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Drug Reference

glyceryl trinitrate

nitrate vasodilator· Brands: Nitrostat, Nitrolingual, Minitran, Nitro-Dur, Transiderm-Nitro, SustacIVPOSLTOP

Mechanism of action
Glyceryl trinitrate is a prodrug. It is biotransformed to nitric oxide (NO) by mitochondrial aldehyde dehydrogenase (ALDH2) in vascular smooth muscle cells. NO stimulates soluble guanylyl cyclase, thereby increasing cyclic guanosine monophosphate (cGMP) levels. Elevated cGMP activates protein kinase G, which phosphorylates multiple proteins and causes relaxation of vascular smooth muscle. The drug predominantly dilates capacitance veins, reducing preload and ventricular wall tension, and at higher concentrations also dilates coronary arteries and arterioles, improving myocardial oxygen delivery. This results in reduced myocardial oxygen demand and increased supply, relieving angina.
Pharmacokinetics
Glyceryl trinitrate undergoes extensive first-pass hepatic metabolism, resulting in negligible oral bioavailability if swallowed. Sublingual and transdermal routes avoid this effect. Onset of action is rapid after sublingual administration, typically within 1 to 3 minutes, with a short duration of 30 to 45 minutes. The drug is highly lipid soluble and penetrates the skin, allowing for effective transdermal delivery. It is metabolised by hepatic glutathione-dependent enzymes (glutathione S-transferase) to dinitrate and mononitrate metabolites, which are further conjugated and excreted in the urine. The elimination half-life is very short, approximately 2 to 5 minutes. Plasma concentrations decline rapidly after discontinuation of intravenous infusion.
Indications & dosing

Acute angina pectoris

Repeat every 5 minutes if pain persists, up to 3 doses. Sit or lie down to reduce hypotension.

  • adult · SL: 0.3–0.6 mg PRN · Repeat every 5 minutes if pain persists, up to 3 doses. Sit or lie down to reduce hypotension.

Prophylaxis of angina pectoris

Apply to a hairless area of skin, e.g. chest or upper arm, for 12-14 hours daily. Allow a 10-12 hour patch-free interval to reduce tolerance.

  • adult · TOP: 5–10 mg once daily · Apply to a hairless area of skin, e.g. chest or upper arm, for 12-14 hours daily. Allow a 10-12 hour patch-free interval to reduce tolerance.

Acute myocardial infarction

Start at 10-20 micrograms/min, titrate according to response and blood pressure. Maximum 200 micrograms/min. Monitor blood pressure closely.

  • adult · IV: 10–200 micrograms/min continuous · Start at 10-20 micrograms/min, titrate according to response and blood pressure. Maximum 200 micrograms/min. Monitor blood pressure closely.
Contraindications & precautions
  • Concurrent use of phosphodiesterase type 5 inhibitors (e.g., sildenafil, vardenafil, tadalafil) · Additive vasodilation can cause severe, potentially fatal hypotension.
  • Severe hypotension (systolic blood pressure < 90 mmHg) · Glyceryl trinitrate may exacerbate hypotension and precipitate cardiovascular collapse.
  • Hypovolaemia · Risk of severe hypotension due to reduced preload.
  • Increased intracranial pressure · Vasodilation may further raise intracranial pressure.
  • Severe anaemia · May worsen tissue oxygenation.
  • Hypertrophic obstructive cardiomyopathy · Nitrates may worsen outflow obstruction.
  • Ensure the patient is seated or lying down when taking sublingual glyceryl trinitrate, as it may cause a rapid drop in blood pressure.
  • Monitor blood pressure before and after administration, especially in patients on antihypertensive therapy or with suspected hypovolaemia.
  • Counsel patients that headache is common and usually a sign of the drug's action; it may be relieved by rest and simple analgesics.
  • Warn patients to avoid concurrent use of phosphodiesterase type 5 inhibitors and to seek medical advice if they experience chest pain after taking these agents.
  • Rotate application sites for topical formulations to prevent skin irritation and ensure consistent absorption.
  • Keep tablets in their original container and discard any that are no longer effective; store away from heat and moisture.
Adverse effects
  • Headache
  • Dizziness
  • Flushing
  • Hypotensionserious
  • Reflex tachycardia
  • Syncopeserious
  • Methemoglobinemiaserious
Monitoring, pregnancy & toxicity
  • Blood pressure · Before and during IV infusion or dose titration
  • Heart rate · Before and during IV infusion or dose titration
  • Signs of hypotension (dizziness, syncope) · During treatment
  • Pregnancy: Use with caution during pregnancy. GTN may cause maternal hypotension and reduce placental perfusion. It may be used for angina when benefits outweigh risks; no evidence of teratogenicity, but consider alternative agents if possible.
  • Toxicity: Severe hypotension, syncope, and reflex tachycardia · Stop treatment, elevate legs, give IV fluids, and consider vasopressors if necessary.
  • Toxicity: Methemoglobinemia (rare, especially with high doses or prolonged use) · Monitor for cyanosis and confirm with blood gas; treat with IV methylene blue if symptomatic.
Clinical notes
Glyceryl trinitrate is used for the rapid relief and prevention of angina pectoris, for the treatment of acute myocardial infarction and acute heart failure, and for blood pressure control during perioperative hypertension. When using sublingual tablets or spray, patients should sit or lie down to avoid postural hypotension. The dose may be repeated after 5 minutes if required, but if pain persists beyond 15 minutes, urgent medical help should be sought. Headache is a very common adverse effect caused by vasodilation; other side effects include flushing, dizziness, and palpitations. Tolerance to the vascular effects occurs with continuous exposure, so a nitrate-free interval of 8 to 12 hours per day is advised for long-acting formulations. Concurrent use with phosphodiesterase type 5 inhibitors is absolutely contraindicated because of the risk of profound hypotension. Glyceryl trinitrate should be used with caution in patients with hypovolaemia, severe hypotension, and in those with raised intracranial pressure.

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BNF; local formulary