Fluoxetine 10 mg Capsule, 100-count — NDC 42543-725-01 (Billing 42543-0725-01)

12 CLINICAL PHARMACOLOGY

12.1Mechanism of Action Although the exact mechanism of fluoxetine is unknown, it is presumed to be linked to its inhibition of CNS neuronal uptake of serotonin.

12.2Pharmacodynamics Studies at clinically relevant doses in man have demonstrated that fluoxetine blocks the uptake of serotonin into human platelets. Studies in animals also suggest that fluoxetine is a much more potent uptake inhibitor of serotonin than of norepinephrine. Antagonism of muscarinic, histaminergic, and α 1 -adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects of classical tricyclic antidepressant (TCA) drugs.

Fluoxetine binds to these and other membrane receptors from brain tissue much less potently in vitro than do the tricyclic drugs.

12.3Pharmacokinetics Systemic Bioavailability — In man, following a single oral 40 mg dose, peak plasma concentrations of fluoxetine from 15 to 55 ng/mL are observed after 6 to 8 hours. Food does not appear to affect the systemic bioavailability of fluoxetine, although it may delay its absorption by 1 to 2 hours, which is probably not clinically significant. Thus, fluoxetine may be administered with or without food.

Protein Binding — Over the concentration range from 200 to 1000 ng/mL, approximately 94.5% of fluoxetine is bound in vitro to human serum proteins, including albumin and α 1 -glycoprotein. The interaction between fluoxetine and other highly protein-bound drugs has not been fully evaluated, but may be important. Enantiomers — Fluoxetine is a racemic mixture (50/50) of R -fluoxetine and S -fluoxetine enantiomers.

In animal models, both enantiomers are specific and potent serotonin uptake inhibitors with essentially equivalent pharmacologic activity. The S -fluoxetine enantiomer is eliminated more slowly and is the predominant enantiomer present in plasma at steady state. Metabolism — Fluoxetine is extensively metabolized in the liver to norfluoxetine and a number of other unidentified metabolites.

The only identified active metabolite, norfluoxetine, is formed by demethylation of fluoxetine. In animal models, S -norfluoxetine is a potent and selective inhibitor of serotonin uptake and has activity essentially equivalent to R - or S -fluoxetine. R -norfluoxetine is significantly less potent than the parent drug in the inhibition of serotonin uptake.

The primary route of elimination appears to be hepatic metabolism to inactive metabolites excreted by the kidney. Variability in Metabolism — A subset (about 7%) of the population has reduced activity of the drug metabolizing enzyme cytochrome P450 2D6 (CYP2D6). Such individuals are referred to as “poor metabolizers” of drugs such as debrisoquin, dextromethorphan, and the TCAs.

In a study involving labeled and unlabeled enantiomers administered as a racemate, these individuals metabolized S -fluoxetine at a slower rate and thus achieved higher concentrations of S -fluoxetine. Consequently, concentrations of S -norfluoxetine at steady state were lower. The metabolism of R -fluoxetine in these poor metabolizers appears normal.

When compared with normal metabolizers, the total sum at steady state of the plasma concentrations of the 4 active enantiomers was not significantly greater among poor metabolizers. Thus, the net pharmacodynamic activities were essentially the same. Alternative, nonsaturable pathways (non-2D6) also contribute to the metabolism of fluoxetine.

This explains how fluoxetine achieves a steady-state concentration rather than increasing without limit. Because fluoxetine’s metabolism, like that of a number of other compounds including TCAs and other selective serotonin reuptake inhibitors (SSRIs), involves the CYP2D6 system, concomitant therapy with drugs also metabolized by this enzyme system (such as the TCAs) may lead to drug interactions [see Drug Interactions (7.7) ] . Accumulation and Slow Elimination — The relatively slow elimination of fluoxeti… [Excerpted — this section continues on DailyMed.]

12.1Mechanism of Action Although the exact mechanism of fluoxetine is unknown, it is presumed to be linked to its inhibition of CNS neuronal uptake of serotonin.

12.3Pharmacokinetics Systemic Bioavailability — In man, following a single oral 40 mg dose, peak plasma concentrations of fluoxetine from 15 to 55 ng/mL are observed after 6 to 8 hours. Food does not appear to affect the systemic bioavailability of fluoxetine, although it may delay its absorption by 1 to 2 hours, which is probably not clinically significant. Thus, fluoxetine may be administered with or without food.

Protein Binding — Over the concentration range from 200 to 1000 ng/mL, approximately 94.5% of fluoxetine is bound in vitro to human serum proteins, including albumin and α 1 -glycoprotein. The interaction between fluoxetine and other highly protein-bound drugs has not been fully evaluated, but may be important. Enantiomers — Fluoxetine is a racemic mixture (50/50) of R -fluoxetine and S -fluoxetine enantiomers.

In animal models, both enantiomers are specific and potent serotonin uptake inhibitors with essentially equivalent pharmacologic activity. The S -fluoxetine enantiomer is eliminated more slowly and is the predominant enantiomer present in plasma at steady state. Metabolism — Fluoxetine is extensively metabolized in the liver to norfluoxetine and a number of other unidentified metabolites.

The only identified active metabolite, norfluoxetine, is formed by demethylation of fluoxetine. In animal models, S -norfluoxetine is a potent and selective inhibitor of serotonin uptake and has activity essentially equivalent to R - or S -fluoxetine. R -norfluoxetine is significantly less potent than the parent drug in the inhibition of serotonin uptake.

The primary route of elimination appears to be hepatic metabolism to inactive metabolites excreted by the kidney. Variability in Metabolism — A subset (about 7%) of the population has reduced activity of the drug metabolizing enzyme cytochrome P450 2D6 (CYP2D6). Such individuals are referred to as “poor metabolizers” of drugs such as debrisoquin, dextromethorphan, and the TCAs.

In a study involving labeled and unlabeled enantiomers administered as a racemate, these individuals metabolized S -fluoxetine at a slower rate and thus achieved higher concentrations of S -fluoxetine. Consequently, concentrations of S -norfluoxetine at steady state were lower. The metabolism of R -fluoxetine in these poor metabolizers appears normal.

When compared with normal metabolizers, the total sum at steady state of the plasma concentrations of the 4 active enantiomers was not significantly greater among poor metabolizers. Thus, the net pharmacodynamic activities were essentially the same. Alternative, nonsaturable pathways (non-2D6) also contribute to the metabolism of fluoxetine.

This explains how fluoxetine achieves a steady-state concentration rather than increasing without limit. Because fluoxetine’s metabolism, like that of a number of other compounds including TCAs and other selective serotonin reuptake inhibitors (SSRIs), involves the CYP2D6 system, concomitant therapy with drugs also metabolized by this enzyme system (such as the TCAs) may lead to drug interactions [see Drug Interactions (7.7) ] . Accumulation and Slow Elimination — The relatively slow elimination of fluoxetine (elimination half-life of 1 to 3 days after acute administration and 4 to 6 days after chronic administration) and its active metabolite, norfluoxetine (elimination half-life of 4 to 16 days after acute and chronic administration), leads to significant accumulation of these active species in chronic use and delayed attainment of steady state, even when a fixed dose is used [see Warnings and Precautions (5.14) ] .

After 30 days of dosing at 40 mg/day, plasma concentrations of fluoxetine in the range of 91 to 302 ng/mL and norfluoxetine in the range of 72 to 258 ng/mL have been observed. Plasma concentrations of fluoxetine were higher than those predicted by single-dose studies, because fluoxetine’s metabolism is not proportional to dose. Norfluoxetine, however, appears to have linear pharmacokinetics.

Its mean… [Excerpted — this section continues on DailyMed.]

12.2Pharmacodynamics Studies at clinically relevant doses in man have demonstrated that fluoxetine blocks the uptake of serotonin into human platelets. Studies in animals also suggest that fluoxetine is a much more potent uptake inhibitor of serotonin than of norepinephrine. Antagonism of muscarinic, histaminergic, and α 1 -adrenergic receptors has been hypothesized to be associated with various anticholinergic, sedative, and cardiovascular effects of classical tricyclic antidepressant (TCA) drugs.

Fluoxetine binds to these and other membrane receptors from brain tissue much less potently in vitro than do the tricyclic drugs.

14 CLINICAL STUDIES Efficacy for fluoxetine was established for the: Acute and maintenance treatment of Major Depressive Disorder in adults, and children and adolescents (8 to 18 years) in 7 short-term and 2 long-term, placebo-controlled trials [see Clinical Studies 14.1 ] . Acute treatment of obsessions and compulsions in adults, and children and adolescents (7 to 17 years) with Obsessive Compulsive Disorder (OCD) in 3 short-term placebo-controlled trials [see Clinical Studies (14.2) ] . Acute and maintenance treatment of binge-eating and vomiting behaviors in adult patients with moderate to severe Bulimia Nervosa in 3 short-term and 1 long-term, placebo-controlled trials [see Clinical Studies (14.3) ] .

Acute treatment of Panic Disorder, with or without agoraphobia, in adult patients in 2 short-term, placebo-controlled trials [see Clinical Studies (14.4) ] . Efficacy for fluoxetine and olanzapine in combination was established for the: Acute treatment of depressive episodes in Bipolar I Disorder in adults, and children and adolescents (10 to 17 years) in 3 short-term, placebo-controlled trials. When using fluoxetine and olanzapine in combination, also refer to the Clinical Studies section of the package insert for Symbyax.

14.1Major Depressive Disorder Daily Dosing Adult — The efficacy of fluoxetine was studied in 5- and 6-week placebo-controlled trials with depressed adult and geriatric outpatients (≥18 years of age) whose diagnoses corresponded most closely to the DSM-III (currently DSM-IV) category of Major Depressive Disorder . Fluoxetine was shown to be significantly more effective than placebo as measured by the Hamilton Depression Rating Scale (HAM-D). Fluoxetine was also significantly more effective than placebo on the HAM-D subscores for depressed mood, sleep disturbance, and the anxiety subfactor.

Two 6-week controlled studies (N=671, randomized) comparing fluoxetine 20 mg and placebo have shown fluoxetine 20 mg daily to be effective in the treatment of elderly patients (≥60 years of age) with Major Depressive Disorder. In these studies, fluoxetine produced a significantly higher rate of response and remission as defined, respectively, by a 50% decrease in the HAM-D score and a total endpoint HAM-D score of ≤8. Fluoxetine was well tolerated and the rate of treatment discontinuations due to adverse reactions did not differ between fluoxetine (12%) and placebo (9%).

A study was conducted involving depressed outpatients who had responded (modified HAMD-17 score of ≤7 during each of the last 3 weeks of open-label treatment and absence of Major Depressive Disorder by DSM-III-R criteria) by the end of an initial 12-week open-treatment phase on fluoxetine 20 mg/day. These patients (N=298) were randomized to continuation on double-blind fluoxetine 20 mg/day or placebo. At 38 weeks (50 weeks total), a statistically significantly lower relapse rate (defined as symptoms sufficient to meet a diagnosis of Major Depressive Disorder for 2 weeks or a modified HAMD-17 score of ≥14 for 3 weeks) was observed for patients taking fluoxetine compared with those on placebo.

Pediatric (children and adolescents) — The efficacy of fluoxetine 20 mg/day in children and adolescents (N=315 randomized; 170 children ages 8 to <13, 145 adolescents ages 13 to ≤18) was studied in two 8- to 9-week placebo-controlled clinical trials in depressed outpatients whose diagnoses corresponded most closely to the DSM-III-R or DSM-IV category of Major Depressive Disorder. In both studies independently, fluoxetine produced a statistically significantly greater mean change on the Childhood Depression Rating Scale-Revised (CDRS-R) total score from baseline to endpoint than did placebo.

Subgroup analyses on the CDRS-R total score did not suggest any differential responsiveness on the basis of age or gender.

14.2Obsessive Compulsive Disorder Adult — The effectiveness of fluoxetine for the treatment of Obsessive Compulsive Disorder (OCD) was demonstrated in two 13… [Excerpted — this section continues on DailyMed.]

13 NONCLINICAL TOXICOLOGY

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenicity — The dietary administration of fluoxetine to rats and mice for 2 years at doses of up to 10 and 12 mg/kg/day, respectively [approximately 1.2 and 0.7 times, respectively, the maximum recommended human dose (MRHD) of 80 mg on a mg/m 2 basis], produced no evidence of carcinogenicity. Mutagenicity — Fluoxetine and norfluoxetine have been shown to have no genotoxic effects based on the following assays: bacterial mutation assay, DNA repair assay in cultured rat hepatocytes, mouse lymphoma assay, and in vivo sister chromatid exchange assay in Chinese hamster bone marrow cells.

Impairment of Fertility — Two fertility studies conducted in adult rats at doses of up to 7.5 and 12.5 mg/kg/day (approximately 0.9 and 1.5 times the MRHD on a mg/m 2 basis) indicated that fluoxetine had no adverse effects on fertility. However, adverse effects on fertility were seen when juvenile rats were treated with fluoxetine [see Use in Specific Populations (8.4) ].

13.2Animal Toxicology and/or Pharmacology Phospholipids are increased in some tissues of mice, rats, and dogs given fluoxetine chronically. This effect is reversible after cessation of fluoxetine treatment. Phospholipid accumulation in animals has been observed with many cationic amphiphilic drugs, including fenfluramine, imipramine, and ranitidine. The significance of this effect in humans is unknown.