Health Tips

Nitrates, Your Chest Pain Saviour

Nitrate therapy is an important therapy for ischemic heart disease, such as chest pain, heart attack and in some heart failure cases. Nitrates are known as vasodilators— they widen the blood vessels, which allow more oxygen-carrying blood to pass through; with that the heart muscle gets adequate oxygen, which reduces the stress on the heart muscle. Essentially, nitrates allow more space for oxygen-rich blood to reach the important organs.

Such therapy has come a long way. In 1879, the first nitrate, called nitroglycerin, was used by William Murrell for the treatment of angina pectoris (chest pain). 

Today, nitrates are still widely used by people who have ischemic heart diseases:

• Sublingual glyceryl trinitrate (GTN) — This is the “emergency medication” for people experienced heart attack or chest pain. It relieves chest pain after placing it under the person’s tongue.

• Isosorbide dinitrate

• Isosorbide-5-mononitrate

Other forms of nitrates are also available, such as nitroglycerin spray, transdermal nitroglycerin patches and injectable nitrates. 

Sublingual glyceryl trinitrate (GTN)

Image credit: Jabatan Farmasi Hospital Kuala Lipis

As mentioned, GTN is an emergency medication that one takes when experiencing chest pain or heart attack. It is not supposed to be taken daily when no chest pain occurs. GTN is taken sublingually, i.e. it should be placed under the tongue. 

Correct ways of taking sublingual GTN

1. When chest pain occurs, stop whatever you’re doing and sit down to rest

2. Put one GTN tablet under your tongue and wait for 5 minutes. Allow the tablet to dissolve slowly – do not suck, chew or swallow it.

3. Rest for a while, and stand up slowly, as the GTN tablet may make you feel dizzy.

4. If the chest pain is not resolved, put another GTN tablet under the tongue again and wait for another 5 minutes

5. If chest pain still persists, put another GTN tablet under the tongue for the third time AND visit the hospital’s emergency department immediately.

6. You may also take one tablet of sublingual GTN before doing any physical activity to prevent any potential chest pain.

Precautions about sublingual GTN:

• Side effects of GTN include dizziness, headache, nausea and irregular and fast heartbeat. Elderly may be more sensitive to these effects after taking GTN. Do not operate machinery or drive shortly after taking GTN.

• GTN tablets come in a dark amber bottle. It’s important that you always keep the tablets in its original bottle and do not transfer them out to other containers. The dark amber bottle is meant to protect the GTN tablets from light.

• Always close the container after using GTN tablets. This prevents the tablets from being damaged by any moisture in the air.

• Do not keep your GTN tablets in an environment of high temperature (e.g. car). Always keep them under room temperature.

• After opening the bottle for the first time, the GTN tablets are only effective for 8 weeks only. Discard any balance after opening for 8 weeks. You may write down the opening date on the bottle.

• Always keep the medications away from children.

• Always make sure you refill your sublingual GTN on time at your pharmacy. 

• Always bring them with you wherever you go!

Longer acting nitrate

There’s a caveat with sublingual GTN: its effect is short-lived and quick to wear off. As such, longer-acting nitrate medications were developed. Examples of longer acting nitrate are Isosorbide dinitrate and isosorbide-5-mononitrate. 

Isosorbide dinitrate

Image credit:https://www.pharmacy.nhg.com.sg/uploadedfiles/apps/medicine/42/Isosorbide%20Dinitrate.pdf 

Initial dose: 5 to 20 mg 2 to 3 times daily; maintenance dose: 10 to 40 mg 2 to 3 times daily

Isosorbide-5-mononitrate

Dose: 30-60 mg once daily, up to 120mg daily

Longer-acting nitrates are beneficial because they prevent chest pain from happening in the first place. However, clinicians soon found out that these longer acting nitrates lose their efficacies over time. It was as if patients developed tolerance towards these nitrates.

Nitrate tolerance

Patients who receive nitrate therapy for long-term may develop nitrate tolerance, of which the nitrate they take loses effects. This is bad because that means the patient is not well protected from the risk of chest pain.

Luckily, the clinicians have come up with a workaround: allow the patient to go on a nitrate-free interval.  That way, the nitrate medication won’t lose much of its effectiveness.

As a result, with all of the long-acting nitrates, patients were recommended to maintain a 10 to 14 hours period daily, when they won’t take any nitrate medications. 

This is why if you are taking isosorbide dinitrate on a three-times daily dosing, your pharmacist would advise you to take the tablet at 8am, 12pm and 5pm OR 8am, 1pm and 6pm. If it’s twice-daily dosing, then take it at 8am and 1pm. 

Whereas for Isosorbide-5-mononitrate, because it’s an once-daily dosing, you’re advised to take the medication at 8am every morning. Try to keep the timing as consistent as possible, as you would want to maintain the nitrate-free period. 

If you have any concerns related to your nitrate therapy, consult your doctor or pharmacist.

Do not forget other medications

Your chest pain treatment consists of many other medications beside nitrate, such as your blood thinner, cholesterol, high blood pressure and heart failure medications. They're equally important to prevent your next chest pain. Always remember to take them as per the doctor’s instructions.

A word from DOC2US

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Written by

Ms Joyce Toh