What is the procedure and preparation for Botox (botulinum toxin) treatment of chronic anal fissure?

Botulinum Toxin Injection for Chronic Anal Fissure: Procedure and Preparation

When to Use Botulinum Toxin

Botulinum toxin injection should be considered when topical calcium channel blockers fail after 8 weeks of conservative management, offering cure rates of 75-95% with low morbidity. 1

The treatment algorithm follows this sequence 1:

• Conservative management (fiber, fluids, sitz baths, topical analgesics) for 2 weeks
• Add topical calcium channel blocker (diltiazem or nifedipine 0.3% with 1.5% lidocaine) if no improvement
• Consider botulinum toxin injection if topical treatments fail after 8 weeks

Preparation and Reconstitution

Dosing Recommendations

The optimal dose remains somewhat controversial, but evidence supports the following 2, 3, 4, 5:

• Standard effective dose: 20-30 units total (approximately 0.3 U/kg) 4
• Lower doses (10-15 units total) show reasonable efficacy with potential cost savings 3, 5
• Higher doses (21 units total) demonstrate better pain relief and reduced need for surgery 5

For practical purposes, use 20-30 units of botulinum toxin type A as the initial dose, which balances efficacy with safety. 4

Reconstitution Technique

Follow standard reconstitution protocols per FDA labeling 2:

• Use preservative-free normal saline for dilution
• Gently mix by rotating the vial (do not shake vigorously to avoid denaturation)
• Use within 4 hours of reconstitution
• Store reconstituted solution refrigerated if not used immediately

Injection Procedure

Injection Sites and Technique

The most effective approach involves bilateral injections into the internal anal sphincter on each side of the fissure 4, 5:

• Primary technique: Inject 10-15 units on each side of the anal sphincter (lateral positions at 3 and 9 o'clock) 4, 5
• Enhanced technique: Add a third injection of 5-10 units directly below the fissure for improved pain relief and healing rates 5

The injection causes temporary chemical denervation of the internal anal sphincter, reducing sphincter spasm for approximately 3 months 6.

Administration Details

• Can be performed as an outpatient procedure 6
• No anesthesia typically required, though local anesthetic may be used for patient comfort
• Inject into the internal anal sphincter muscle, not subcutaneously
• Multiple puncture sites (3 locations) appear more effective than bilateral injection alone 5

Post-Injection Follow-Up and Outcomes

Expected Timeline

• Pain relief: 78% of patients experience pain relief within the first week 6
• Initial healing assessment: Evaluate at 1 month post-injection 3
• Complete healing: 73-82% heal after single injection by 2-3 months 4, 6
• Duration of effect: Sphincter paresis lasts approximately 3 months 6

Repeat Injection Protocol

If the patient reports persistent pain at the 1-month follow-up visit, this is the strongest predictor of treatment failure and need for repeat injection (odds ratio 3.92). 3

• Consider repeat injection at 2 months if incomplete healing 4
• Second injection increases overall healing rate to 87% by 6 months 4
• However, long-term healing rates at 12 months drop to 75%, with recurrence rates of 32% 3, 4

Safety Profile and Complications

Botulinum toxin has a significantly better safety profile than surgical sphincterotomy, with no permanent incontinence reported in major studies. 4, 6

Adverse Effects

• Transitory fecal incontinence: 7% of patients, lasting only 1 day 6, 7
• No permanent damage to continence mechanism 5
• Significantly faster return to daily activities (1 day) compared to surgery (14.8 days) 4

Critical Warnings

Per FDA labeling, be aware of distant spread of toxin effect, though this is rare with proper dosing and technique 2. Contraindications include known hypersensitivity to botulinum toxin and infection at injection sites 2.

Comparison to Surgical Options

While lateral internal sphincterotomy shows higher healing rates at 2 months (98% vs 87%) and 12 months (94% vs 75%), surgery carries an 8% risk of anal incontinence compared to 0% with botulinum toxin 4. Botulinum toxin should be exhausted before considering sphincterotomy due to the permanent risk of incontinence with surgery. 1, 4

Key Clinical Pitfalls to Avoid

• Never perform manual dilation—it carries high risk of permanent incontinence (up to 10%) 1, 8
• Do not use botulinum toxin products interchangeably; they are not equivalent 2
• Ensure patients continue conservative measures (high-fiber diet, adequate fluids, sitz baths) during treatment 1, 9
• Monitor closely at 1-month visit; persistent pain indicates likely treatment failure requiring repeat injection 3