of lidocaine. For a full list see the leaflet inside your medicine packet. You can report any suspected side effect to the UK safety scheme. Lidocaine is generally considered safe to use during pregnancy and breastfeeding. However, check with your doctor, a pharmacist or your midwife first. Tell your pharmacist or doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.
Lidocaine can potentially affect the way other medicines work. However, this more likely when you're using lidocaine at higher doses or if you're having lidocaine injections. If you're using your lidocaine skin cream as directed, it usually will not affect any other medicines. For safety, tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements. Lidocaine is a local anaesthetic , which numbs the area where you've used it.
Using lidocaine skin cream beforehand will ease any pain at the site of the procedure such as a needle being used to take blood. You will use lidocaine skin cream as a one-off, before a minor procedure like taking a blood sample.
There are a number of creams made for numbing the skin before procedures. They work in the same way and are likely to have a similar effect. However, it does not treat infections or shorten the duration or lessen the severity of an infection. It works quickly to numb the area it is applied to. For example in pregnant or breast feeding women, patients who are acutely ill, debilitated, or elderly, people with severe liver disease, and people who are allergic to any of the active or inactive ingredients.
Tell the doctor if you are taking any other medicines, either from your GP or purchased from a pharmacy. It's very important to give a full picture of your general health in the consultation, to make sure the doctor has all the information required to assess the safety and suitability of treatment for you.
Side effects that are considered to be common include skin irritation, rashes, itching, or redness at the site the ointment is applied to. On rare occasions, it can cause an allergic reaction. It should be kept away from the eyes.
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