For the treatment of moderate to severe dementia of the Alzheimer's type.
Memantine, an amantadine derivative, is an NMDA receptor antagonist used in the treatment of Alzheimer's disease. It differs from traditional agents used in Alzheimer's disease by acting on glutamatergic neurotransmission, rather than cholinergic. There is some evidence that dysfunction of glutamatergic neurotransmission, manifested as neuronal excitotoxicity, is involved in the aetiology of Alzheimer's disease (Cacabelos et al., 1999). As such, targeting the glutamatergic system, specifically NMDA receptors, was a novel approach to treatment in view of the limited efficacy of existing drugs targeting the cholinergic system. A systematic review of randomised controlled trials found that memantine has a positive effect on cognition, mood, behaviour, and the ability to perform daily activities. There is no evidence that memantine prevents or slows neurodegeneration in patients with Alzheimer's disease.
Mode of Action:
Memantine exerts its action through uncompetitive NMDA receptor antagonism, binding preferentially to the NMDA receptor-operated cation channels. Prolonged increased levels of glutamate in the brain of demented patients are sufficient to counter the voltage-dependent block of NMDA receptors by Mg2+ ions and allow continuous influx of Ca2+ ions into cells, ultimately resulting in neuronal degeneration. Studies suggest that memantine binds more effectively than Mg2+ ions at the NMDA receptor, and thereby effectively blocks this prolonged influx of Ca2+ ions through the NMDA channel whilst preserving the transient physiological activation of the channels by higher concentrations of synaptically released glutamate. Thus memantine protects against chronically elevated concentrations of glutamate. Memantine also has antagonistic activity at the type _ serotonergic (5-HT_) receptor with a potency that is similar to that at the NMDA receptor, and lower antagonistic activity at the nicotinic acetylcholine receptor. This drug has no affinity for _-aminobutyric acid (GABA), benzodiazepine, dopamine, adrenergic, histamine, or glycine receptors or for voltage-dependent calcium, sodium, or potassium channels.
Excreted largely unchanged. About 20% is metabolized to 1-amino-3-hydroxymethyl-5-methyl-adamantane and 3-amino-1-hydroxy-5,7-dimethyl-adamantane.
Side effects include pain, abnormal crying, leg pain, fever, increased apetite. Adverse drug reactions include: dizziness, confusion, headache, hallucinations, tiredness. Less common side effects include: vomiting, anxiety, hypertonia, cystitis, and increased libido. Doses of up to 400 mg have been tolerated.
Cacabelos R, Takeda M, Winblad B: The glutamatergic system and neurodegeneration in dementia: preventive strategies in Alzheimerês disease. Int J Geriatr Psychiatry. 1999 Jan;14(1):3-47. Pubmed Rogawski MA, Wenk GL: The neuropharmacological basis for the use of memantine in the treatment of Alzheimerês disease. CNS Drug Rev. 2003 Fall;9(3):275-308. Pubmed Robinson DM, Keating GM: Memantine: a review of its use in Alzheimerês disease. Drugs. 2006;66(11):1515-34. Pubmed Rogawski MA: Low affinity channel blocking (uncompetitive) NMDA receptor antagonists as therapeutic agentsãtoward an understanding of their favorable tolerability. Amino Acids. 2000;19(1):133-49. Pubmed Rammes G, Rupprecht R, Ferrari U, Zieglgansberger W, Parsons CG: The N-methyl-D-aspartate receptor channel blockers memantine, MRZ 2/579 and other amino-alkyl-cyclohexanes antagonise 5-HT receptor currents in cultured HEK-293 and N1E-115 cell systems in a non-competitive manner. Neurosci Lett. 2001 Jun 22;306(1-2):81-4. Pubmed
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