Ranitidine: single dose pharmacokinetics and absolute bioavailability in man.

Area of Science:

• Pharmacology
• Drug Metabolism
• Clinical Pharmacokinetics

Background:

• Understanding ranitidine's absorption, distribution, metabolism, and excretion (ADME) is crucial for optimizing its therapeutic use.
• Previous studies have provided insights into ranitidine pharmacokinetics, but detailed bioavailability and route-specific excretion patterns require further elucidation.

Purpose of the Study:

• To determine the single-dose pharmacokinetics and absolute bioavailability of ranitidine in healthy male volunteers.
• To compare the pharmacokinetic profiles and excretion patterns of orally administered versus intravenously administered ranitidine.

Main Methods:

• Five healthy male volunteers received a 150 mg dose of ranitidine intravenously (bolus injection) and orally (tablet formulation) on separate occasions after an overnight fast.
• Plasma concentrations were measured over time to determine pharmacokinetic parameters, including half-life, volume of distribution, and clearance.
• Urinary excretion of unchanged ranitidine was quantified for both administration routes.

Main Results:

• Intravenous ranitidine exhibited a plasma half-life of 1.7 hours, while oral administration resulted in a significantly longer half-life of 2.3 hours.
• Absolute oral bioavailability was determined to be 60%.
• Renal excretion of unchanged ranitidine was significantly higher after intravenous administration (79%) compared to oral administration (27%).

Conclusions:

• Oral ranitidine undergoes more extensive biotransformation and likely biliary excretion of metabolites compared to intravenous administration.
• Intravenously administered ranitidine is preferentially excreted unchanged in the urine.