Cimetidine: Formula, Indications, Mechanism of Action, Dosage, Side Effects, Warnings, Contraindications and Interactions

It is a histamine H2 receptor antagonist, which inhibits the production of stomach acid.

Cimetidine inhibits gastric acid secretion , as well as pepsin and gastrins.

It is available without a prescription and is used primarily in the treatment of heartburn and peptic ulcers .

The development of longer-acting H2 receptor antagonists with fewer drug interactions and adverse effects, such as ranitidine and famotidine, decreased the use of cimetidine and, although it is still used, cimetidine is no longer among the most widely used drugs in the world. H2 receptor antagonists.

Chemical formula of cimetidine

  • C10H16N6S.


The drug comes as a tablet or liquid to take by mouth and without a prescription (OTC).

Indications of cimetidine

Cimetidine is used to treat heartburn, heartburn, and stomach ulcers.

This medicine is commonly used to:

  • Gastroesophageal reflux disease.
  • Acidity.
  • Gastric hypersecretion.
  • Cutaneous mastocytosis.
  • Carcinoma broncogénico.
  • Duodenal ulcer prophylaxis.
  • Esofagitis erosive.
  • Indigestion.
  • Stomach ulcer.
  • Upper gastrointestinal bleeding.
  • Zollinger-Ellison syndrome.
  • Active duodenal ulcer.
  • Benign gastric ulcers.
  • Duodenal ulcer maintenance therapy.

Mechanism of action

Cimetidine binds to an H2 receptor located on the basolateral membrane of the gastric parietal cell, blocking the effects of histamine.

This competitive inhibition produces a reduction in gastric acid secretion and a reduction in gastric volume and acidity.

It is important to note that these drugs inhibit basal (fasting) and nocturnal acid secretion and that stimulated by food, sham feeding, fundic distension and various pharmacological agents; this property reflects the vital role of histamine in mediating the effects of various stimuli.

The production of pepsin , which is secreted by the main cells of the gastric glands (mainly under cholinergic control), generally falls in parallel with the reduction in the volume of gastric juice.

Cimetidine blocks H2 receptors, which are partly responsible for the inflammatory response, in human skin blood vessels.

Cimetidine dosage

Your dose will depend on the medical condition and response to treatment.

Generally the indicated dose is 1200 mg per day orally, or two to four times a day with meals and at bedtime.

Parenterally, the dose is 300 mg intravenously or intramuscularly every 6 hours.

To prevent heartburn, take cimetidine 30 minutes before eating foods or drinks that usually cause your symptoms.

Side effects

Cimetidine is a well-tolerated and safe drug with a very low incidence of side effects.

However, side effects such as fatigue, dizziness, drowsiness, headache, constipation , diarrhea, and muscle pain have been reported .

Other side effects of cimetidine have been reported, you should tell your doctor immediately if you experience any of the following serious side effects such as:

  • Confusion.
  • Depression .
  • Nervousness.
  • Anxiety.
  • Increase in breast size.
  • Decreased sexual ability.
  • Fast or slow heartbeat
  • Muscle pain and weakness
  • Hallucinations (seeing or hearing things that are not there).
  • Unusual bruising or bleeding.
  • Severe stomach pain or stomach pain that does not go away.
  • Signs of an allergic reaction, including itching, hives , difficulty breathing, tightness in the chest, or swelling of the face, mouth, lips, or tongue.

Warnings and Contraindications

Before taking cimetidine, you should tell your doctor if you have or have ever had:

  • Kidney diseases.
  • Liver diseases
  • Extreme stomach pain or stomach ulcers.
  • PAGE.

In addition, the doctor should be informed if the patient smokes or has swallowing problems before taking cimetidine.

Over-the-counter cimetidine should not be taken for more than two weeks unless directed by your doctor.

You should stop taking this medicine and call your doctor if your symptoms of heartburn, acid indigestion, or a sour taste in your mouth last longer than two weeks.

Cimetidine should be taken for the recommended time, even if the patient feels better.

Stopping treatment too soon can delay the healing process.

This drug is generally not recommended for older adults because it is not as safe as other drugs that can treat the same condition.

In patients over 65 years of age, its use should be restricted and administered only under medical supervision.

Cimetidine should also not be used in children under 12 years of age.

Cimetidine is unlikely to harm an unborn baby, however the doctor should be informed if the patient is pregnant or planning to become pregnant before taking this medication.

Do not take cimetidine if you are breastfeeding, this drug passes into breast milk.

Cimetidine can make you dizzy or drowsy. So it is not advisable to drive cars or machinery.

Alcohol can make drowsiness and dizziness worse.

Cimetidine interactions

Cimetidine can interact with medications such as:

  • Antacids such as maalox, mylanta, and tums.
  • Blood thinners such as warfarin .
  • Antidepressivos como amitriptilina (Elavil), amoxapina (Asendin), clomipramina (Anafranil), desipramina (Norpramin), doxepina (Adapin,Sinequan), imipramina (Tofranil), nortriptilina (Aventyl, Pamelor), protriptilina (Vivactil) y trimipramina (Surmontil).
  • Clordiazepóxido (Librium).
  • Clopidogrel (Plavix).
  • Diazepam (Valium).
  • Digoxin (Lanoxin).
  • Herbal or dietary supplements.
  • Iron salts.
  • Ketoconazole (Nizoral).
  • Lidocaine (Xylocaine).
  • Metronidazole (Flagyl).
  • Nifedipine (Adalat, Procardia).
  • Fenitoína (Dilantin).
  • Propranolol (Inderal).
  • Teofilina (Theobid, Theo-Dur).