Siamidine Mechanism of Action

Pharmacology: Pharmacodynamics: Cimetidine is a H₂ antagonist which is a competitive H₂ blocker that inhibit histamine at H₂ receptor of gastric parietal cells which inhibits gastric acid secretion. Cimetidine inhibits both daytime and nighttime basal gastric acid, and also when stimulated by food, insulin, histamine, pentagastrin, and caffeine.
Pharmacokinetics: Film-coated tablet: Cimetidine is rapidly and well absorbed following oral administration, the bioavailability is approximately 60%. Peak plasma concentration occurs after about 45-90 minutes and the blood concentration remain above those required to provide 80% inhibition of basal gastric acid secretion for 4-5 hours following a 300 mg dose. Cimetidine is widely distributed and has a volume of distribution of about 1 L/Kg and is weakly bound to plasma protein about 20%. Cimetidine crosses the placenta and is distributed into breast milk. Cimetidine is metabolized in the liver to the major metabolite sulfoxide and also 5-hydroxymetyl derivatives. 48% of an oral dose is excreted unchanged in urine. The elimination half-life from plasma is about 2 hours.
Injection: The blood concentration of Cimetidine remains above those required to provide 80% inhibition of basal gastric acid secretion for 4-5 hours following a parenteral dose of 300 mg. Cimetidine is widely distributed and has a volume of distribution of about 1 L/Kg and is weakly bound to plasma protein about 20%. Cimetidine crosses the placenta and is distributed into breast milk. Cimetidine is metabolized in the liver to the major metabolite sulfoxide and 5-hydroxylmetyl derivatives. 75% of an intravenous dose is excreted unchanged in urine. The elimination half-life from plasma is about 2 hours.