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Organic nitrate Pregnancy: UK SPC §4.6 (infusion), verbatim: 'Developmental toxicity studies performed in rats and rabbits using various routes of administration did not reveal any effect on the embryos, fetuses or the young animals even at toxic doses for the dam.' No human pregnancy statement is given. Breast-feeding: 'Available evidence is inconclusive or inadequate for determining infant risk when used during breastfeeding. There is data that nitrates are excreted in breast milk and may cause methaemoglobinaemia in infants. The extent of excretion of nitroglycerin in human breast milk has not been determined. A risk to the suckling child cannot be excluded. A decision must be made whether to discontinue breast-feeding or to discontinue/abstain from Glyceryl Trinitrate therapy...' Fertility: reproduction toxicity studies 'did not reveal any effect on mating, fertility and general reproductive parameters'; there is no human fertility data. US sublingual-tablet label §8.1: 'Limited published data on the use of nitroglycerin are insufficient to determine a drug associated risk of major birth defects or miscarriage.'

Glyceryl trinitrate (GTN)

Brand names: GTN spray, Nitrolingual, Transiderm-Nitro, Rectogesic

Used in: Acute Coronary Syndrome & Chest Pain

Glyceryl trinitrate (GTN) is a short-acting nitrate vasodilator used for acute relief and prophylaxis of angina and, intravenously, for acute heart failure, pulmonary oedema and hypertensive emergencies.

Adult dose

Dose: Acute anginal attack, sublingual (US label): one nitroglycerin sublingual tablet - the product is supplied as 0.3 mg, 0.4 mg and 0.6 mg tablets - under the tongue or in the buccal pouch at the first sign of an attack. Intravenous infusion (UK SPC): 10 - 200 micrograms/min, adjusted to the individual patient; unstable angina, an initial dose of 10 micrograms/min.
Route: Sublingual / buccal tablet, and intravenous infusion by pump. SCOPE - these are the two routes the fetched sources cover. The transdermal patch and the rectal ointment for anal fissure listed on this page are NOT covered here: no source for either was fetched, so no patch or Rectogesic dose is asserted. The sublingual figures are US tablet labelling; the metered spray was not sourced.
Frequency: Sublingual: at the onset of an attack, then 'One additional tablet may be administered every 5 minutes until relief is obtained'; may also be used prophylactically '5 to 10 minutes prior to engaging in activities that might precipitate an acute attack'. Intravenous: continuous infusion at a constant rate, adjusted to clinical response.
Max: Maximum for the sublingual dose shown - US label: 'No more than three tablets are recommended within a 15-minute period', and 'If the pain persists after a total of 3 tablets in a 15-minute period, or if the pain is different than is typically experienced, seek prompt medical attention.' No maximum dose is stated for the intravenous infusion.
Verbatim, US sublingual-tablet label §2: 'Administer one tablet under the tongue or in the buccal pouch at the first sign of an acute anginal attack. Allow tablet to dissolve without swallowing. One additional tablet may be administered every 5 minutes until relief is obtained... Administer nitroglycerin sublingual tablets at rest, preferably in the sitting position.' Strengths are pinned by §3: 'Sublingual tablets, 0.3 mg; 0.4 mg; 0.6 mg'. Verbatim, UK SPC §4.2 (infusion): 'The dose of Glyceryl Trinitrate should be adjusted to meet the individual needs of the patient. The recommended dosage range is 10 - 200 micrograms/min but up to 400 micrograms/min may be necessary during some surgical procedures.' Indication-specific starting rates in the same SPC: unstable angina 'An initial dose of 10 micrograms/min is recommended with increments of 10 micrograms/min being made at approximately 30 minute intervals'; perioperative myocardial ischaemia 'may be started with a dose of 15 - 20 micrograms/min, with subsequent increments of 10 - 15 micrograms/min'; unresponsive congestive heart failure 'The recommended starting dose is 20 - 25 micrograms/min... increased in steps of 20-25 micrograms/min every 15 - 30 minutes'; control of hypertension or induced hypotension during surgery 'A starting dose of 25 micrograms/min... increased by increments of 25 micrograms/min at 5 minute intervals'. The 400 micrograms/min figure is an infusion RATE quoted for surgical procedures, not a ceiling for the doses above, which is why it is not in maxDose. Administration: 'Glyceryl Trinitrate should not be given by bolus injection' and must be given 'by means of a micro-drip set infusion pump or similar device which permits maintenance of constant infusion rate'. Dilution example from §4.2: 'To obtain an admixture of Glyceryl Trinitrate at a concentration of 100 micrograms/ml, add 50 ml Glyceryl Trinitrate solution (containing 50 mg glyceryl trinitrate) to 450 ml of infusion vehicle to give a final volume of 500 ml. A dosage of 100 micrograms/min. can be obtained by giving 60 ml of the admixture per hour.' PAEDIATRIC: paedDose is null because both labels decline to dose children - UK SPC §4.2 'The safety and efficacy of Glyceryl Trinitrate has not yet been established in children'; US label §8.4 'The safety and effectiveness of nitroglycerin in pediatric patients have not been established.' ELDERLY: UK SPC §4.2 'There is no evidence that a posology adjustment is required in the elderly'; the US label advises cautious dose selection, 'usually starting at the low end of the dosing range'.

Dose adjustments

Renal

UK SPC §4.2: 'Additional dose adjustments in patients with severe hepatic insufficiency or severe renal failure may be necessary and require additional monitoring.' No numeric adjustment is given. §4.4 adds: 'Caution should be exercised in patients with severe liver or renal disease, hypothermia, hypothyroidism.' The US sublingual-tablet label carries no renal dosing statement in any fetched section.

Hepatic

UK SPC §4.2: 'Additional dose adjustments in patients with severe hepatic insufficiency or severe renal failure may be necessary and require additional monitoring.' No numeric adjustment is given; §4.4 repeats that caution is needed in severe liver disease. The US sublingual-tablet label carries no hepatic dosing statement in any fetched section.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • UK SPC §4.3: 'Hypersensitivity to the active substance, other nitrates or any of the excipients listed in Section 6.1'
  • UK SPC §4.3: 'During nitrate therapy, phosphodiesterase inhibitors type 5 (PDE5) (e. g. sildenafil, vardenafil, tadalafil) must not be used because PDE5 inhibitors may amplify the vasodilatory effects of Glyceryl Trinitrate resulting in severe hypotension'; §4.4 adds it 'must not be used in patients known to be taking phosphodiesterase inhibitor-containing products ... in the intervening 24 hours (48 hours for tadalafil)'
  • UK SPC §4.3: 'During nitrate therapy, the soluble guanylate cyclase stimulator riociguat must not be used'
  • UK SPC §4.3: 'Acute circulatory failure (shock, collapse)' and 'Cardiogenic shock (unless a sufficient end-diastolic pressure is maintained by appropriate measures)'
  • UK SPC §4.3: 'Uncorrected hypovolaemia and hypotensive shock'
  • UK SPC §4.3: 'Severe anaemia' - the US label explains that 'large doses of nitroglycerin may cause oxidation of hemoglobin to methemoglobin and could exacerbate anemia'
  • UK SPC §4.3: 'Severe cerebral haemorrhage', 'Head trauma' and 'Conditions associated with an increased intracranial pressure'
  • UK SPC §4.3: 'Arterial hypoxaemia and angina caused by hypertrophic obstructive cardiomyopathy'
  • UK SPC §4.3: 'Myocardial insufficiency due to obstruction, aortic or mitral stenosis, hypertrophic obstructive cardiomyopathy or constrictive pericarditis'
  • UK SPC §4.3: 'Constrictive pericarditis' and 'Pericardial tamponade'
  • UK SPC §4.3: 'Toxic pulmonary oedema'

Side effects

  • Very common (>=1/10), UK SPC §4.8: headache - 'Like other nitrate preparations, Glyceryl Trinitrate commonly causes dose-dependent headaches due to cerebral vasodilation. These often regress after a few days despite the maintenance of therapy.'
  • Common (>=1/100 to <1/10), UK SPC §4.8: dizziness (including postural dizziness), somnolence; tachycardia; orthostatic hypotension; asthenia
  • Uncommon (>=1/1,000 to <1/100), UK SPC §4.8: enhanced angina pectoris symptoms; circulatory collapse (sometimes accompanied by bradyarrhythmia and syncope); nausea, vomiting; allergic skin reactions (e.g. rash) and allergic contact dermatitis; pruritus, burning, erythema and irritation
  • Very rare (<1/10,000), UK SPC §4.8: heartburn
  • Frequency not known, UK SPC §4.8: palpitations; flushing; hypotension; exfoliative dermatitis; generalised rash; increased heart rate
  • UK SPC §4.8: 'Severe hypotensive responses have been reported for organic nitrates and include nausea, vomiting, restlessness, pallor and excessive perspiration.'
  • UK SPC §4.8: 'During treatment with Glyceryl Trinitrate, a temporary hypoxemia may occur due to a relative redistribution of the blood flow in hypoventilated alveolar areas. Particularly in patients with coronary artery disease this may lead to a myocardial hypoxia.'
  • UK SPC §4.4: methaemoglobinaemia has been reported - and 'Treatment of methaemoglobinaemia with methylene blue is contraindicated in patients with glucose-6-phosphate deficiency or methaemoglobin-reductase deficiency'
  • US label §6: 'Most common adverse reactions occurring at a frequency greater than 2% are headache, dizziness and paresthesia'; also vertigo, weakness, palpitation and other manifestations of postural hypotension, syncope, flushing, drug rash and exfoliative dermatitis
  • Tolerance, UK SPC §4.4: 'The development of tolerance and cross tolerance to other nitro compounds has been described.' US label §5.1: 'Excessive use may lead to the development of tolerance. Only the smallest dose required for effective relief of the acute angina attack should be used.'

Monitoring

  • UK SPC §4.2: 'During Glyceryl Trinitrate administration there should be close haemodynamic monitoring of the patient. The posology of Glyceryl Trinitrate i.v. should be adjusted to achieve the desired clinical response.'
  • UK SPC §4.4: in low filling pressures - e.g. acute myocardial infarction or impaired left ventricular function - 'Reducing systolic blood-pressure below 90 mmHg must be avoided'.
  • UK SPC §4.2: 'Additional dose adjustments in patients with severe hepatic insufficiency or severe renal failure may be necessary and require additional monitoring.'
  • Watch for methaemoglobinaemia (UK SPC §4.4) and for the temporary hypoxaemia / ventilation-perfusion mismatch described in §4.4 and §4.8, particularly in patients with severe anaemia (including G6PD-deficiency forms), lung disease or ischaemic heart failure.
  • US label §2 (sublingual): if pain persists after a total of 3 tablets in a 15-minute period, or if the pain differs from what is typically experienced, seek prompt medical attention.
  • Ask about PDE-5 inhibitors and riociguat before every dose - UK SPC §4.4 requires patients on GTN to be warned not to take PDE-5 inhibitor products.
  • Infusion set material, UK SPC §4.4: PVC or polyurethane 'has been shown to induce a loss of the active substance due to adsorption. If these materials are used the dose must be adjusted to suit patient's needs.'

Clinical monograph

How it works

It is metabolised to nitric oxide, which raises vascular smooth-muscle cyclic GMP to cause vasodilatation, predominantly venous, reducing cardiac preload and myocardial oxygen demand and relieving coronary spasm.

Prescribing in practice

  • It is contraindicated with phosphodiesterase-5 inhibitors such as sildenafil because the combination can cause profound, life-threatening hypotension.
  • Sublingual tablets and sprays act within minutes for acute angina; if chest pain is not relieved after repeated dosing, emergency help should be sought as this may indicate myocardial infarction.
  • Continuous nitrate exposure causes tolerance, so a nitrate-free interval is needed with longer-acting use, and abrupt withdrawal of intravenous nitrate should be avoided.

Monitoring

With intravenous use monitor blood pressure and heart rate closely; for oral and sublingual use review symptom control and tolerance.

Counselling the patient

  • Sit down before using a sublingual dose as it can cause headache and dizziness.
  • Never use with erectile-dysfunction medicines such as sildenafil.
  • If angina is not relieved after repeated doses, call emergency services.

Evidence & guidelines

Sublingual and intravenous GTN are long-standing guideline-recommended treatments for angina and acute cardiogenic pulmonary oedema.

Reference: ESC ACS guidelines; NICE NG106; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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