Source of information: Drugbank (External Link). Last updated on: 3rd July 18
*Trade Name used in the content below may not be the same as the HSA-registered product.
Active Ingredient / Synonyms
Elafax | Venlafaxina | Venlafaxine | Venlafaxinum | Venlafaxine |
Venlafaxine (Effexor) is an antidepressant of the serotonin-norepinephrine reuptake inhibitor (SNRI) class first introduced by Wyeth in 1993. It is prescribed for the treatment of clinical depression and anxiety disorders. Due to the pronounced side effects and suspicions that venlafaxine may significantly increase the risk of suicide it is not recommended as a first line treatment of depression. However, it is often effective for depression not responding to SSRIs. Venlafaxine was the sixth most widely-used antidepressant based on the amount of retail prescriptions in the US (17.1 million) in 2006.
For the management of major depressive disorder (MDD), generalized anxiety disorder (GAD), social anxiety disorder (social phobia), panic disorder with or without agoraphobia, vasomotor symptoms in women with breast cancer and in postmenopausal women, and neuropathic pain.
Mechanism of Action
The exact mechanism of action of venlafaxine is unknown, but appears to be associated with the its potentiation of neurotransmitter activity in the CNS. Venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV), inhibit the reuptake of both serotonin and norepinephrine with a potency greater for the 5-HT than for the NE reuptake process. Both venlafaxine and the ODV metabolite have weak inhibitory effects on the reuptake of dopamine but, unlike the tricyclics and similar to SSRIs, they are not active at histaminergic, muscarinic, or alpha(1)-adrenergic receptors.
Venlafaxine potentiates the neurotransmitter activity in the central nervous system. Furthermore, venlafaxine and its metabolite, O-desmethylvenlafaxine (ODV) potently inhibit the reuptake of serotonin and norepinephrine and weakly inhibit dopamine reuptake. Both molecules do not bind to muscarinic, histaminergic, or alpha-1 adrenergic receptors. Pharmacologic activity at these receptors is hypothesized to be associated with the various anticholinergic, sedative, and cardiovascular effects seen with other psychotropic drugs. Both also do not have any monoamine oxidase (MAO) inhibitory activity.
Venlafaxine is well absorbed. Food does not effect the absorption of venlafaxine or its subsequent metabolism into ODV. Bioavailability is 45% following oral administration. Time to steady state = 3 days.
* 7.5 ± 3.7 L/kg [venlafaxine] * 5.7 ± 1.8 L/kg [O-desmethylvenlafaxine(active metabolite)]
Undergoes extensive first pass metabolism in the liver to its major, active metabolite, ODV, and two minor, less active metabolites, N-desmethylvenlafaxine and N,O-didesmethylvenlafaxine. Formation of ODV is catalyzed by cytochrome P450 (CYP) 2D6, whereas N-demethylation is catalyzed by CYP3A4, 2C19 and 2C9. ODV possesses antidepressant activity that is comparable to that of venlfaxine.
Renal elimination of venlafaxine and its metabolites is the primary route of excretion. Approximately 87% of a venlafaxine dose is recovered in the urine within 48 hours as either unchanged venlafaxine (5%), unconjugated ODV (29%), conjugated ODV (26%), or other minor inactive metabolites (27%).
Steady state plasma clearance, venlafaxine = 1.3 ± 0.6 L/h/kg; Steady state plasma clearance, ODV = 0.4 ± 0.2 L/h/kg.
Most patients overdosing with venlafaxine develop only mild symptoms. However, severe toxicity is reported with the most common symptoms being CNS depression, serotonin toxicity, seizure, or cardiac conduction abnormalities. Venlafaxine's toxicity appears to be higher than other SSRIs, with a fatal toxic dose closer to that of the tricyclic antidepressants than the SSRIs. Doses of 900 mg or more are likely to cause moderate toxicity. Deaths have been reported following large doses.
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