Cimetidine Drug Profile

What is Cimetidine?

Cimetidine is a histamine H2-receptor antagonist, commonly known as an H2 blocker, that reduces stomach acid production. It belongs to a class of medications used to treat acid-related digestive disorders. Cimetidine was one of the first H2 blockers developed and has been widely used since the 1970s for conditions involving excess stomach acid.

Uses

Cimetidine is approved for several acid-related conditions:

• Peptic ulcers: Treats and prevents stomach and duodenal ulcers by reducing acid that can irritate ulcerated tissue
• Gastroesophageal reflux disease (GERD): Helps heal esophageal inflammation caused by stomach acid backing up into the esophagus
• Zollinger-Ellison syndrome: Manages excessive acid production caused by gastrin-secreting tumors
• Heartburn and acid indigestion: Provides relief from occasional digestive discomfort related to excess acid
• Erosive esophagitis: Helps heal damage to the esophageal lining caused by chronic acid exposure

How it works

Cimetidine works by blocking histamine H2 receptors located on acid-producing cells in the stomach lining called parietal cells. When these receptors are blocked, the cells produce significantly less hydrochloric acid. This reduction in stomach acid allows ulcers to heal, reduces inflammation in the esophagus, and provides relief from acid-related symptoms.

Side effects

Common side effects include:

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• Headache
• Dizziness
• Diarrhea
• Constipation
• Nausea
• Fatigue
• Muscle pain
• Skin rash

Serious side effects to watch for:

• Confusion or mental changes, especially in elderly patients
• Gynecomastia (breast enlargement) in men with long-term use
• Severe allergic reactions with difficulty breathing or swelling
• Irregular heartbeat or chest pain
• Signs of liver problems such as yellowing of skin or eyes

Warnings and precautions

• Kidney impairment: Patients with reduced kidney function may need dosage adjustments as cimetidine is primarily eliminated through the kidneys
• Elderly patients: More susceptible to central nervous system side effects like confusion and should be monitored closely
• Pregnancy and breastfeeding: Should be used only when clearly needed during pregnancy; cimetidine passes into breast milk
• Liver disease: Patients with liver impairment may require monitoring as cimetidine can affect liver enzyme activity
• Gastric malignancy: Symptoms should be properly evaluated before treatment, as acid reduction may mask signs of stomach cancer

Interactions

Cimetidine has numerous drug interactions due to its effects on liver enzymes:

• Warfarin: Cimetidine can increase warfarin levels, raising bleeding risk and requiring INR monitoring
• Theophylline: Blood levels may increase, potentially causing toxicity symptoms like nausea and irregular heartbeat
• Phenytoin: Cimetidine can increase phenytoin levels, potentially leading to increased side effects
• Ketoconazole and itraconazole: Reduced stomach acid decreases absorption of these antifungal medications
• Calcium channel blockers: Blood levels may increase, potentially causing low blood pressure or heart rhythm changes
• Tricyclic antidepressants: Cimetidine may increase levels of these medications, intensifying side effects
• Benzodiazepines: Some benzodiazepines may have increased effects when taken with cimetidine
• Iron supplements: Reduced stomach acid can decrease iron absorption, potentially affecting treatment of iron deficiency

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Dosage

Typical adult dosages vary depending on the condition being treated:

• Active ulcer disease: 800 mg at bedtime or 400 mg twice daily for 4-6 weeks
• Ulcer prevention: 400 mg at bedtime
• GERD: 400 mg twice daily or 800 mg twice daily for more severe cases
• Heartburn relief: 200 mg as needed, not exceeding 400 mg in 24 hours for self-treatment

Dosage adjustments are necessary for patients with kidney impairment. Treatment duration and specific dosing should always be determined by a healthcare provider based on individual patient factors and response to therapy.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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