Botulinum Toxin (Botox) for Anal Fissure

What is an anal fissure?

An anal fissure is a small longitudinal tear in the delicate lining of the anal canal. Hard or bulky stools and straining commonly trigger it; diarrhoea, childbirth and anal trauma can also contribute. It is common and can occur at any age.

What are the symptoms?

Symptom duration and severity vary. Common symptoms include:

• Sharp, tearing or burning pain during and after a bowel movement.
• Pain lasting minutes or sometimes hours after passing stool.
• Bright red blood on toilet paper or on the stool.
• Itching and burning around the anus.
• A small sentinel skin tag at the anal margin in chronic fissure.

Acute versus chronic fissure

An acute fissure is generally a superficial tear present for less than six weeks. Many improve with fibre, appropriate fluids, clinician-advised stool softeners and warm sitz baths.

A chronic fissure commonly persists beyond six to eight weeks, with hardened edges and sometimes visible internal sphincter fibres at its base. Persistent sphincter spasm reduces local blood flow and impairs healing. Botox may be considered to reduce that spasm temporarily.

How can botulinum toxin (Botox) help a fissure heal?

Botulinum toxin type A temporarily relaxes the internal anal sphincter to allow healing. This is sometimes called chemical sphincterotomy: relaxation is sought with a reversible drug effect rather than surgically dividing part of the muscle.

Botox inhibits acetylcholine release at nerve endings, reducing the contraction signal. Muscle relaxation lowers anal pressure and may improve blood flow. Its clinical muscle-relaxing effect typically wanes over about two to three months; the aim is for the fissure to heal during this window. Duration varies.

The active substance is botulinum toxin type A, also used cosmetically, but the purpose, dose and injection site differ.

1. The tear causes pain.
2. Pain increases internal sphincter spasm.
3. Spasm reduces blood flow to the area.
4. Reduced blood supply impairs healing, perpetuating pain and spasm.

Who may be suitable?

Botox may be considered for chronic fissure, particularly when avoiding surgery or protecting continence is a priority. ASCRS describes results similar to topical treatments as first-line therapy and a modest healing benefit as second-line treatment after topical therapy fails.

• Fissures persisting for six to eight weeks despite stool regulation and suitable topical medicines such as nitroglycerin or diltiazem.
• People unable to tolerate topical treatment, for example because of headaches.
• People preferring to avoid surgery or with elevated surgical or anaesthetic risk.
• People requiring particular continence assessment because of difficult childbirth, previous anal surgery or existing muscle weakness; age is also considered.
• Selected patients with recurrent fissure after surgery.

When may treatment be unsuitable?

Share your medical history, allergies and all medicines before treatment. The following may require avoiding injection or further assessment:

• Pregnancy and breastfeeding.
• Neuromuscular junction disorders such as myasthenia gravis or Lambert–Eaton syndrome.
• Known allergy to botulinum toxin or product components.
• Active infection or abscess at the injection site.
• An associated anal fistula, which requires assessment of the accompanying disease.
• Atypical fissures potentially associated with Crohn’s disease, sexually transmitted infections, tuberculosis or cancer. The underlying cause must be investigated first.
• Medicines that may enhance toxin effects, including aminoglycoside antibiotics.

Preparing for treatment

Botox injection alone is a short procedure without an incision. Technique, anaesthesia and dose are individualised; there is no single universal protocol.

• Examination confirms the diagnosis and checks for atypical fissure or associated disease.
• Tell the clinician about medicines, particularly anticoagulants, allergies and previous surgery.
• Some centres request an enema. If sedation or general anaesthesia is planned, fasting and escort instructions are provided.

How is Botox administered?

Most patients can go home on the day of treatment. Preparation and observation depend on the anaesthetic and individual circumstances.

1. The patient lies on their side or in another suitable examination position.
2. Local anaesthesia, sedation or a short general anaesthetic may be selected according to the patient and setting.
3. A fine needle delivers botulinum toxin to the internal sphincter, often at two to four sites.
4. Injection takes a few minutes. Including preparation and observation, the visit often takes 30–60 minutes, although longer monitoring may be needed.

Dose and possible additional procedures

Published studies use varying doses, including 20–100 units. In the survey by Borsuk and colleagues published in 2023, about 90% of 216 colorectal surgeons reported using 50–100 units. This does not establish a dose suitable for everyone.

Lin and colleagues’ meta-analysis of 18 trials reported similar efficacy with lower doses and favourable findings for some continence and recurrence outcomes. Study methods differ. The clinician selects the product, dose and sites; units of different toxin products are not interchangeable. These figures are not an individual dosing recommendation.

In selected cases, fissurectomy to remove hardened edges or removal of a sentinel tag may be added. Potential benefit is assessed individually. These additional procedures may involve an incision and alter aftercare.

Healing rates and comparison with other treatments

Botox can achieve healing similar to topical treatments without permanently dividing the sphincter. However, healing may be lower and recurrence higher than with lateral internal sphincterotomy (LIS).

The 2017 network meta-analysis by Ebinger, Warschkow and colleagues included 44 randomised trials and 3,268 patients. The pooled estimates below were reported at a median follow-up of two months.

What do the figures mean in practice?

Different studies report Botox healing rates around 60–80%; selection, technique and follow-up influence results. The AAFP summary of the ASCRS guideline reports transient incontinence in about 5%, often gas leakage or minor soiling.

• Advantages: Botox alone requires neither an incision nor surgical division of the muscle. Recovery and return to work can be short; leakage, if it occurs, is usually temporary. Risk is not zero.
• Limitations: The fissure may not heal or may recur months to years later. Repeat injection or surgery may be required.
• Combination with creams: Adding a topical nitrate may help selected patients and should be clinician-directed.
• LIS surgery: It offers the highest healing probability in selected patients. Because part of the muscle is permanently divided, continence risk needs individual assessment and may persist in some patients.

Possible adverse effects

Many adverse effects are mild and temporary. A temporary muscle effect does not mean every complication resolves on its own; report new or worsening symptoms.

• Temporary gas leakage, minor soiling or altered bowel control.
• Injection-site pain, tenderness, minor bleeding or bruising.
• Perianal haematoma or a thrombosed haemorrhoid.
• Rare infection or abscess.
• Rare flu-like symptoms or fatigue.
• Failure of healing or recurrence.