1. What are cholinesterase inhibitors?

These are the main drugs used for Alzheimer's disease. Three drugs are currently licensed: Donepezil (Aricept), Galantamine (Reminyl）and Rivastigmine（Exelon).

There are no major differences between these drugs. They may help with the symptoms of Alzheimer's disease - for example, memory loss and anxiety.

2. What are the effects of cholinesterase inhibitors?

Although they cannot reverse the deterioration in cognitive functioning, they can help to preserve it for a certain period of time. They may slow the progression of memory deterioration in Alzheimer’s dementia and also have general benefits including improving alertness and motivation. Some people feel brighter in their mood and will be able to do things that were too difficult for them, such as going to the market.

3. How do cholinesterase inhibitors work?

They cannot stop the disease process of Alzheimer's disease, i.e. unable to stop the destruction of brain cells, but they can slow down the breakdown of acetylcholine in the brain. Acetylcholine is a chemical that helps to pass messages between certain brain cells involved in memory. In Alzheimer's disease, the amount of acetylcholine is very much reduced. Memory starts to suffer. The increase in the level of acetylcholine in the brain allows it to continue its function and reduces some of the symptoms of Alzheimer's disease.

It may take some months for there to be a noticeable improvement or slowing down of memory loss.

When a significant amount of brain cells is being destroyed and there is too little acetylcholine left, the medication will be no longer effective. Therefore it is not suitable for severe Alzheimer’s dementia.

4. How well do they work?

About half of people on these drugs show a slight improvement or a stabilisation of their condition over 6 months. Not everyone benefits from these drugs. Regular monitoring of cognitive functioning is needed. If no improvement is seen in the first few months, then they should be stopped. These drugs should only be given to people in mild to moderate stages of the illness.

5. What are the side-effects?

The most common side-effects are nausea, reduced appetite, tiredness, diarrhoea, muscle cramps and poor sleep. These may be reduced or avoided by increasing the dose slowly, or taking the medicine after meal. The side-effects usually fade after a few weeks and will disappear if the medicine is stopped.

6. How to take these drugs?

It is usual to start on a low dose which is gradually increased. They may be taken once or twice daily. They come in tablet and patch to be stuck on your skin. The drugs need to be taken every day for them to be effective.

7. How long should these drugs be taken?

These drugs are usually prescribed for a trial period of 3 to 4 months. If it is found that they are not working, the doctor will recommend stopping them. If these drugs do work, there is no clear view as to how long they should be taken. The mini-mental state examination scoring is a commonly used tool to monitor cognitive function. According to some guidelines, if the scoring is less than 10, the drugs should be gradually stopped.

8. What is Memantine?

Memantine is also known as Ebixa. It works in a different way comparing to the cholinesterase inhibitors. It is thought to work by affecting a chemical in the brain called glutamate. In Alzheimer's disease, too much glutamate leaks out of the damaged brain cells which destructs nerve cells in the brain and stops them working properly. Learning and memory will be affected. It reduces the activity of glutamate and has been associated with reducing the rate of deterioration on global, cognitive and behavioural improvements. It is usually used for severe Alzheimer's disease. The main side-effects are dizziness, constipation and headache which are usually mild.