Our benzocaine, lidocaine, tetracaine anesthetic cream is used by dermatologists and other healthcare professionals throughout the country. In the majority of cases this cream is applied correctly and there are no serious adverse effects. However, negligence does occur in some cases when proper precautions are not followed. It is important to understand BLT cream before using it on a patient and understand the symptoms of anesthetic toxicity.

What is BLT Cream?

BLT is the combination of three effective anesthetic ingredients – benzocaine, lidocaine, and tetracaine – in one cream. This combination is not available commercially and must be made by a compounding pharmacy. Our compounding pharmacy makes each cream individually at our accredited facility in Los Angeles, California. Compounded topical anesthetics like BLT Cream allow healthcare providers to offer stronger topical anesthesia, with a faster onset and longer duration of action, than can be obtained with most commercially available numbing creams.

What is important to remember about compounded topical anesthetics is that the concentrations of anesthetic are much higher than any commercially available product. For example, EMLA cream (eutectic mixture of local anesthetics), which has been available for many years, includes lidocaine 2.5% and prilocaine 2.5%. Compare this to our most powerful topical anesthetic, the Baddest Topical in Town, which contains lidocaine 12.5%, tetracaine 12.5%, prilocaine 3%, and phenylephrine 3%. As you can tell from these concentrations, this topical anesthetic is much more powerful than EMLA cream or any OTC numbing cream. Because of this it is important to pay attention to proper usage and dosing to prevent systemic toxicity.

In studies it has been shown that OTC products and creams like EMLA actually can produce higher plasma concentrations of lidocaine than BLT cream. EMLA cream is made with an oil-in-water mixture that enhances absorption. This results in greater systemic levels of lidocaine despite the lower concentration. However it is still important to pay closer attention to signs of toxicity when multiple anesthetic ingredients are combined.

Skin Absorption of Topical Anesthetics

In general, administering topical anesthetic on the skin is safer than other methods when used properly. Intravenous, epidural, and subcutaneous methods all have the potential to increase systemic levels of an anesthetic more quickly. The skin significantly slows absorption of the anesthetic and minimizes systemic absorption. However there are several ways this natural protective process can be interrupted or sabotaged.

Damaged Skin

If the skin becomes damaged or broken, for example, the rate of absorption increases. When more anesthetic is absorbed through broken skin, the systemic levels of anesthetic in the body can substantially increase. In some cases, practitioners use the increase in absorption through broken skin to their advantage so they can increase the anesthetic effects of a cream. They may use a laser device to lightly damage the skin in order to increase penetration. There have even been studies of dermatologists using this technique with BLT cream with good results and no side effects. While this may work for some practitioners, we usually would advise against using this technique with a compounded anesthetic cream like BLT. Until it is better understood how a patient will respond to a topical anesthetic cream, it is better to be more conservative in how it is applied.

Occlusion

Another way that the skin’s protective ability can be altered is with the use of occlusion. This involves applying a cream to the skin, then covering the area completely with plastic wrap or another material. The occlusion enhances the permeability of the cream into the skin by trapping moisture. Numerous beneficial examples of skin occlusion exist including antibacterial placed under a band-aid and drug-delivery devices like nicotine patches. This type of technique is even commonly used by dermatologists applying numbing creams. The occlusion improves the permeability of the anesthetic ingredients and helps the patient become better anesthetized. The problem is that occlusion also increases absorption of ingredients on the skin into the blood. When occlusion is used for long periods of time, plasma concentrations of anesthetic can reach toxic levels. Occlusion is not necessary with a compounded topical anesthetic as the ingredients are already powerful enough to produce effective numbing.

BLT Cream – Not for Use by Patients!

There have been serious adverse reactions when patients were given compounded topical anesthetics to take home. Most cases of systemic toxicity from these anesthetics occurred when a patient applied cream to the entire legs under occlusion prior to laser hair removal. Patients should never be given a compounded topical anesthetic to use on their own. There are significant risks of misuse when a prescription-strength product is given without proper instructions.

Lidocaine, Benzocaine, and Tetracaine Toxicity

Most research into the toxicity of topical anesthetics involves lidocaine. This is because of the widespread use of lidocaine and its increased potential for producing systemic toxicity compared to other topical anesthetics. Lidocaine is metabolized through the liver while benzocaine and tetracaine are not. Metabolism of amide anesthetics like lidocaine occurs more slowly than with ester anesthetics that are mainly metabolized through the plasma. The higher potency of lidocaine means that it is usually the culprit in cases of systemic toxicity.

Benzocaine is more likely to be the cause of methemoglobinemia, although other anesthetics can also contribute to this. The primary sign of methemoglobinemia is a bluish discoloration to the skin. This may be followed by lightheadedness, headache, and chest pain. In more severe cases heart problems, seizures, and delirium can result. Primary treatment for acquired methemoglobinemia is infusion with methylene blue. While most cases are related to application of benzocaine to mucous membranes and not the skin, practitioners should still be aware of the symptoms.

CNS Toxicity and Cardiotoxicity

Local anesthetics block sodium channels that are essential to the functioning of multiple parts of the body. It is important to pay attention to the warning signs of toxicity.

In general, the first signs of toxicity from local anesthetics will be related to the central nervous system. The CNS is more sensitive to effects of local anesthetics. The initial symptoms of CNS toxicity can include tinnitus, blurred vision, dizziness, and numbness of the tongue. Further signs of toxicity may include nervousness, agitation, restlessness, and muscle twitching. The early signs and symptoms advance to CNS depression with slurred speech, drowsiness, unconsciousness, and then respiratory arrest. For patients who are being given a topical anesthetic cream, the CNS symptoms will most likely be noticed before there are cardiotoxic symptoms. Cardiotoxic symptoms from lidocaine are rare, especially with topical lidocaine, although they can occur in rare situations. High concentrations of local anesthetic can potentially have cardiac effects that may be associated with acidosis, hypercapnia and hypoxia

Differences in Individual Responses to Topical Anesthetics

It is important to remember that individual responses to topical anesthetics can vary, and that predicting these differences can be difficult. Some individuals can have unpredictably high rates of absorption.

• Skin thickness can alter the rate of absorption. Areas of the body with thinner skin will absorb the anesthetic ingredients more quickly than areas where the skin is thicker.
• Patients with liver or kidney problems will have a reduced capacity for lidocaine metabolism and therefore will have greater circulating levels of the drug. Any condition that slows hepatic blood flow or impairs the liver’s ability to produce enzymes can affect toxicity of amide anesthetics.
• For elderly and pediatric patients, anesthetics can have an increased half-life. Onset of symptoms of toxicity may happen more quickly in these populations.
• Patients taking certain drugs are more susceptible to lidocaine toxicity. Cimetidine and propranolol decrease hepatic blood flow, so they also inhibit lidocaine clearance.
• Hormonal changes and other factors related to pregnancy can increase the potency of local anesthetics.

BLT Cream Application Instructions

1. Clean the area where the topical anesthetic will be applied and pat dry with a towel.
2. Develop a plan for how you will apply the cream. If a large area is to be done, it may be beneficial to anesthetize the area strategically in sections. This will help reduce systemic absorption and also ensure that the skin does not lose numbness in an area before you get to it. In general, it is better to limit the application area to no larger than the face and use no more than 1g of cream per 10cm area. If larger areas need to be anesthetized, it may be preferable to break the treatment up into multiple sessions to limit systemic levels of the anesthetic ingredients.
3. Apply the cream 20-30 minutes before the procedure. Using an applicator to apply the cream is ideal to avoid contact with your hands. Always remember to wear gloves when handling to avoid unwanted anesthetic effects.
4. Check patient for numbness and side effects. If it is determined the patient is not sufficiently numb you can leave the cream on for an additional 10-15 minutes.
5. Wipe off the cream completely and clean skin thoroughly. There should not be numbing cream leftover that can enter broken skin that may result from the procedure.

Articles

Topical Lidocaine Enhanced by Laser Pretreatment: A Safe and Effective Method of Analgesia for Facial Rejuvenation – Aesthetic Surgery Journal

Comparison of Five Commonly-Available, Lidocaine-Containing Topical Anesthetics and Their Effect on Serum Levels of Lidocaine and Its Metabolite Monoethylglycinexylidide (MEGX) – Aesthetic Surgery Journal