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Biogenic Amine Theory of Alzheimer's Disease
The biogenic amine theory suggests that abnormalities in neurotransmitter systems, particularly acetylcholine, play a central role in Alzheimer's disease. Acetylcholine deficiency is considered the hallmark, leading to cognitive deficits, while changes in dopamine, serotonin, and norepinephrine also contribute to the symptoms.
Classification of Alzheimer's Drugs
Alzheimer's disease medications can be classified into two major categories:
- Cholinesterase Inhibitors
- NMDA Receptor Antagonists
1. Cholinesterase Inhibitors
Examples:
- Donepezil
- Rivastigmine
- Galantamine
Mechanism of Action:
Cholinesterase inhibitors block the enzyme acetylcholinesterase, preventing the breakdown of acetylcholine, thereby increasing its availability in the brain and improving cognitive functions.
Therapeutic Uses:
- Used in the treatment of mild to moderate Alzheimer's disease.
- Improve memory and cognitive function.
Adverse Effects:
- Gastrointestinal: Nausea, vomiting, diarrhea.
- Cardiovascular: Bradycardia, syncope.
- CNS: Insomnia, dizziness, headaches.
Contraindications:
- Bradycardia or significant cardiac arrhythmias.
- Peptic Ulcer Disease.
- Asthma/COPD.
2. NMDA Receptor Antagonists
Example:
- Memantine
Mechanism of Action:
Memantine blocks NMDA receptors, regulating glutamate activity to prevent excitotoxicity, which is linked to neurodegeneration in Alzheimer's disease.
Therapeutic Uses:
- Used in moderate to severe Alzheimer's disease.
- Helps stabilize symptoms by reducing excitotoxicity.
Adverse Effects:
- CNS: Dizziness, confusion, hallucinations.
- Gastrointestinal: Constipation.
- Cardiovascular: Hypertension.
Contraindications:
- Severe renal impairment.
- Seizure disorders.
