Parkinson’s disease is a progressive neurodegenerative disease characterized by the loss of dopamine-producing nerve cells in the brain. Dopamine is a neurotransmitter, or cell-signaling molecule, that relays information between nerve cells and the rest of the body. The loss of these nerve cells causes a wide range of symptoms. Doctors may prescribe anticholinergic medications to help treat some of these symptoms, such as tremors and rigidity. Anticholinergics may also help with dystonia associated with peak-dose and wearing-off effects of other Parkinson’s medications.
How anticholinergics work
In the brain, there is normally a balance between two neurotransmitters: acetylcholine and dopamine. In Parkinson’s disease, the death of dopamine-producing nerve cells throws off the balance between these two neurotransmitters, causing many of the disease’s symptoms. Anticholinergics work by blocking the acetylcholine receptors on nerve cells without activating them. This helps reduce the effect of acetylcholine and balance the effect of decreased amounts of dopamine.
Types of anticholinergics used in Parkinson’s disease
Anticholinergics were the first form of treatment for Parkinson’s disease and have been used to treat Parkinson’s-related tremors and dystonia for a long time. The earliest reports of anticholinergic medications for Parkinson’s are from the 19th century. Many anticholinergic medications have been developed, with a wide assortment marketed in the mid-20th century.
Other anticholinergics include Norflex (orphenadrine), also available as a generic, and profenamine, available in Canada. Kemadrin (procyclidine) is no longer available in the U.S. but is available in Europe and as a generic in Canada.
Anticholinergics in clinical trials for Parkinson’s disease
Several studies have shown that anticholinergics are useful in reducing tremors. Two studies, one published in Movement Disorders and the other in Archives of Neurology, found that anticholinergics, as well as dopamine agonists (medications that mimic the effect of dopamine), are effective at reducing tremors in Parkinson’s disease. Some patients responded better to one treatment than the other.
Studies have also shown, however, that anticholinergics may be associated with greater cognitive decline in Parkinson’s patients. A meta-analysis study (a study of many previous studies) showed that anticholinergics lead to a definite improvement in motor symptoms but are also associated with side effects including cognitive decline and hallucinations. The study analyzed six anticholinergics but did not have enough evidence to compare their efficacy.
The most common side effects of anticholinergics include blurred vision, dry mouth, constipation, nausea, difficulty emptying the bladder, impaired sweating, and rapid heart rate. Some side effects that are usually more noticeable in older adults include issues with memory, confusion, and hallucinations. For this reason, anticholinergics are usually not prescribed to patients over age 70.
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