G Sorbide

Indications

Isosorbide Dinitrate is a nitrate medicine used to prevent and treat angina (chest pain caused by reduced blood flow to the heart). The fast acting sublingual (under the tongue) tablets relieve an attack or prevent one before activities known to bring on pain. Regular tablets help prevent angina, and the medicine is also sometimes used with Hydralazine for heart failure.

How It Works

Isosorbide Dinitrate releases nitric oxide in the body, which relaxes and widens blood vessels, especially veins. This reduces the amount of blood returning to the heart and the pressure the heart pumps against, so the heart needs less oxygen. It also widens the heart's own arteries, improving blood supply to the heart muscle.

Dosage and Administration

For an angina attack: place one 5 mg sublingual tablet under the tongue and let it dissolve while sitting down; it may be repeated as directed by the doctor. If chest pain is not better 5 minutes after the first dose, call for emergency help. For prevention, take regular tablets exactly as prescribed, often 2 to 3 times a day with a nitrate free gap (for example overnight) to stop the medicine losing effect.

Interactions

• Never take with Sildenafil, Tadalafil, Vardenafil or Riociguat: blood pressure can fall dangerously.
• Other blood pressure medicines, alcohol and some antidepressants can add to low blood pressure and dizziness.
• Heparin effect may be reduced when given with intravenous nitrates.

Contraindications

• Allergy to nitrates.
• Very low blood pressure, shock or severe anaemia.
• Raised pressure in the brain, such as after head injury or brain bleeding.
• Certain heart conditions such as severe aortic or mitral valve narrowing, hypertrophic obstructive cardiomyopathy or constrictive pericarditis.
• Use with Sildenafil or similar medicines.

Side Effects

Headache is very common, especially at the start, and usually eases with time. Others include flushing, dizziness, light headedness on standing, fast heartbeat, nausea and weakness.

Get urgent medical help if you faint, have a very slow or very fast heartbeat, chest pain that does not improve within 5 minutes, blue lips or fingertips, or swelling of the face or throat.

Pregnancy and Lactation

Use in pregnancy and breastfeeding only if the doctor considers it necessary, as information is limited.

Precautions and Warnings

• Sit or lie down when taking a sublingual tablet, as it can cause dizziness.
• Do not stop regular treatment suddenly; angina may worsen.
• Avoid alcohol, which increases dizziness.
• Use with care in low blood pressure, recent heart attack, and in older people.

Overdose

Overdose causes severe headache, flushing, very low blood pressure, fainting, fast heartbeat and, rarely, blue colouring of the skin due to methaemoglobinaemia. Lie the person down with legs raised and seek emergency help.

Therapeutic Class

Organic nitrate, antianginal vasodilator.

Storage

Store below 30°C in a dry place, away from light and out of the reach of children. Keep tablets in their original pack.