Drug reference

Cimetidine

h2 Receptor Antagonist · Antiulcerant

h2 Receptor AntagonistAntiulcerant

CDSCO approvedOTC

EXCRETION

—

not curated

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

FDA category + note

Top interactionssee all 12 →

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Mechanism

Cimetidine reduces gastric acid output by competitively blocking histamine H2-receptors in the stomach. This action leads to a decrease in acid secretion, providing symptomatic relief and facilitating ulcer healing. It is used to manage conditions like gastro-oesophageal reflux disease and various types of ulceration.

Indications

Benign duodenal ulcerationBenign gastric ulcerationGastro-oesophageal reflux diseaseProphylaxis of bleeding from gastroduodenal erosions in hepatic comaProphylaxis of bleeding from gastroduodenal erosions in other conditions requiring intensive careReduction of acid aspiration risk in obstetric patients at delivery (Mendelson's syndrome)Short-term symptomatic relief of heartburnShort-term symptomatic relief of dyspepsiaShort-term symptomatic relief of hyperacidityProphylactic management of nocturnal heartburnShort bowel syndromeGastric ulcer (to promote healing)Duodenal ulcer (to promote healing)Gastroesophageal reflux disease (uncomplicated)Prevention of stress ulcersDuodenal ulcerGastric ulcerStress ulcers and gastritisZollinger-Ellison syndromeGastroesophageal reflux disease (GERD) (mild or stage-1 cases)Prophylaxis of aspiration pneumoniaUrticaria (adjuvant to H1 antagonist)Interstitial Cystitis/Bladder Pain Syndrome (off-label, limited evidence)

Dosing

Adult: Benign duodenal ulceration: 400 mg orally twice daily for at least 4 weeks (with breakfast and at night), or 800 mg orally once daily for at least 4 weeks (at night). May be increased up to 400 mg 4 times a day if necessary. Maintenance: 400 mg orally once daily (at night) or 400 mg orally twice daily (morning and night). Benign gastric ulceration: 400 mg orally twice daily for 6 weeks.…
Pediatric: 20–40 mg/kg/day divided every 6 h for 8–12 weeks
Renal adjustment: Reduce dose to 200 mg 4 times daily if eGFR 30–50 mL/minute/1.73 m2. Reduce dose to 200 mg 3 times daily if eGFR 15–30 mL/minute/1.73 m2. Reduce dose to 200 mg twice daily if eGFR less than 15 mL/minute/1.73 m2.
Hepatic adjustment: Reduce dose due to increased risk of confusion.
Max dose: 1600 mg daily (prescription); 800 mg daily (OTC)

Pharmacokinetics

Onset

Therapeutic levels achieved rapidly after intravenous dosing.

Half-life

1 to 3 h (adults); faster in children (t1/2 reduced by ~30%)

Bioavailability

60–80%

Protein binding

Only a small fraction is protein bound.

Metabolism

Metabolized by FMO3.

Excretion

About 2/3 of a dose is excreted unchanged in urine and bile, the rest as oxidized metabolites.

Contraindications

Undiagnosed gastric malignancy (due to potential for masking symptoms)
Not recommended for treating active ulcers (bleeding ulcers or erosive disease)

Side effects

Common

ConstipationDiarrhoeaDizzinessFatigueHeadacheMyalgiaSkin reactionsDiarrheaDrowsinessMuscular painGynecomastiaImpotenceBowel upsetDry mouthRashes

Serious

Confusion
Depression
Erectile dysfunction
Gynaecomastia
Hallucination
Hepatic disorders
Leucopenia
Tachycardia
Agranulocytosis
Alopecia
Arthralgia
Atrioventricular block
Fever
Galactorrhoea
Pancytopenia
Thrombocytopenia
Vasculitis
CNS effects (confusion, delirium, hallucinations, slurred speech, headaches), primarily with IV administration or in elderly
Various blood disorders (e.g., thrombocytopenia)
Vitamin B12 deficiency
Loss of libido
Impotence
Temporary decrease in sperm count
Transient elevation of plasma aminotransferases (hepatotoxicity is rare)
Confusional state (with rapid or higher dose i.v. injection)
Hallucinations (with rapid or higher dose i.v. injection)
Convulsions (with rapid or higher dose i.v. injection)
Bradycardia (with rapid or higher dose i.v. injection)
Arrhythmias (with rapid or higher dose i.v. injection)
Coma (with rapid or higher dose i.v. injection)
Cardiac arrest (with rapid or higher dose i.v. injection)