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Isosorbide mononitrate, Isosorbide dinitrate, Glyceryl trinitrate (GTN)

Drug Class: Commonly Known As: Category:
Cardiovascular Agent Adult

Isosorbide mononitrate, Isosorbide dinitrate, Glyceryl trinitrate (GTN) - Dosage and How to Use

How should Isosorbide mononitrate, Isosorbide dinitrate, Glyceryl trinitrate (GTN) be used?

You should use this medication as told by your doctor or pharmacist.

(a) For oral tablets

  • Available oral forms of nitrates are isosorbide dinitrate and isosorbide mononitrate.
  • When swallowed, nitrates are used to reduce the number of angina attacks that occur. They do not act fast enough to relieve the pain of an angina attack.
  • Nitrate tablets are usually taken on an empty stomach (at least 30mins to 1 hour before food or 2 hours after meals) with a full glass of water.
  • The regular release tablet is taken once every 6 to 8 hours.
  • The extended-release tablet can be taken less frequently: 1 to 2 times a day is sufficient. These tablets should NOT be crushed or chewed.

(b) Sublingual tablet / Mouth spray

  • Available sublingual form is glyceryl trinitrate (GTN).
  • GTN is available in the form of oral tablet and mouth spray.
  • GTN sublingual tablets or mouth spray can be used to relieve the pain of angina attacks or to prevent an expected angina attack, e.g. moments before exercising.
  • The tablet or spray should be used at the first sign of an attack of angina. DO NOT wait until severe pain develops.
  • This medicine usually gives relief in less than 5 minutes. Detailed steps of how to use this medicine in emergency situations are provided below:
    • Place 1 tablet or spray under the tongue when you encounter chest pain or breathing difficulties.
    • In the event that the pain is not relieved, use a second tablet or spray. Call for an ambulance immediately.
    • If the pain still persists after 5 minutes from the second administration, a third tablet or spray may be used.
    • If you are using GTN to prevent an expected angina attack, you may either dissolve the tablet under your tongue or administer a spray 5 to 10 minutes before engaging in the angina-inducing activity.
  • Directions on how to take GTN sublingual tablets:
    • Place a tablet under your tongue and allow it to dissolve completely.
    • You may chew the tablet to small pieces to aid absorption.
  • Directions on how to use GTN mouth spray:
    • Before using GTN mouth spray for the first time, check that the spray is working by pressing the spray button a few times until it produces a fine mist of liquid.
    • If you do not need to use GTN mouth spray very often, remember to check the spray regularly to see that it still works properly.
    • Remove the plastic cover, and do NOT shake the plastic bottle.
    • Holding the bottle upright and close to your mouth, press the button to deliver one medicated spray under your tongue.
    • Release the button and close your mouth. Avoid swallowing immediately after using the spray, and note NOT to inhale the spray.
    • Do not use Glytrin if you are near a naked flame, e.g. a cigarette.

(c) Topical / transdermal patches

  • Available topical form of nitrates is the GTN patches.
  • Topical nitrates are used to reduce the number of angina attacks.
  • Apply the patch to clean, dry skin with little or no hair, free from scars, cuts or irritation.
  • Remove the previous patch before applying a new one, and apply a new patch If the patch falls off or comes loose.
  • Apply each patch to a different area of the skin to prevent skin irritation.
  • Do NOT trim or cut the adhesive patch to adjust the dosage of GTN. Speak to your doctor if you see the need to adjust your dosage, or if you think your medication is not working.
  • The dose of GTN is different for different patients; follow your doctor’s instructions on when to apply and remove the skin patch. The patch Is usually left on for 12 to 18 hours a day.

What should I do if I miss a dose?

  • If you miss a dose, take the missed dose as soon as you remember.
  • If it is almost time for your next dose, take only the usual dose.
  • Do not double the dosage

What should I do if I overdose?

  • Updated on Friday, February 1, 2019
  • Article contributed by Department of Pharmacy National Heart Centre Singapore

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