Ranitidine - How It Works
Clinical pharmacology details from the US FDA-approved label: how Ranitidine works in your body, how it's absorbed, how long it stays active, and how it's eliminated.
CLINICAL PHARMACOLOGY Ranitidine Tablets are a competitive, reversible inhibitor of the action of histamine at the histamine H 2 -receptors, including receptors on the gastric cells.
Ranitidine Tablets do not lower serum Ca++ in hypercalcemic states.
Ranitidine Tablets are not an anticholinergic agent.
Pharmacokinetics Absorption: Ranitidine Tablets are 50% absorbed after oral administration, compared to an intravenous (IV) injection with mean peak levels of 440 to 545 ng/mL occurring 2 to 3 hours after a 150 mg dose.
Absorption is not significantly impaired by the administration of food or antacids.
Propantheline slightly delays and increases peak blood levels of ranitidine, probably by delaying gastric emptying and transit time.
In one study, simultaneous administration of high-potency antacid (150 mmol) in fasting subjects has been reported to decrease the absorption of Ranitidine Tablets.
Distribution: The volume of distribution is about 1.4 L/kg.
Serum protein binding averages 15%.
Metabolism: In humans, the N-oxide is the principal metabolite in the urine; however, this amounts to < 4% of the dose.
Other metabolites are the S-oxide (1%) and the desmethyl ranitidine (1%).
The remainder of the administered dose is found in the stool.
Studies in patients with hepatic dysfunction (compensated cirrhosis) indicate that there are minor, but clinically insignificant, alterations in ranitidine half-life, distribution, clearance, and bioavailability.
Excretion: The principal route of excretion is the urine, with approximately 30% of the orally administered dose collected in the urine as unchanged drug in 24 hours.
Renal clearance is about 410 mL/min, indicating active tubular excretion.
The elimination half-life is 2.5 to 3 hours.
Four patients with clinically significant renal function impairment (creatinine clearance 25 to 35 mL/min) administered 50 mg of ranitidine intravenously had an average plasma half-life of 4.8 hours, a ranitidine clearance of 29 mL/min, and a volume of distribution of 1.76 L/kg.
In general, these parameters appear to be altered in proportion to creatinine clearance (see DOSAGE AND ADMINISTRATION ).
Geriatrics: The plasma half-life is prolonged and total clearance is reduced in the elderly population due to a decrease in renal function.
The elimination half-life is 3 to 4 hours.