Botulinum Toxin Injections for the Treatment of Anal Fissure
Botulinum toxin type A injections are one of the minimally invasive treatment options used in proctology for chronic anal fissure. The preparation is injected into the anal sphincter muscles to temporarily reduce excessive muscle tension and spasm. This may relieve pain and create more favourable conditions for the fissure to heal.
Botulinum toxin therapy is most commonly considered for chronic anal fissure, particularly when conservative treatment has not provided sufficient improvement or when a sphincter-preserving alternative to surgical sphincterotomy is preferred. The treatment strategy is determined by the doctor after an individual assessment of the patient.
What is an anal fissure?
An anal fissure is a small tear or ulcer-like lesion in the lining of the anal canal. It may cause sharp or burning pain during and after bowel movements, as well as a small amount of bright red bleeding.
Anal fissures are often caused by mechanical trauma to the mucosa, for example from hard stools and constipation. Pain may in turn trigger spasm of the internal anal sphincter, reducing blood supply to the affected area and potentially delaying healing.
In many cases, acute anal fissures heal with conservative treatment. If the fissure does not heal over a prolonged period and becomes chronic, additional medical or surgical treatment may be necessary.
How does botulinum toxin help in the case of an anal fissure?
Botulinum toxin temporarily inhibits the release of acetylcholine from nerve endings, thereby reducing the tone and spasm of the anal sphincter muscle. After the injection:
excessive sphincter tension is reduced;
pain and spasms may decrease;
conditions for improved blood flow in the affected area may be created;
the fissure is given an opportunity to heal gradually.
Unlike lateral internal sphincterotomy, the muscle is not surgically divided. The effect of botulinum toxin is temporary.
When may botulinum toxin injections be suitable?
A doctor may consider botulinum toxin therapy in patients with a chronic anal fissure, particularly when dietary measures, bowel movement regulation and topical medical treatment have not provided sufficient improvement.
The method may also be suitable when a sphincter-preserving treatment option is preferred in order to avoid or postpone surgical sphincterotomy.
Botulinum toxin therapy is not equally suitable for all types of anal fissures. In cases of atypical fissure location, low sphincter tone, inflammatory bowel disease, infection or other possible secondary causes, more detailed diagnostic evaluation and an individual treatment strategy are required.
How is the procedure performed?
Before the procedure, the doctor assesses the patient’s symptoms, the characteristics of the anal fissure, previous treatment, sphincter function, general health and possible contraindications.
Botulinum toxin is injected with a fine needle into one or more precisely selected points in the anal sphincter muscles. The dose, number of injections and injection sites are determined individually, as different treatment protocols are used in clinical practice.
The procedure is usually performed on an outpatient basis. The need for pain relief or anaesthesia is determined by the doctor according to the extent of the procedure and the individual situation.
When does the effect appear?
Botulinum toxin begins to work gradually. As sphincter spasm decreases, pain may lessen and more favourable conditions for fissure healing may develop.
Complete healing of the fissure does not occur immediately and may take several weeks. Even after symptoms improve, it is important to follow the doctor’s recommendations and maintain regular, soft bowel movements, as hard stools and repeated trauma may delay healing or contribute to recurrence.
How effective is botulinum toxin therapy?
Botulinum toxin therapy may promote healing of a chronic anal fissure, but the result is not guaranteed and may vary between patients. A 2025 meta-analysis of randomised studies found healing after the first botulinum toxin injection in approximately 73% of patients overall, although there were significant differences between the studies.
Surgical lateral internal sphincterotomy is generally more effective in terms of healing chronic anal fissures, but it has a different risk profile. Therefore, the most appropriate treatment is selected individually by weighing the expected benefits and possible risks.
What should be observed after the procedure?
The doctor’s individual recommendations should be followed after the procedure. It is particularly important to prevent constipation and repeated trauma to the anal canal.
The treatment plan may include:
drinking sufficient fluids;
ensuring adequate dietary fibre intake;
using stool-softening medication if prescribed by the doctor;
avoiding excessive straining during bowel movements;
continuing topical or other treatment prescribed by the doctor.
A botulinum toxin injection does not eliminate the need to address factors that may contribute to recurrence of the fissure.
Possible side effects and risks
Botulinum toxin injections are generally well tolerated; however, adverse reactions may occur.
Temporary pain or tenderness at the injection site, slight bleeding and temporary changes in anal sphincter function may occur. Some patients may temporarily experience reduced control of gas or liquid stool. The latest meta-analysis found a low overall complication rate, although the individual risk depends on the technique used, the dose and the patient’s individual situation.
In very rare cases, the effects of botulinum toxin may spread beyond the injection area. Pronounced muscle weakness or problems with swallowing, speaking or breathing require immediate medical attention.
Contraindications and precautions
Before the procedure, the doctor should be informed about all medical conditions, medications, previous botulinum toxin injections, pregnancy or breastfeeding.
The procedure is not performed in cases of known hypersensitivity to the ingredients of the preparation used or if there is an infection at the intended injection site. Particular caution is required in certain neuromuscular diseases and when using medications that affect neuromuscular transmission.
Specific contraindications also depend on the botulinum toxin preparation used; therefore, suitability for the procedure is always assessed by a doctor.
What is important to know about anal fissure treatment?
Botulinum toxin injection is only one of the treatment options for chronic anal fissure.
Initial treatment often includes regulation of bowel movements, a fibre-rich diet, adequate fluid intake and topical medical therapy. If the fissure does not heal, the doctor may consider botulinum toxin injections or surgical treatment.
If pain or bleeding from the anal area persists, self-diagnosis is not recommended. Similar symptoms may also be caused by other proctological conditions, so consultation with a specialist is necessary.
