Q:

9/8/2013
We would like to develop a protocol that would allow our patients, especially younger patients, the option to use a topical anesthetic cream (such as Emla or LMX4) prior to getting their IT injections. Many of our younger patients, and their parents, have verbalized fears and concerns of receiving repeated injections over several years. Parents whose children have behavioral issues and/or special needs are especially concerned about subjecting their children to repeated painful procedures and therefore, reluctant to begin IT even though they know it will improve the quality of their child's life.
My questions are, one, has it been used safely and effectively when applied at least 30 minutes in advance of an injection, and two, are there any safety concerns regarding absorption if 1-2 inches of topical anesthetic cream are applied 1-2 times per week?

A:

Thank you for your inquiry.

Unfortunately, to my knowledge there has never been an evaluation of the safety of topical lidocaine used once or twice a week for a number of years. Therefore, since we do not have definitive data, the best answer I can give you is one based upon the use of lidocaine patches for chronic pain (in adults). As you can see from the abstract copied below by Dr. Argoff, used in this setting, lidocaine patches appear to be safe.

On the other hand, as with many drugs, when one looks at reported potential side effects due to the administration of lidocaine patches (please see the link to Drugs.com copied below), one notes that there are a number of potential side effects which may be perhaps more significant in children.

The other issue is the potential for sensitizing a child over time to this drug. We know that sensitization can occur through the skin, and that atopic children may have increased cutaneous permeability with enhanced absorption and a greater potential toward sensitization because of filaggrin defects.

So, even though in general the use of topical lidocaine seems to be safe, the chronic administration could theoretically result in sensitization, and the population with which you deal would perhaps be more subject to becoming sensitized than children in the population as a whole.

The other issue which is of note is that most would consider the pain caused by an allergy injection administered with proper technique, using a syringe (allergy syringe) designed to give the shot, quite minimal. At least in our experience, it is not the pain per se that has been the issue, but the anticipation of the pain and the fear of the needle that gives the most difficulty. At least in our experience, most children, once they have received one or two injections, seeing that they are not very painful, are not put off by the pain itself. Quite often it is the anticipation of the injection and seeing the needle in many instances, more than the actual pain per se, that causes the problems.

Thus, I am not sure that the strategy of employing a lidocaine patch would significantly, in many instances, reduce the emotional trauma associated with the injection.

Finally, applying lidocaine would also add at least 30 minutes to the visit and thus possibly diminish long term adherence to trearmeent.

In summary, in the final analysis, the decision as to whether or not to employ topical lidocaine in children receiving injections would have to be made purely on clinical judgment due to the fact that we do not have any true long-term studies of safety of the administration of lidocaine administered over months to years on a weekly or bi-weekly basis, and there are no trials comparing patients who have been given injections with lidocaine versus those without, to assess adherence rates and other comparisons between these two practices.

The issues, however, that I pointed out above would make me personally feel that the potential benefit would not compare favorably with the additional time (30 minutes added to the visit), and potential for sensitization and other possible side effects (regardless of the fact that these would probably be quite rare).

Thank you again for your inquiry and we hope this response is helpful to you.

New Analgesics for Neuropathic Pain: The Lidocaine Patch
Clinical Journal of Pain
June 2000 - Volume 16 - Issue 2 - p S62–S66
Argoff, Charles E. M.D
Abstract: Despite the availability of different pharmacologic agents for the treatment of various chronic neuropathic pain syndromes, complete symptom reduction and/or complete functional restoration is rarely achieved. New, safe, and effective treatments for chronic neuropathic pain, therefore, must be developed. One such agent, the lidocaine patch (Lidoderm, Endo Pharmaceuticals, Inc., Chadds Ford, PA), has been approved recently by the US Food and Drug Administration for the treatment of postherpetic neuralgia. Like other local anesthetics, the lidocaine patch results in sodium channel blockade, dampening, both peripheral nociceptor sensitization and, ultimately, central nervous system hyperexcitability. The Lidoderm patch is a topical agent and, consequently, insignificant serum levels are achieved even with chronic use. This fact enhances its safety. Recent studies have suggested that the lidocaine patch may be effective for chronic neuropathic pain conditions other than postherpetic neuralgia as well.

Emla Side Effects

Sincerely,
Phil Lieberman, M.D.

AAAAI - American Academy of Allergy Asthma & Immunology