Cimetidine

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Drugs Dictionary: Cimetidine

Cimetidine

Trade Name

Tagamet, Tagamet HB (OTC); generic cimetidine

Classification

Histamine H2-receptor antagonist; antiulcer agent, antacid

Dosage/Route

* Dosage:
- – Tablets: 200 mg, 300 mg, 400 mg, 800 mg
- – Liquid: 300 mg/5 mL
- – Injection: 150 mg/mL
* Route: Oral (PO), intravenous (IV), intramuscular (IM)

Usual Dosage

* Adults:
- – GERD/PUD: 800 mg PO at bedtime or 400 mg PO BID; max 2.4 g/day
- – OTC (Heartburn): 200 mg PO up to BID; max 400 mg/day
- – IV/IM: 300 mg every 6-8 hours; max 2.4 g/day
* Children: 20-40 mg/kg/day PO/IV divided q6h
* Duration: 4-8 weeks (PUD); 2 weeks max for OTC

Mechanism of Action

Competitively blocks histamine H2 receptors on parietal cells in the stomach, reducing gastric acid secretion and increasing gastric pH. Decreases acid-related damage in GERD, ulcers, and stress-induced gastritis

Side Effects & Adverse Effects

* Side Effects: Headache, dizziness, diarrhea, constipation
* Adverse Effects:
- – Gynecomastia, impotence (rare, high doses/long-term; anti-androgenic)
- – Confusion (elderly, high doses, renal/hepatic impairment)
- – Bone marrow suppression (rare; leukopenia, thrombocytopenia)
- – Drug interactions (CYP450 inhibitor; affects warfarin, theophylline)

Nursing Management (Implications & Teachings)

* Implications:
- – Monitor mental status (confusion in elderly), CBC (rare hematologic effects)
- – IV: Dilute in 50-100 mL NS/D5W, infuse over 15-20 min; IM undiluted
- – Assess GI symptoms (pain, bleeding); check renal/liver function (dose adjust)
- – Avoid antacids within 1 hour (interferes with absorption)
* Teachings:
- – Take PO with meals or at bedtime; OTC: 30 min before trigger foods
- – Report confusion, breast changes, or black stools
- – Avoid alcohol, smoking (increases acid)
- – List all meds (drug interaction risk)