Famotidine (Page 4 of 6)

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:

Infants from birth to 12 Months

After a single oral dose administration of 0.5 mg/kg orally in patients from birth to 12 months, the bioavailability is approximately 42%.

The AUC increased 1.4-fold after single oral dose of 1 mg/kg compared to 0.5 mg/kg and 2.7-fold after multiple oral doses of 1 mg/kg compared to 0.5 mg/kg.

Plasma clearance is reduced and elimination half-life is prolonged in pediatric patients from birth to 3 months of age compared to older pediatric patients. Following intravenous administration of 0.5 mg/kg, CL Total was 0.13 ± 0.06 L/hr/kg, 0.21 ± 0.06 L/hr/kg, and 0.49 ± 0.17 L/hr/kg in pediatric patients <1 month of age, <3 months of age, and >3 to 12 months of age, respectively. Elimination half-life was 10.5 hours, 8.1 hours, and 4.5 hours in pediatric patients <1 month of age, <3 months of age, and >3 to 12 months of age, respectively.

Patients 11 Years to 15 Years

The mean bioavailability in 8 pediatric patients was 50% compared to adult values of 42% to 49%.

Pharmacokinetic parameters in pediatrics 11 years to 15 years is compared to infants from birth to 12 months in Table 5.

Table 5: Mean Pharmacokinetic Parameters Following a Single Oral Dose of 0.5 mg/kg in Infants and Pediatric Patients

Infants from Birth to 12 Months (N=5) Pediatric Patients 11 Years to 15 Years (N=8)
AUC 0 to ∞ (ng*hr/mL) a 645 ± 249 580 ± 60
C max (ng/mL) 79.2 97.3
T max (hr) b 2.0 (1.0, 4.1) c 2.3 (2.1, 2.9) d
T 1/2 (hr) 5.82 2.13

a arithmetic mean ± S.D.

b median

c observed minimum and maximum values

d reported minimum and maximum values

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 adult 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 (2.3), USE IN SPECIFIC POPULATIONS (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.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis & Mutagenesis & Impairment Of Fertility

Carcinogenic potential of famotidine was assessed in a 106-week oral carcinogenicity study in rats and a 92-week oral carcinogenicity study in mice. In the 106-week study in rats and the 92-week study in mice at oral doses of up to 2000 mg/kg/day (approximately 243 and 122 times, respectively, based on body surface area, the recommended human dose of 80 mg per day for the treatment of erosive esophagitis), there was no evidence of carcinogenic potential for famotidine.

Famotidine was negative in the microbial mutagen test (Ames test) using Salmonella typhimurium and Escherichia coli with or without rat liver enzyme activation at concentrations up to 10,000 mcg/plate. In in vivo studies in mice, with a micronucleus test and a chromosomal aberration test, no evidence of a mutagenic effect was observed.

In studies with rats given oral doses of up to 2000 mg/kg/day (approximately 243 times, based on body surface area, the recommended human dose of 80 mg per day) fertility and reproductive performance were not affected.

14 CLINICAL STUDIES

The safety and effectiveness of famotidine for oral suspension have been established based on adequate and well-controlled studies of another oral famotidine product . The following is a summary of the efficacy results reported in those studies.

14.1 Active Duodenal Ulcer

In a U.S. multicenter, double-blind trial in adult outpatients with endoscopically confirmed duodenal ulcer (DU), orally administered famotidine was compared to placebo. As shown in Table 6, 70% of patients treated with famotidine 40 mg at bedtime were healed by Week 4. Most patients’ DU healed within 4 weeks.

Patients not healed by Week 4 were continued in the trial. By Week 8, 83% of patients treated with famotidine had healed DU, compared to 45% of patients treated with placebo. The incidence of DU healing with famotidine was greater than with placebo at each time point based on proportion of endoscopically confirmed healed DUs. Trials have not assessed the safety of famotidine in uncomplicated active DU for periods of more than 8 weeks.

Table 6: Patients with Endoscopically Confirmed Healed Duodenal Ulcers

Famotidine 40 mg at bedtime (N=89) Famotidine 20 mg twice daily (N=84) Placebo at bedtime (N=97)
Week 2 32% a 38% a 17%
Week 4 70% a 67% a 31%

a p<0.001 vs. placebo

In this study, time to relief of daytime and nocturnal pain was shorter for patients receiving famotidine than for patients receiving placebo; patients receiving famotidine also took less antacid than patients receiving placebo.

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