Paroxetine 7.5 mg Capsule, 30-count — NDC 0574-0279-30 (Billing 00574-0279-30)

12 CLINICAL PHARMACOLOGY

12.1Mechanism of Action Nonclinical studies have shown that paroxetine is an SSRI. Paroxetine capsules are not an estrogen, and its mechanism of action for the treatment of VMS is unknown.

12.2Pharmacodynamics Studies at clinically relevant doses in humans have demonstrated that paroxetine blocks the uptake of serotonin into human platelets. In vitro studies in animals also suggest that paroxetine is a selective inhibitor of neuronal serotonin reuptake and has weak effects on norepinephrine and dopamine neuronal reuptake. In vitro radioligand binding studies indicate that paroxetine has little affinity for muscarinic alpha 1 -, alpha 2 -, beta-adrenergic-, dopamine (D 2 )-, 5-HT 1 -, 5-HT 2 -, and histamine (H 1 )-receptors.

12.3Pharmacokinetics Absorption, Distribution, Metabolism and Excretion Absorption Paroxetine is completely absorbed after oral dosing of the mesylate salt. In a study in which healthy postmenopausal women (n=24) received paroxetine 7.5 mg capsules as a daily dose for 14 days, steady-state paroxetine concentrations were achieved by approximately 12 days of dosing for most subjects, although it may take substantially longer in an occasional patient. Peak concentrations were reached at a median of 6 hours (3 to 8 hours range).

Steady-state mean values of C max , C min , and AUC 0-last were 13.10 ng/mL (CV 91%), 7.17 ng/mL (CV 99%), and 237 hr*ng/mL (CV 94%), respectively. Steady-state AUC 0-24 values were about 3 times those of AUC 0-inf following a single dose, indicating non-linear pharmacokinetics. Steady-state C max values were approximately 5 times greater than those attained after a single dose and steady-state exposure based on AUC 0-24 was about 10 times greater than AUC 0-24 after a single dose.

The nonlinear kinetics and excess accumulation are due to the fact that CYP2D6, an enzyme that is in part responsible for paroxetine metabolism, is readily saturable. The effects of food on the bioavailability of paroxetine were studied with paroxetine tablets at higher strength. AUC was only slightly increased (6%) when drug was administered with food but the C max was 29% greater, while the time to reach peak plasma concentration decreased from 6.4 hours post-dosing to 4.9 hours.

Paroxetine capsules can be taken with or without food. Distribution Paroxetine distributes throughout the body, including the central nervous system, with only 1% remaining in the plasma. Approximately 95% and 93% of paroxetine is bound to plasma protein at 100 ng/mL and 400 ng/mL, respectively.

Under clinical conditions, paroxetine concentrations would normally be less than 100 ng/mL. Paroxetine does not alter the in vitro protein binding of phenytoin or warfarin. Metabolism Paroxetine is extensively metabolized after oral administration.

The principal metabolites are polar and conjugated products of oxidation and methylation, which are readily cleared. Conjugates with glucuronic acid and sulfate predominate, and major metabolites have been isolated and identified. Data indicate that the metabolites have no more than 1/50 the potency of the parent compound at inhibiting serotonin uptake.

The metabolism of paroxetine is accomplished in part by cytochrome CYP2D6. Saturation of this enzyme at clinical doses appears to account for the nonlinearity of paroxetine kinetics with increasing dose and increasing duration of treatment. The role of this enzyme in paroxetine metabolism also suggests potential drug-drug interactions [see Drug Interactions (7)] .

At steady state, when the CYP2D6 pathway is essentially saturated, paroxetine clearance is governed by alternative P450 isozymes, which, unlike CYP2D6, show no evidence of saturation. Excretion Approximately 64% of a 30 mg oral solution of paroxetine was excreted in the urine with 2% as the parent compound and 62% as metabolites over a 10-day post-dosing period. About 36% of the dose was excreted in the feces (probably via the bile), mostly as metabolites and… [Excerpted — this section continues on DailyMed.]

12.1Mechanism of Action Nonclinical studies have shown that paroxetine is an SSRI. Paroxetine capsules are not an estrogen, and its mechanism of action for the treatment of VMS is unknown.

12.3Pharmacokinetics Absorption, Distribution, Metabolism and Excretion Absorption Paroxetine is completely absorbed after oral dosing of the mesylate salt. In a study in which healthy postmenopausal women (n=24) received paroxetine 7.5 mg capsules as a daily dose for 14 days, steady-state paroxetine concentrations were achieved by approximately 12 days of dosing for most subjects, although it may take substantially longer in an occasional patient. Peak concentrations were reached at a median of 6 hours (3 to 8 hours range).

Steady-state mean values of C max , C min , and AUC 0-last were 13.10 ng/mL (CV 91%), 7.17 ng/mL (CV 99%), and 237 hr*ng/mL (CV 94%), respectively. Steady-state AUC 0-24 values were about 3 times those of AUC 0-inf following a single dose, indicating non-linear pharmacokinetics. Steady-state C max values were approximately 5 times greater than those attained after a single dose and steady-state exposure based on AUC 0-24 was about 10 times greater than AUC 0-24 after a single dose.

The nonlinear kinetics and excess accumulation are due to the fact that CYP2D6, an enzyme that is in part responsible for paroxetine metabolism, is readily saturable. The effects of food on the bioavailability of paroxetine were studied with paroxetine tablets at higher strength. AUC was only slightly increased (6%) when drug was administered with food but the C max was 29% greater, while the time to reach peak plasma concentration decreased from 6.4 hours post-dosing to 4.9 hours.

Paroxetine capsules can be taken with or without food. Distribution Paroxetine distributes throughout the body, including the central nervous system, with only 1% remaining in the plasma. Approximately 95% and 93% of paroxetine is bound to plasma protein at 100 ng/mL and 400 ng/mL, respectively.

Under clinical conditions, paroxetine concentrations would normally be less than 100 ng/mL. Paroxetine does not alter the in vitro protein binding of phenytoin or warfarin. Metabolism Paroxetine is extensively metabolized after oral administration.

The principal metabolites are polar and conjugated products of oxidation and methylation, which are readily cleared. Conjugates with glucuronic acid and sulfate predominate, and major metabolites have been isolated and identified. Data indicate that the metabolites have no more than 1/50 the potency of the parent compound at inhibiting serotonin uptake.

The metabolism of paroxetine is accomplished in part by cytochrome CYP2D6. Saturation of this enzyme at clinical doses appears to account for the nonlinearity of paroxetine kinetics with increasing dose and increasing duration of treatment. The role of this enzyme in paroxetine metabolism also suggests potential drug-drug interactions [see Drug Interactions (7)] .

At steady state, when the CYP2D6 pathway is essentially saturated, paroxetine clearance is governed by alternative P450 isozymes, which, unlike CYP2D6, show no evidence of saturation. Excretion Approximately 64% of a 30 mg oral solution of paroxetine was excreted in the urine with 2% as the parent compound and 62% as metabolites over a 10-day post-dosing period. About 36% of the dose was excreted in the feces (probably via the bile), mostly as metabolites and less than 1% as the parent compound over the 10-day post-dosing period.

Specific Populations Renal and Liver Impairment Increased plasma concentrations of paroxetine occur in subjects with renal and hepatic impairment. The mean plasma concentration in patients with creatinine clearance below 30 mL/min was approximately 4 times greater than seen in normal volunteers. Patients with creatinine clearance of 30 to 60 mL/min and patients with hepatic impairment had about a 2-fold increase in plasma concentrations (AUC, C max ).

No paroxetine capsules dose adjustment is considered necessary in patients with renal or hepatic impairment. Elderly Patients In a multiple-dose study in the elderly at daily paroxetine doses of 20, 30, and 40 mg, C min concentration… [Excerpted — this section continues on DailyMed.]

12.2Pharmacodynamics Studies at clinically relevant doses in humans have demonstrated that paroxetine blocks the uptake of serotonin into human platelets. In vitro studies in animals also suggest that paroxetine is a selective inhibitor of neuronal serotonin reuptake and has weak effects on norepinephrine and dopamine neuronal reuptake. In vitro radioligand binding studies indicate that paroxetine has little affinity for muscarinic alpha 1 -, alpha 2 -, beta-adrenergic-, dopamine (D 2 )-, 5-HT 1 -, 5-HT 2 -, and histamine (H 1 )-receptors.

14 CLINICAL STUDIES The efficacy of paroxetine capsules as a treatment for moderate to severe VMS associated with menopause was established in two Phase 3 studies (at a dose of 7.5 mg once daily at bedtime) in 1174 postmenopausal women with a minimum of 7-8 moderate to severe vasomotor symptoms per day at baseline (≥ 50 per week) for 30 days prior to receiving study drug. Study 1 was a 12-week, randomized, double-blind, placebo-controlled clinical trial with a total of 606 postmenopausal women (average age 55 years, 65% Caucasian and 33% African American, 18% surgically menopausal and 82% naturally menopausal).

Study 2 was a 24-week, randomized, double-blind, placebo-controlled clinical trial with a total of 568 postmenopausal women (average age 54 years, 76% Caucasian and 22% African American, 20% surgically menopausal and 81% naturally menopausal). The co-primary efficacy endpoints for both studies were the reduction from baseline in VMS frequency and severity at Weeks 4 and 12. Data from Study 1 showed a statistically significant reduction from baseline in the frequency of moderate to severe vasomotor symptoms at Week 4 and Week 12 and a statistically significant reduction in the severity of moderate to severe VMS at Week 4 for paroxetine capsules compared to placebo (Table 4).

Data from Study 2 showed a statistically significant reduction from baseline in the frequency and severity of moderate to severe vasomotor symptoms at Week 4 and Week 12 for paroxetine capsules compared to placebo (Table 5). Table 4 Study 1: Changes in the Daily Frequency and Daily Severity of Moderate to Severe VMS at Weeks 4 and 12 (MITT Population) Frequency Severity Paroxetine Capsules Placebo Paroxetine Capsules Placebo Baseline n Median 301 10.4 305 10.4 301 2.5 305

2.5Change from baseline at Week 4 n Median Treatment Difference * P -value # 289 -4.3 -1.2 <0.01 293 -3.1 281 -0.05 -0.05 <0.01 289

0.00Change from baseline at Week 12 n Median Treatment Difference * P -value # 264 -5.9 -0.9 <0.01 274 -5.0 236 -0.06 -0.04 0.17 253 -0.02 MITT population: all consented and randomized subjects with valid baseline daily hot flash diary data who had taken at least 1 dose of study medication and had at least 1 day of on-treatment daily hot flash diary data. * Treatment Difference: the difference between the median changes from baseline. # P -value is obtained from rank-ANCOVA model. Table 5 Study 2: Changes in the Daily Frequency and Daily Severity of Moderate to Severe VMS at Weeks 4 and 12 (MITT Population) Frequency Severity Paroxetine Capsules Placebo Paroxetine Capsules Placebo Baseline n Median 284 9.9 284 9.6 284 2.5 284

2.5Change from baseline at Week 4 n Median Treatment Difference * P-value # 276 -3.8 -1.3 <0.01 274 -2.5 268 -0.04 -0.03 0.04 271 -0.01 Change from baseline at Week 12 n Median Treatment Difference * P-value # 257 -5.6 -1.7 <0.01 244 -3.9 245 -0.05 -0.05 <0.01 236

0.00MITT population: all consented and randomized subjects with valid baseline daily hot flash diary data who had taken at least 1 dose of study medication and had at least 1 day of on-treatment daily hot flash diary data. * Treatment Difference: the difference between the median changes from baseline. # P -value is obtained from rank-ANCOVA model. Persistence of benefit at 24 weeks in Study 2 was evaluated with a responder analysis where responders were defined as those patients who achieved ≥ 50% reduction from baseline in the frequency of moderate to severe VMS at Week 24.

The proportion of patients achieving a ≥ 50% reduction in the frequency of moderate to severe VMS from baseline to Week 24 was 48% in the paroxetine capsules group and 36% in the placebo group at Week 24.

13 NONCLINICAL TOXICOLOGY

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis Two-year carcinogenicity studies were conducted in rodents given paroxetine in the diet at 1, 5, and 25 mg/kg/day (mice) and 1, 5, and 20 mg/kg/day (rats). The doses used in these carcinogenicity studies were approximately 16 (mouse) and 26 (rat) times the MHRD for VMS. There was a significantly greater number of male rats in the high-dose group with reticulum cell sarcomas (1/100, 0/50, 0/50, and 4/50 for control, low-, middle-, and high-dose groups, respectively) and a significantly increased linear trend across groups for the occurrence of lymphoreticular tumors in male rats.

Female rats were not affected. Although there was a dose-related increase in the number of tumors in mice, there was no drug-related increase in the number of mice with tumors. The relevance of these findings to humans is unknown.

Mutagenesis Paroxetine produced no genotoxic effect in a battery of 5 in vitro and 2 in vivo assays that included the following: bacterial mutation assay, mouse lymphoma mutation assay, unscheduled DNA synthesis assay, and tests for cytogenetic aberrations in vivo in mouse bone marrow and in vitro in human lymphocytes and in a dominant lethal test in rats. Impairment of Fertility A reduced pregnancy rate was found in reproduction studies in rats at a paroxetine dose of 15 mg/kg/day, which is 19 times the MRHD for VMS on an mg/m 2 basis.

Irreversible lesions occurred in the reproductive tract of male rats after dosing in toxicity studies for 2 to 52 weeks. These lesions consisted of vacuolation of epididymal tubular epithelium at 50 mg/kg/day and atrophic changes in the seminiferous tubules of the testes with arrested spermatogenesis at 25 mg/kg/day (65 times and 32 times the MHRD for VMS on an mg/m 2 basis, respectively).