2.1  Dosage Information

The recommended dosage of Paroxetine Capsules for the treatment of moderate to severe VMS is 7.5 mg once daily, at bedtime, with or without food.

2.2  Use of Paroxetine Capsules Before or After a Monoamine Oxidase Inhibitor (MAOI)

Wait at least 14 days after discontinuation of an MAOI before initiating therapy with Paroxetine Capsules. Conversely, allow at least 14 days after stopping Paroxetine Capsules before starting an MAOI [see Contraindications (4.1), Warnings and Precautions (5.2) and Drug Interactions (7.3)].

4.1  Monoamine Oxidase Inhibitors

Concomitant use of an MAOI with Paroxetine Capsules or within 14 days of stopping treatment with Paroxetine Capsules is contraindicated because of an increased risk of serotonin syndrome. The use of Paroxetine Capsules within 14 days of stopping an MAOI is also contraindicated [see Dosage and Administration (2.2), Warnings and Precautions (5.2) and Drug Interactions (7.3)].

Starting Paroxetine Capsules in a patient who is being treated with linezolid or intravenous methylene blue, both of which inhibit monoamine oxidase, is also contraindicated because of an increased risk of serotonin syndrome [see Dosage and Administration (2.2), Warnings and Precautions (5.2) and Drug Interactions (7.3)].

4.2  Thioridazine

Concomitant use of Paroxetine Capsules with thioridazine is contraindicated, because thioridazine prolongs the QT interval, and paroxetine can increase thioridazine levels [see Drug Interactions (7.1)].

4.3  Pimozide

Concomitant use of Paroxetine Capsules with pimozide is contraindicated because pimozide prolongs the QT interval, and paroxetine increases pimozide levels [see Drug Interactions (7.1)].

4.4  Hypersensitivity to any Ingredient in Paroxetine Capsules 

Paroxetine Capsules are contraindicated in patients with a history of hypersensitivity to paroxetine or any of the other ingredients in Paroxetine Capsules.

4.5  Pregnancy

Menopausal VMS does not occur during pregnancy and Paroxetine Capsules may cause fetal harm [see Use in Specific Populations (8.1)].

5.1  Suicidal Thoughts and Behaviors

Paroxetine Capsules are not approved for any psychiatric condition.

Antidepressants, including those that contain an SSRI, increase the risk of suicidal thinking and behavior (suicidality) in pediatric and young adult patients when used to treat major depressive disorder (MDD) and other psychiatric disorders. There is limited information regarding suicidality in women who use Paroxetine Capsules for treatment of VMS. The Paroxetine Capsules trials excluded women with a presence or history of previous psychiatric disorders.

Consider discontinuing Paroxetine Capsules in patients with worsening depression or those who experience emergent suicidality or symptoms that might be precursors to worsening depression or suicidality, especially if these symptoms are severe, abrupt in onset, or were not part of the patient’s presenting symptoms.

All patients being treated with Paroxetine Capsules should be observed closely for clinical worsening, suicidality, and unusual changes in behavior, especially during the initial few months of treatment.

Anxiety, agitation, panic attacks, insomnia, irritability, hostility, aggressiveness, impulsivity, akathisia (psychomotor restlessness), hypomania, and mania have been reported in patients being treated with antidepressants for MDD as well as for other psychiatric and nonpsychiatric indications. Although a causal link between the emergence of such symptoms and either the worsening of depression and/or the emergence of suicidal impulses has not been established, there is concern that such symptoms may represent precursors to emerging suicidality.

Families and caregivers of patients being treated with Paroxetine Capsules should be alerted about the need to monitor patients for the emergence of agitation, irritability, unusual changes in behavior, and the other symptoms described above, as well as the emergence of suicidality, and to report such symptoms immediately to healthcare providers.

5.2  Serotonin Syndrome

The development of a potentially life-threatening serotonin syndrome has been reported with SSRIs, including paroxetine, alone but particularly with concomitant use of serotonergic drugs (including triptans, tricyclic antidepressants, fentanyl, lithium, tramadol, tryptophan, buspirone, amphetamines, and St. John’s Wort), and with drugs that impair metabolism of serotonin (in particular, MAOIs, both those intended to treat depression and others such as linezolid and intravenous methylene blue).

Serotonin syndrome symptoms may include mental status changes (e.g., agitation, hallucinations, delirium, and coma), autonomic instability (e.g., tachycardia, labile blood pressure, dizziness, diaphoresis, flushing, hyperthermia), neuromuscular symptoms (e.g., tremor, rigidity, myoclonus, hyperreflexia, incoordination), and/or gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea). Monitor patients for the emergence of serotonin syndrome.

The concomitant use of Paroxetine Capsules with MAOIs is contraindicated. Do not start Paroxetine Capsules in a patient who is being treated with MAOIs such as linezolid or intravenous methylene blue. All reports with methylene blue that provided information on the route of administration involved intravenous administration in the dose range of 1 mg/kg to 8 mg/kg. No reports involved the administration of methylene blue by other routes (such as oral tablets or local tissue injection) or at lower doses. There may be circumstances when it is necessary to initiate treatment with an MAOI such as linezolid or intravenous methylene blue in a patient taking Paroxetine Capsules. Paroxetine Capsules should be discontinued before initiating treatment with the MAOI [see Contraindications (4.1) and Dosage and Administration (2.2)].

If concomitant use of Paroxetine Capsules with other serotonergic drugs (e.g., triptans, tricyclic antidepressants, fentanyl, lithium, tramadol, tryptophan, buspirone, amphetamines, and St. John’s Wort) is clinically warranted, consider the increased risk of serotonin syndrome and carefully observe the patient, particularly during treatment initiation [see Contraindications (4.1) Drug Interactions (7.3)].

Discontinue Paroxetine Capsules and any concomitant serotonergic agents immediately if the above events occur and initiate supportive symptomatic treatment.

5.3  Potential Impact on Tamoxifen Efficacy

It is uncertain whether the co-administration of paroxetine and tamoxifen has a significant adverse effect on the efficacy of tamoxifen. Some studies have shown that the efficacy of tamoxifen, as measured by the risk of breast cancer relapse/mortality, may be reduced when co-prescribed with paroxetine as a result of paroxetine’s irreversible inhibition of CYP2D6 [see Drug Interactions (7.1)]. However, other studies have failed to demonstrate such a risk. When tamoxifen is used for the treatment or prevention of breast cancer, weigh the likely benefit of Paroxetine Capsules for treating VMS vs. the risk of possible decreased tamoxifen effectiveness, and consider avoiding the concomitant use of Paroxetine Capsules for VMS treatment.

5.4  Abnormal Bleeding

SSRIs, including Paroxetine Capsules, may increase the risk of bleeding events. Concomitant use of aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin, and other anticoagulants may add to this risk. Case reports and epidemiological studies (case-control and cohort design) have demonstrated an association between use of drugs that interfere with serotonin reuptake and the occurrence of gastrointestinal bleeding. Bleeding events related to SSRIs have ranged from ecchymosis, hematoma, epistaxis, and petechiae to life-threatening hemorrhages. Caution patients about the risk of bleeding associated with the concomitant use of Paroxetine Capsules and NSAIDs, aspirin, or other drugs that affect coagulation [see Drug Interactions (7.1)].

5.5 Angle-Closure Glaucoma

The pupillary dilation that occurs following use of many antidepressants and Paroxetine Capsules may trigger an angle closure attack in a patient with anatomically narrow angles who does not have a patent iridectomy.

5.6  Hyponatremia

Hyponatremia may occur as a result of treatment with SSRIs, including Paroxetine Capsules. Elderly patients may be at greater risk. In many cases, the hyponatremia appears to be the result of the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Cases with serum sodium lower than 110 mmol/L have been reported in patients using SSRIs. Also, patients taking diuretics or who are volume-depleted can be at greater risk. Consider discontinuation of Paroxetine Capsules in patients with symptomatic hyponatremia and institute appropriate medical intervention.

Signs and symptoms of hyponatremia include headache, difficulty concentrating, memory impairment, confusion, weakness, and unsteadiness, which can lead to falls. Signs and symptoms associated with more severe and/or acute cases have included hallucination, syncope, seizure, coma, respiratory arrest, and death.

5.7  Bone Fracture

Epidemiological studies on bone fracture risk following exposure to SSRIs have reported an association between SSRI treatment and fractures. It is unknown to what extent fracture risk is directly attributable to SSRI treatment. If a Paroxetine Capsules-treated patient presents with unexplained bone pain, point tenderness, swelling, or bruising, consider the possibility of a fragility fracture.

5.8  Screening Patients for Bipolar Disorder and Monitoring for Mania/Hypomania

Paroxetine Capsules are only indicated for the treatment of moderate to severe VMS and are not approved for use in treating either depression or bipolar depression. However, prior to initiating treatment with Paroxetine Capsules, all patients should be adequately screened to determine if they are at risk for bipolar disorder; such screening should include a detailed psychiatric history, including a family history of suicide, bipolar disorder, and depression. It is generally believed (though not established in controlled trials) that use of an antidepressant alone may increase the likelihood of precipitation of a mixed/manic episode in patients at risk for bipolar disorder.

5.9  Seizures

In premarketing testing of paroxetine, seizures occurred in 0.1% of paroxetine-treated patients. Use Paroxetine Capsules cautiously in patients with a history of seizures or with conditions that potentially lower the seizure threshold. Evaluate and consider discontinuing use in any patient who develops seizures.

5.10  Akathisia

The use of paroxetine or other SSRIs has been associated with the development of akathisia, which is characterized by an inner sense of restlessness and psychomotor agitation such as an inability to sit or stand still usually associated with subjective distress. This is most likely to occur within the first few weeks of treatment. Discontinue treatment with Paroxetine Capsules if akathisia occurs.

5.11 Potential for Cognitive and Motor Impairment

Paroxetine Capsules have the potential to impair judgment, thinking, or motor skills. Patients should be cautioned about operating hazardous machinery, including motor vehicles, until they are reasonably certain that the drug treatment does not affect them adversely.

6.1  Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot directly be compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The data described below reflect exposure to Paroxetine Capsules in the one 8-week Phase 2 randomized, placebo-controlled trial and the two Phase 3 randomized, placebo-controlled, 12-week and 24-week trials for the treatment of moderate to severe VMS [see Clinical Studies (14)]. In these trials, a total of 635 women were exposed to Paroxetine Capsules 7.5 mg administered orally once daily and 641 women received placebo. The majority of Paroxetine Capsules-treated patients were Caucasian (68%) and African American (30%), with a mean age of 55 years (range 40 to 73 years). Women with a history of suicidal ideation or suicidal behavior were excluded from these studies.

Adverse Reactions Leading to Study Discontinuation: A total of 4.7% of women taking Paroxetine Capsules discontinued from the clinical trials due to an adverse reaction, compared to 3.7% of women on placebo; the most frequent adverse reactions leading to discontinuation among paroxetine-treated women were: abdominal pain (0.3%), attention disturbances (0.3%), headache (0.3%), and suicidal ideation (0.3%).

Common Adverse Reactions: Overall, based on investigators’ determinations about what events were likely to be drug-related, about 20% of women treated with Paroxetine Capsules reported at least 1 adverse reaction in the three controlled studies. The most common adverse reactions (≥ 2% and more common among Paroxetine Capsules-treated women) reported in these studies were headache, fatigue/malaise/lethargy, and nausea/vomiting. Of these commonly reported adverse reactions, nausea occurred primarily within the first 4 weeks of treatment and fatigue occurred primarily within the first week of treatment, and decreased in frequency with continued therapy.

The adverse reactions that occurred in at least 2% of patients in the Paroxetine Capsules group and at a higher incidence than placebo are shown in Table 1 for the pooled Phase 2 and Phase 3 trials.

Certain symptoms were seen more frequently in women at the time of discontinuation of Paroxetine Capsules compared to women discontinuing placebo, and have also been reported upon discontinuation of other formulations of paroxetine, particularly when abrupt. These include increased dreaming/nightmares, muscle cramps/spasms/twitching, headache, nervousness/anxiety, fatigue/tiredness, restless feeling in legs, and trouble sleeping/insomnia. While these events are generally self-limiting, there have been reports of serious discontinuation symptoms with other formulations of paroxetine.

Serious Adverse Reactions: In the pooled Phase 2 and Phase 3 trials, three Paroxetine Capsules-treated patients reported a serious adverse reaction of suicidal ideation and one Paroxetine Capsules-treated patient reported a serious adverse reaction of suicide attempt. There were no serious adverse reactions of suicidal ideation or suicide attempt reported among the placebo-treated patients.

6.2  Postmarketing Experience

The following adverse reactions have been identified from clinical studies of paroxetine and during post-approval use of other formulations of paroxetine. Because some of these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Blood and Lymphatic System Disorders: Idiopathic thrombocytopenic purpura, Events related to impaired hematopoiesis (including aplastic anemia, pancytopenia, bone marrow aplasia, agranulocytosis).

Cardiac Disorders: Atrial fibrillation, Pulmonary edema, Ventricular fibrillation, Ventricular tachycardia (including torsades de pointes).

Gastrointestinal Disorders: Pancreatitis, Pancreatitis hemorrhagic, Vomiting.

General Disorders and Administration Site Conditions: Death, Drug withdrawal syndrome, Malaise.

Hepatobiliary Disorders: Drug-induced liver injury, Hepatic failure, Jaundice.

Immune System Disorders: Anaphylactoid reaction, Angioedema, Toxic epidermal necrolysis.

Investigations: Elevated liver tests (the most severe cases were deaths due to liver necrosis, and grossly elevated transaminases associated with severe liver dysfunction).

Metabolism and Nutrition Disorders: Diabetes mellitus inadequate control, Type 2 diabetes mellitus.

Nervous System Disorders: Neuroleptic malignant syndrome, Paresthesia, Somnolence, Tremor.

Psychiatric Disorders: Aggression, Agitation, Anxiety, Confusional state, Depression, Disorientation, Homicidal ideation, Insomnia, Restlessness.

Respiratory, Thoracic and Mediastinal Disorders: Pulmonary hypertension.

Skin and Subcutaneous Tissue Disorders: Hyperhidrosis, Stevens-Johnson syndrome.

7.1  Potential for Paroxetine Capsules to Affect Other Drugs

Paroxetine is a strong CYP2D6 inhibitor. Clinical drug interaction studies have been performed with substrates of CYP2D6 and show that paroxetine can inhibit the metabolism of drugs metabolized by CYP2D6 [see Clinical Pharmacology (12.3)]. Table 2 contains examples of drugs with a metabolism that may be affected by co-administration with Paroxetine Capsules.

Use caution if co-administering Paroxetine Capsules with other drugs that are metabolized by CYP2D6, including nortriptyline, amitriptyline, imipramine, desipramine, fluoxetine, phenothiazines, risperidone, and Type 1C antiarrhythmics (e.g., propafenone, flecainide, and encainide).

7.2  Potential for Other Drugs to Affect Paroxetine Capsules

The metabolism and pharmacokinetics of paroxetine may be affected by the induction and inhibition of drug metabolizing enzymes such as CYP2D6. Table 3 contains a list of drugs that may affect the pharmacokinetics of Paroxetine Capsules when administered concomitantly [see Clinical Pharmacology (12.3)].

Use caution if co-administering Paroxetine Capsules with other drugs that inhibit CYP2D6 (e.g., quinidine).

7.3  Other Potentially Significant Drug Interactions

Monoamine Oxidase Inhibitors (MAOIs)

Serious adverse reactions such as serotonin syndrome have been reported in patients receiving a concomitant SSRI and MAOI, in patients started on an SSRI who recently received an MAOI and in patients started on an MAOI who recently received an SSRI. Therefore, concomitant use of MAOIs with Paroxetine Capsules or use of Paroxetine Capsules and an MAOI within 14 days of each other is contraindicated [see Dosage and Administration (2.2), Contraindications (4.1) and Warnings and Precautions (5.2)].

Serotonergic Drugs

If concomitant use of Paroxetine Capsules with other serotonergic drugs (e.g., triptans, tricyclic antidepressants, fentanyl, lithium, tramadol, tryptophan, buspirone, amphetamines, and St. John’s Wort) is clinically warranted, consider the increased risk of serotonin syndrome and carefully observe the patient, particularly during treatment initiation [see Warnings and Precautions (5.2)].

An interaction between paroxetine and tryptophan may occur when they are co-administered. Adverse experiences, consisting primarily of headache, nausea, sweating, and dizziness, have been reported when tryptophan was administered to patients taking paroxetine. Consequently, concomitant use of Paroxetine Capsules with tryptophan is not recommended.

If concomitant use of Paroxetine Capsules with a serotonergic drug is warranted, carefully observe the patient, particularly during treatment initiation. There have been postmarketing reports of serotonin syndrome with the use of an SSRI and a triptan.

Paroxetine Capsules contain paroxetine, which is also the active ingredient in other drugs. The concomitant use of Paroxetine Capsules with other paroxetine products is not recommended [see Indications and Usage (1)].

Drugs that Interfere with Hemostasis (e.g., NSAIDs, Aspirin, and Warfarin)

Altered anticoagulant effects, including increased bleeding, have been reported when SSRIs are co-administered with NSAIDs, aspirin, and warfarin or other drugs that affect coagulation. There may be a pharmacodynamic interaction between paroxetine and warfarin that causes an increased bleeding diathesis despite unaltered prothrombin time. Carefully monitor patients receiving warfarin therapy when Paroxetine Capsules are initiated or discontinued [see Warnings and Precautions (5.4)].

8.1  Pregnancy

Pregnancy Category X

Risk Summary

Paroxetine Capsules are contraindicated in pregnant women because menopausal VMS does not occur during pregnancy and paroxetine can cause fetal harm. Epidemiological studies have shown that infants exposed to paroxetine in the first trimester of pregnancy may have an increased risk of cardiovascular malformations. Cardiac malformations are a common congenital abnormality. These data would suggest that the risk of a cardiac abnormality following paroxetine exposure in the first trimester may increase the risk from 1% to 2%. Exposure to SSRIs in late pregnancy may lead to an increased risk for neonatal complications requiring prolonged hospitalization, respiratory support, and tube feeding, and/or persistent pulmonary hypertension of the newborn (PPHN). No teratogenicity was seen in reproductive development studies conducted in rats and rabbits. However, an increase in rat pup deaths was seen during the first 4 days of lactation when dosing occurred during the last trimester of gestation and continued throughout lactation, at a dose approximately equal to the maximum recommended human dose (MRHD) for VMS (7.5 mg) on an mg/m2 basis. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to a fetus.

Human Data

First-Trimester Pregnancy Exposure

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Epidemiologic studies which include data from the Swedish National Registry, a retrospective cohort study using United Healthcare data and a meta-analysis of studies (1992-2008) have shown a less than 2-fold increased risk of cardiac malformations, primarily ventricular septal and atrial septal defects, with first-trimester paroxetine exposure. Two case-control studies using separate databases with > 9000 birth defect cases and > 4000 controls showed 7 and 6 paroxetine-exposed infants respectively, with right ventricular outflow tract obstructions, a 2-to 3-fold increased risk. An increase in overall congenital malformations with first-trimester paroxetine use was not observed in all studies.

Third-Trimester Pregnancy Exposure

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Neonates exposed to SSRIs late in the third trimester have developed complications requiring prolonged hospitalization, respiratory support, and tube feeding. Such complications can arise immediately upon delivery. Reported clinical findings have included respiratory distress, cyanosis, apnea, seizures, temperature instability, feeding difficulty, vomiting, hypoglycemia, hypotonia, hypertonia, hyperreflexia, tremor, jitteriness, irritability, and constant crying. These features are consistent with either a direct toxic effect of SSRIs or, possibly, a drug discontinuation syndrome. It should be noted that in some cases, the clinical picture is consistent with serotonin syndrome [see Warnings and Precautions (5.2)].

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Infants exposed to SSRIs in late pregnancy may have an increased risk for persistent pulmonary hypertension of the newborn (PPHN). PPHN occurs in 1 - 2 per 1000 live births in the general population and is associated with substantial neonatal morbidity and mortality. In a retrospective case-control study of 377 women whose infants were born with PPHN and 836 women whose infants were born healthy, the risk for developing PPHN was approximately 6-fold higher for infants exposed to SSRIs after the 20th week of gestation compared to infants who had not been exposed to antidepressants during pregnancy. There is currently no corroborative evidence regarding the risk for PPHN following exposure to SSRIs in pregnancy; this is the first study that has investigated the potential risk. The study did not include enough cases with exposure to individual SSRIs to determine if all SSRIs posed similar levels of PPHN risk.

Animal Data

Reproduction studies were performed at doses up to 50 mg/kg/day in rats and 6 mg/kg/day in rabbits administered during organogenesis. These doses are approximately 65 (rat) and 16 (rabbit) times the maximum recommended human dose (MRHD) for VMS on an mg/m2 basis. There were no teratogenic effects. However, in rats, there was an increase in pup deaths during the first 4 days of lactation when dosing occurred during the last trimester of gestation and continued throughout lactation. This effect occurred at a dose of 1 mg/kg/day or approximately equal to the MRHD for VMS on an mg/m2 basis. The no-effect dose for rat pup mortality was not determined. The cause of these deaths is unknown.

8.3  Nursing Mothers

Paroxetine is excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from Paroxetine Capsules, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

8.4  Pediatric Use

Safety and effectiveness in pediatric patients have not been established; Paroxetine Capsules are not indicated in the pediatric population.

8.5  Geriatric Use

Clinical studies of Paroxetine Capsules did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Elderly patients may have elevated paroxetine plasma concentrations compared to younger patients. However, no Paroxetine Capsules dose adjustment is considered necessary in elderly patients [see Clinical Pharmacology (12.3)].

SSRIs have been associated with cases of clinically significant hyponatremia in elderly patients, who may be at greater risk for this adverse event [see Warnings and Precautions (5.6)].

8.6  Renal Impairment

No Paroxetine Capsules dose adjustment is considered necessary in patients with renal impairment [see Clinical Pharmacology (12.3)].

8.7  Hepatic Impairment

No Paroxetine Capsules dose adjustment is considered necessary in patients with liver impairment [see Clinical Pharmacology (12.3)].

10.1 Human Experience with Overdosage

There is limited clinical experience with Paroxetine Capsules overdosage in humans, as there were no overdoses reported in the clinical studies.

Spontaneous cases of deliberate or accidental overdosage during paroxetine treatment have been reported; some of these cases were fatal and some of the fatalities appeared to involve paroxetine alone. Of nonfatal cases with known outcome, most recovered without sequelae. The largest known ingestion involved 2000 mg of paroxetine (267 times the maximum recommended daily dose) in a patient who recovered.

Commonly reported adverse reactions associated with paroxetine overdosage include somnolence, coma, nausea, tremor, tachycardia, confusion, vomiting, and dizziness. Other notable signs and symptoms observed with overdoses involving paroxetine (alone or with other substances) include mydriasis, convulsions (including status epilepticus), ventricular dysrhythmias (including torsades de pointes), hypertension, aggressive reactions, syncope, hypotension, stupor, bradycardia, dystonia, rhabdomyolysis, symptoms of hepatic dysfunction (including hepatic failure, hepatic necrosis, jaundice, hepatitis, and hepatic steatosis), serotonin syndrome, manic reactions, myoclonus, acute renal failure, and urinary retention.

10.2 Management of Overdosage

Treatment should consist of those general measures employed in the management of overdosage with any SSRI. Consult with a certified poison control center for up-to-date guidance and advice on treatment of overdosage.

Ensure an adequate airway, oxygenation, and ventilation. Monitor cardiac rhythm and vital signs. General supportive and symptomatic measures are also recommended. Induction of emesis is not recommended. In managing overdosage, consider the possibility of multiple drug involvement.

12.1 Mechanism of Action

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

12.2 Pharmacodynamics

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 alpha1-, alpha2-, beta-adrenergic-, dopamine (D2)-, 5-HT1-, 5-HT2-, and histamine (H1)-receptors.

12.3 Pharmacokinetics

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 Capsules 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 Cmax, Cmin, and AUC0-last were 13.10 ng/mL (CV 91%), 7.17 ng/mL (CV 99%), and 237 hr*ng/mL (CV 94%), respectively.

Steady-state AUC0-24 values were about 3 times those of AUC0-inf following a single dose, indicating non-linear pharmacokinetics. Steady-state Cmax values were approximately 5 times greater than those attained after a single dose and steady-state exposure based on AUC0-24 was about 10 times greater than AUC0-24 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 Cmax 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, Cmax). 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, Cmin concentrations were about 70% to 80% greater than the respective Cmin concentrations in nonelderly subjects. No Paroxetine Capsules dose adjustment is considered necessary in elderly patients.

Drug Interaction Studies

Potential Effect of Paroxetine Capsules on Other Drugs

Drugs Metabolized by CYP3A4

An in vivo drug interaction study involving the co-administration under steady-state conditions of paroxetine and terfenadine, a substrate for cytochrome CYP3A4, revealed no effect of paroxetine on terfenadine pharmacokinetics. In vitro studies have shown ketoconazole, a potent inhibitor of CYP3A4 activity, to be at least 100 times more potent than paroxetine as an inhibitor of the metabolism of several substrates for CYP3A4, including astemizole, triazolam, and cyclosporine. Based on the assumption that the relationship between paroxetine’s in vitro Ki and its lack of effect on terfenadine’s in vivo clearance predicts its effect on other CYP3A4 substrates, paroxetine’s extent of inhibition of CYP3A4 activity is not likely to be of clinical significance.

Drugs Metabolized by CYP2D6

Many drugs are metabolized by the cytochrome P450 isozyme CYP2D6. Like other agents that are metabolized by CYP2D6, paroxetine may significantly inhibit the activity of this isozyme. In most patients (> 90%), this CYP2D6 isozyme is saturated early during paroxetine dosing.

Specific studies investigating the effect of paroxetine on drugs metabolized by CYP2D6 are listed below:

Pimozide: Higher doses of paroxetine have been shown to elevate plasma levels of pimozide. In a controlled study of healthy volunteers, after paroxetine was titrated to 60 mg daily, co-administration of a single dose of 2 mg pimozide was associated with mean increases in pimozide AUC of 151% and Cmax of 62%, compared to pimozide administered alone [see Drug Interactions (7.1)].

Tamoxifen: It is uncertain whether the co-administration of paroxetine and tamoxifen has a significant adverse effect on the efficacy of tamoxifen. Some studies have shown that the efficacy of tamoxifen, as measured by the risk of breast cancer relapse/mortality, may be reduced when co-prescribed with paroxetine as a result of paroxetine’s irreversible inhibition of CYP2D6. However, other studies have failed to demonstrate such a risk [see Warnings and Precautions (5.3) and Drug Interactions (7.1)].

Desipramine: In one study, daily dosing of paroxetine (20 mg once daily) under steady-state conditions increased single dose desipramine (100 mg) Cmax, AUC, and T1/2 by an average of approximately 2-, 5-, and 3-fold, respectively [see Drug Interactions (7.1)].

Risperidone: Daily dosing of paroxetine 20 mg in patients stabilized on risperidone (4 to 8 mg/day), a CYP2D6 substrate, increased mean plasma concentrations of risperidone approximately 4-fold, decreased 9-hydroxyrisperidone concentrations approximately 10%, and increased concentrations of the active moiety (the sum of risperidone plus 9-hydroxyrisperidone) approximately 1.4-fold [see Drug Interactions (7.1)].

Atomoxetine: The effect of paroxetine on the pharmacokinetics of atomoxetine has been evaluated when both drugs were at steady state. In healthy volunteers who were extensive metabolizers of CYP2D6, paroxetine 20 mg daily was given in combination with 20 mg atomoxetine every 12 hours. This resulted in increases in steady-state atomoxetine AUC values that were 6-to 8-fold greater and in atomoxetine Cmax values that were 3-to 4-fold greater than when atomoxetine was given alone [see Drug Interactions (7.1)].

Digoxin: Mean digoxin AUC at steady state decreased by 15% in the presence of paroxetine [see Drug Interactions (7.1)].

Beta Blockers: In a study in which propranolol (80 mg twice daily) was dosed orally for 18 days, the steady-state plasma concentrations of propranolol were unaltered during co-administration with paroxetine (30 mg once daily) for the final 10 days. The effects of propranolol on paroxetine have not been evaluated.

Potential Effect of Other Drugs on Paroxetine Capsules

Concomitant use of paroxetine with other drugs that alter CYP enzymes activities including CYP2D6 may affect the plasma concentrations of paroxetine. Specific studies investigating the effect of other drugs on paroxetine are listed below:

Cimetidine: Cimetidine inhibits many cytochrome P450 enzymes. In a study in which paroxetine (30 mg once daily) was dosed orally for 4 weeks, steady-state plasma concentrations of paroxetine were increased by approximately 50% during co-administration with oral cimetidine (300 mg three times daily) for the final week [see Drug Interactions (7.2)].

Phenobarbital: Phenobarbital induces many cytochrome P450 enzymes. When a single oral 30 mg dose of paroxetine was administered at phenobarbital steady state (100 mg once daily for 14 days), paroxetine AUC and T1/2 were reduced (by an average of 25% and 38%, respectively) compared to paroxetine administered alone. The effect of paroxetine on phenobarbital pharmacokinetics was not studied. Because paroxetine exhibits nonlinear pharmacokinetics, the results of this study may not address the case where the 2 drugs are both being chronically dosed [see Drug Interactions (7.2)].

Phenytoin: When a single oral 30 mg dose of paroxetine was administered at phenytoin steady state (300 mg once daily for 14 days), paroxetine AUC and T1/2 were reduced (by an average of 50% and 35%, respectively) compared to paroxetine administered alone. In a separate study, when a single oral 300 mg dose of phenytoin was administered at paroxetine steady state (30 mg once daily for 14 days), phenytoin AUC was slightly reduced (12% on average) compared to phenytoin administered alone. Because both drugs exhibit nonlinear pharmacokinetics, the above studies may not address the case where the 2 drugs are both being chronically dosed [see Drug Interactions (7.2)].

Digoxin: A clinical drug interaction study showed that concurrent use of digoxin did not affect paroxetine exposure.

Diazepam: A clinical drug interaction study showed that concurrent use of diazepam did not affect paroxetine exposure.

13.1 Carcinogenesis, 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/m2 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/m2 basis, respectively).