Paroxetine: Core Clinical Profile (80/20 Summary)

1. Fundamental Overview & Warnings Paroxetine is an oral selective serotonin reuptake inhibitor (SSRI). It carries a severe Boxed Warning for increasing the risk of suicidal thoughts and behaviors in children, adolescents, and young adults (under 24 years old). It is not FDA-approved for pediatric patients, and chronic use may cause pediatric growth inhibition by suppressing growth hormone secretion. The National Institute for Occupational Safety and Health (NIOSH) classifies it as a hazardous drug, requiring specialized protective equipment (e.g., gloves, protective gowns) during handling, manipulation, or administration. It must not be used during pregnancy due to the risk of teratogenesis.

2. Indications & Administration Paroxetine is indicated for major depression, obsessive-compulsive disorder (OCD), social anxiety disorder, generalized anxiety disorder (GAD), panic disorder, posttraumatic stress disorder (PTSD), premenstrual dysphoric disorder (PMDD), and menopausal vasomotor symptoms (hot flashes). It is also utilized off-label for premature ejaculation.

• Administration: It is given as a single daily dose, typically in the morning. Controlled-release (CR) tablets are enteric-coated and must be swallowed whole without cutting, chewing, or crushing, and should not be co-administered with antacids. Food does not affect bioavailability but can minimize gastrointestinal adverse effects.

3. Core Dosing & Adjustments

• Adult Dosing: For depression, GAD, and PTSD, the starting immediate-release (IR) dose is 20 mg/day, capped at a maximum of 50 mg/day. For OCD and panic disorder, the target dose is higher at 40 mg/day, with a maximum of 60 mg/day.
• Menopausal Hot Flashes: A specific 7.5 mg IR capsule is dosed once daily at bedtime.
• Special Populations: Geriatric patients, as well as those with severe renal (CrCl < 30 mL/min) or hepatic impairment, require lower initial dosing (10 mg/day IR) and have a strict maximum limit of 40 mg/day IR.

4. Pharmacology & CYP450 Interactions Paroxetine blocks neuronal serotonin reuptake, boosting serotonin availability. It requires 1 to 4 weeks of therapy for therapeutic onset due to the delayed down-regulation and desensitization of serotonin autoreceptors. Notably, it possesses the highest anticholinergic activity of all SSRIs. It is 93% to 95% bound to plasma protein.

• Drug Interactions: Paroxetine is a potent inhibitor of the CYP2D6 isoenzyme. It saturates CYP2D6 early in dosing (within 10-14 days), leading to nonlinear pharmacokinetics, excess drug accumulation, and a shift toward clearance via the CYP3A4 pathway.

5. Primary Adverse Reactions

• Neurological/Psychiatric: Drowsiness (9-24%), insomnia (8-24%), asthenia (12-22%), headache, and tremor. Severe risks include serotonin syndrome, seizures, and withdrawal symptoms upon rapid cessation.
• Sexual Dysfunction: Extremely common, featuring ejaculation dysfunction (13-28%), erectile dysfunction (4-10%), and decreased libido.
• Gastrointestinal & Systemic: Nausea (4-26%), xerostomia/dry mouth (3-18%), hyperhidrosis/sweating (6-11%), constipation, and diarrhea.
• Other Severe Risks: Hyponatremia/SIADH, bleeding/platelet dysfunction, and bone fractures.