Several mechanism exist to get lidocaine through the hydrophobic skin.  One of the more interesting is iontophoresis, but others are dsscribed below. 

Iontophoresis is a non-invasive method of drug delivery which uses a small electrical charge to drive medications into the skin.

In more technical terms, Iontophoresis uses a low-voltage electrical current to drive the positively charged end of medications, such as lidocaine, through the epidermis.(1,2) As the current flows to the negative reservoir, the drug in the positive reservoir is carried into the skin. The current flow is noxious to some children, but those who tolerate the device find pain control equivalent and may prefer it. Galinkin et al found, in a crossover trial, that 11/22 children preferred iontophoresis, five (including two who did not tolerate iontophoresis) preferred EMLA, and six children did not care.(3)

Cost of the method includes the delivery device (ActivaTek, $290; Iomed $695), and each individual use lidocaine reservoir packet (from $5 – 14, e.g. Iomed $64/6). Time of application is at a minimum 10 minutes with newer delivery systems, such as Lidosite™.

 Iontophoresis effectiveness:

The delivery system is indicated for children over the age of five, and is contraindicated in children with pacemakers. It should not be used over broken skin or through mucus membranes, palms, or soles where the conduction is either enhanced or impeded, respectively. In one placebo controlled study of 500 subjects with a more rapid device, one subject experienced a partial thickness burn.(4)

Other Devices to Enhance Topical Lidocaine Absorption -
Intradermal Lidocaine Delivery

Even the few minutes needed to apply creams or run current are a barrier to their use. While the following methods are by definition NOT topical, they should be considered as alternate modalities for venipuncture when time is the reason not to use pain management.

One rapidly effective and well-tolerated pain relief method is simply to inject buffered lidocaine using a 30G needle prior to venipuncture.(5) Luhmann et al found no difference in pain comparing this method to LMX-4 for pediatric cannulation using 22-gauge needles. Patterson et al included unbuffered lidocaine in a comparison with cold spray, EMLA, and injected benzyl alcohol, and found the former to be cheapest and most effective, though more painful upon application because it was unbuffered.(6) Use of this method is inexpensive, depending on bundled hospital charges for the extra needle, syringe and buffered lidocaine.

A newer product, the J-tip (National Medical Products, Irvine CA), puts lidocaine under the skin via a jet of compressed carbon dioxide. Early studies found the delivery method less painful than a 25G needle, but found the numbing less effective. Subsequent venipuncture investigations in children have had better results, with better pain relief from J-tip use than EMLA. Of note, 81% found J-tip lidocaine administration painless compared to 64% who felt pain with removal of EMLA’s occlusive dressing.(7) The price for the single use disposable unit is $2-4.   As with the other devices, if the prepared area is not subsequently used, the cost recurs in a newly chosen site.

Several products enhance absorption of LMX-4, decreasing time until efficacy. One product, Sonoprep, improved pain control versus placebo by pretreating with ultrasound for 15 seconds, then applying LMX-4 for five minutes.(8) A low power erbium:YAG laser (Epiture Easytouch, Norwood Abbey) was tested with 10 seconds of laser versus sham laser prior to five minute LMX-4 application. The $2500 laser significantly reduced pain of cannulation in the 47 children randomized to the laser group. (Platform presentation, AAP 2006 Toronto),

See also a cost-benefit analysis : Pershad J. et al, Cost-effectiveness analysis of Anesthetic Agents During Peripheral Intravenous Cannulation in the Pediatric Emergency Department.    Arch Pediatr Adolesc Med. 2008;162(10):952-961.

References:

1. Fetzer SJ. Reducing the pain of venipuncture. J Perianesth Nurs 1999;14(2):95-101, 12.

2. Zempsky WT, Parkinson TM. Lidocaine iontophoresis for topical anesthesia before dermatologic procedures in children: a randomized controlled trial. Pediatr Dermatol 2003;20(4):364-8.

3. Galinkin JL, Rose JB, Harris K, Watcha MF. Lidocaine iontophoresis versus eutectic mixture of local anesthetics (EMLA) for IV placement in children. Anesth Analg 2002;94(6):1484-8, table of contents.

4. Zempsky WT, Sullivan J, Paulson DM, Hoath SB. Evaluation of a low-dose lidocaine iontophoresis system for topical anesthesia in adults and children: a randomized, controlled trial. Clin Ther 2004;26(7):1110-9.

5.  Luhmann J, Hurt S, Shootman M, Kennedy R. A comparison of buffered lidocaine versus ELA-Max before peripheral intravenous catheter insertions in children. Pediatrics 2004;113(3 Pt 1):e217-20.

6.. Patterson P, Hussa AA, Fedele KA, Vegh GL, Hackman CM. Comparison of 4 analgesic agents for venipuncture. Aana J 2000;68(1):43-51.

7. Jimenez N, Bradford H, Seidel KD, Sousa M, Lynn AM. A comparison of a needle-free injection system for local anesthesia versus EMLA for intravenous catheter insertion in the pediatric patient. Anesth Analg 2006;102(2):411-4.

8.. Becker BM, Helfrich S, Baker E, Lovgren K, Minugh PA, Machan JT. Ultrasound with topical anesthetic rapidly decreases pain of intravenous cannulation. Acad Emerg Med 2005;12(4):289-95.