tacrine (Parkinson’s disease)

An acetylcholinesterase inhibitor medication taken to improve cognitive function. Tacrine (Cognex) is U.S. Food and Drug Adminis-tration-(FDA)-approved in the United States for treatment of cognitive impairment and dementia of people with Alzheimer’s disease. Its use in people with Parkinson’s is open-label. Because there is a significant overlap in disease processes between Alzheimer’s and Parkinson’s, some neurologists prescribe acetylcholinesterase inhibitors for people with Parkinson’s who have dementia, memory loss, hallucinations, and cognitive impairment even when Alzheimer’s is not present. Though there are reports of its effectiveness in Lewy body dementia and the dementia of Parkinson’s disease, its effectiveness is inconsistent; some people notice measurable improvement, and others experience no difference. There does not appear to be a way to assess who is likely to respond and who is not; when significant cognitive impairment is a factor in Parkinson’s, many people consider it worth the effort to try tacrine to see whether it produces improvement. However, tacrine can cause worsened motor function in people with Parkinson’s.

Tacrine and other acetylcholinesterase inhibitors work by preventing the enzyme acetylcholinesterase from metabolizing acetylcholine, a brain neurotransmitter important to cognitive function that becomes depleted in Alzheimer’s disease. Acetylcholine also affects muscle activity and in excess causes tremors, dystonia, and other dyskinesias. By extending acetylcholine’s availability in the brain, tacrine can significantly worsen the neu-romuscular symptoms of Parkinson’s or cause such symptoms to emerge in people with Alzheimer’s. Each acetylcholinesterase inhibitor has somewhat different actions in the brain, so if tacrine is ineffective or causes undesired side effects, one of the other medications in this classification may be more effective. rivastigmine has the most evidence of both its usefulness and safety in people with Parkinson’s, hence it is currently the first choice of Parkinson’s experts for treating dementia.

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