Cardiovascular
Nitrates
e.g. GTN, isosorbide — Relieve and prevent angina by widening blood vessels.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Nitrates are used to relieve and prevent the chest pain of angina, and sometimes in heart failure. Short-acting forms work within minutes; long-acting forms give sustained cover.
How it works
They release nitric oxide, which relaxes vascular smooth muscle. Widening the veins reduces the heart's workload, and widening the coronary arteries improves its blood supply, easing angina.
In practice
In practice short-acting GTN (spray or sublingual tablet) is for relief of an angina attack and can be used just before exertion, while long-acting nitrates prevent symptoms. Long-acting use needs a daily nitrate-free interval to prevent tolerance. The absolute contraindication to remember is recent use of a PDE-5 inhibitor (erectile-dysfunction drugs such as sildenafil), which can cause dangerous hypotension with nitrates.
Examples
Practical use
How to take it & use it well
- Use a GTN spray under the tongue when you have angina chest pain, or before activity you know may bring it on; sit down before using it.
- If the pain does not ease after using it as directed, treat it as an emergency and call for urgent help.
- For longer-acting nitrates like isosorbide mononitrate, take them as a regular daily tablet to help prevent angina.
- A nitrate-free interval each day, usually overnight, helps stop your body getting used to the medicine and losing the effect.
- If you miss a dose of your regular nitrate, take it when you remember unless the next is nearly due; do not double up.
- Store the GTN spray properly and check it has not expired, so it works when you need it.
Common uses
- Relief of acute angina (short-acting GTN)
- Prevention of angina (long-acting nitrates)
- Heart failure (specialist regimens)
Monitoring
- Symptom control and blood pressure
- Frequency of GTN use (rising use signals worsening angina)
Weighing it up
Advantages & disadvantages
Advantages
- They quickly relieve angina chest pain by widening blood vessels and easing the heart's workload.
- The spray works fast and can also be used to prevent pain before exertion.
- Longer-acting forms help prevent angina attacks through the day.
- They are well established with a long history of use.
- They give people with angina more confidence to stay active.
Disadvantages
- They commonly cause headaches, flushing and light-headedness, especially at first.
- The body can get used to them, so a daily nitrate-free interval is needed to keep them working.
- They can lower blood pressure too much, causing dizziness or faintness.
- They relieve symptoms but do not treat the underlying cause of the heart condition.
- They must never be combined with certain erectile dysfunction medicines.
Key safety principles
What to watch for
- Do NOT combine with PDE-5 inhibitors (e.g. sildenafil) — risk of severe hypotension.
- Headache, flushing and dizziness are common, especially at first.
- Long-acting nitrates need a nitrate-free interval to avoid tolerance.
Key interactions
What to avoid or check alongside
- PDE5 inhibitors used for erectile dysfunction must never be taken with nitrates, as the combination can cause a dangerous drop in blood pressure.
- Other blood-pressure-lowering medicines can add to dizziness and low blood pressure.
- Alcohol can increase the blood-pressure-lowering and dizzying effects.
- Some medicines for pulmonary high blood pressure work in a similar way and should not be combined.
- Standing up quickly while on nitrates can worsen light-headedness, so move slowly.
Patient & carer advice
- Sit down to use your GTN; if pain is not relieved after the advised steps, call 999
- A brief headache after GTN is expected
- Never use with erectile-dysfunction tablets — tell us if you take them
Use with
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Answers
Nitrates: frequently asked questions
What should I do if my GTN spray does not stop the pain?
If your chest pain does not ease after using the spray as directed, treat it as a possible heart attack and call emergency services straight away.
Why do I get a headache after using it?
Nitrates widen blood vessels, which often causes a short-lived headache and flushing. This usually settles as your body gets used to the medicine.
What is a nitrate-free interval?
It is a daily gap, often overnight, when you have no active nitrate in your body. This stops you building up tolerance, which would otherwise reduce the medicine's effect.
Why can I not take erectile dysfunction tablets with nitrates?
Both lower blood pressure, and together they can cause a sudden, dangerous drop. This combination must always be avoided.
Can I use the spray before exercise?
Yes. If activity tends to trigger angina, the spray can be used beforehand to help prevent pain, as advised by your prescriber.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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