Famotidine (Page 2 of 4)

7. Drug Interactions

7.1 Drugs Dependent on Gastric pH for Absorption

Famotidine can reduce the absorption of other drugs, due to its effect on reducing intragastric acidity, leading to loss of efficacy of the concomitant drug.
Concomitant administration of famotidine with dasatinib, delavirdine mesylate, cefditoren, and fosamprenavir is not recommended.
See the prescribing information for other drugs dependent on gastric pH for absorption for administration instructions, including atazanavir, erlotinib, ketoconazole, itraconazole, ledipasvir/sofosbuvir, nilotinib, and rilpivirine.

7.2 Tizanidine (CYP1A2 Substrate)

Although not studied clinically, famotidine is considered a weak CYP1A2 inhibitor and may lead to substantial increases in blood concentrations of tizanidine, a CYP1A2 substrate. Avoid concomitant use with famotidine. If concomitant use is necessary, monitor for hypotension, bradycardia or excessive drowsiness. Refer to the full prescribing information for tizanidine.

8. Use in Specific Populations

8.1 Pregnancy

Risk Summary
Available data with H 2-receptor antagonists, including famotidine, in pregnant women are insufficient to establish a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. In animal reproduction studies, no adverse development effects were observed with oral administration of famotidine at doses up to approximately 243 and 122 times, respectively, the recommended human dose of 80 mg per day for the treatment of erosive esophagitis (see Data).
The estimated background risk for major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.
Data
Animal Data
Reproductive studies have been performed in rats and rabbits at oral doses of up to 2000 and 500 mg/kg/day, respectively, and in both species at intravenous doses of up to 200 mg/kg/day, and have revealed no significant evidence of impaired fertility or harm to the fetus due to famotidine. While no direct fetotoxic effects have been observed, sporadic abortions occurring only in mothers displaying marked decreased food intake were seen in some rabbits at oral doses of 200 mg/kg/day (about 49 times the recommended human dose of 80 mg per day, based on body surface area) or higher. There are, however, no adequate or well-controlled studies in pregnant women. Because animal reproductive studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.

8.2 Lactation

Risk Summary
There are limited data available on the presence of famotidine in human breast milk. There were no effects on the breastfed infant. There are no data on famotidine effects on milk production. Famotidine is present in the milk of lactating rats (see Data).
The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for famotidine and any potential adverse effects on the breastfed child from famotidine or from the underlying maternal condition.
Data
Animal Data
Transient growth depression was observed in young rats suckling from mothers treated with maternotoxic doses of famotidine at least 600 times the usual human dose.

8.4 Pediatric Use

The safety and effectiveness of famotidine have been established in pediatric patients for the treatment of peptic ulcer disease (i.e., duodenal ulcer, gastric ulcer) and GERD (i.e., symptomatic nonerosive GERD, erosive esophagitis as diagnosed by endoscopy). The use of famotidine and the recommended dosage of famotidine in these pediatric patients is supported by evidence from adequate and well-controlled studies of famotidine in adults and published pharmacokinetic and pharmacodynamic data in pediatric patients [see Dosage and Administration ( 2.1), Clinical Pharmacology ( 12.2, 12.3)]. In pediatric patients, the safety and effectiveness for the treatment of pathological hypersecretory conditions and reduction of risk of duodenal ulcer recurrence have not been established.
Famotidine 20 and 40 mg tablets are not recommended for use in pediatric patients weighing less than 40 kg because these tablet strengths exceed the recommended dose for these patients [see Dosage and Administration ( 2.1)]. For pediatric patients weighing less than 40 kg, consider another famotidine formulation (e.g., oral suspension, lower dose tablet).

8.5 Geriatric Use

Of the 1442 famotidine-treated patients in clinical studies, approximately 10% were 65 and older. In these studies, no overall differences in safety or effectiveness were observed between elderly and younger patients. In postmarketing experience, CNS adverse reactions have been reported in elderly patients with and without renal impairment receiving famotidine [see Warnings and Precautions ( 5.1)].
Famotidine is known to be substantially excreted by the kidney, and the risk of adverse reactions to famotidine may be greater in elderly patients, particularly those with impaired renal function [see Use in Specific Populations ( 8.6)].
In general, use the lowest effective dose of famotidine for an elderly patient and monitor renal function [see Dosage and Administration ( 2.2)].

8.6 Renal Impairment

CNS adverse reactions and prolonged QT intervals have been reported in patients with moderate and severe renal impairment [see Warnings and Precautions ( 5.1)]. The clearance of famotidine is reduced in adults with moderate and severe renal impairment compared to adults with normal renal function [see Clinical Pharmacology ( 12.3)]. No dosage adjustment is needed in patients with mild renal impairment (creatinine clearance greater than or equal to 60 mL/minute). Dosage reduction is recommended in adult and pediatric patients greater than or equal to 40 kg with moderate or severe renal impairment (creatinine clearance less than 60 mL/minute) [see Dosage and Administration ( 2.2)].

10. Overdosage

The types of adverse reactions in overdosage of famotidine are similar to the adverse reactions encountered with use of recommended dosages [see Adverse Reactions ( 6.1)].
In the event of overdosage, treatment should be symptomatic and supportive. Unabsorbed material should be removed from the gastrointestinal tract, the patient should be monitored, and supportive therapy should be employed. Due to low binding to plasma proteins, famotidine is eliminated by hemodialysis. There is limited experience on the usefulness of hemodialysis as a treatment for famotidine overdosage.

11. Description

The active ingredient in famotidine tablets, USP is a histamine-2 (H 2) receptor antagonist. Famotidine is N’-(aminosulfonyl)-3-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl] thio]propanimidamide. The empirical formula of famotidine is C 8H 15N 7O 2S 3 and its molecular weight is 337.45. Its structural formula is:

Description
(click image for full-size original)

Each famotidine tablet, USP for oral administration contains either 20 mg or 40 mg of famotidine and the following inactive ingredients: corn starch, hypromellose, magnesium stearate, microcrystalline cellulose, sodium starch glycolate and film coating contains carnauba wax, hydroxypropyl cellulose, hypromellose, talc, titanium dioxide; and additionally 20 mg contains iron oxide red and iron oxide yellow.
Famotidine, USP is a white to pale yellowish white crystalline powder that is freely soluble in dimethyl formamide, glacial acetic acid, slightly soluble in methanol, very slightly soluble in water, and practically insoluble in acetone, in alcohol, in chloroform, in ether and ethyl acetate.

12. Clinical Pharmacology

12.1 Mechanism of Action

Famotidine is a competitive inhibitor of histamine-2 (H 2) receptors. The primary clinically important pharmacologic activity of famotidine is inhibition of gastric secretion. Both the acid concentration and volume of gastric secretion are suppressed by famotidine, while changes in pepsin secretion are proportional to volume output.

12.2 Pharmacodynamics

Adults
Famotidine inhibited both basal and nocturnal gastric secretion, as well as secretion stimulated by food and pentagastrin. After oral administration of famotidine, the onset of the antisecretory effect occurred within one hour; the maximum effect was dose-dependent, occurring within one to three hours. Duration of inhibition of secretion by doses of 20 mg and 40 mg was 10 to 12 hours.
Single evening oral doses of 20 mg and 40 mg inhibited basal and nocturnal acid secretion in all subjects; mean nocturnal gastric acid secretion was inhibited by 86% and 94%, respectively, for a period of at least 10 hours. The same doses given in the morning suppressed food-stimulated acid secretion in all subjects. The mean suppression was 76% and 84%, respectively, 3 to 5 hours after administration, and 25% and 30%, respectively, 8 to 10 hours after administration. In some subjects who received the 20 mg dose, however, the antisecretory effect was dissipated within 6 to 8 hours. There was no cumulative effect with repeated doses. The nocturnal intragastric pH was raised by evening doses of 20 mg and 40 mg of famotidine to mean values of 5.0 and 6.4 respectively. When famotidine was given after breakfast, the basal daytime interdigestive pH at 3 and 8 hours after 20 mg or 40 mg of famotidine was raised to about 5.
Famotidine had little or no effect on fasting or postprandial serum gastrin levels. Gastric emptying and exocrine pancreatic function were not affected by famotidine.
In clinical pharmacology studies, systemic effects of famotidine in the CNS, cardiovascular, respiratory or endocrine systems were not noted. Also, no anti-androgenic effects were noted. Serum hormone levels, including prolactin, cortisol, thyroxine (T 4), and testosterone, were not altered after treatment with famotidine.
Pediatric Patients
Pharmacodynamics of famotidine, assessed by gastric pH, were evaluated in 5 pediatric patients 2 to 13 years of age using the sigmoid E max model. These data suggest that the relationship between serum concentration of famotidine and gastric acid suppression is similar to that observed in adults (see Table 3). Table 3: Serum Concentrations of Famotidine Associated with Gastric Acid Reduction in Famotidine-Treated Pediatric and Adult Patien ts a

EC 50 (ng/mL) a
Pediatric Patients 26 ± 13
Adults
Healthy adult subjects 26.5 ± 10.3
Adult patients with upper GI bleeding 18.7 ± 10.8

a Using the Sigmoid E max model, serum concentrations of famotidine associated with 50% maximum gastric acid reduction are presented as means ± SD.

In a study examining the effect of famotidine on gastric pH and duration of acid suppression in pediatric patients, four pediatric patients ages 11 to 15 years of age using the oral formulation at a dose of 0.5 mg/kg, maintained a gastric pH above 5 for 13.5 ± 1.8 hours.

12.3 Pharmacokinetics

Absorption
Famotidine is incompletely absorbed. The bioavailability of oral doses is 40 to 45%. Bioavailability may be slightly increased by food, or slightly decreased by antacids; however, these effects are of no clinical consequence.
Peak famotidine plasma levels occur in 1 to 3 hours. Plasma levels after multiple dosages are similar to those after single doses.
Distribution
Fifteen to 20% of famotidine in plasma is protein bound.
Elimination
Metabolism
Famotidine undergoes minimal first-pass metabolism. Twenty-five to 30% of an oral dose was recovered in the urine as unchanged compound. The only metabolite identified in humans is the S-oxide.
Excretion
Famotidine has an elimination half-life of 2.5 to 3.5 hours. Famotidine is eliminated by renal (65 to 70%) and metabolic (30 to 35%) routes. Renal clearance is 250 to 450 mL/minute, indicating some tubular excretion.
Specific Populations
Pediatric Patients
Bioavailability studies of 8 pediatric patients (11 to 15 years of age) showed a mean oral bioavailability of 0.5 compared to adult values of 0.42 to 0.49. Oral doses of 0.5 mg per kg achieved AUCs of 580 ± 60 ng•hr/mL in pediatric patients 11 to 15 years of age, compared to 482 ± 181 ng•hr/mL in adults treated with 40 mg orally.
Patients with Renal Impairment
In adult patients with severe renal impairment (creatinine clearance less than 30 mL/minute), the systemic exposure (AUC) of famotidine increased at least 5-fold. In patients with moderate renal impairment (creatinine clearance between 30 to 60 mL/minute), the AUC of famotidine increased at least 2-fold [see Dosage and Administration ( 2.2), Use in Specific Population ( 8.6)].
Drug Interaction Studies
Human Organic Anion Transporter (OAT) 1 and 3: In vitro studies indicate that famotidine is a substrate for OAT1 and OAT3. Following coadministration of probenecid (1500 mg), an inhibitor of OAT1 and OAT3, with a single oral 20 mg dose of famotidine in 8 healthy subjects, the serum AUC 0 to 10h of famotidine increased from 424 to 768 ng•hr/mL and the maximum serum concentration (C max) increased from 73 to 113 ng/mL. Renal clearance, urinary excretion rate and amount of famotidine excreted unchanged in urine were decreased. The clinical relevance of this interaction is unknown.
Multidrug and Toxin Extrusion Protein 1 (MATE-1): An in vitro study showed that famotidine is an inhibitor of MATE-1. However, no clinically significant interaction with metformin, a substrate for MATE-1, was observed.
CYP1A2: Famotidine is a weak CYP1A2 inhibitor.

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