Cimetid

Indications

Cimetidine is an H2 blocker that reduces stomach acid. It is used to treat and prevent stomach and duodenal ulcers, gastro-oesophageal reflux disease (acid reflux and heartburn), indigestion caused by acid, Zollinger-Ellison syndrome (a rare condition with very high acid), and to protect the stomach in some situations such as before anaesthesia.

How It Works

Cimetidine blocks histamine H2 receptors on the acid-producing cells of the stomach lining. This lowers the amount of acid made, both during the day and at night, which relieves heartburn and allows ulcers and an inflamed food pipe to heal.

Dosage and Administration

Adults: for ulcers, usually 400 mg twice a day (with breakfast and at bedtime) or 800 mg at bedtime, for at least 4 to 8 weeks, as prescribed. For reflux disease, usually 400 mg four times a day or 800 mg twice a day for 4 to 8 weeks, as prescribed. For occasional heartburn, 200 mg can be taken when symptoms occur, up to the limit stated on the label. Swallow tablets with water. The dose is lower in kidney disease. Injections, where used, are given by a doctor or nurse. Children: as prescribed.

Interactions

Cimetidine slows the liver's breakdown of many medicines, raising their levels:

• Warfarin: higher bleeding risk; INR should be checked.
• Phenytoin, Theophylline, Lidocaine and Carbamazepine: risk of toxicity.
• Some benzodiazepines (such as Diazepam), tricyclic antidepressants and Metoprolol or Propranolol.
• Ketoconazole, Itraconazole, Atazanavir and Dasatinib: absorption is reduced because they need stomach acid; avoid together or separate doses.
• Antacids: take at least 1 hour apart.

Contraindications

Do not take if you are allergic to cimetidine or other H2 blockers.

Side Effects

• Headache, dizziness, tiredness.
• Diarrhoea, rash, muscle pain.
• Breast swelling or tenderness in men and reduced sex drive or erection problems with long-term, high doses.
• Confusion, especially in elderly or very ill people.
• Rarely: slow heartbeat, liver inflammation, low blood counts.

Get urgent medical help for swelling of the face or throat, difficulty breathing, a severe skin rash, yellow skin or eyes, unusual bleeding or bruising, confusion or hallucinations, black or bloody stools, or vomiting blood.

Pregnancy and Lactation

Cimetidine crosses the placenta and passes into breast milk. Use in pregnancy only if your doctor advises it. It is generally not recommended while breastfeeding; other acid-reducing medicines may be preferred.

Precautions and Warnings

See a doctor before using it for indigestion if you are over 45 with new symptoms, have unintended weight loss, difficulty swallowing, persistent vomiting, black stools or anaemia, as these may signal a more serious condition, including stomach cancer, which cimetidine can mask. Use with care in kidney or liver disease and in the elderly. Tell your doctor about all medicines you take because of its many interactions.

Overdose

Overdose is usually not serious but may cause confusion, slow heartbeat or breathing problems, especially in high amounts. Seek medical help.

Therapeutic Class

H2 receptor antagonist (acid-reducing medicine).

Storage

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