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Anti-dementia drug mechanisms matter because Alzheimer's disease (a progressive brain disease causing dementia, a decline in memory and thinking severe enough to disrupt daily life) involves a loss of acetylcholine, a brain chemical needed for memory and learning. Restoring acetylcholine and protecting against a different toxic process are two separate treatment strategies, not one drug doing both jobs. Cholinesterase inhibitors, such as donepezil, rivastigmine and galantamine, raise acetylcholine and are used in mild to moderate Alzheimer's disease. Memantine works a different way entirely and is reserved for moderate to severe disease. For example, imagine a newly diagnosed patient with mild memory loss started on donepezil, versus a patient with advanced disease who can no longer manage daily tasks and is started on memantine instead.

Donepezil, rivastigmine and galantamine block acetylcholinesterase, the enzyme that normally breaks down acetylcholine, so more acetylcholine remains available at the synapseThe tiny gap between two nerve cells where a chemical signal passes from one to the other.Read more → (the gap between two nerve cells) for memory and learning. Because acetylcholine also acts throughout the gut, heart and airways, raising it causes predictable cholinergic side effects: nausea, diarrhoea, and bradycardia (a slow heart rate). Memantine instead is an NMDA (N-methyl-D-aspartate) receptor antagonistA drug that blocks a receptor, stopping it from being activated.Read more →, blocking a receptor that, when overactivated by excess glutamate, contributes to nerve cell damage in more advanced disease. For example, imagine a patient on donepezil who develops persistent diarrhoea and a resting heart rate of 48 beats per minute: this is a predictable cholinergic effect, not a new illness. In practice, this means anticholinergicBlocking the action of acetylcholine, a nerve chemical, causing effects like a dry mouth and blurred vision.Read more → drugs (drugs that block acetylcholine) should not be co-prescribed with a cholinesterase inhibitor, since they work in directly opposing directions and cancel each other out.

• A trainee asks why memantine does not simply abolish normal glutamate signalling despite blocking its receptor. Which property of the drug best explains this?
• Cholinesterase inhibitors are used in Alzheimer's disease because of a specific transmitter deficit. Degeneration of which nucleus is the main source of that deficit?
• A man newly diagnosed with mild Alzheimer's disease asks which drug class current national guidance recommends first for him. What is the appropriate answer?
• A woman on oral rivastigmine has troublesome nausea and vomiting that limits her dose. Which change is most likely to improve tolerability while keeping the same drug?

• Cholinesterase inhibitors, raise acetylcholine and are used in mild-moderate disease, unlike memantine's NMDA-receptor mechanism reserved for moderate-severe disease.
• Memantine, NMDA receptorA glutamate receptor in the brain involved in learning and memory, and a target of drugs like ketamine and memantine.Read more → antagonism protecting against glutamate excitotoxicity, rather than boosting a neurotransmitterA chemical messenger that nerve cells release to signal to the next cell.Read more → directly.
• Anticholinergic drugs, block acetylcholine and worsen cognition, whereas cholinesterase inhibitors raise acetylcholine and aim to improve it.
• Vascular dementia, caused by cerebrovascular disease rather than the cholinergic deficit targeted by cholinesterase inhibitors in Alzheimer's disease.

• Irreversible binding would abolish normal signalling rather than preserve it.
• The drug acts within the channel pore, not at the transmitter binding site.
• The channel must be open for the drug to enter and block it.
• That nucleus supplies dopamine to motor circuits instead.
• That area supplies dopamine to limbic and cortical regions.

• Identify the drug, receptor, enzyme or pharmacokinetic change named in the stem.
• Translate it into the immediate mechanism before looking at the options.
• Use timing and the adverse-effect pattern to separate the nearest alternatives.
• Check whether the question asks for mechanism, clinical consequence, monitoring or management.