Indications
Paroxetine is indicated in:
Major Depressive Disorder
Obsessive Compulsive Disorder
Panic Disorder
Social Anxiety Disorder
Generalized Anxiety Disorder
Posttraumatic Stress Disorder.
Therapeutic Class
SSRIs & related anti-depressant drugs
Pharmacology
The efficacy of Paroxetine 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.
Dosage & Administration
Major Depressive Disorder:
Usual Initial Dosage: Paroxetine (Paroxetine hydrochloride) should be administered as a single daily dose with or without food, usually in the morning. The recommended initial dose is 20 mg/day. Some patients not responding to a 20 mg dose may benefit from dose increases, in 10 mg/day increments, up to a maximum of 50 mg/day. Dose changes should occur at intervals of at least 1 week.
Maintenance Therapy: Systematic evaluation of the efficacy of Paroxetine hydrochloride has shown that efficacy is maintained for periods of up to 1 year with doses that averaged about 30 mg.
Obsessive Compulsive Disorder (OCD):
Usual Initial Dosage: Paroxetine (Paroxetine hydrochloride) should be administered as a single daily dose with or without food, usually in the morning. The recommended dose of Paroxetine in the treatment of OCD is 40 mg daily. Patients should be started on 20 mg/day and the dose can be increased in 10 mg/day increments. Dose changes should occur at intervals of at least 1 week.
Maintenance Therapy: Dosage adjustments should be made to maintain the patient on the lowest effective dosage, and patients should be periodically reassessed to determine the need for continued treatment.
Panic Disorder:
Usual Initial Dosage: Paroxetine should be administered as a single daily dose with or without food, usually in the morning. The target dose of Paroxetine in the treatment of panic disorder is 40 mg/day. Patients should be started on 10 mg/day. Dose changes should occur in 10 mg/day increments and at intervals of at least 1 week. The maximum dosage should not exceed 60 mg/day.
Maintenance Therapy: Dosage adjustments should be made to maintain the patient on the lowest effective dosage, and patients should be periodically reassessed to determine the need for continued treatment.
Social Anxiety Disorder (SAD):
Usual Initial Dosage: Paroxetine should be administered as a single daily dose with or without food, usually in the morning. The recommended initial dosage is 20 mg/day.
Maintenance Therapy: Dosage adjustments should be made to maintain the patient on the lowest effective dosage, and patients should be periodically reassessed to determine the need for continued treatment.
Generalized Anxiety Disorder (GAD):
Usual Initial Dosage: Paroxetine should be administered as a single daily dose with or without food, usually in the morning. The recommended starting dosage and the established effective dosage is 20 mg/day.
Maintenance Therapy: Dosage adjustments should be made to maintain the patient on the lowest effective dosage, and patients should be periodically reassessed to determine the need for continued treatment.
Posttraumatic Stress Disorder (PTSD):
Usual Initial Dosage: Paroxetine should be administered as a single daily dose with or without food, usually in the morning. The recommended starting dosage and the established effective dosage is 20 mg/day. Dose changes, if indicated, should occur in 10 mg/day increments and at intervals of at least 1 week.
Maintenance Therapy: Dosage adjustments should be made to maintain the patient on the lowest effective dosage, and patients should be periodically reassessed to determine the need for continued treatment.
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Interaction
Food/antacids: The absorption and pharmacokinetics of Paroxetine are not affected by food or antacids.
Tryptophan: As with other 5-HT re uptake inhibitors, animal studies indicate that an interaction between Paroxetine and Tryptophan may occur, resulting in a ‘serotonin syndrome’ suggested by a combination of agitation, restlessness and gastrointestinal symptoms including diarrhoea.
Drug metabolizing enzyme inducers /inhibitors: The metabolism and pharmacokinetics of Paroxetine may be affected by drugs, which induce or inhibit hepatic drug metabolizing enzymes. When Paroxetine is to be coadministered with a known drug metabolizing inhibitor, consideration should be given to using doses at the lower end of the range. No initial dosage adjustment of Paroxetine is considered necessary when it is to be co-administered with known drug metabolizing enzyme inducers. Any subsequent dosage adjustment should be guided by clinical effect (tolerabilityand efficacy).
Alcohol: Although Paroxetine does not increase the impairment of mental and motor skill caused by alcohol, the concomitant use of Paroxetine and alcohol in depressed patients is not advised.
Haloperidol/amylobarbitone/oxazepam: Experience in a limited number of healthy subjects has shown that Paroxetine did not increase the sedation and drowsiness associated with haloperidol, amylobarbitone or oxazepam when given in combination.
MAOls: As with other 5-HT re uptake inhibitors, animal studies indicate that an interaction between Paroxetine and monoamine oxidase (MAO) inhibitors may occur.
Lithium: Since there is little clinical experience, and there have been reports of interaction of lithium with other 5-HT re-uptake inhibitors, the concurrent administration of Paroxetine and lithium should be undertaken with caution.
Lithium levels should be monitored. Phenytoin / anticonvulsants: Co-administration of Paroxetine and phenytoin is associated with decreased plasma concentrations of Paroxetine and increased adverse experiences. Co-administration of Paroxetine with other anticonvulsants may also be associated with an increased incidence of adverse experiences.
Warfarin: Preliminary data suggest that there may be a pharmacodynamic interaction between Paroxetine and warfarin, which may result in increased bleeding in the presence of unaltered prothrombin times. Paroxetine should therefore be administered with great caution to patients receiving oral anticoagulants.
Contraindications
Concomitant use in patients taking either monoamine oxidase inhibitors (MAOIs) or thioridazine is contraindicated. This is contraindicated in patients with a hypersensitivity to Paroxetine.
Side Effects
Major depressive disorder: Asthenia, sweating, nausea, decreased appetite, somnolence, dizziness, insomnia, tremor, nervousness, ejaculatory disturbance and other male genital disorders.
Obsessive compulsive disorder: Nausea, dry mouth, decreased appetite, constipation, dizziness, somnolence, tremor, sweating, impotence and abnormal ejaculation.
Panic disorder: Asthenia, sweating, decreased appetite, decreased libido , tremor, abnormal ejaculation, female genital disorders and impotence.
Social anxiety disorder: Sweating, nausea, dry mouth, constipation, decreased appetite, somnolence, tremor, decreased libido, yawn, abnormal ejaculation, female genital disorders and impotence.
Generalised anxiety disorder: Asthenia, infection, constipation, decreased appetite, dry mouth, nausea, decreased libido, somnolence, tremor, sweating and abnormal
ejaculation.
Post-traumatic stress disorder: Asthenia, sweating nausea, dry mouth, diarrhoea, decreased appetite, somnolence, decreased libido, abnormal ejaculation, female genital disorders and impotence.
Pregnancy & Lactation
This drug should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Labor and Delivery: The effect of Paroxetine on labor and delivery in humans is unknown.
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