How effective are cholinesterase inhibitors?

In people with advanced Alzheimer’s disease, certain nerve cells are much less active. This means that it takes longer for brain signals to be sent. Cholinesterase inhibitors can increase communication between the nerve cells to improve the symptoms of Alzheimer’s. These medications have been approved for use in mild to moderate Alzheimer’s disease. In Germany, three different cholinesterase inhibitors are currently available: donepezil, galantamine and rivastigmine. They are taken in the form of tablets or capsules. Rivastigmine is also available in a patch. Here the drug is absorbed into the body through the skin.

Various systematic reviews analyzed the results of controlled studies on the effectiveness of cholinesterase inhibitors in people with Alzheimer's disease. In these studies, either one group of participants took one of the three cholinesterase inhibitors and a control group took a placebo (a dummy treatment), or the drugs were compared directly with each other. The researchers wanted to see whether the medication improved people’s mental performance, reduced mental health problems or made it easier for them to perform daily tasks. There are many good-quality studies on these effects, so it's possible to properly assess the short-term advantages and disadvantages. But most of these studies lasted for six months at the most, so it's difficult to see what the effects of long-term use would be.

The studies show that the cholinesterase inhibitors donepezil, galantamine and rivastigmine can slightly delay the loss of mental abilities in people who have mild to moderate Alzheimer’s disease. For instance, some of the people with Alzheimer’s who regularly took one of these medications were able to remember things more easily.

More specifically, taking the example of galantamine: The medication has a positive effect on thinking skills and memory in about 14 out of 100 people who use it. Galantamine is just used as an example here, and this doesn't imply that any one of the three medications is more effective than the others. It is believed that the different drugs have a similar effect on cognitive performance.

All three cholinesterase inhibitors were found to have a stronger effect when taken in moderate to high doses than when taken in very low doses. However, donepezil already has an effect in smaller doses, whereas galantamine and rivastigmine probably don't.

The rivastigmine patch is available in different doses. Unlike rivastigmine capsules or tablets, there is only weak evidence suggesting that the patch improves mental performance. But this was only observed with the higher dose of 9.5 mg of rivastigmine released every 24 hours.

Doctors still recommend starting the treatment with the low dose (4.6 mg every 24 hours). People who tolerate it well can change to the higher dose after at least four weeks. After at least six months, the dose can be increased again to 13.3 mg every 24 hours if the Alzheimer's symptoms have got noticeably worse.

Some studies suggest that people can cope with their daily lives better when they use cholinesterase inhibitors. But it is not clear whether these medications can help with mental health problems associated with Alzheimer's, such as depression or anxiety.

It hasn't yet been possible to tell whether the drugs can improve disease-related quality of life and delay the move to a nursing home. It is also not known whether age, sex or accompanying conditions might influence the effects of the drugs.

All three medications can cause side effects like nausea, vomiting, loss of appetite, dizziness or diarrhea. Some people might stop taking them as a result. Higher doses are more likely to cause side effects. Depending on which medication they take, about 1 to 3 out of 10 people feel nauseous or have to vomit.

Rivastigmine patches do not generally have fewer side effects than the rivastigmine capsules, but the patch causes fewer gastrointestinal problems. It can cause skin redness and itching, though:

• About 13 out of 100 people have skin redness due to the patch.
• About 10 out of 100 people have itching due to the patch.

The medications didn't cause any serious side effects. But the data from the studies didn't provide any information about rare side effects or side effects that only occur after long-term use.

It is also not clear what sort of long-term benefits cholinesterase inhibitors may have, or how they compare to other medications or non-drug treatment options.