Glyceryl Trinitrate — NZ Medication Guide

What is Glyceryl Trinitrate?

Glyceryl Trinitrate (generic name: glyceryl trinitrate (GTN)) is a medication used primarily for acute angina relief and prevention of angina attacks in coronary artery disease. GTN is funded on the Pharmaceutical Schedule by Pharmac in sublingual spray (Nitrolingual), sublingual tablets, and transdermal patches (GTN Patch).

In New Zealand, GTN sublingual spray (Nitrolingual) and patches are funded under the Pharmaceutical Schedule. All patients with confirmed angina or coronary artery disease should have sublingual GTN readily available at all times. Special Authority is not required. Cardiac rehabilitation guidelines from the Heart Foundation of New Zealand recommend patient education on correct GTN use as part of secondary prevention.

What is Glyceryl Trinitrate Used For?

Glyceryl Trinitrate is prescribed by healthcare professionals in New Zealand for the following indications:

• Acute relief of angina pectoris (chest pain)
• Prophylactic prevention of angina before physical activity or emotional stress
• Management of stable and unstable angina
• Heart failure (IV formulations in hospital settings)
• Hypertensive emergencies (IV, hospital use)

How Does Glyceryl Trinitrate Work?

Glyceryl trinitrate (GTN) is an organic nitrate that releases nitric oxide in vascular smooth muscle, causing venodilation and mild arterial dilation. This reduces cardiac preload and afterload, decreasing myocardial oxygen demand and relieving ischaemic chest pain. GTN also dilates coronary arteries, improving blood supply to the heart muscle.

How to Take Glyceryl Trinitrate

For acute angina: spray 1–2 sprays under the tongue (sublingual) at the onset of chest pain, or use a sublingual tablet. Sit down before use as GTN can cause dizziness. If pain persists after 5 minutes, repeat the dose. If pain remains after 3 doses (15 minutes), call 111 immediately — this may indicate a heart attack. For prevention: apply a GTN patch to clean, dry skin (usually the chest, upper arm, or back) and remove after 12–14 hours to prevent tolerance. Store sublingual spray or tablets in the original container away from heat and light.

Common Side Effects

Like all medications, Glyceryl Trinitrate may cause side effects. Common side effects include:

• Headache (very common — due to vasodilation)
• Flushing and feeling of warmth
• Dizziness or lightheadedness
• Low blood pressure (hypotension), especially when standing
• Skin irritation at patch application site
• Tolerance with continuous use (prevent by having nitrate-free periods)

Serious Side Effects — Seek Medical Attention

Contact your doctor or call 111 immediately if you experience any of the following serious effects:

• Severe hypotension — fainting, loss of consciousness
• Methaemoglobinaemia (rare) — blue-grey skin discolouration, confusion
• Angina not relieved after 3 doses in 15 minutes — call 111 (possible MI)
• Hypersensitivity reaction — rash, difficulty breathing

Drug Interactions

Always inform your prescriber and pharmacist of all medications, supplements, and herbal products you are taking. Notable interactions with Glyceryl Trinitrate include:

• Phosphodiesterase-5 inhibitors (sildenafil, tadalafil, vardenafil) — CONTRAINDICATED; severe life-threatening hypotension
• Other antihypertensives — additive blood pressure lowering effect
• Alcohol — enhanced hypotensive effect
• Heparin — GTN infusions may reduce heparin efficacy
• Ergotamine — may reduce GTN efficacy and cause coronary vasoconstriction

New Zealand Prescribing Information

In New Zealand, GTN sublingual spray (Nitrolingual) and patches are funded under the Pharmaceutical Schedule. All patients with confirmed angina or coronary artery disease should have sublingual GTN readily available at all times. Special Authority is not required. Cardiac rehabilitation guidelines from the Heart Foundation of New Zealand recommend patient education on correct GTN use as part of secondary prevention.

Frequently Asked Questions

How do I use GTN spray correctly?

Sit or lie down before using GTN spray. Hold the spray upright and press the button firmly under your tongue — do not inhale. Close your mouth and wait for the spray to be absorbed. Take 1–2 sprays at the start of chest pain. If pain is not relieved in 5 minutes, take a second dose. After 3 doses (15 minutes) with no relief, call 111 immediately.

Why do I get a headache after GTN?

Headaches are the most common side effect of GTN and occur because the medication dilates blood vessels throughout the body, including in the brain. The headaches usually improve as your body adjusts to the medication. Paracetamol can be taken for GTN-related headaches if needed.

Can I take GTN with my erectile dysfunction medication?

No — this is a dangerous combination. GTN and medications like sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra) together can cause a severe, potentially fatal drop in blood pressure. Never use these medications together. Discuss safe alternatives with your doctor.

References & Further Information

The following New Zealand and international resources were used to inform this page:

• New Zealand Formulary — Glyceryl Trinitrate
• Pharmac — Funded Medicines Schedule
• Heart Foundation New Zealand — Angina Guidelines
• Medsafe — Nitrolingual Consumer Information

Reviewed by a Registered Pharmacist — KiwiMeds New Zealand