Memantine

Absorption

After an oral dose, memantine is well absorbed. Its peak drug concentrations are attained in about 3-7 hours. Memantine shows linear pharmacokinetics when given at normal therapeutic doses. This drug can be taken without regard to food, as there is no effect of food on memantine absorption .

Toxicity

LD50
Oral LD50, mouse 437-498 mg/kg Oral LD50, rat 328-370 mg/kg
Carcinogenesis, Mutagenesis, Impairment of Fertility
No evidence of carcinogenicity was seen in mouse and rat models administered memantine at doses equivalent to supratherapeutic human doses . Additionally, no genotoxic potential was noted when a battery of assays was performed. No effects on fertility or reproductive performance were noted in rats given to 18 mg/kg/day (equivalent to 9 times the maximum recommended human dose) orally from 14 days preceding mating through gestation and lactation in females, or for 60 preceding mating activity in males animals .
Use in pregnancy
This drug is considered a pregnancy category B drug, meaning no sufficiently controlled and adequate studies of memantine in pregnant women have been performed. This drug should be taken during pregnancy only if the potential benefit justifies the possible fetal risk .
Use in nursing
It is unknown whether memantine is excreted in human milk. Due to that fact that many drugs are found excreted in human milk, caution should be observed when this drug is taken by a nursing mother .

Description

Memantine is a potent antagonist of the N-methyl-D-aspartate (NMDA) receptor. Experimentally, memantine inhibits and reverses the abnor-mal activity of a protein phosphatase (PP-2A) that leads to tauhyperphosphorylation and to neurofibrillary degeneration inAD. Memantine is effective and well toler-ated in patients with severe AD and wasapproved by the FDA for the treatment of moderate-to-severe AD.

The Uses of Memantine

Recent phase 3 clinical trials have shown that Memantine is an effective way of treatment of both mild and moderate-to-severe Alzheimer''s disease and possibly vascular dementia (multi-infarct dementia). Memantine’s method of action involves an uncompetitive, low-affinity, open-channel blocker; it enters the receptor-associated ion channel preferentially when it is excessively open, and, most importantly, its off-rate is relatively fast so that it does not substantially accumulate in the channel to interfere with normal synaptic transmission.

Background

Initially approved by the FDA in 2013, memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist used in the management of Alzheimer's Disease (AD). It is different from many other Alzheimer's Disease medications, as it works by a different mechanism than the cholinesterase enzyme inhibitors normally employed in the management of Alzheimer's disease . Memantine blocks the effects of glutamate, a neurotransmitter in the brain that leads to neuronal excitability and excessive stimulation in Alzheimer's Disease .
In 2010, it was estimated that 36 million people worldwide live with Alzheimer's Disease. In 2013, this number increased to 44 million. Almost doubling every 20 years, the prevalence of Alzheimer's Disease is predicted to reach 66 million by 2030 and to 115 million by 2050 . In December 2013, the G8 dementia summit concluded that dementia should be considered a global priority with the objective of developing a cure or a disease-modifying therapy by the year 2025 .

Indications

Memantine is used to manage moderate to severe Alzheimer's dementia .
A more recent systemic review and meta-analysis indicates that memantine is beneficial as a first line drug for the treatment of Alzheimer's dementia. Cholinesterase inhibitors may be added to memantine for further beneficial effects on behavioral symptoms and other symptoms of dementia .

Pharmacokinetics

General effects
This drug inhibits calcium influx into cells that is normally caused by chronic NMDA receptor activation by glutamate . This leads to the improvement of Alzheimer's dementia symptoms, demonstrated by increased cognition and other beneficial central nervous system effects .
Effects on neuroplasticity
Like other NMDA receptor antagonists, memantine at high doses can reduce neuronal synaptic plasticity that is involved in learning and memory processes. At lower concentrations, which are normally used in the clinical setting, memantine can enhance neuronal synaptic plasticity in the brain, improve memory, and act as a neuroprotectant against the destruction of neurons caused by excitatory neurotransmitters .
Effect on various receptors
Memantine has demonstrated minimal activity for GABA, benzodiazepine, dopamine, adrenergic, histamine, and glycine receptors, as well as voltage-dependent Ca2+, Na+ or K+ channels. This drug has shown antagonist activity at the 5HT3 receptors. Laboratory studies suggest that memantine does not affect the reversible inhibition of the acetylcholinesterase normally caused by donepezil, galantamine, or tacrine .

Metabolism

This drug is partially metabolized in the liver. The hepatic CYP450 enzyme system does not majorly contribute to the metabolism of this drug .