Raxide Mechanism of Action

Pharmacology: Pharmacodynamics: Serum concentrations necessary to inhibit 50% of stimulated gastric acid secretion are estimated to be 36 to 94 ng/mL. Following a single oral dose of 150 mg, serum concentrations of ranitidine are in this range up to 12 hours. However, blood levels bear no consistent relationship to dose or degree of acid inhibition.
Pharmacokinetics: Ranitidine is readily absorbed from the gastrointestinal tract with peak concentrations in plasma occurring about 2 to 3 hours after administration by mouth. The bioavailability of Ranitidine following oral administration is about 50% due to first-pass metabolism. The elimination half-life from plasma is around 2 to 3 hours and Ranitidine is weakly bound, about 15% plasma proteins.
A small proportions of Ranitidine is metabolized in the liver to the N-oxide, the S-oxide, and desmethylranitidine; the N-oxide is the major metabolite but accounts only for 4 to 6% of a dose. Approximately 30% of an oral dose and 70% of an intravenous dose is excreted unchanged in the urine in 24 hours; there is some excretion in the faeces. Ranitidine crosses the placental barrier and is excreted in breast milk where concentrations are reported to be higher than those in plasma. It does not readily cross the blood-brain barrier but adverse effects on the nervous system have been reported.