2910 Paroxetine Paroxetine hydrochloride and paroxetine mesylate belong to a class of antidepressant agents known as selective serotonin-reuptake inhibitors (SSRIs). Despite distinct structural differences between compounds in this class, SSRIs possess similar pharmacological activity. As with other antidepressant agents, several weeks of therapy may be required before a clinical effect is seen. SSRIs are potent inhibitors of neuronal serotonin reuptake. They have little to no effect on norepinephrine or dopamine reuptake and do not antagonize &alpha;- or &beta;-adrenergic, dopamine D₂ or histamine H₁ receptors. During acute use, SSRIs block serotonin reuptake and increase serotonin stimulation of somatodendritic 5-HT_1A and terminal autoreceptors. Chronic use leads to desensitization of somatodendritic 5-HT_1A and terminal autoreceptors. The overall clinical effect of increased mood and decreased anxiety is thought to be due to adaptive changes in neuronal function that leads to enhanced serotonergic neurotransmission. Side effects include dry mouth, nausea, dizziness, drowsiness, sexual dysfunction and headache (see Toxicity section below for a complete listing of side effects). Side effects generally occur during the first two weeks of therapy and are usually less severe and frequent than those observed with tricyclic antidepressants. Paroxetine hydrochloride and mesylate are considered therapeutic alternatives rather than generic equivalents by the US Food and Drug Administration (FDA); both agents contain the same active moiety (i.e. paroxetine), but are formulated as different salt forms. Clinical studies establishing the efficacy of paroxetine in various conditions were performed using paroxetine hydrochloride. Since both agents contain the same active moiety, the clinical efficacy of both agents is thought to be similar. Paroxetine may be used to treat 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). Paroxetine has the most evidence supporting its use for anxiety-related disorders of the SSRIs. It has the greatest anticholinergic activity of the agents in this class and compared to other SSRIs, paroxetine may cause greater weight gain, sexual dysfunction, sedation and constipation. 61869-08-7 43815 C19H20FNO3 329.142720 White powder. 147-150°C (mesylate salt) >1 g/mL (mesylate salt) Paroxetine hydrochloride is slowly, but completely absorbed following oral administration. Paroxetine mesylate salt is also completely absorbed after oral dosing. The oral bioavailability appears to be low due to extensive first-pass metabolism. Paroxetine hydrochloride oral tablets and suspension are reportedly bioequivalent. Absorption of either salt form is not substantially affected by food. Peak concentrations of Brisbelle (mesylate salt) were reached at 6 hours (3 to 8 hours range). Steady state Cmax was 13.10 ng/mL. The steady state AUC (0-last) was 237 hr*ng/mL. Paroxetine mesylate generally follows non-linear pharmacokinetics because CYP2D6, the enzyme that is part responisible for paroxetine metabolism, is readily saturable. 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. The mechanism of action for the treatment of vasomotor symptoms is unknown. Paroxetine is extensively metabolized after oral administration, 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: Approximately 64% of a 30 mg oral solution of paroxetine was excreted in the urine with 2% as the parent compound and 62% as metabolites. Approximately 36% of the dose was excreted in the feces (via bile), mostly as metabolites and less than 1% as parent compound. Half Life: 21-24 hours LD50: 500mg/kg (Oral, Mouse) (A308) No indication of carcinogenicity to humans (not listed by IARC). 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. Brisdelle, which consists of paroxetine mesylate is indicated for the treatment of moderate to severe vasomotor symptoms (like hot flashes) associated with menopause. Coma, dizziness, drowsiness, facial flushing, nausea, sweating, tremor, vomiting Treatment should consist of those general measures employed in the management of overdosage with any drugs effective in the treatment of major depressive disorder. Ensure an adequate airway, oxygenation, and ventilation. Monitor cardiac rhythm and vital signs. General supportive and symptomatic measures are also recommended. Induction of emesis is not recommended. Gastric lavage with a large-bore orogastric tube with appropriate airway protection, if needed, may be indicated if performed soon after ingestion, or in symptomatic patients. Activated charcoal should be administered. Due to the large volume of distribution of this drug, forced diuresis, dialysis, hemoperfusion, and exchange transfusion are unlikely to be of benefit. No specific antidotes for paroxetine are known. (L1712) 2009-07-21T20:27:29Z 2014-12-24T20:25:52Z Paroxetine C07415 7936 Paroxetine DB00715 true [H][C@@]1(COC2=CC3=C(OCO3)C=C2)CNCC[C@@]1([H])C1=CC=C(F)C=C1 C19H20FNO3 InChI=1S/C19H20FNO3/c20-15-3-1-13(2-4-15)17-7-8-21-10-14(17)11-22-16-5-6-18-19(9-16)24-12-23-18/h1-6,9,14,17,21H,7-8,10-12H2/t14-,17-/m0/s1 InChIKey=AHOUBRCZNHFOSL-YOEHRIQHSA-N 329.3654 329.142721716 Exogenous Solid 3.6 HMDB14853 CHEMBL490 39888 <p>Charles M. Zepp, Yun Gao, Donald L. Heefner, &#8220;Method of preparing optically pure precursors of paroxetine.&#8221; U.S. Patent US5258517, issued January, 1976.</p>