# Thermal Stability of Botulinum Toxin Type A Formulations Exposed to Heat In Vitro, Assessed by an In Vivo Mouse Potency Bioassay

## TL;DR

This study tested how heat affects the potency of different botulinum toxin type A products, finding that only one liquid formulation remained stable.

## Contribution

The study provides new empirical evidence on the thermal stability of commercial botulinum toxin type A formulations.

## Key findings

- InnoBoNT/A maintained potency after 25 minutes at 60°C, unlike other formulations.
- OnaBoNT/A lost 32% potency after 25 minutes at 60°C and was ineffective after 40 minutes.
- Only the liquid-stabilized formulation preserved potency under thermal stress.

## Abstract

Energy-based devices (EBDs), such as high-intensity focused ultrasound, radiofrequency, and microwave, are increasingly used for facial rejuvenation, raising concerns about whether heat exposure may affect the potency of botulinum toxin.

This study investigated the thermal stability of 4 commercial botulinum toxin type A (BoNT/A) products under conditions simulating EBD-related heat exposure, which includes 1 liquid formulation (INNOTOX, Medytox, Seoul, South Korea; hereafter referred to as innoBoNT/A) and 3 powder formulations: onabotulinumtoxinA (onaBoNT/A, BOTOX, Allergan, an Abbvie company, North Chicago, IL), incobotulinumtoxinA (incoBoNT/A, XEOMIN, Merz, Frankfurt, Germany), and abobotulinumtoxinA (aboBoNT/A, DYSPORT, Ipsen, Boulogne-Billancourt, France).

Mouse intraperitoneal LD50 potency assays were performed after exposing reconstituted and liquid formulations to 60°C for 10 to 40 min. Relative and normalized potency values were compared before and after exposure.

InnoBoNT/A maintained its potency after 25 min of exposure at 60°C, showing no significant loss of biological activity. In contrast, onaBoNT/A, incoBoNT/A, and aboBoNT/A displayed marked reduction in potency under the same conditions. In particular, onaBoNT/A showed a 32% decrease upon exposure at 60°C for 25 min and a complete loss of measurable potency at when exposed at 60°C for 40 min.

Among the BoNT/A formulations evaluated, only the liquid-stabilized preparation preserved potency during thermal stress.