Injections of botulinum toxin (Botox) may help heal a tear (fissure) in the
anus.
The internal anal sphincter, one of two muscles that control the
anus, is always under tension. If this tension (also called resting pressure)
is too high, spasms and reduced blood flow can cause an anal fissure or prevent
an existing one from healing. Botulinum toxin, the poison that causes
botulism, temporarily paralyzes the internal anal
sphincter. This reduces the spasm and allows the fissure to heal.
Botulinum injections may be more helpful than nitroglycerin
ointment, but the studies do not all agree.1 One study found that two botulinum injections
worked better than nitroglycerin ointment to heal long-term (chronic)
fissures.2 However, fissures may return after
treatment with Botox is discontinued.
The people in this study had no side effects, such as inability to
control gas or stool. However, other studies have reported that some people
have temporary inability to control gas or (rarely) stool. Pain from the
injections may occur. Infection or hematoma (a pooling of blood in body tissue)
at the injection site is a slight risk.