Home Drug Guide Cimetidine

Drug Guide

Generic Name

Cimetidine

Brand Names Tagamet, Tagamet Hb, Tagamet Hb 200

Classification

Therapeutic: Digestive system agent (Ulcer-healing agent)

Pharmacological: H2 histamine receptor antagonist

FDA Approved Indications

Duodenal ulcer
Gastric ulcer
GERD (Gastroesophageal reflux disease)
Erosive esophagitis
Zollinger-Ellison syndrome

Mechanism of Action

Cimetidine decreases stomach acid production by blocking H2 histamine receptors on gastric parietal cells, leading to reduced acid secretion.

Dosage and Administration

Adult: Typically 800 mg daily in divided doses or as a single dose at bedtime, adjusted based on clinical response.

Pediatric: Dosage varies; generally 20-40 mg/kg/day divided into 2-4 doses for children aged 1-16 years.

Geriatric: Use with caution; monitor kidney function as decreased clearance is common in elderly.

Renal Impairment: Adjust dose based on renal function, often reduced for impaired renal clearance.

Hepatic Impairment: Use with caution; hepatic metabolism may be affected, and dose adjustments may be necessary.

Pharmacokinetics

Absorption: Well absorbed orally, with bioavailability around 60-70%.

Distribution: Widely distributed; crosses the blood-brain barrier and placental barrier.

Metabolism: Metabolized minimally in the liver, with some hepatic metabolism.

Excretion: Primarily excreted unchanged in the urine.

Half Life: Approximately 1.5 to 2 hours, prolonged in renal impairment.

Contraindications

Hypersensitivity to cimetidine or other H2 blockers.

Precautions

Use with caution in elderly, patients with renal or hepatic impairment, and in pregnancy/lactation. Monitor for CNS adverse effects in elderly and those with renal impairment.

Adverse Reactions - Common

Headache (Common)
Diarrhea or constipation (Common)
Gynecomastia in men and galactorrhea in women (Less common)

Adverse Reactions - Serious

CNS effects like confusion, hallucinations (more common in elderly or renal impairment) (Rare)
Liver dysfunction, hepatitis (Rare)
Blood dyscrasias (Very rare)

Drug-Drug Interactions

Warfarin (increased bleeding risk)
Phenytoin (altered metabolism)
Theophylline

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Assessment: Monitor for signs of bleeding, CNS effects, and liver function. Assess renal function for dose adjustments.

Diagnoses:

Risk for bleeding
Impaired renal function

Implementation: Administer as prescribed; monitor for adverse effects; educate patient on signs of bleeding and CNS effects.

Evaluation: Assess symptom relief and monitor for adverse reactions.

Patient/Family Teaching

Take medication as directed, usually with or without food.
Report any unusual side effects such as mental confusion, dizziness, or signs of bleeding.
Avoid alcohol and smoking, as these may aggravate gastrointestinal symptoms.

Special Considerations

Black Box Warnings: N/A

Genetic Factors: N/A

Lab Test Interference: May affect serum creatinine and liver function tests.

Overdose Management

Signs/Symptoms: Dizziness, confusion, hallucinations, slurred speech, hypotension, dry mouth.

Treatment: Supportive care; activated charcoal if ingestion was recent; dialysis may be considered in severe cases, especially in renal impairment.

Storage and Handling

Storage: Store at room temperature away from moisture and light.

Stability: Stable when stored properly.