Mirastad Tác dụng


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Khuong Duy
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Pharmacotherapeutic Group: Other antidepressants. ATC Code: N06AX11.
Pharmacology: Pharmacodynamics: Mirtazapine is an antidepressant which can be given as treatment for episodes of major depression. The presence of symptoms, e.g. anhedonia, psychomotor inhibition, sleep disturbances (early wakening) and weight loss, increase the chance of a positive response. Other symptoms are loss of interest, suicidal thoughts and changes in mood (better in the evening than in the morning). Mirtazapine begins to exert its effect in general after 1-2 weeks of treatment.
Mirtazapine is a centrally active presynaptic α2-antagonist, which increases central noradrenergic and serotonergic neurotransmission. The enhancement of serotonergic neurotransmission specifically mediated via 5-HT1 receptors, because 5-HT2 and 5-HT3 receptors are blocked by mirtazapine. Both enantiomers of mirtazapine are presumed to contribute to the antidepressant activity, the S(+) enantiomer by blocking α2 and 5-HT2 receptors and the R(-) enantiomer by blocking 5-HT3 receptors. The histamine H1-antagonistic activity of mirtazapine is associated with its sedative properties. Mirtazapine is usually well tolerated. It has practically no anticholinergic activity and, at therapeutic doses, has practically no effect on the cardiovascular system.
Pharmacokinetics: After oral administration of mirtazapine, the active substance mirtazapine is rapidly and well absorbed (bioavailability 50%), reaching peak plasma levels after approximately two hours.
Binding of mirtazapine to plasma proteins is approximately 85%. Mirtazapine is extensively metabolised in the liver by CYP2D6, CYP1A2, CYP3A4. Elimination is via urine (75%) and faeces (15%). The mean half-life of elimination is 20-40 hours; longer half-lives, up to 65 hours, have occasionally been recorded and short half-lives have been seen in young men. The half-life of elimination is sufficient to justify once-a-day dosing. Steady state is reached after 3-4 days, after which there is no further accumulation. Mirtazapine displays linear pharmacokinetics within the recommended dose range. Mirtazapine is extensively metabolized and eliminated via the urine and faeces within few days. Major pathways of biotransformation are demethylation and oxidation, followed by conjugation. The demethyl metabolite is pharmacologically active and appears to have the same pharmacokinetic profile as the parent compound. The clearance of mirtazapine may be decreased as a result of renal or hepatic impairment.
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