Cimetidine pharmacology
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Cimetidine Mechanism of Action: Histamine H2-Receptor Antagonism
Cimetidine is a specific and competitive antagonist of histamine H2-receptors. It works by blocking these receptors in the gastric mucosa, which leads to a reduction in gastric acid secretion. This effect is observed both in vitro and in vivo, where cimetidine effectively inhibits histamine- and pentagastrin-stimulated acid secretion in animal models and humans. It is less effective against carbachol-stimulated secretion, but it also reduces basal gastric acid output 16.
Pharmacokinetics of Cimetidine: Absorption, Distribution, and Excretion
Cimetidine is well absorbed when taken orally, with a blood half-life of about two hours in humans. It is rapidly excreted by the kidneys, and approximately 70% of the excreted drug remains unchanged. The drug’s effective concentration for 50% inhibition of gastric acid secretion (EC50) is about 2.5 μM in humans 12. Cimetidine’s low acute toxicity and lack of significant long-term toxic effects have been demonstrated in animal studies .
Clinical Uses: Peptic Ulcer Disease and Other Indications
Cimetidine is effective in healing most duodenal ulcers and reducing the frequency of ulcer recurrence. It is also the preferred treatment for Zollinger-Ellison syndrome and has shown efficacy in healing benign gastric ulcers. Some patients with reflux esophagitis benefit from cimetidine, but it is not considered first-line therapy for this condition. There is some evidence suggesting cimetidine may help prevent bleeding from acute gastric erosions and acid aspiration syndrome, but it is not effective for acute upper gastrointestinal hemorrhage or acute pancreatitis 35.
Drug-Drug Interactions: Effects on Renal Drug Elimination
Cimetidine can inhibit renal transporters such as organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1). This inhibition can decrease the clearance and increase the systemic exposure of drugs like procainamide and its metabolite N-acetylprocainamide, leading to potential drug-drug interactions. These effects are important for understanding how cimetidine may alter the pharmacokinetics of other medications eliminated by the kidneys .
Endocrine and Antiandrogenic Effects
Cimetidine has been associated with antiandrogenic effects, such as gynecomastia in men. It can compete with dihydrotestosterone for binding to androgen receptors, acting as a nonsteroidal antiandrogen. This property may explain some of the hormonal side effects observed in patients treated with cimetidine 89.
Immunomodulatory and Anticancer Properties
Beyond its gastric effects, cimetidine has immunomodulatory properties. It can reverse histamine-mediated immunosuppression and stimulate various immune cells, including neutrophils, macrophages, dendritic cells, and T cells. These effects have led to investigations of cimetidine as a potential treatment for immune-related diseases and as an adjunct in cancer therapy, where it may interfere with tumor cell adhesion, angiogenesis, and proliferation 710.
Conclusion
Cimetidine is a well-established histamine H2-receptor antagonist with primary use in reducing gastric acid secretion for the treatment of peptic ulcer disease and related conditions. It is well absorbed, rapidly excreted, and generally safe, though it can interact with other drugs and has notable antiandrogenic and immunomodulatory effects. These additional properties have expanded interest in cimetidine’s potential roles beyond acid suppression, including cancer therapy and immune modulation.
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Most relevant research papers on this topic
The pharmacology of cimetidine, a new histamine H2‐receptor antagonist
Cimetidine effectively inhibits histamine and pentagastrin-stimulated gastric secretion, but shows less effectiveness in inhibiting carbachol-stimulated secretion, with no known toxicity.
Pharmacological evaluation of cimetidine, a new histamine H2-receptor antagonist, in healthy man.
Cimetidine, a new H2-receptor antagonist, effectively inhibits gastric acid and pepsin secretion in healthy men, with a blood half-life of 2 hours and rapid kidney excretion.
Physiologically-Based Pharmacokinetic Modeling for Drug-Drug Interactions of Procainamide and N-Acetylprocainamide with Cimetidine, an Inhibitor of rOCT2 and rMATE1, in Rats
Cimetidine increases systemic exposure and decreases renal clearance of procainamide and N-acetylprocainamide in rats, potentially impacting their renal elimination.
Cimetidine. I. Developments, pharmacology, and efficacy.
Cimetidine effectively heals duodenal ulcers and reduces reulceration, is preferred for Zollinger-Ellison syndrome, and may help heal benign gastric ulcers.
Cimetidine: an anticancer drug?
Cimetidine has shown anticancer effects by affecting tumor cell adhesion, angiogenesis, and proliferation, as well as inhibiting postoperative immunosuppression.
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