Nitroglycerin Ointment

Description

Presenting Complaint

Sharp, tearing pain during and after bowel movements, sometimes with a small amount of bright red blood on the tissue. This is the textbook presentation of an anal fissure — a small tear in the lining of the anal canal, usually caused by passing a large or hard stool, chronic constipation, or ongoing irritation from haemorrhoids.

Most fissures that are caught early settle with basic measures — more fibre, more fluids, warm baths. The ones that don't, and drag on past several weeks, are classified as chronic, and that's typically where a doctor reaches for glyceryl trinitrate (GTN) ointment, sold in Canada as Rectogesic and under various generic names.

Why the Pain Sticks Around

The anal fissure itself isn't usually the whole problem. What keeps it from healing is a vicious cycle: the tear causes the internal anal sphincter to spasm and tighten, that tightening reduces blood flow to the area, and reduced blood flow means the tissue can't heal properly — which keeps the fissure open, which keeps triggering the spasm. Round and round it goes.

GTN ointment is specifically designed to break that cycle, not just numb the pain.

The Medication

How It Works

Glyceryl trinitrate is a nitric oxide donor. Once applied, it releases nitric oxide into the surrounding tissue, which relaxes the smooth muscle of the internal anal sphincter — the same basic mechanism that makes nitroglycerin useful for chest pain, just applied locally instead of systemically. A relaxed sphincter means lower pressure in the anal canal, and that lower pressure allows blood flow to return to the damaged tissue, which is what actually lets the fissure heal.

It's worth being clear about what it isn't: it's not a numbing agent, and it doesn't disinfect or clean the wound. It's addressing the mechanical cause of why the fissure won't close.

Plan: How to Apply It

1. Wash and dry your hands first.
2. Squeeze out a 2.5cm strip of ointment — most packs include a measuring guide for this.
3. Apply it to the anal area using a clean fingertip (some people cover the finger with cling film first).
4. Spread it gently around the affected area rather than deep insertion, unless your specific product's instructions say otherwise — formulations and applicators vary by brand, so always follow the leaflet that comes with your particular pack.
5. Repeat every 12 hours, generally not exceeding 8 weeks of continuous use.
6. Wash your hands thoroughly afterward — accidental transfer to eyes, nose, or other sensitive areas can cause irritation.

A detail that actually helps: applying it while lying down, rather than standing, tends to reduce how sharply the headache hits, since it blunts the sudden drop in blood pressure to the head that standing can worsen.

Monitoring: What to Watch For

Very common (worth expecting, not alarming on its own):

• Headache — this is the single most reported side effect, and for a meaningful number of patients it's significant enough that some clinicians recommend taking a standard dose of paracetamol before each application as a preventive measure
• Dizziness or lightheadedness, especially when standing up quickly after applying

Less common:

• Flushing or a warm sensation
• Mild skin irritation at the application site
• Nausea

Serious — stop and seek care:

• Fainting or a significant drop in blood pressure
• Chest pain or a racing heartbeat
• Severe, persistent headache that doesn't respond to normal pain relief
• Signs of an allergic reaction — swelling, rash, difficulty breathing
• Sudden vision changes (rare, but documented in case reports linked to overuse)

Contraindications: When This Isn't the Right Plan

• Concurrent use of PDE5 inhibitors (sildenafil, tadalafil, vardenafil) — this combination can cause a severe, dangerous drop in blood pressure and is generally avoided altogether. This is worth flagging specifically for anyone also managing erectile dysfunction with medication.
• Pregnancy and breastfeeding — not recommended; safety data is insufficient to support use in either situation.
• Severe anaemia — nitrates can worsen the reduced oxygen-carrying capacity that comes with this.
• Increased intracranial pressure or recent head injury — the vasodilation effect can raise pressure further.
• Severe hypotension or significant heart conditions — needs specific medical clearance beforehand.
• Closed-angle glaucoma — nitrates can increase eye pressure in susceptible patients.

Interaction Notes

Follow-Up

Most patients notice reduced pain within the first couple of weeks, though full healing of the fissure itself generally takes longer — assessment at around 6 to 8 weeks is standard. If there's no meaningful improvement by then, the usual next step isn't simply continuing the same treatment — it's revisiting the diagnosis with a doctor, since options like calcium-channel blocker ointments (diltiazem), botulinum toxin injection, or in some cases minor surgery become the more relevant conversation at that point.