Review of Topical Anesthetic Creams

Updated 3/2017-- all links removed as many are no longer active. 

Topical anesthetic creams can be useful. Patients love them because there is no needle needed. Doctors love them because they make the patient less anxious and can eliminate the edema of an injection at the surgical site.

Topical anesthetic creams can not replace local injections/blocks for all procedures. When used properly and in selected situations, they are a wonderful addition. They can and have been used before routine biopsies, minor operations, laser removal of hair, veins, and tattoos, and botulinum toxin type A and filler placement.

SAFETY FIRST

It is safest to use standard formulas of anesthetic creams. With the standard formulas, it is easier to predict the systemic blood levels that will be obtained by use of the topical. Absorption of topical anesthetic creams is a side effect of the desired local effect. It is affected by the surface area covered by the cream and the duration of application. Systemic blood levels of the local anesthetic will depend on the absorption, patient size, rate of elimination, and type of surface (for example, mucosal versus extramucosal and intact versus broken skin). The blood level of lidocaine approaches that obtained after parenteral use when lidocaine is applied to a mucosal surface.

For most topical anesthetic creams, the systemic blood levels reached with proper use are a small fraction of the blood levels that will produce toxicity. A good example is: 60 gm of EMLA cream ( placed on a 400-cm² area for 4 hours produce peak blood levels of lidocaine that are 1/20th the systemic toxic level of lidocaine and 1/36th the toxic level of prilocaine. This makes its application very safe, with levels well below the concentration that would cause systemic toxicity.

When compounded (non-standard) formulas are used, it is much easier to get into trouble. Take the example (hopefully an extreme example) of the 22 yo college student who died in 2001 from lidocaine toxicity after applying a 10% lidocaine and 10% tetracaine cream from her waist to her feet for her laser hair removal. Note the high concentration of lidocaine/tetracaine and the very high surface area covered.

Ester anesthetics, such as procaine and tetracaine, stimulate the central nervous system, causing restlessness, agitation, and excitement, which may eventually lead to seizure activity.

Amide anesthetics, such as lidocaine, mepivacaine, and bupivaine, resist hydrolysis by plasma esterases and produce a more prompt and longer-lasting anesthesia. They result in central nervous depression, which can result in drowsiness, lethargy, and sleep.

AVAILABLE TOPICALS

BLT: Triple Anesthetic Gel

• is a triple anesthetic gel consisting of 20% benzocaine, 6% lidocaine, and 4% tetracaine. It is formulated in dimethyl sulfoxide and pluronic lecithin organogel, which increases its absorption through the skin.
• It is usually applied to INTACT skin 10 to 30 minutes before surgery.
• Because it contains ester anesthetics, its use is contraindicated for patients allergic to p-aminobenzoic acid, hair dyes, and sulfonides.

EMLA Cream

• an oil-in-water emulsion of 2.5% lidocaine and 2.5% prilocaine.
• It should be used on INTACT skin. An occlusive dressing increases its penetration.
• It must be left on for 0.5 to 2 hours, depending on location and depth of penetration.
• Its use must be avoided near the eyes, since sodium hydroxide is a component of the cream to allow for proper penetration.
• EMLA cream has been shown to be safe and efficacious in geriatric patients (65 years or older), but its use is controversial in neonates less than 3 months of age.
• It is similar to TAC in effectiveness.
• Transient blanching and erythema appear at the site of application due to peripheral vasoconstriction.
• Contact dermatitis is occasionally reported secondary to the prilocaine.
• A very rare methemoglobinemia can develop in patients less than 1 year of age who take medications that exacerbate the methemoglobinemia or who have a congenital methemoglobinemia or a glucose 6-PO4 dehydrogenase deficiency.
• Cost is approximately $11 per 5 gm tube and occlusive dressing.
• Recommended Dose/Area/Time use for EMLA

Pt Age/ Wgt	Max Dose	Max Area	Max Applied Time
0-3 months or less than 5 kg	1 gm	10 sq cm	1 hr
3-12 mo AND more than 5 kg	2 gm	20 sq cm	4 hr
1-6 yr AND more than 10 kg	10 gm	100 sq cm	4 hr
7-12 yr AND more than 20 kg	20 gm	200 sq cm	4 hr

LET

• composed of 0.5% tetracaine, 1:2000 epinephrine, and 4% lidocaine.
• When used for laceration repair--a shred of LET-soaked cotton or LET mixed with methylcellulose is placed directly in the wound prior to cleansing and repair. The solution or gel can be held in place with an occlusive dressing, tape, or bandage.
• The wound edges blanch when numb, usually after 20 minutes (15 - 30 min). Anesthesia lasts an average of 21 minutes after removal.
• LET has been found to be just as efficacious as TAC with no severe side effects.
• LET cost per application is approximately $3.00 compared to $35.00 for TAC

LMX-4

• LMX-4 (formerly ELA-max4) or LMX-5 (formerly ELA-max5) contains 4% or 5% liposomal lidocaine, respectively.
• The cream is usually applied for 15 to 40 minutes to intact skin with no occlusion necessary.
• The rapid absorption also results in a rapid dissipation of the drug, with diminishing anesthesia approximately 40-60 minutes after application.
• A transient erythema may occur, but no serious adverse side effects have been seen.
• To prevent toxic systemic levels, it has been recommended that LMX be applied to an area less than 100 cm² in children weighing less than 20 kg.
• Its effectiveness is similar to that of EMLA.
• LMX-4 can be purchased over the counter. Cost is similar, $6-7 per 1- to 2-gm application [approx $30 per 0.54 oz tube]
• It can be used before superficial and medium-depth peels without affecting the results of the peel.

S-Caine Peel

• developed as a local anesthetic peel (Zars Pharma).
• This cream dries on exposure to air and becomes a flexible membrane that is easily peeled off. This eases the delivery of the anesthetic to contoured regions of body.
• It has been shown to provide a highly effective local anesthesia. It should be applied 20-30 minutes prior to procedures such as dermal filler injections or facial laser ablation, and for 60 minutes prior to procedures such as laser treatment of leg veins and tattoo removal.
• It could be used for minor surgery as well.

Synera (Formerly S-Caine Patch)

• Tetracaine and lidocaine mixed 7%/7% in a self-contained patch have been studied for venipuncture.
• It is designed to look like a child's bandage and is recommended for children aged 3 years and older.
• It contains a heating element that, when activated, enhances absorption, allowing for rapid anesthesia and some degree of vasodilation.
• Cost is approximately $12 per patch.

TAC

• Was one of the first topical anesthetic creams to be developed. Initially it was composed of 0.5% tetracaine, 1:2000 epinephrine, and 11.8% cocaine.
• Later the tetracaine was increased to 1% and the cocaine decreased to 4%. It was found that the effectiveness remained the same.
• It should be applied 30 minutes before the procedure.
• Its effectiveness is comparable to that of lidocaine infiltration when used properly.
• The effectiveness of most anesthetic creams is compared with that of TAC.
• Inadvertent mucosal application or overdose can result in significant cocaine absorption, leading to serious adverse effects such as seizures and cardiac arrest.
• TAC is also very expensive at about $350 per 35-gm tube.

Topicaine

• is a 4% lidocaine gel.
• It is usually applied 30 to 60 minutes before the procedure with occlusion.
• Erythema, blanching, and edema at the site appear to be mild and transient.
• Allergic contact reactions to this ester group of anesthetics are common.
• Effective anesthesia with topicaine can be obtained after 30 minutes.

If a medical-grade occlusive dressing is not available, occlusion can be obtained with Glad Press-n-Seal. The product is not sterile, but over unbroken skin this is not an issue. It does not contain latex and has the added benefit of painless removal.

REFERENCES

Topical Anesthetic Creams [Safety and Efficacy Report]; Plastic and Reconstructive Surgery:Volume 121(6)June 2008, pp 2161-2165; Kaweski, Susan M.D.; Plastic Surgery Educational Foundation Technology Assessment Committee

Topical Anesthetics in Children; Medscape CME Article, Feb 19, 2008; Amy L Baxter MD