Lidocaine 4% and benzocaine 20% formulations administered through a novel transdermal delivery system perform in a similar fashion to compounded lidocaine 23%/tetracaine 7% (23/7) for lessening discomfort during the administration of microfocused ultrasound with visualization (MFU-V), according to the results of a randomized double-blind split-face study published in the Journal of Drugs in Dermatology.

The investigators sought to compare 2 topical analgesics (lidocaine 4% and benzocaine 20%) formulated with a novel transdermal delivery system with compounded 23/7 for the mitigation of discomfort during MFU-V therapy. At 1 hour prior to MFU-V, a total of 14 female participants received 50 mg intramuscular (IM) meperidine/25 mg IM promethazine/5 mg oral diazepam. At 15 minutes prior to the treatment, 1 side of each participant’s face was treated with 1 application of 4% lidocaine, followed by 1 application of 20% benzocaine. The other side of that same participant’s face was treated with 2 applications of 23/7 in order to maintain blinding.

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Numbness was assessed by a blinded evaluator (1=completely numb to 4=not numb) pretreatment. All participants’ pain scores (0=no pain to 10=worst pain) were collected post-treatment. Subjective clinical measures and adverse events were also evaluated.

Mean participant pain scores with 23/7 and lidocaine 4%/benzocaine 20% were 5.6 and 5.7, respectively. Mean numbness scores were also similar (2.5 with 23/7 vs 3.0 with lidocaine 4%/benzocaine 20%). The clinicians rated both products as being “very easy” to apply. With lidocaine 4%/benzocaine 20%, overall, 7.1% of participants required no pauses during treatment compared with 14.3% who required pauses with 23/7. More participants required 4+ pauses with 23/7 than with lidocaine 4%/benzocaine 20% (21.4% vs 7.1%, respectively).

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Lidocaine 4%/benzocaine/20% was preferred by 78.5% of participants, with 35.7% rating lidocaine 4%/benzocaine 20% as “very effective” vs 7.1% for 23/7. No adverse events were reported.

The investigators concluded that fewer treatment pauses due to patient discomfort in participants using the lidocaine 4%/benzocaine 20% formulation may translate into time efficiency.


Palm MD, Misell LM. Topical transdermally delivered lidocaine and benzocaine compared to compounded lidocaine/tetracaine during microfocused ultrasound with visualization treatment. J Drugs Dermatol. 2018;17(7):729-734.