| Indication | Labeled indications include: major depressive disorder (MDD), panic disorder with or without agoraphobia, obsessive-compulsive disorder (OCD), social anxiety disorder (social phobia), generalized anxiety disorder (GAD), post-traumatic stress disorder (PTSD), and premenstrual dysphoric disorder (PMDD). Unlabeled indications include: eating disorders, impulse control disorders, vasomotor symptoms of menopause, obsessive-compulsive disorder (OCD) in children, and mild dementia-associated agitation in nonpsychotic individuals. |
| Pharmacodynamics | Paroxetine, an antidepressant drug of the selective serotonin reuptake inhibitor (SSRI) type, has no active metabolites and has the highest specificity for serotonin receptors of all the SSRIs. It is used to treat depression resistant to other antidepressants, depression complicated by anxiety, panic disorder, social and general anxiety disorder, obsessive-compulsive disorder (OCD), premenstrual dysphoric disorder, premature ejaculation, and hot flashes of menopause in women with breast cancer. |
| Mechanism of action | Paroxetine is a potent and highly selective inhibitor of neuronal serotonin reuptake. Paroxetine likely inhibits the reuptake of serotonin at the neuronal membrane, enhances serotonergic neurotransmission by reducing turnover of the neurotransmitter, therefore it prolongs its activity at synaptic receptor sites and potentiates 5-HT in the CNS; paroxetine is more potent than both sertraline and fluoxetine in its ability to inhibit 5-HT reuptake. Compared to the tricyclic antidepressants, SSRIs have dramatically decreased binding to histamine, acetylcholine, and norepinephrine receptors. |
| Absorption | Paroxetine hydrochloride is slowly, but completely absorbed following oral administration. The oral bioavailability appears to be low due to extensive first-pass metabolism. Paroxetine hydrochloride oral tablets and suspension are reportedly bioequivalent. Paroxetine mesylate is completely following oral administration. Absorption of either salt form is not substantially affected by food. |
| Volume of distribution | 3.1-28 L/kg observed in animal studies |
| Protein binding | ~ 95% bound to plasma proteins. |
| Metabolism | Paroxetine is extensively metabolized, likely in the liver. The main metabolites are polar and conjugated products of oxidation and methylation, which are readily eliminated by the body. The predominant metabolites are glucuronic acid and sulfate conjugates. Paroxetine metabolites do not possess significant pharmacologic activity (less than 2% that of parent compound). Paroxetine is metabolized by cytochrome P450 (CYP) 2D6. Enzyme saturation appears to account for the nonlinear pharmacokinetics observed with increasing dose and duration of therapy. |
| Route of elimination | Paroxetine is extensively metabolized and the metabolites are primarily excreted in the urine and to some extent in the feces. |
| Half life | 21-24 hours |
| Clearance | Not Available |
| Toxicity | LD50=500mg/kg (orally in mice). Symptoms of overdose include: coma, dizziness, drowsiness, facial flushing, nausea, sweating, tremor, vomiting. Side effects include: nervous system effects such as asthenia, somnolence, dizziness, insomnia, tremor, and nervousness; GI effects such as nausea, decreased appetite, constipation, diarrhea, and dry mouth; impotence, ejaculatory dysfunction (principally ejaculatory delay), and other male genital disorders; female genital disorders (principally anorgasmia or difficulty reaching climax/orgasm); and sweating. Discontinuation syndrome may occur with abrupt withdrawal. Symptoms of discontinuation syndrome include flu-like symptoms, insomnia, nausea, imbalance, sensory changes, and hyperactivity. |