Glyceryl Trinitrate

1. Introduction

Glyceryl trinitrate (GTN) is a nitrate vasodilator used primarily to treat angina pectoris, heart failure, and hypertensive emergencies. It works by releasing nitric oxide, which relaxes vascular smooth muscle, leading to vasodilation and reduced myocardial oxygen demand.

2. Indications

  • Approved Indications:
    • Acute angina pectoris (prevention and relief).
    • Chronic angina management (long-acting formulations).
    • Heart failure (acute decompensated heart failure or after myocardial infarction).
    • Hypertensive emergencies.
  • Off-Label Uses:
    • Oesophageal spasm (relief of chest pain due to oesophageal motility disorders).

3. Dosage

  • Acute Angina (Sublingual):
    • 300–600 mcg (tablet) or 400–800 mcg (spray) under the tongue; may repeat every 5 minutes as needed, up to 3 doses in 15 minutes.
  • Chronic Angina (Long-acting Formulations):
    • Tablets: 2.5–10 mg orally 2–3 times daily.
    • Patches: Apply one 5 mg patch daily, remove after 12–14 hours to avoid tolerance.
  • Acute Heart Failure/Hypertensive Emergencies (IV):
    • Initial infusion: 5 mcg/min, titrate every 3–5 minutes based on response. Maximum: 200 mcg/min.

4. Administration

  • Sublingual: Place the tablet or spray under the tongue and allow it to dissolve completely. Do not swallow or chew.
  • Oral: Take tablets on an empty stomach for better absorption.
  • Patch: Apply to clean, dry, and hairless skin. Rotate sites to prevent irritation.
  • Intravenous: Administer via infusion pump with continuous haemodynamic monitoring.

5. Forms Available

  • Sublingual tablets: 300 mcg, 500 mcg, 600 mcg.
  • Sublingual spray: 400 mcg per spray.
  • Oral tablets (extended-release): 2.5 mg, 5 mg, 10 mg.
  • Transdermal patches: 5 mg, 10 mg, 15 mg (released over 24 hours).
  • Intravenous solution: 5 mg/mL.

6. Side Effects

6.1. Common Side Effects

  • Headache (common and dose-dependent).
  • Dizziness.
  • Hypotension (especially postural).
  • Flushing.

6.2. Less Common Side Effects

  • Reflex tachycardia.
  • Nausea.

6.3. Rare but Serious Side Effects

  • Severe hypotension or syncope.
  • Methaemoglobinaemia (very rare).

7. Warnings

  • Hypotension: GTN may cause severe hypotension, particularly in patients who are volume-depleted or taking other antihypertensives.
  • Tolerance: Continuous use can lead to nitrate tolerance. A nitrate-free interval of 10–12 hours daily is recommended to prevent this.
  • Interaction with Phosphodiesterase Inhibitors: Avoid concomitant use with drugs like sildenafil (Viagra), as it may cause life-threatening hypotension.

8. Precautions

  • Use cautiously in patients with:
    • Hypovolaemia or severe anaemia.
    • Aortic or mitral stenosis.
    • Cerebral vascular disease (risk of headache and dizziness).

9. Interactions

  • Drug-Drug Interactions:
    • Phosphodiesterase inhibitors (e.g., sildenafil, tadalafil): Severe hypotension.
    • Antihypertensives (e.g., beta-blockers, calcium channel blockers): Additive hypotensive effects.
    • Alcohol: Increased risk of hypotension and dizziness.
  • Drug-Food Interactions:
    • No significant interactions, but alcohol should be avoided.

10. Monitoring Parameters

  • Blood pressure and heart rate (to assess for hypotension or reflex tachycardia).
  • Symptom relief (angina or chest pain).
  • Signs of tolerance (reduced efficacy over time).

11. Use in Children

  • Not commonly used in children; safety and efficacy data are limited.

12. Use in Pregnancy

  • Category C: Use only if the potential benefits outweigh the risks. Limited human data are available, but animal studies have shown some risk.

13. Use in Elderly

  • Safe but use with caution due to increased risk of hypotension and dizziness. Start at the lowest effective dose.

14. Use in Kidney Disease

  • No dose adjustment is necessary, as GTN is not renally excreted.

15. Use in Liver Disease

  • Use cautiously in severe hepatic impairment, as GTN metabolism occurs in the liver.

16. Patient Counselling Points

  • For acute angina relief, take GTN as soon as symptoms start. If symptoms persist after 3 doses within 15 minutes, seek emergency medical attention.
  • Store sublingual tablets in their original container, tightly closed, to maintain potency.
  • Avoid standing up quickly after taking GTN to prevent dizziness or fainting.
  • Do not use GTN patches continuously for 24 hours; follow prescribed on/off intervals to avoid tolerance.
  • Avoid alcohol while using GTN, as it can increase the risk of dizziness and hypotension.

17. Table of Brand Names, Manufacturers, and Prices

Brand NameManufacturerPrice (USD)
Nitrostat (sublingual)Pfizer$20–40 (25 tablets, 500 mcg)
Nitrolingual (spray)G. Pohl-Boskamp$50–70 (200 doses, 400 mcg/spray)
Nitro-Dur (patch)Merck & Co.$30–50 (30 patches, 5 mg)
Generic GTNVarious manufacturers$5–15 (25 tablets, 500 mcg)

18. FAQs (15 Questions)

  1. What is glyceryl trinitrate used for?
    It is used to treat and prevent angina, manage heart failure, and in hypertensive emergencies.
  2. How does GTN work?
    GTN releases nitric oxide, which relaxes blood vessels, improving blood flow and reducing the heart’s oxygen demand.
  3. How should GTN sublingual tablets be taken?
    Place under the tongue and allow it to dissolve completely. Do not swallow.
  4. How long does GTN take to work?
    Sublingual tablets or sprays usually relieve angina within 2–5 minutes.
  5. What are the common side effects of GTN?
    Headache, dizziness, flushing, and hypotension.
  6. Can GTN be used during pregnancy?
    Use only if the benefits outweigh the risks. Consult your doctor before use.
  7. How should GTN patches be used?
    Apply to a clean, hairless area and rotate the site daily. Remove after 12–14 hours to prevent tolerance.
  8. Can GTN cause tolerance?
    Yes, continuous use can lead to reduced effectiveness. A nitrate-free interval of 10–12 hours is recommended.
  9. Can I use GTN with sildenafil (Viagra)?
    No, combining these drugs can cause severe, life-threatening hypotension.
  10. What should I do if angina persists after GTN use?
    If pain persists after 3 doses within 15 minutes, seek emergency medical help.
  11. Does GTN affect blood pressure?
    Yes, it can lower blood pressure, sometimes causing dizziness or fainting.
  12. How should GTN be stored?
    Store in a cool, dry place. Sublingual tablets should remain in their original container.
  13. Can I drink alcohol while using GTN?
    Avoid alcohol, as it increases the risk of dizziness and hypotension.
  14. Is GTN suitable for elderly patients?
    Yes, but start at the lowest dose and monitor for side effects like hypotension.
  15. Can GTN be used for headaches?
    No, GTN is not used for headaches and may cause headaches as a side effect.
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