Molecular Mechanism of Action
From a pharmacodynamic standpoint, memantine acts as a non-competitive, low-affinity NMDA receptor antagonist. Under physiological conditions, the ion channel of this receptor is blocked by magnesium ions ($Mg^{2+}$). The drug has a significantly higher affinity for this receptor than endogenous magnesium.
By binding to the receptor, the active substance blocks the ion channel securely. This shortens the duration during which calcium ions ($Ca^{2+}$) can enter the nerve cell. As a result, there is a pronounced decrease in neuronal membrane depolarization. The main outcome of this process is the prevention of the neurotoxic effects of the neurotransmitter glutamate, known in medicine as excitotoxicity (cell damage and death due to overstimulation).
Additional Targets and Clinical Effects
Although NMDA receptors are the primary target, the drug also actively interacts with other structures of the nervous system. Specifically, it affects nicotinic acetylcholine receptors (specifically alpha-7nAChR) and serotonin receptors (5-HT3 subtype). This complex interaction is believed to contribute significantly to the overall therapeutic effect.
At the clinical level, the pharmacodynamic effects manifest as follows:
- Moderate restoration of mnemonic functions, meaning the patient experiences improved memory.
- Correction of various behavioral disturbances characteristic of neurodegenerative processes.
- A notable increase in the patient's ability to perform activities of daily living, significantly facilitating caregiving.
The potential use of this agent in other central nervous system pathologies beyond dementia is currently under active investigation.
Indications and Adverse Reactions
The primary indication for prescribing the drug is Alzheimer-type dementia at moderate to severe stages.
Despite its proven efficacy, therapy may be accompanied by a range of adverse effects affecting various organ systems:
- Central nervous system: reactions can be depressive (lethargy, dizziness) or paradoxically stimulating (agitation, insomnia, and even hallucinations).
- Cardiovascular system: possible elevation of blood pressure, development of hypertension.
- Urinary system: cases of cystitis have been reported during treatment.
Metabolic Cerebroprotectants
In the context of psychotropic drugs and agents that improve brain function, it is also important to mention the group of metabolic cerebroprotectants. Typical representatives of this group include hopantenic acid and pyritinol.
General characteristics of these drugs include a pronounced antihypoxic effect (increasing tissue resistance to oxygen deprivation) and the ability to improve metabolism in neural tissue. An important advantage of this group is its wide therapeutic index, indicating high safety in clinical use. Pyritinol (trade name Encephabol) deserves special attention. Chemically, this compound consists of two vitamin B6 (pyridoxine) molecules linked by a disulfide bridge. Because of this structural similarity, strict precautions are required: it must be prescribed with extreme caution to patients with a history of allergy or hypersensitivity to pyridoxine.