Dermal thickness, rather than drug concentration and injection speed, influences the effective area of botulinum toxin type A in the dermis

Background

Recently, microbotulinum, a new technique that involves injecting botulinum toxin type A (BoNTA) microdroplets into superficial cutaneous tissue, has gained popularity. The precise distribution of BoNTA in the targeted area profoundly affects outcomes. Many factors may influence the effective area of BoNTA in the dermis. This study aimed to determine the dermal distribution properties of BoNTA to guide microbotulinum injection.

Methods

Ten healthy males aged 18–65 years without BoNTA treatment in the previous year were recruited to receive intradermal injections in the chest and back. Ultrasound was used to ensure the intradermal delivery of injections and measure the dermal thickness. The minor iodine starch test was performed at baseline and 3 days, 7 days, 21 days, 1 month, and 2 months after treatment.

Results

All participants received intradermal injections. The dermis was thinner on the chest (thickness, 0.20 ± 0.03 ​cm) than on the back (thickness, 0.39 ​± ​0.07 ​cm) ​(P<0.05). An injection in the thicker dermis had a significantly smaller effective area at every follow-up visit. The drug concentration did not affect the effective area except at 3 days after treatment. Injection speed did not influence the effective area at any follow-up visits.

Conclusion

An injection in a thicker dermis leads to a smaller effective area for intradermal injections. When the BoNTA dose is the same, the drug concentration and injection speed do not matter.

Trial registration

ChiCTR, ChiCTR2100046507. Registered May 18, 2021. Retrospective registration, https://www.chictr.org.cn/ChiCTR2100046507.