Comparison between intramuscular and perimuscular injections of botulinum toxin type A

Botulinum toxin type A (BTX-A) must be injected in the intramuscular area to exert its paralytic effect. The durability of the BTX-A effect varies in different patients, and this fact can result from different locations of the drug injection, for example, the muscle peripheral area (perimuscular). This study aimed to evaluate whether a difference exists in the effect duration of the muscle paralysis between intramuscular and perimuscular injections of BTX-A.

This study used 18 male New Zealand rabbits divided into two groups (A and B) based on the location of the BTX-A injection. The group A animals received 10 units of BTX-A diluted with 0.1 ml of normal saline injected perimuscularly. The group B animals received the same dosage injected in the intramuscular area of the left masseter muscle. An electroneurophysiologic study was performed 1 week before the experiment for all the animals, then repeated 1, 4, and 8 weeks after the toxin injection.

The amplitude values recorded in the masseter muscle were significantly lower in both groups throughout the study than the physiologic amplitude. The comparison between groups A and B did not show any statistically significant amplitude variations throughout the 8 weeks.

No significant difference in the neuromuscular blockade induced by botulinum toxin type A was observed between injections into the muscle peripheral area and intramuscular injections.