At a glance
GTN (glyceryl trinitrate) and diltiazem are the two most commonly prescribed topical treatments for anal fissures. Both work by relaxing the internal anal sphincter, reducing spasm, and improving blood flow to help the fissure heal. They achieve this through different mechanisms — and they cause different side effects.
Switching between them is common. It is not a sign of failure. It is a normal part of finding the right treatment for your body. This guide covers why people switch, what to expect during the transition, and what comes next if neither medication does the job.
Why people switch
The most common reason for switching is side effects. Both medications work well enough that healing rates are broadly similar — the deciding factor is often which one you can actually tolerate using twice a day for six to eight weeks.
GTN to diltiazem (the more common direction)
This is the switch people describe most frequently. The trigger is almost always headaches.
GTN is a vasodilator. It works by releasing nitric oxide, which relaxes smooth muscle — including in blood vessels throughout the body. The headaches are a direct result of this mechanism: the same blood vessel dilation that helps the fissure also affects vessels in the head.
People describe these headaches as:
- Starting within minutes of application
- Ranging from mild and tolerable to severe and debilitating
- Sometimes improving over the first one to two weeks, sometimes not
- Occasionally accompanied by dizziness, light-headedness, or a flushing sensation
For some people, the headaches are manageable. Paracetamol, smaller application amounts, or timing the application before bed can help. For others, the headaches are severe enough that they cannot use the medication consistently — and a treatment you cannot apply is a treatment that is not working.
Diltiazem works through a different pathway (calcium channel blockade). It can cause headaches too, but people consistently report them as less frequent and less intense.
Diltiazem to GTN (less common, but it happens)
The main reason people switch in this direction is skin irritation. Diltiazem cream can cause:
- Localised redness and itching around the application area
- A rash that may develop after days or weeks of use
- Burning or stinging on application
- Skin sensitivity that worsens over the treatment course rather than improving
Some people find the skin reaction manageable. Others find it makes a painful condition even more miserable. In those cases, switching to GTN — and accepting the headache trade-off — may be the better option.
Occasionally, people switch back to GTN because the diltiazem simply did not seem to be helping the fissure heal, even without significant side effects. Different fissures may respond differently to the two mechanisms.
How the switch works
The washout question
One of the most common questions people have is whether they need to stop one medication and wait before starting the other. The answer varies by doctor, but in general:
- Many doctors advise starting the new medication immediately or within a day of stopping the old one. The goal is to maintain continuous sphincter relaxation to give the fissure the best chance of healing.
- Some doctors recommend a gap of one to three days, particularly if the reason for switching is a skin reaction that needs time to settle before a new cream is applied to the same area.
- There is no standard washout period based on pharmacological concerns — the medications are applied topically and do not build up in the body in a way that would cause interactions.
The most important thing is to follow your doctor’s specific guidance. If you are unsure, call and ask rather than making the decision yourself.
What to expect when starting the new medication
When switching from GTN to diltiazem:
- The headaches should stop within a day of stopping GTN
- Diltiazem side effects, if they occur, typically appear within the first few days to two weeks
- You may notice a different sensation during application — some people describe diltiazem as having a slight cooling effect
- The fissure healing process is not reset. If your fissure had begun to improve on GTN, switching to diltiazem continues the same healing trajectory.
When switching from diltiazem to GTN:
- Skin irritation should begin to settle within days of stopping diltiazem
- GTN headaches, if they occur, typically start with the first or second application
- Some people find that applying a smaller amount initially and gradually increasing can help their body adjust
- Applying GTN before bed means you may sleep through the worst of the headache
Practical tips for the transition
- Keep using stool softeners and sitz baths. The topical medication is one part of fissure management. The supporting measures remain important regardless of which cream you are using.
- Give the new medication a fair trial. Side effects from the new treatment may appear in the first week and then settle. Do not give up too quickly unless the side effects are severe.
- Track your experience. Note when you apply, what you feel, and how the fissure seems to be doing. This helps your doctor make decisions at follow-up.
- Application technique matters. Poor application — too much, too deep, too rough — can create problems that are not actually caused by the medication itself. Our guide to applying topical treatments covers this in detail.
When neither medication works
This is the situation many people dread, and it is more common than you might think. Topical treatments have healing rates typically reported in the range of 50 to 70 percent for chronic fissures. That means a meaningful proportion of people will try both GTN and diltiazem and still have a fissure that has not healed.
If you have completed adequate courses of both medications — generally at least six weeks each, applied consistently — and the fissure persists, the conversation with your doctor typically moves to:
Botox injection
Botox (botulinum toxin) is injected directly into the internal sphincter under anaesthesia. It temporarily paralyses the muscle, reducing spasm for two to three months. This gives the fissure a window to heal without the need for a permanent change to the sphincter.
Many people describe botox as the step between “topicals did not work” and “I am not ready for surgery.” It is less invasive than surgical options and any effects on continence are temporary.
Surgical options
If topical treatments and botox have not resolved the fissure, surgery becomes the next consideration. The most common options are:
- LIS (lateral internal sphincterotomy) — a small, controlled cut in the internal sphincter
- Fissurectomy — removal of the chronic fissure tissue, often combined with botox
- Fissurectomy with sphincterotomy — a combination approach
Your surgeon will discuss which option suits your specific situation. This is not a failure — it is a normal progression through the treatment pathway.
The emotional side of switching
It is worth acknowledging that switching medications can feel discouraging. You may have spent weeks using a treatment, managing its side effects, and hoping it would work — only to be told it is time to try something different. That is frustrating.
Some things people find helpful to remember:
- Switching is a normal, expected part of fissure treatment. Your doctor has seen this many times.
- The fact that one medication did not work does not mean the next one will not.
- Each treatment you try gives your doctor more information about how your fissure responds, which helps with future decisions.
- The goal is healing — and sometimes the path to healing involves trying more than one approach.
When to contact your doctor
Seek medical attention if you experience:
- Heavy bleeding
- Worsening pain that does not follow the pattern of gradual improvement
- Signs of infection — increasing redness, warmth, swelling, or discharge
- Severe side effects from either medication, including fainting, severe dizziness, or signs of an allergic reaction
- If you have been using topical treatment consistently and the fissure is not improving after six to eight weeks, contact your doctor to discuss next steps