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Antidepressants, Venlafaxine and Mirtazapine
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- 1Indications for venlafaxine & mirtazapine.• Major depression - where 1st line SSRI's are ineffective/ not tolerated
• Generalised anxiety disorder (venlafaxine) - 2MOA of venlafaxine & mirtazapine.Venlafaxine is a serotonin & noradrenaline reuptake inhibitor (SNRI), interfering with uptake of these neurotransmitters from the synaptic cleft. Mirtazapine is an antagonist of inhibitory pre-synaptic α2-adrenoceptors. Both drugs increase availability of monoamines for neurotransmission, which appears to be the mechanism whereby they improve mood & physical symptoms in moderate-to-severe (but not mild) depression.
Venlafaxine is a weaker antagonist of muscarinic & histamine (H1) receptors than tricyclic antidepressants, whereas mirtazapine is a potent antagonist of histamine (H1) but not muscarinic receptors. They therefore have fewer antimuscarinic side effects than tricyclic antidepressants, although mirtazapine commonly causes sedation. - 3SE's of venlafaxine & mirtazapine.• GI upset
• CNS effects (headache, abnormal dreams, insomnia, confusion, convulsions)
• Hyponatraemia
• Serotonin syndrome - see SSRI's
• Suicidal thoughts & behaviour
• Prolongs QT interval
• ^Risk of ventricular arrhythmias
• Sudden drug withdrawal - GI upset, neurological & flu like symptoms, sleep disturbance - 4CI's, cautions, & important interactions of venlafaxine & mirtazapine.CI's:
• None
Cautions:
• Elderly
• Renal impairment (reduce dose)
• Hepatic impairment (reduce dose)
• CVD associated with inc risk of arrhythmias
Important interactions:
The combination of these drugs with drugs from other antidepressant classes can ^risk of adverse effects (including serotonin syndrome, see Antidepressants, selective serotonin reuptake inhibitors) & should, in general, be avoided.