cimetidine, Tagamet

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GENERIC NAME: cimetidine


DRUG CLASS AND MECHANISM: Cimetidine belongs to a class of medications called histamine H2-antagonists. Histamine is a natural chemical that stimulates stomach cells to produce acid. Histamine H2-antagonists inhibit the action of histamine on the acid-producing cells of the stomach and reduce stomach acid. Cimetidine was approved by the FDA in 1977.



PREPARATIONS: Tablets: 200, 300, 400, and 800 mg. Liquid: 300 mg/5 mL. Injection: 150 mg/mL.

STORAGE: Store at room temperature 15-30°C (59-86°F).

PRESCRIBED FOR: Cimetidine is used for the treatment of duodenal ulcers, active gastric ulcers, gastroesophageal reflux disease (GERD), pathological hypersecretory conditions (e.g., Zollinger Ellison syndrome), heartburn and the prevention of gastrointestinal bleeding.


  • Duodenal ulcers are treated with 800 mg at bedtime, 300 mg 4 times a day at meal times and bedtime, or 400 mg twice a day for 4-6 weeks. Maintenance therapy is 400 mg at bedtime.
  • Active gastric ulcers are treated with 800 mg at bedtime or 300 mg 4 times a day at meal times and bedtime for up to 8 weeks.
  • The regimen for GERD is 800 mg twice a day or 400 mg 4 times a day for 12 weeks.
  • Pathological hypersecretory conditions are treated with 300 mg 4 times daily up to 2400 mg daily.
  • Heartburn, indigestion and sour stomach may be treated with 200 mg once or twice daily and may be administered up to 30 minutes before ingestion of food or beverages that may cause heart burn.
  • For hospitalized patients who cannot take oral medications, 300 mg of cimetidine may be administered by intravenous or intramuscular injection every 6-8 hours. A continuous intravenous infusion of 37.5 to 50 mg/hour also may be used.

DRUG INTERACTIONS: Cimetidine may increase the blood levels of several drugs by reducing their elimination by the liver. This interaction may occur between cimetidine and warfarin (Coumadin), a commonly used blood thinning agent. Patients taking both medications should have frequent blood monitoring to avoid accumulation of high levels of warfarin leading to excessive blood thinning and bleeding. Cimetidine also may increase the blood levels phenytoin, theophylline, lidocaine, amiodarone, metronidazole, loratadine, calcium channel blockers (e.g., diltiazem, felodipine, nifedipine), bupropion, carbamazepine and fluvastatin. Because cimetidine reduces stomach acid, it may reduce the absorption of drugs (e.g., ketoconazole) that are best absorbed in acidic conditions. Such drugs should be administered at least 2 hours before the administration of cimetidine.

PREGNANCY: There are no adequate studies of cimetidine in pregnant women.

NURSING MOTHERS: Cimetidine is excreted in breast milk.

SIDE EFFECTS: Side effects due to cimetidine are rare and generally reversible once the medication is stopped. Minor side effects include constipation, diarrhea, fatigue, headache, insomnia, muscle pain, nausea, and vomiting. Major side effects include confusion and hallucinations (usually in elderly or critically ill patients); enlargement of the breasts; impotence (usually seen in patients on high doses for prolonged periods); decreased white blood cell counts. Other side effects include irregular heartbeat, impotence, rash, visual changes, allergic reactions, and hepatitis.

Reference: FDA Prescribing Information

Last Editorial Review: 12/13/2005

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