A Pilot Study of Differences in Antibody Responses of Intradermal and Intramuscular Injections of Botulinum Toxin Type A.

Introduction: Botulinum toxin type A (BoNT/A) is commonly used for both medical and aesthetic purposes. However, approximately 3% of long-term recipients develop resistance, potentially due to antibody formation. Injection technique may influence immunogenicity, yet comparative data remain limited.

Methods: This pilot study evaluated antibody responses following intradermal versus intramuscular injection of six BoNT/A formulations: incobotulinumtoxinA, onabotulinumtoxinA, abobotulinumtoxinA, letibotulinumtoxinA1, letibotulinumtoxinA2, and prabotulinumtoxinA. A total of 120 subjects were divided into intradermal and intramuscular groups, with equal distribution across toxin types. Blood samples were collected and analyzed using ELISA to quantify human IgG (hIgG) targeting whole BoNT/A molecules, functional domains, and complexing proteins.

Results: Intradermal injections consistently induced higher BoNT/A-specific hIgG levels than intramuscular injections, except with letibotulinumtoxinA. Anti-functional domain hIgG levels peaked at day 30 and declined thereafter, aligning with the 90-day retreatment interval commonly recommended. Anti-complexing protein hIgG levels remained relatively stable across time points. Notably, all antibody levels remained below thresholds associated with clinical nonresponse.

Conclusion: Intradermal injection of BoNT/A appears to elicit a stronger immunogenic response than intramuscular administration, although antibody levels did not reach clinically significant thresholds. These findings underscore the importance of injection technique and interval planning to mitigate immunogenicity. Given the widespread use of intradermal techniques in aesthetic practice, this study provides important clinical insight into optimizing BoNT/A administration.

Thai clinical trials registry number: TCTR20211215001.