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Prescription Medications

Paroxetine

PAROXETINE- paroxetine hydrochloride hemihydrate tablet
International Labs, Inc.

Suicidality and Antidepressant Drugs

Antidepressants increased the risk compared to placebo of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term Studies of major depressive disorder (MDD) and other psychiatric disorders.

Anyone considering the use of paroxetine tablets or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. Short-term studies did not show an increase in the risk of suicidality with antidepressants compared to placebo in adults beyond age 24; there was a reduction in risk with antidepressants compared to placebo in adults aged 65 and older. Depression and certain other psychiatric disorders are themselves associated with increases in the risk of suicide. Patients of all ages who are started on antidepressant therapy should be monitored appropriately and observed closely for clinical worsening, suicidality, or unusual changes in behavior. Families and caregivers should be advised of the need for close observation and communication with the prescriber. Paroxetine tablets are not approved for use in pediatric patients (see WARNINGS: Clinical Worsening And Suicide Risk, PRECAUTIONS: Information For Patients, and PRECAUTIONS: Pediatric Use).

DESCRIPTION

Paroxetine tablets, USP are an orally administered psychotropic drug. It is the hydrochloride salt of a phenylpiperidine compound identified chemically as (-)-trans -4R -(4′- fluorophenyl)-3S -[(3',4'-methylenedioxyphenoxy) methyl] piperidine hydrochloride hemihydrate and has the molecular formula of C19 H20 FNO3 •HCl•1/2H2 O. The molecular weight is 374.8 (329.4 as free base). The structural formula of paroxetine hydrochloride hemihydrate is:

Structured formula for Paroxetine

Paroxetine hydrochloride, USP is an odorless, white to off-white crystalline powder, having a melting point range of 120° to 138°C. It is freely soluble in methanol, soluble in ethanol, sparingly soluble in dichloromethane and slightly soluble in water.

Each paroxetine tablet, USP intended for oral administration contains paroxetine hydrochloride hemihydrate equivalent to 10 mg or 20 mg or 30 mg of paroxetine. In addition, each tablet contains the following inactive ingredients: dibasic calcium phosphate anhydrous, hypromellose 6 cP, lactose anhydrous, magnesium stearate, polyethylene glycol 6000, povidone, sodium starch glycolate, talc, and titanium dioxide.

CLINICAL PHARMACOLOGY

Pharmacodynamics:

The efficacy of paroxetine in the treatment of major depressive disorder, social anxiety disorder, obsessive compulsive disorder (OCD), panic disorder (PD), and generalized anxiety disorder (GAD) is presumed to be linked to potentiation of serotonergic activity in the central nervous system resulting from inhibition of neuronal reuptake of serotonin (5-hydroxy-tryptamine, 5-HT). 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 potent and highly selective inhibitor of neuronal serotonin reuptake and has only very 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; antagonism of muscarinic, histaminergic, and alpha1 -adrenergic receptors has been associated with various anticholinergic, sedative, and cardiovascular effects for other psychotropic drugs.

Because the relative potencies of paroxetine’s major metabolites are at most 1/50 of the parent compound, they are essentially inactive.

Pharmacokinetics:

Paroxetine hydrochloride is completely absorbed after oral dosing of a solution of the hydrochloride salt. The mean elimination half-life is approximately 21 hours (CV 32%) after oral dosing of paroxetine tablets, 30 mg daily for 30 days. Paroxetine is extensively metabolized and the metabolites are considered to be inactive. Nonlinearity in pharmacokinetics is observed with increasing doses. Paroxetine metabolism is mediated in part by CYP2D6, and the metabolites are primarily excreted in the urine and to some extent in the feces. Pharmacokinetic behavior of paroxetine has not been evaluated in subjects who are deficient in CYP2D6 (poor metabolizers).

In a meta analysis of paroxetine from 4 studies done in healthy volunteers following multiple dosing of 20 mg/day to 40 mg/day, males did not exhibit a significantly lower Cmax or AUC than females.

Absorption and Distribution:

Paroxetine hydrochloride hemihydrate is completely absorbed after oral dosing of a solution of the hydrochloride salt. In a study in which normal male subjects (n = 15) received 30 mg tablets daily for 30 days, steady-state paroxetine concentrations were achieved by approximately 10 days for most subjects, although it may take substantially longer in an occasional patient. At steady state, mean values of Cmax , Tmax , Cmin , and T1/2 were 61.7 ng/mL (CV 45%), 5.2 hr. (CV 10%), 30.7 ng/mL (CV 67%), and 21.0 hours (CV 32%), respectively. The steady-state Cmax and Cmin values were about 6 and 14 times what would be predicted from single-dose studies. Steady-state drug exposure based on AUC0-24 was about 8 times greater than would have been predicted from single-dose data in these subjects. The excess accumulation is a consequence of the fact that 1 of the enzymes that metabolizes paroxetine is readily saturable.

The effects of food on the bioavailability of paroxetine were studied in subjects administered a single dose with and without food. 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 distributes throughout the body, including the CNS, 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 400 ng/mL. Paroxetine does not alter the in vitro protein binding of phenytoin or warfarin.

Metabolism and Excretion:

The mean elimination half-life is approximately 21 hours (CV 32%) after oral dosing of paroxetine tablets, 30 mg tablets daily for 30 days. In steady-state dose proportionality studies involving elderly and nonelderly patients, at doses of 20 mg to 40 mg daily for the elderly and 20 mg to 50 mg daily for the nonelderly, some nonlinearity was observed in both populations, again reflecting a saturable metabolic pathway. In comparison to Cmin values after 20 mg daily, values after 40 mg daily were only about 2 to 3 times greater than doubled.

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 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 PRECAUTIONS: Drugs Metabolized by CYP2D6).

Approximately 64% of a 30-mg oral solution dose 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% 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.

Other Clinical Pharmacology Information

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