The Impact of Dosage and Injection Site on Type A Botulinum Toxin Treatment for Oral Commissure Ptosis: A Prospective Study.

[OBJECTIVE] Botulinum toxin type A (BTX-A) is a simple and effective method for treating drooping mouth corners. However, the effective dosage and injection sites remain controversial. The authors propose a triangular three-point injection technique and compare the effects of different dosages tailored to varying severity levels of drooping mouth corners.

[METHODS] Before the start of this prospective self-controlled study, subjects with drooping mouth corners received two treatment methods. First, participants received a single-point injection of 3 U of BTX-A per side. Four months later, an individualized approach was adopted, with 3-15 U of BTX-A injected at three sites per side based on severity. Data were collected at baseline and at 4- and 12-week follow-ups.

[RESULTS] Fifty-one subjects were enrolled. At 4 weeks after injection, both methods significantly improved drooping mouth corners, with the indicators returning to baseline levels by 12 weeks (P < 0.05). Based on clinical manifestations, subjects were categorized into mild, moderate, severe, and most severe cases, receiving 3 U, 6/9 U, 9/12 U, and 12/15 U per side, respectively. The results showed that 3 U/side for mild cases, 6 U/side for moderate cases, and 12 U/side for severe cases were the safest and most effective dosages, while most severe cases still did not achieve satisfactory results even at 15 U/side. Overall, at 4 weeks post-treatment, the reduction in the vertical distance from the mouth corner to the pupillary line and the angle of drooping were significantly greater with the triangular three-point injection technique compared to the single-point injection (P ≤ 0.05). No adverse events were observed in any subjects.

[CONCLUSION] It is necessary to increase the injection dosage according to the severity of drooping mouth corners. The new triangular three-point injection technique is safe and demonstrates favorable clinical outcomes.

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