Cimetidine

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Generic Name of Cimetidine - Learn More

Cimetidine

Cimetidine Precaution - What You Need to Know

When using cimetidine, several precautions should be considered to avoid adverse outcomes:

- Pregnancy and breastfeeding:
- Cimetidine is categorized as FDA pregnancy category B, which means it is considered safe for use during pregnancy when clearly needed, based on animal studies showing no harm to the fetus. However, due to limited human data, its use should be considered only if the benefits outweigh the risks.
- For breastfeeding mothers, cimetidine is excreted in breast milk, but the amount is minimal and unlikely to affect the infant. However, caution is advised, particularly in neonates or preterm infants, and should be used only if necessary.

- Renal and hepatic impairment:
- Cimetidine is primarily excreted by the kidneys and metabolized by the liver, so patients with renal or hepatic impairments may require dosage adjustments. Patients with renal insufficiency or chronic kidney disease may experience an accumulation of the drug, leading to increased side effects such as confusion, dizziness, or a higher risk of drug interactions.
- In severe liver disease, cimetidine clearance may be reduced, requiring dose adjustment or careful monitoring of side effects.

- Gastrointestinal disorders:
- While cimetidine is used to treat gastrointestinal conditions such as peptic ulcers and gastroesophageal reflux disease (GERD), patients with gastric malignancy (such as gastric cancer) should be closely monitored when using cimetidine, as the drug may mask symptoms of these diseases.
- Prolonged use of cimetidine can also cause gastrointestinal infections by altering the natural gastric pH, which can impact the body’s ability to fight infections.

- CNS effects:
- Cimetidine has been known to cross the blood-brain barrier, leading to central nervous system (CNS) side effects like confusion, headache, dizziness, and in rare cases, hallucinations. This is particularly important in elderly patients or those with existing CNS disorders.

- Drug interactions:
- Cimetidine is a cytochrome P450 (CYP450) enzyme inhibitor, particularly CYP3A4, CYP2C19, and CYP1A2. It can significantly interact with other drugs that rely on these enzymes for metabolism. This may lead to altered drug levels and increased risk of toxicity for certain medications.

Cimetidine Indication - Uses and Benefits

Cimetidine is primarily used for managing conditions associated with excessive stomach acid production. Its main indications include:

- Peptic ulcer disease (PUD):
- Cimetidine is used to treat gastric ulcers and duodenal ulcers by inhibiting acid secretion. It works by blocking histamine H2 receptors in the stomach lining, which reduces acid production, aiding in the healing of ulcers and alleviating symptoms like pain and discomfort.

- Gastroesophageal reflux disease (GERD):
- Cimetidine is used in the treatment of GERD, a condition where stomach acid backs up into the esophagus, causing heartburn, regurgitation, and damage to the esophagus. By inhibiting acid production, it helps alleviate these symptoms and prevents esophageal damage.

- Zollinger-Ellison syndrome:
- Cimetidine can be used to manage Zollinger-Ellison syndrome, a rare condition where the stomach produces excess acid due to gastrin-secreting tumors. Cimetidine reduces acid secretion, helping to control the disease and manage related symptoms.

- Off-label uses:
- While not officially approved for all, cimetidine has been studied for use in the management of acid reflux conditions beyond GERD, such as laryngopharyngeal reflux (LPR). It is sometimes also used off-label to treat conditions like urticaria or chronic idiopathic urticaria, due to its potential role in blocking histamine activity, though further evidence is needed.

Cimetidine Contraindications - Important Warnings

Cimetidine has several contraindications that should be considered before prescribing:

- Hypersensitivity:
- Cimetidine should not be used in patients with a known allergy or hypersensitivity to the drug or any of its components. Symptoms of an allergic reaction can include skin rash, itching, swelling, and difficulty breathing.

- Severe renal impairment:
- In patients with severe renal impairment, cimetidine should be used with extreme caution, as decreased renal clearance can lead to drug accumulation and an increased risk of side effects. In these cases, dose adjustments or alternative therapies should be considered.

- Severe hepatic disease:
- Cimetidine is metabolized by the liver, and in patients with severe liver disease, its metabolism may be significantly impaired, leading to increased drug levels and a heightened risk of toxicity. It is contraindicated in patients with acute liver failure or severe liver dysfunction.

- Drug interactions:
- Cimetidine is contraindicated in certain combinations of drugs due to the potential for significant interactions. Notably, it can interfere with the metabolism of drugs that rely on CYP450 enzymes, including warfarin, theophylline, phenytoin, and benzodiazepines. It is essential to evaluate and manage the risk of drug interactions before initiating therapy.

Cimetidine Side Effects - What to Expect

Cimetidine is generally well-tolerated, but side effects can occur, ranging from mild to more serious:

- Common side effects:
- Headache, dizziness, and fatigue are the most commonly reported side effects of cimetidine.
- Gastrointestinal disturbances, such as nausea, vomiting, diarrhea, or constipation, may occur.

- Serious side effects:
- Confusion, hallucinations, and delirium have been reported in older adults, especially those with renal impairment. These effects are often reversible upon discontinuation of the drug.
- Endocrine effects: Cimetidine can cause gynecomastia (enlarged breast tissue in men) or impotence due to its anti-androgenic properties. These effects are usually reversible after stopping the medication.
- Severe allergic reactions such as anaphylaxis (though rare), characterized by swelling, itching, and trouble breathing, may occur.

- Long-term use:
- Long-term use of cimetidine can increase the risk of gastric infections and potentially affect vitamin B12 absorption, leading to deficiency. Periodic monitoring is advised.

Cimetidine Pregnancy Category ID - Safety Information

2

Cimetidine Mode of Action - How It Works

Cimetidine works as a histamine H2 receptor antagonist. It blocks the action of histamine on the H2 receptors in the parietal cells of the stomach, which are responsible for secreting gastric acid. By inhibiting these receptors, cimetidine reduces gastric acid secretion, helping to treat conditions like peptic ulcers, GERD, and Zollinger-Ellison syndrome.

- Pharmacodynamics: By blocking the H2 receptors, cimetidine decreases both basal and stimulated acid secretion. This results in increased gastric pH, providing relief from symptoms like heartburn and ulcer pain.

- Pharmacokinetics: Cimetidine is well absorbed after oral administration, but its bioavailability can be affected by food. It is metabolized primarily by the liver and excreted through the kidneys. The drug has a half-life of about 2-3 hours and reaches its peak plasma concentration within 1-2 hours after ingestion.

Cimetidine Drug Interactions - What to Avoid

Cimetidine interacts with a range of medications, which can lead to increased drug levels and potential toxicity:

- Anticoagulants (Warfarin):
- Cimetidine can increase warfarin levels by inhibiting the enzyme responsible for its metabolism. This interaction heightens the risk of bleeding. Close monitoring of INR (International Normalized Ratio) is necessary when both drugs are used together, and a dosage adjustment of warfarin may be required.

- Benzodiazepines (Diazepam, Lorazepam):
- By inhibiting CYP3A4, cimetidine can increase the blood levels of benzodiazepines, which may lead to excessive sedation, respiratory depression, or hypotension. Dose reductions or alternative treatments should be considered.

- Phenytoin:
- Cimetidine may increase the levels of phenytoin, an anticonvulsant, by inhibiting its metabolism. This interaction can lead to phenytoin toxicity, manifested by nystagmus, ataxia, and confusion. Careful monitoring of phenytoin blood levels is necessary.

- Theophylline:
- Cimetidine may elevate the plasma concentration of theophylline, a drug used to treat asthma and COPD, increasing the risk of toxicity, which may include tachycardia, nausea, and seizures. Dosage adjustments should be made based on therapeutic drug monitoring.

- Food and alcohol:
- Alcohol can increase the gastric irritation caused by cimetidine and should be consumed in moderation, if at all, while taking the drug. Additionally, food may delay the absorption of cimetidine, though its overall bioavailability is not significantly affected.

Cimetidine Adult Dose - Recommended Dosage

- Peptic ulcer disease: 400 mg twice daily or 800 mg at bedtime for maintenance therapy. For active ulcers, the dose may be increased to 800 mg twice daily for 4-6 weeks.
- GERD: 200-400 mg twice daily for symptom relief.
- Zollinger-Ellison syndrome: Starting dose of 300 mg four times daily, with possible adjustments based on clinical response.

Cimetidine Child Dose - Dosage for Children

- The pediatric dose of cimetidine varies by weight and age. For children aged 1-16 years, doses generally range from 20 mg/kg/day in divided doses for peptic ulcers. Dosage adjustments may be needed for those with renal or hepatic impairment.

Cimetidine Renal Dose - Dosage for Kidney Conditions

- In patients with renal impairment, particularly those with creatinine clearance < 30 mL/min, the dose of cimetidine should be reduced or the dosing interval extended. Monitoring of renal function is important during therapy.