ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Nitrate / Acute Angina Pregnancy: Use with caution — sublingual GTN may be used for acute hypertensive emergencies in pregnancy; IV GTN used in pre-eclampsia/eclampsia management. Monitor fetal heart rate.

Glyceryl Trinitrate (Sublingual / IV)

Brand names: GTN spray (Nitrolingual), GTN tablets (Nitrostat), IV: Nitronal

Adult dose

Dose: Sublingual spray: 400 mcg (1 spray) under the tongue; repeat after 5 minutes if needed (max 3 sprays in 15 minutes). IV infusion: 10-200 mcg/min, titrated.
Route: Sublingual spray or tablet; IV infusion
Frequency: PRN sublingual (max 3 doses/episode); continuous IV infusion
Max: 3 sprays per acute episode (sublingual); 200 mcg/min (IV)
Sublingual: rapid onset (1-3 min); short duration (20-30 min). Patient should sit down before use (postural hypotension). IV: used in acute HF, ACS, hypertensive urgency — tolerance develops within 24-48h (nitrate-free period needed). Use glass bottle and non-PVC tubing — GTN adsorbs to PVC.

Paediatric dose

Dose: 1-3 mcg/min/kg
Route: IV infusion
Frequency: Continuous infusion
Max: 10 mcg/kg/min
Specialist paediatric cardiology for IV use. Sublingual not licensed in children.

Dose adjustments

Renal

No dose adjustment required

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Specialist paediatric cardiology for IV use. Sublingual not licensed in children.

Clinical pearls

  • Patient education for sublingual GTN: (1) sit down first — standing causes postural hypotension and fainting; (2) spray or place tablet under tongue; (3) wait 5 minutes; (4) if pain persists after 3 doses in 15 minutes — CALL 999 (possible MI). This 3-dose rule is critical.
  • PVC adsorption: IV GTN adsorbs significantly to PVC administration sets — up to 40-80% lost. Use non-PVC (polyethylene) tubing and glass bottles. If PVC unavoidable, increase dose accordingly.
  • GTN spray vs tablets: spray has longer shelf life (3 years vs 8 weeks for sublingual tablets once opened). Spray is preferred for most patients — tablets lose potency rapidly after opening.
  • IV GTN in acute HF: reduces pulmonary congestion by venodilation (reduces preload). Start at 10-20 mcg/min. Tolerance develops at continuous doses — use intermittent boluses or nitrate-free periods in prolonged use.
  • Methaemoglobinaemia: high-dose IV GTN over many hours can cause methaemoglobinaemia (GTN metabolites oxidise haemoglobin). Pulse oximetry reads falsely high (~85%) — co-oximetry needed. Treatment: methylene blue 1-2 mg/kg IV.

Contraindications

  • Concomitant PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) — ABSOLUTE (potentially fatal hypotension)
  • Concomitant riociguat — ABSOLUTE
  • Severe hypotension (systolic <90 mmHg)
  • Hypovolaemia
  • HOCM
  • Severe aortic stenosis
  • Raised intracranial pressure

Side effects

  • Headache (vasodilation — almost universal at initiation)
  • Postural hypotension/syncope (patient must sit down — advise before use)
  • Flushing
  • Tachycardia (reflex)
  • Tolerance (IV — use intermittent dosing or nitrate-free periods)
  • Methaemoglobinaemia (IV — high doses, prolonged infusion)

Interactions

  • PDE-5 inhibitors — ABSOLUTE CONTRAINDICATION (minimum 24h gap after sildenafil, 48h after tadalafil before any nitrate)
  • Riociguat — ABSOLUTE CONTRAINDICATION
  • Antihypertensives/diuretics — additive hypotension
  • Ergotamine — nitrates can precipitate ergotamine-induced vasospasm

Monitoring

  • Blood pressure (sitting and standing — sublingual; continuous — IV)
  • Heart rate (reflex tachycardia)
  • Headache symptoms
  • SpO2 (methaemoglobinaemia sign: SpO2 ~85% despite adequate oxygenation — prolonged IV)

Reference: BNFc; BNF 90; ESC Stable CAD Guidelines 2019; NICE CG126 (Stable Angina); NICE NG185 (ACS); SPC Nitrolingual. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways