Effects of injection of botulinum toxin type B into the external anal sphincter on anal pressure of horses.
OBJECTIVE
To determine effects on anal pressure of horses after local injection of the external anal sphincter with Clostridium botulinum toxin type B.


METHODS
11 healthy adult horses.


METHODS
Peak and resting anal sphincter pressures were measured with a custom-made rectal probe that was connected to a pressure transducer. Pressures were measured before treatment and after injection with botulinum toxin type B (BTB) or saline (0.9% NaCl) solution. Dose titration with 500, 1,000, 1,500, and 2,500 U of BTB was completed. Physical changes, behavior, and anal pressure were recorded for each horse.


RESULTS
Injection of 1,000 U of BTB caused a significant reduction in peak anal pressure from days 2 to 84, compared with pressure in control horses. Maximal effect of the toxin was observed within the first 15 days after injection, followed by a slow return to baseline during the 168-day period. Injection of 2,500 U of BTB in the anal sphincter in 1 horse resulted in lethargy, generalized weakness, and dysphagia for 14 days. Adverse clinical effects were not observed in horses after injections with 500, 1,000, or 1,500 U of BTB.


CONCLUSIONS
The effect of focal intramuscular injection of BTB in horses is similar to that reported for other species. However, horses appear to be more sensitive to BTB, compared with other species, and clinical signs of botulism may develop at doses exceeding 1,500 U. Injections of BTB in the external anal sphincter of mares may be useful to reduce incisional dehiscence after repair of perineal lacerations.
Adam-Castrillo
David
D
Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Leesburg, VA 20176, USA.
White
Nathaniel A
NA
Donaldson
Lydia L
LL
Furr
Martin O
MO
D001003:Anal Canal / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D019274:Botulinum Toxins, Type A; D006736:Horses / Q000502:physiology*; D007273:Injections, Intramuscular; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology
C096323:rimabotulinumtoxinB; D001905:Botulinum Toxins; D019274:Botulinum Toxins, Type A