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 Oxat are not affected by food or antacids.

Tryptophan: As with other 5-HT re uptake inhibitors, animal studies indicate that an interaction between Oxat 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 Oxat may be affected by drugs, which induce or inhibit hepatic drug metabolizing enzymes. When Oxat 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 Oxat 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 Oxat does not increase the impairment of mental and motor skill caused by alcohol, the concomitant use of Oxat and alcohol in depressed patients is not advised.

Haloperidol/amylobarbitone/oxazepam: Experience in a limited number of healthy subjects has shown that Oxat 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 Oxat 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 Oxat and lithium should be undertaken with caution.

Lithium levels should be monitored. Phenytoin / anticonvulsants: Co-administration of Oxat and phenytoin is associated with decreased plasma concentrations of Oxat and increased adverse experiences. Co-administration of Oxat 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 Oxat and warfarin, which may result in increased bleeding in the presence of unaltered prothrombin times. Oxat 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.

Nursing Mothers: Like many other drugs, Paroxetine is secreted in human milk, and caution should be exercised when Paroxetine hydrochloride is administered to a nursing woman.
Precautions & Warnings
Cardiac conditions: Oxat does not produce clinically significant changes in blood pressure, heart rate and ECG. Nevertheless, as with all psychoactive drugs, caution is advised when treating patients with cardiac conditions.

Epilepsy: As with other antidepressants, Oxat should be used with caution in-patients with epilepsy.

Seizures: Overall, the incidence of seizures is < 0.1% in patients treated with Oxat. Oxat should be discontinued in any patient who develops seizures.

ECT: There is little clinical experience of concurrent administration of Oxat with ECT.

Ability to drive/use machines: Clinical experience has shown that therapy with Oxat is not associated with impairment of cognitive or psychomotor function. However, as with all psychoactive drugs, patients should be cautioned about their ability to drive a car and operate machinery.

Discontinuation of Treatment with Oxat: Recent clinical trials supporting the various approved indications of Oxat employed a taper phase regimen, rather than an abrupt discontinuation of treatment. The taper phase regimen used in GAD and PTSD clinical trials involved an incremental decrease in the daily dose by 10 mg/day at weekly intervals. When a daily dose of 20 mg/day was reached, patients were continued on this dose for 1 week before treatment was stopped.
Use in Special Populations
Dosage for Elderly or Debilitated, and Patients with Severe Renal or Hepatic Impairment: The recommended initial dose is 10 mg/day for elderly patients, debilitated patients, and/or patients with severe renal or hepatic impairment. Increases may be made if indicated. Dosage should not exceed 40 mg/day.
Therapeutic Class
SSRIs & related anti-depressant drugs
Storage Conditions
Keep out of the reach of children. Store at a cool and dry place. Protect from light and moisture.