- Last edited on May 27, 2021
Paroxetine (Paxil)
Primer
Paroxetine (Trade name: Paxil) is an antidepressant in the selective seronin reuptake inhibitor (SSRI) class used in the treatment various psychiatric disorders including: major depressive disorder, generalized anxiety disorder, posttraumatic stress disorder, social anxiety disorder, and obsessive compulsive disorder.
Pharmacokinetics
See also article: Introduction to Pharmacology
Pharmacokinetics of Paroxetine
See also article: Cytochrome (CYP) P450 Metabolism
Paroxetine: Cytochrome P450 Metabolism
Substrate of (Metabolized by) | |
---|---|
Induces | |
Inhibits | 1A2, 2D6 (potent!) |
Pharmacodynamics
Mechanism of Action
- Paroxetine is a very “sloppy” SSRI, meaning it targets other receptors like histamine (sedation and weight gain) and muscarinic receptors (which makes it highly anticholinergic)
- When it is discontinued, there can be high cholinergic rebound when you stop paroxetine
- When H1 is suddenly unblocked, people get jittery and insomnia
- Paroxetine also has adrenergic effects, it could almost be considered like a serotonin norepinephrine reuptake inhibitor.
Toxicity
Indications
Dosing
Dosing for Paroxetine
Starting | 20 mg PO daily |
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Titration | |
Maximum | 60 mg PO daily |
Taper |
Formulations
- Paroxetine comes in oral formulation.
Monitoring
Withdrawal
See main article: Antidepressant Withdrawal (Discontinuation) Syndrome
- Paroxetine is a very potent serotonergic agent, hence why the discontinuation and withdrawal symptoms can be so bad!
- This is one reason to avoid using paroxetine as the first medication of choice, even though there are many studies on it.
- The half-life also varies significantly, complicating withdrawal symptoms.
- If a patient has difficulty tapering off paroxetine due to discontinuation symptoms, fluoxetine can be added as a 2 week course of therapy to help with taper (e.g. 10 mg fluoxetine)
Contraindications
Absolute
Relative
Drug-Drug Interactions
- Tamoxifen - paroxetine inhibits CYP 2D6 which inhibits the conversion of tamoxifen to its active metabolite. Do not use paroxetine in women with breast cancer on tamoxifen!
Side Effects
Adverse Events
Clinical Pearls
- Anticholinergic activity can cause more sedation compared to other SSRIs
- Nitric oxide synthetase inhibition may also increase sexual dysfunction
Special Populations
Geriatric
See main article: Geriatric Pharmacology
Pediatric
See main article: Pediatric Pharmacology
Obstetric and Fetal
See main article: Obstetric and Fetal Pharmacology
- Paroxetine is associated with increased risk for cardiac defects in the fetus, and should not be used in pregnant women.[1]
Medically Ill
See main article: Psychotropic Dosing in the Medically Ill