In the next few years, expect intradermal injections of botulinum toxin A for the improvement in the appearance of pores, sebum, skin texture, and rosacea to gain a foothold in dermatology practices, Jeremy B. Green, MD, predicts.
"This technique is more popular in Asia than it is here in the US," Dr. Green, who practices dermatology in Coral Gables, Florida, said at the Annual Meeting of the American Academy of Dermatology. As opposed to intramuscular injections, "it's an intradermal delivery, so you use numbing cream prior, and you're injecting botulinum toxin A nearly parallel to the skin surface with the bevel of the needle up," he said. "You want to use a precise product. It's uncomfortable delivering volume so superficially due to the tissue distention, so I also use a massager. I inject approximately 0.05 mL to 0.1 mL per point. This does really work."
This mode of delivery was evaluated in a prospective, double-blind, split-face study in South Korea, which enrolled 18 volunteers who received an intradermal injection of botulinum toxin A into one cheek and normal saline into the contralateral side as a control. Participants were between 30 and 54 years of age and were seen at the clinic 2, 4, 8, and 12 weeks after the injection. At each visit, investigators took photographs, used a facial analyzer to evaluate the pores and wrinkles of the infraorbital area, and used a Sebumeter to evaluate sebum secretions from both cheeks. Improvement or aggravation in skin texture was evaluated by both volunteers and clinicians on a numeric scale from –4 (severe aggravation) to +4 (marked improvement) at each visit, and following photographic review, the wrinkle score of the nasolabial fold was graded on a 5-point scale.
The researchers observed no significant effects on the wrinkles of the infraorbital area and on sebum secretion. However, on the side where botulinum toxin A was injected, there were significant improvements in the wrinkles of the nasolabial fold and skin texture, they reported. The effects on nasolabial fold wrinkles lasted 12 weeks, effects on skin texture lasted 8 weeks, and improvement in pore size was only observed at week 2, they wrote. One serious adverse event occurred: a case of facial palsy after the injection of 30 units of botulinum toxin A in one cheek. However, injection of 20 units of botulinum toxin A in one cheek was not associated with any adverse events.
"The duration of these treatments is yet to be determined, but I think this is definitely going to gain popularity in the US," said Dr. Green, clinical assistant professor of dermatology at the University of Miami Department of Dermatology and Cutaneous Surgery.
Recently Approved Neurotoxin
He also discussed letibotulinumtoxinA-wlbg (Letybo), an injectable neurotoxin long used in South Korea, which the US Food and Drug Administration (FDA) approved for the temporary improvement in the appearance of moderate to severe glabellar (frown) lines in adults on March 4, 2024. Approval was based on positive results from three phase 3 trials of letibotulinumtoxinA-wlbg that enrolled more than 1,000 individuals in the United States and Europe.
"This is the sixth approved neurotoxin in the US," Dr. Green said. "It is derived from the CBFC26 strain of Clostridium botulinum, and it's a purified 900 kDa type A toxin complex with human serum albumin and sodium chloride as its excipients." It comes in a 50-unit or 100-unit vial and requires refrigeration. "To me, the most fascinating thing about this product is that it has been the number-one selling botulinum toxin on the South Korea market for the last 5 years," he said. "But what do we know about its characteristics?"
In a non-inferiority trial, Chinese researchers enrolled 500 patients with moderate to severe glabellar wrinkles to investigate the efficacy and safety of letibotulinumtoxinA-wlbg and onabotulinumtoxinA. Participants were randomized 3:1 to receive 20 U of letibotulinumtoxinA-wlbg or onabotulinumtoxinA and then observed them for 16 weeks. The primary endpoint was noninferiority in the proportion of study participants who received a score of 0 or 1 for glabellar wrinkles on a four-point photographic evaluation scale, as assessed by an evaluator at maximum frown at 4 weeks.
At week 4, 88.49% of participants in the letibotulinumtoxinA-wlbg arm achieved a score of 0 or 1 for glabellar wrinkles, compared with 87.39% of those in the onabotulinumtoxinA arm (P = .7469). No significant differences were observed for secondary efficacy or safety endpoints between the two treatments. "It will be interesting to see how this product does when it's available to us," Dr. Green said.
Another potential newcomer is ready-to-use liquid botulinum neurotoxin. RelabotulinumtoxinA is a complex, protein-free, ready-to-use liquid botulinum toxin A designed to avoid the traditional requirement to reconstitute it from powder, according to Galderma. It features a saline phosphate buffer solution, so it contains no human or animal-derived excipients, Dr. Green pointed out, and it eliminates the variability, errors, and risks associated with reconstitution.
"There was a report in the neurology literature of botulinum toxin being reconstituted with sterile water for cervical dystonia," he noted. "When this was injected, it was excruciatingly painful, because it created an osmotic gradient within the muscle. So, if we can take a step away from human error, that would be a good thing."
To date, Dr. Green said, four phase 3 trials of relabotulinumtoxinA involving more than 1,900 patients have been conducted in the United States and Canada evaluating its use for glabellar frown lines and lateral canthal lines, "and the data is impressive," he said. This product is still investigational, said Dr. Green, who has not had experience injecting it in the clinical trial program.
The idea of a rapid onset botulinum toxin is also emerging. TrenibotulinumtoxinE, which is being developed by Allergan, "is similar to a type A neurotoxin," Dr. Green said. "It inhibits neuromuscular transmission via presynaptic vesicular protein synaptosomal-associated protein (SNAP)-25 but at a different cleavage site. It has a faster onset — within one day — but a shorter duration — 3-4 weeks."
In a dose escalation study of its use for glabellar frown lines, 80% of participants achieved a two-grade investigator-rated improvement in glabellar frown line severity at maximum frown at the highest dose. The maximum clinical effect of trenibotulinumtoxinE was seen within 24 hours and lasted between 14 and 30 days.
"The question is, if it is approved by the FDA, where would this product fit in our practices?" Dr. Green asked. "The effect is gone in 3 weeks as opposed to 4 months," so this may be an option to recommend for someone who is reticent to try neurotoxins, he said, "or a patient who comes to you on a Friday and says, 'I have a gala tomorrow night'."
Dr. Green disclosed that he is a consultant to, a speaker for, and/or a member of the advisory board for many pharmaceutical companies, including Allergan and Galderma.
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