Glyceryl Trinitrate

What is glyceryl trinitrate?

Glyceryl trinitrate is a nitrate medicine that relaxes and widens blood vessels. This reduces the heart's workload and improves blood flow. It is mainly used to treat and prevent chest pain (angina), as well as topically in the treatment of anal fissures. Glyceryl trinitrate is available on prescription, but certain forms can also be bought in a pharmacy (if classified as a P Medicine), however, rectal ointment is only available on prescription[1]. 

What is glyceryl trinitrate used for?

Glyceryl trinitrate is prescribed for the following conditions[1]: 

• Relieving angina (chest pain) caused by reduced blood flow to the heart 

• Preventing angina attacks before physical exertion 

• Treating anal fissures (painful tears in the lining of the anus) 

• Some brands of patches are licensed for venous patency (‘5’ Minitran® patch) and preventing phlebitis and extravasation (‘5’ Transiderm-Nitro® patch) 

How does glyceryl trinitrate work?

Glyceryl trinitrate works by affecting the smooth muscle in blood vessel walls[1]: 

• It relaxes the blood vessels, widening both arteries and veins 

• This reduces the amount of work the heart needs to do 

• It increases oxygen delivery to the heart muscle, helping relieve angina pain 

Who can take glyceryl trinitrate?

Glyceryl trinitrate is generally safe for most adults aged 18 and over, but it may not be suitable if you[1]: 

• Have low blood pressure 

• Are taking PDE5 inhibitors (like sildenafil) 

• Have severe anaemia or glaucoma 

• Have had an allergic reaction to glyceryl trinitrate, other nitrates or another ingredient listed as part of your medicine 

• Have had recent brain or head injuries or conditions 

• Have ever had a stroke 

• Are pregnant or breastfeeding without medical advice 

Please note this is not a complete list, tell your doctor or pharmacist about any conditions you may have or medication you take before you start treatment, and always follow the instructions in the Patient Information Leaflet[2]. 

How do you take glyceryl trinitrate?

Glyceryl trinitrate should be used according to its form[1]: 

• Tablets or spray: Sit down and place under the tongue; do not swallow or chew 

• Patches: Apply to clean, dry, hairless skin and rotate the site daily 

• Ointment: Use the dosing line provided to measure the correct amount before applying 

What is the typical dosage of glyceryl trinitrate?

The dose of glyceryl trinitrate depends on the condition and formulation: 

• For angina (tablets or spray): 

• During an attack: 1 tablet or 1-2 sprays under the tongue; repeat after 5 minutes if needed, up to a maximum of 3 tablets/sprays in total. Seek urgent medical attention if symptoms have not resolved 5 minutes after the second dose, or earlier if the pain is intensifying or the person is unwell. 

• Before activity: 1 tablet or 1-2 sprays 5-10 minutes beforehand 

• For prevention (patches): 

• Apply 1 patch as directed and replace every 24 hours rotating patch location to different areas or intermittently removing the patch at night to reduce the risk of tolerance 

• For anal fissures (ointment): 

• Apply 2.5cm (375mg) of ointment to the anal canal twice a day for a maximum of 8 weeks 

Can you stop taking glyceryl trinitrate?

You should not stop using glyceryl trinitrate suddenly, especially if you use patches regularly. Always consult your doctor before stopping, as sudden withdrawal may worsen symptoms[1]. 

What do you do if you take too much glyceryl trinitrate?

If you take more than your prescribed dose of GTN spray, sit down and put your feet up if you feel faint. 

If you take more than your prescribed dose of tablets, remove any tablets that are left undissolved in your mouth. 

If you use more than your prescribed number of patches, remove them. 

If you use more than your prescribed dose of ointment, wash it off. 

Taking too much glyceryl trinitrate can cause severe headache, dizziness or fainting and rapid heartbeat. You should seek emergency medical help immediately if you use more than your prescribed dose of GTN and your mouth (lips, tongue or gums), face or skin start to look blue or grey – if you have brown or black skin, this may be easier to see on your lips, tongue and gums or around your eyes [1]. 

What do you do if you forget to take glyceryl trinitrate

If using tablets or spray, take only when needed. If using patches or ointment, apply as soon as you remember unless it is close to your next scheduled dose. Do not use a double dose to make up for a missed one[1]. 

What medicines can’t you take with glyceryl trinitrate?

Some substances can interact dangerously with glyceryl trinitrate[1]: 

• PDE5 inhibitors for erection problems (such as sildenafil or tadalafil) 

• Heparin-containing blood thinners  

• Other blood pressure-lowering drugsincluding some mental health and depression medicine and antihypertensivesAlcohol, which can worsen side effects like dizziness 

• Previous use of long-acting nitrates such as isosorbide mononitrate may require a higher dose of GTN 

You can take glyceryl trinitrate with painkillers like paracetamol, but try not to take it too often with non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, aspirin, or naproxen, as it may make your angina worse[1]. 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of glyceryl trinitrate?

The most common side effects include[1]: 

• Headaches, especially at the beginning of treatment 

• Dizziness or light-headedness 

• Flushing 

• Low blood pressure 

• Skin irritation at the patch site 

Seek immediate medical help if you experience chest pain that does not improve with glyceryl trinitrate, your lips, tongue, face, or skin turn blue or grey, your heart beats faster or slower than normal, your chest pain is worse than usual, or you have fainted. 

In rare cases, the medicine may cause a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe this is happening[1]. 

Symptoms of anaphylaxis include[1]:  

• Difficulty breathing  

• Tightness in throat and chest  

• Swelling of the tongue or throat  

• Feeling faint or dizzy  

• Blue/grey skin or lips  

• Loss of consciousness 

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2]. 

Frequently asked questions about glyceryl trinitrate

How quickly does glyceryl trinitrate work? 
Glyceryl trinitrate tablets and spray usually begin working within 1 to 3 minutes[1]. 

Can I drive after taking GTN? 
Avoid driving if you feel dizzy or light-headed after using glyceryl trinitrate[1]. 

Can I drink alcohol while using glyceryl trinitrate? 
Alcohol can intensify side effects like dizziness, so it’s best to avoid it[1]. 

Do glyceryl trinitrate tablets go out of date? 
Yes, they expire 8 weeks after the bottle is first opened. Keep a note of the date when you first open the bottle of tablets[1]. 

Is glyceryl trinitrate safe during pregnancy? 
It may be used if prescribed, but only under medical supervision[1]. 

For the official NHS guide to glyceryl trinitrate, visit their website.