Topical Anesthesia

Updated: Nov 20, 2018
  • Author: Bassem Abraham, MD; Chief Editor: Erik D Schraga, MD  more...
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Overview

Overview

Topical anesthesia is gaining more popularity and utilization especially with the increased number of out of operating room procedures. The control of procedure-related-pain is an integral factor for hospitals trying to attain high patient satisfaction scores. There are multiple medication formulations to provide topical anesthesia. Administration of topical anesthetics to control pain associated with procedures, such as laceration repair, may avoid the need for infiltrative local anesthesia injections and associated pain from these injections. [1] Topical anesthesia also avoids the risk of wound margin distortion that exists with infiltrative injection administration. Many dosage forms exist (eg, gels, sprays, creams, ointments, patches) and provide the clinician with precise options for application under various circumstances.

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Mechanism of Action

Topical anesthetics reversibly block nerve conduction near their site of administration, thereby producing temporary loss of sensation in a limited area. Nerve impulse conduction is blocked by decreasing nerve cell membrane permeability to sodium ions, possibly by competing with calcium-binding sites that control sodium permeability. This change in permeability results in decreased depolarization and an increased excitability threshold that, ultimately, prevents the nerve action potential from forming. [2, 3, 4]

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Absorption

Skin absorption is highly variable. Most anesthetic agents exist as solids and are only superficially absorbed through intact skin. Eutectic mixtures result in liquids that melt at lower temperatures than their single components. This permits higher concentrations of anesthetics, which results in superior dermal anesthesia for intact skin. Other methods of increasing skin penetration include liposomal preparations, iontophoresis, and transdermal patches. [2, 4, 5]

A recent double-blind, paired study of 82 adult volunteers compared a lidocaine/tetracaine transdermal patch (Synera) with lidocaine/prilocaine cream prior to vascular access at the antecubital site. The lidocaine/tetracaine patch provided effective anesthesia in as little as 10 minutes and results showed superior anesthesia at all application times less than 60 minutes. [6]

Novel Techniques for Applying Topical Anesthesia

Novel techniques for applying topical anesthesia include the following. 

Transcriptional transactivator peptide-decorated ropivacaine-loaded nanocarrier systems are useful for overcoming the barrier function of the skin and decreasing the dose of ropivacaine and also boosting its effectiveness. [7]

A study reported that laser assisted transdermal delivery of topical lidocaine was confirmed with laser pretreatment while maintaining safe blood serum levels for facial rejuvenation. [8]

Another study reported that thermoresponsive-tailored mixed micellar nanogel of lidocaine and prilocaine was effective. [9]

 

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Indications

Venipuncture and intra arterial catheterization  

In the pediatric population, topical anesthesia is frequently utilized. Applying topical anesthetic cream to the venipuncture site is effective among children. [10]

In children with intellectual and disabilities combining topical anesthesia with behavior techniques, specifically distraction techniques, results in better outcome than in patients who received only topical anesthesia. [11]

In adults, the application of topical anesthesia during intravenous catheter insertion results in less venipuncture and catheter insertion associated pain. [12]

The use of lidocaine/ prilocaine anesthetic ointment instead of injectable local lidocaine in transradial catheterization was found to be equally effective. [13]

Bronchoscopy

For fiberoptic bronchoscopy. The American College of Chest Physicians issued a consensus statement to consider using topical anesthesia during such procedures. [14]

One-percent lignocaine was found to be effective for topical anesthesia during fiberoptic bronchoscopy [15] .

Ophthalmology Procedures

In a randomized controlled clinical trial that included 120 patients, Rafailov et al concluded that when compared to transcutaneous anesthesia in patients undergoing outpatient eyelid surgery, topical anesthesia with 2% lidocaine combined with transconjunctival local anesthesia results in a decrease in perceived pain. [16]

Topical anesthesia proved to result in lower complications for phacoemulsification and intraocular lens implant patients when  compared to  patients who had the procedure done under peribulbar anesthesia. [17]

Urologic and Gynecologic Procedures

Topical application of EMLA 5% cream on genital mucosa of postmenopausal women before vaginal examination significantly reduces pain associated with speculum application. [18]

A systematic review and meta-analysis study showed that topical intrarectal anesthesia reduces pain after probe insertion. When combined with periprostatic nerve block, it also reduced pain related to prostate biopsy. [19]

A systematic review study showed that topical anesthetic agents has been shown to be effective and well tolerated for patients with primary premature ejaculation proving improvement in intravaginal ejaculatory latency time. [20]

A retrospective study conducted by Burstein et al that included 46 pediatric patients compared patients who received topical anesthesia for paraphimosis reduction to those who received intravenous sedation. When compared to the intravenous sedation group, topical anesthesia patients had reduced stay in the emergency department and fewer adverse events. [21]

 

 

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Dosage Guidelines and Administrative Techniques

See the list below:

  • Apply the cream, ointment, or solution to the chosen area in incremental amounts.

  • The total dose for a topical anesthetic is smaller than that used for subcutaneous infiltration.

  • EMLA cream does not require an occlusive dressing (eg, DuoDERM, Tegaderm, Saran Wrap); however, when an occlusive dressing is applied, absorption is improved and time of onset is decreased. [3, 4, 22, 23]

  • Viscous lidocaine may be used alone or in a compounded mixture as a mouthwash (ie, swish and expectorate). [4]

  • Iontophoresis has been used to improve the effects of topical anesthesia; however, the equipment is expensive and bulky, and some patients experience discomfort from the mild electrical sensation. [2, 4]

  • Sequential layered application of topical lidocaine with epinephrine (TLE) has been described for small facial or scalp wounds. One-hundred patients were enrolled in a randomized controlled trial, with 50 in each group. The study group received TLE using a unique method of "sequential layered application." The control group received 2% lidocaine infiltration anesthesia. Patients rated the pain from the application of anesthesia and from suturing, using a 0-10 visual analog pain scale. [24]

  • Follow-up interviews were conducted to assess for complications and to rate patients' wound repair experience. Patients in the study group reported significantly less pain from TLE application, with 66% reporting no pain vs 0% reporting no pain from the infiltration in the control group (P< 0.001). No difference in pain during wound repair was noted between the 2 groups (P 0.59). On follow-up, 95% of patients contacted in the TLE group rated their experience in regard to pain as "excellent," compared to 5% of patients in the control group (P< 0.001). [25]

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Deciphering Drug Concentration

Drug concentration is expressed as a percentage (eg, dibucaine 1%, benzocaine 0.5%).

Percentage is measured in grams per 100 mL (ie, 1% is 1 g/100 mL [1000 mg/100 mL] or 10 mg/mL)

Calculate the mg/mL concentration quickly from the percentage by moving the decimal point 1 place to the right, as follows:

  • Dyclonine 0.5% = 5 mg/mL

  • Viscous lidocaine 2% = 20 mg/mL

  • Benzocaine 20% = 200 mg/mL

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Adverse Effects

Adverse effects are usually caused by high plasma concentrations of topical anesthetics that typically result in excessive exposure caused by application to abraded or torn skin. [3, 26]

Possible adverse effects include the following:

Burning or stinging may occur local to the administration site. Oral viscous lidocaine may cause systemic toxicity, particularly with repeated use in infants or children.

CNS: High plasma concentration initially produces CNS stimulation (including seizures), followed by CNS depression (including respiratory arrest). The CNS stimulatory effect may be absent in some patients, particularly when amides (eg, tetracaine) are administered. Solutions that contain epinephrine may add to the CNS stimulatory effect.

Cardiovascular: High plasma levels typically depress the heart and may result in bradycardia, arrhythmias, hypotension, cardiovascular collapse, and cardiac arrest. Local anesthetics that contain epinephrine may cause hypertension, tachycardia, and angina.

Gag-reflex suppression may occur with oral administration.

Methemoglobinemia though very rare, it can be life threatening. In adults, pre-TEE lidocaine anesthesia in recommended dosage results in significant increase in methemoglobin blood levels which however does not exceed normal values and does not result in clinically evident methemoglobinemia. [27] The risk of methemoglobinemia after TEE increases in patients with active infection. [28]

Some individuals have unpredictably high absorption levels for lidocaine and methemoglobinemia. Even OTC local anesthetic formulations can result in that level of absorption and potential methemoglobinemia in those patients. This effect was shown in a prospective study that included 26 patients.(33). Also another prospective study showed that the metabolism of lidocaine varies significantly between individuals and that caution should be exercised especially when occlusive dressing is applied. [29]

In a double-blinded randomized prospective self-controlled study, New formulation which is a combination of lidocaine 10%, dimethylsulfoxide 10% (permeability enhancer) and castor oil 20% or 10% as oil base results in less methemoglobin blood level and same potency  with a better cost / benefit ratio compared to EMLA cream. [30]

A 10-year retrospective cohort study evaluated 33 patients who developed methemoglobinemia showed that the overall prevalence of methemoglobinemia is low as 0.035%. The risk increases in hospitalized patients  who receive benzocaine based anesthetics. [31]

There is also increased aspiration risk when topical anesthetics are provided for patients undergoing nasendoscopy. [32]

 

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Warnings Regarding Cocaine as a Topical Anesthetic

Various anesthetic mixtures that contain cocaine have been used to anesthetize minor skin lacerations, especially on the face or scalp. One such combination that is extemporaneously prepared by hospital pharmacies includes tetracaine 0.5%, epinephrine (Adrenaline) 1:2000, and cocaine 11.8%. This combination is commonly referred to as TAC solution. Its use results in decreased pain on application and may provide better patient tolerance of suturing, particularly in those who are unable to tolerate injections or who have difficulty following instructions or sitting still (eg, children, individuals with mental disabilities). However, serious toxic effects (eg, seizures, cardiac death) have been described following topical cocaine application, particularly in infants and children. [3, 26] Because of increased toxicity, expense, and federal regulatory issues, cocaine is no longer recommended for topical anesthesia.

Compounded mixtures such as lidocaine, epinephrine, tetracaine (LET) solutions, have replaced cocaine with lidocaine 4% because of their superior safety when applied to nonintact skin. Still, these solutions should not be applied to wounds with end-arteriolar blood supply.

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Allergic Reaction to Local Anesthetics

Actual hypersensitivity is rare and accounts for less than 1% of all reactions to local anesthetics. Allergic reactions may be attributed to other factors such as acute toxicity, concurrent drug therapy (eg, tachycardia caused by epinephrine), or preservatives, such as paraben or sulfites, that the product may contain. [3, 26]

Local anesthetics with a para -amino benzoic acid (PABA) ester-type structure seem to cause most anesthesia-related allergic reactions. Consequently, use esters (eg, tetracaine, benzocaine) with caution or use a topical anesthetic from the amide class (eg, dibucaine, lidocaine). Documented cross-sensitivity has been exhibited within the ester-based local anesthetics and structurally related compounds (eg, paraben preservatives). Hypersensitivity to the amide local anesthetics is rare. [2, 4] To quickly determine whether an anesthetic agent is an ester or an amide, note whether the generic name contains the letter i once or twice. Esters contain the letter i once in their generic names, whereas the generic names for amides contain the letter i twice.

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Physiochemical Variables

Onset of action, anesthesia depth, and duration of action are determined by the pKa level, pH level, lipid solubility, protein binding, and vasodilatory effects of the specific local anesthetic. These factors also depend on the area of the skin to which the anesthetic is applied, the vascularity of tissues, the surface area, and anesthesia technique. Duration of application is important to improve topical anesthetic properties. [4]

Table 1. Common Topical Anesthesia [33, 2, 3, 4, 26] (Open Table in a new window)

Anes-thetic Class

Generic Name (Trade Name)

Available/ Recom-

mended Concent-

ration(s), %*

Dosage Form(s)

Max. Adult Topical Dose, mg

Max. Adult Mucosal Dose, mg

Max. Pediatric Mucosal Dose, mg/kg

Peak Effect, Minutes

Duration, Minutes

Amides

Dibucaine (Nupercainal)

1

Cream, ointment

25

--

--

< 5

30-60

 

Lidocaine (Xylocaine, ELA-Max, Lidoderm)

2-5

Viscous jelly, patch, ointment, liposomes

Variable depending on dosage form

250-300

3-4

2-5 Liposome: 30

15-45

Esters

Benzocaine

(Americaine, Cetacaine, Dermoplast, Solarcaine)

0.5-20

Aerosol, cream, gels, lotion, ointment, solution

--

--

--

< 5

15-45

 

Cocaine†

4-10

Solution

200

1 mg/kg

1

1-5

30-60

 

Tetracaine

(Pontocaine)

No longer available in US

0.5-2

Solution, gel, cream

50

20

0.75

3-8

30-60

Misc.

Dyclonine

(Cepacol, Sucrets)

0.5-1

Aerosol, lozenge

--

50

--

< 10

< 60

 

Pramoxine

(ProctoFoam, Caladryl Cream for Kids)

1

Aerosol foam, pledgets, cream, ointment

200

--

--

3-5

--

 

Lidocaine/

Prilocaine

(EMLA)

2.5/2.5

Cream,

trans-

dermal patch

1 g/10 cm2

--

--

60: 3 cm depth

120: 5 cm depth

30-60 after removal

 

Lidocaine 70 mg and tetracaine 70 mg (Synera Patch)

--

Trans-

dermal

patch

Adults or children:

Apply 1 patch 20-30 min before superficial dermato-

logical procedure

--

--

100

--

*Use lower concentrations for children or patients who are elderly or debilitated.

† Cocaine is generally not recommended for topical or mucosal application (see warnings above).

‡This dose also applies to the pediatric population (maximum application time in children aged < 3 mo = 1 h; >3 mo = 4 h).

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