Pharmacokinetics

Pharmacodynamics

Serum concentrations necessary to inhibit 50% of stimulated gastric acid secretion are estimated to be 36 ng/mL 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.

Antisecretory Activity

Other Pharmacologic Actions

a. Gastric bacterial flora – increase in nitrate-reducing organisms, significance not known.
b. Prolactin levels – no effect in recommended dosage.
c. Other pituitary hormones – no effect on serum gonadotropins, TSH, or GH. Possible impairment of vasopressin release.
d. No change in cortisol, aldosterone, androgen, or estrogen levels.
e. No antiandrogenic action.
f. No effect on count, motility, or morphology of sperm.

Pediatrics

Oral doses of 6 mg/kg to 10 mg/kg per day in two or three divided doses maintain gastric pH > 4 throughout most of the dosing interval.

Clinical Trials

General

1. Symptomatic response to therapy with ranitidine does not preclude the presence of gastric malignancy.
2. Since ranitidine is excreted primarily by the kidney, dosage should be adjusted in patients with impaired renal function (see DOSAGE AND ADMINISTRATION).  Caution should be observed in patients with hepatic dysfunction since ranitidine is metabolized in the liver.
3. Rare reports suggest that ranitidine may precipitate acute porphyric attacks in patients with acute porphyria.  Ranitidine should therefore be avoided in patients with a history of acute porphyria.

Laboratory Tests

False-positive tests for urine protein with Multistix® may occur during ranitidine therapy, and therefore testing with sulfosalicylic acid is recommended.

Drug Interactions

Ranitidine has been reported to affect the bioavailability of other drugs through several different mechanisms such as competition for renal tubular secretion, alteration of gastric pH, and inhibition of cytochrome P450 enzymes.

Procainamide:  Ranitidine, a substrate of the renal organic cation transport system, may affect the clearance of other drugs eliminated by this route.  High doses of ranitidine (e.g., such as those used in the treatment of Zollinger-Ellison syndrome) have been shown to reduce the renal excretion of procainamide and N-acetylprocainamide resulting in increased plasma levels of these drugs.  Although this interaction is unlikely to be clinically relevant at usual ranitidine doses, it may be prudent to monitor for procainamide toxicity when administered with oral ranitidine at a dose exceeding 300 mg per day.

Warfarin:  There have been reports of altered prothrombin time among patients on concomitant warfarin and ranitidine therapy.  Due to the narrow therapeutic index, close monitoring of increased or decreased prothrombin time is recommended during concurrent treatment with ranitidine.

Ranitidine may alter the absorption of drugs in which gastric pH is an important determinant of bioavailability.  This can result in either an increase in absorption (e.g., triazolam, midazolam, glipizide) or a decrease in absorption (e.g., ketoconazole, atazanavir, delavirdine, gefitinib). Appropriate clinical monitoring is recommended.

Atazanavir: Atazanavir absorption may be impaired based on known interactions with other agents that increase gastric pH. Use with caution.  See atazanavir label for specific recommendations.

Delavirdine:  Delavirdine absorption may be impaired based on known interactions with other agents that increase gastric pH.  Chronic use of H2-receptor antagonists with delavirdine is not recommended.

Gefitinib:  Gefitinib exposure was reduced by 44% with the coadministration of ranitidine and sodium bicarbonate (dosed to maintain gastric pH above 5.0). Use with caution.

Glipizide:  In diabetic patients, glipizide exposure was increased by 34% following a single 150-mg dose of oral ranitidine.  Use appropriate clinical monitoring when initiating or discontinuing ranitidine.

Ketoconazole:  Oral ketoconazole exposure was reduced by up to 95% when oral ranitidine was coadministered in a regimen to maintain a gastric pH of 6 or above.  The degree of interaction with usual dose of ranitidine (150 mg twice daily) is unknown.

Midazolam:  Oral midazolam exposure in 5 healthy volunteers was increased by up to 65% when administered with oral ranitidine at a dose of 150 mg twice daily.  However, in another interaction study in 8 volunteers receiving intravenous midazolam, a 300 mg oral dose of ranitidine increased midazolam exposure by about 9%.  Monitor patients for excessive or prolonged sedation when ranitidine is coadministered with oral midazolam.

Triazolam:  Triazolam exposure in healthy volunteers was increased by approximately 30% when administered with oral ranitidine at a dose of 150 mg twice daily.  Monitor patients for excessive or prolonged sedation.

Carcinogenesis, Mutagenesis, Impairment of Fertility

There was no indication of tumorigenic or carcinogenic effects in life-span studies in mice and rats at dosages up to 2,000 mg/kg per day.

Ranitidine was not mutagenic in standard bacterial tests (Salmonella, Escherichia coli) for mutagenicity at concentrations up to the maximum recommended for these assays.

In a dominant lethal assay, a single oral dose of 1,000 mg/kg to male rats was without effect on the outcome of two matings per week for the next 9 weeks.

Pregnancy

Nursing Mothers

Ranitidine is secreted in human milk.  Caution should be exercised when ranitidine is administered to a nursing mother.

Pediatric Use

The safety and effectiveness of ranitidine has been established in the age-group of 1 month to 16 years for the treatment of duodenal and gastric ulcers, gastroesophageal reflux disease and erosive esophagitis, and the maintenance of healed duodenal and gastric ulcer.  Use of ranitidine in this age-group is supported by adequate and well-controlled studies in adults, as well as additional pharmacokinetic data in pediatric patients and an analysis of the published literature (see CLINICAL PHARMACOLOGY: Pediatrics and DOSAGE AND ADMINISTRATION: Pediatric Use).

Safety and effectiveness in pediatric patients for the treatment of pathological hypersecretory conditions or the maintenance of healing of erosive esophagitis have not been established.

Safety and effectiveness in neonates (less than one month of age) have not been established (see CLINICAL PHARMACOLOGY: Pediatrics).

Geriatric Use

Of the total number of subjects enrolled in US and foreign controlled clinical trials of oral formulations of ranitidine, for which there were subgroup analyses, 4,197 were 65 and over, while 899 were 75 and over.  No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out.

This drug is known to be substantially excreted by the kidney and the risk of toxic reactions to this drug may be greater in patients with impaired renal function.  Because elderly patients are more likely to have decreased renal function, caution should be exercised in dose selection, and it may be useful to monitor renal function (see CLINICAL PHARMACOLOGY: Pharmacokinetics: Geriatrics and DOSAGE AND ADMINISTRATION: Dosage Adjustment for Patients with Impaired Renal Function).

Central Nervous System

Rarely, malaise, dizziness, somnolence, insomnia, and vertigo. Rare cases of reversible mental confusion, agitation, depression, and hallucinations have been reported, predominantly in severely ill elderly patients.  Rare cases of reversible blurred vision suggestive of a change in accommodation have been reported.  Rare reports of reversible involuntary motor disturbances have been received.

Cardiovascular

As with other H2-blockers, rare reports of arrhythmias such as tachycardia, bradycardia, atrioventricular block, and premature ventricular beats.

Gastrointestinal

Constipation, diarrhea, nausea/vomiting, abdominal discomfort/pain, and rare reports of pancreatitis.

Hepatic

There have been occasional reports of hepatocellular, cholestatic, or mixed hepatitis, with or without jaundice.  In such circumstances, ranitidine should be immediately discontinued.  These events are usually reversible, but in rare circumstances death has occurred. Rare cases of hepatic failure have also been reported.  In normal volunteers, SGPT values were increased to at least twice the pretreatment levels in 6 of 12 subjects receiving 100 mg 4 times daily intravenously for 7 days, and in 4 of 24 subjects receiving 50 mg intravenously 4 times daily for 5 days.

Musculoskeletal

Rare reports of arthralgias and myalgias.

Hematologic

Blood count changes (leukopenia, granulocytopenia, and thrombocytopenia) have occurred in a few patients.  These were usually reversible. Rare cases of agranulocytosis, pancytopenia, sometimes with marrow hypoplasia, and aplastic anemia and exceedingly rare cases of acquired immune hemolytic anemia have been reported.

Endocrine

Controlled studies in animals and man have shown no stimulation of any pituitary hormone by ranitidine and no antiandrogenic activity, and cimetidine-induced gynecomastia and impotence in hypersecretory patients have resolved when ranitidine has been substituted.  However, occasional cases of impotence and loss of libido have been reported in male patients receiving ranitidine, but the incidence did not differ from that in the general population.  Rare cases of breast symptoms and conditions, including galactorrhea and gynecomastia, have been reported in both males and females.

Integumentary

Rash, including rare cases of erythema multiforme.  Rare cases of alopecia and vasculitis.

Respiratory

A large epidemiological study suggested an increased risk of developing pneumonia in current users of histamine-2-receptor antagonists (H2RAs) compared to patients who had stopped H2RA treatment, with an observed adjusted relative risk of 1.63 (95% CI, 1.07-2.48).  However, a causal relationship between use of H2RAs and pneumonia has not been established.

Other

Rare cases of hypersensitivity reactions (e.g., bronchospasm, fever, rash, eosinophilia), anaphylaxis, angioneurotic edema, acute interstitial nephritis, and small increases in serum creatinine.

Active Duodenal Ulcer

The current recommended adult oral dosage of ranitidine for duodenal ulcer is 150 mg twice daily.  An alternative dosage of 300 mg once daily after the evening meal or at bedtime can be used for patients in whom dosing convenience is important.  The advantages of one treatment regimen compared to the other in a particular patient population have yet to be demonstrated (see CLINICAL PHARMACOLOGY: Clinical Trials: Active Duodenal Ulcer).  Smaller doses have been shown to be equally effective in inhibiting gastric acid secretion in US studies, and several foreign trials have shown that 100 mg twice daily is as effective as the 150 mg dose.

Antacid should be given as needed for relief of pain (see CLINICAL PHARMACOLOGY: Pharmacokinetics).

Maintenance of Healing of Duodenal Ulcers

The current recommended adult oral dosage is 150 mg at bedtime.

Pathological Hypersecretory Conditions (such as Zollinger-Ellison syndrome)

The current recommended adult oral dosage is 150 mg twice a day.  In some patients it may be necessary to administer ranitidine 150 mg doses more frequently.  Dosages should be adjusted to individual patient needs, and should continue as long as clinically indicated.  Dosages up to 6 g/day have been employed in patients with severe disease.

Benign Gastric Ulcer

The current recommended adult oral dosage is 150 mg twice a day.

Maintenance of Healing of Gastric Ulcers

The current recommended adult oral dosage is 150 mg at bedtime.

GERD

The current recommended adult oral dosage is 150 mg twice a day.

Erosive Esophagitis

The current recommended adult oral dosage is 150 mg four times a day.

Maintenance of Healing of Erosive Esophagitis

The current recommended adult oral dosage is 150 mg twice a day.

Pediatric Use

The safety and effectiveness of ranitidine has been established in the age-group of 1 month to 16 years.  There is insufficient information about the pharmacokinetics of ranitidine in neonatal patients (less than 1 month of age) to make dosing recommendations.

The following 3 subsections provide dosing information for each of the pediatric indications.

Dosage Adjustment for Patients with Impaired Renal Function

On the basis of experience with a group of subjects with severely impaired renal function treated with ranitidine, the recommended dosage in patients with a creatinine clearance <50 mL/min is 150 mg every 24 hours.  Should the patient’s condition require, the frequency of dosing may be increased to every 12 hours or even further with caution.  Hemodialysis reduces the level of circulating ranitidine.  Ideally, the dosing schedule should be adjusted so that the timing of a scheduled dose coincides with the end of hemodialysis.

Elderly patients are more likely to have decreased renal function, therefore caution should be exercised in dose selection, and it may be useful to monitor renal function (see CLINICAL  PHARMACOLOGY: Pharmacokinetics: Geriatrics and PRECAUTIONS: Geriatric Use).