Anticholinergic Drugs in the treatment of Parkinson's Disease
Anticholinergic drugs, including Benztropine mesylate, Biperiden, Diphenhydramine, and Trihexyphenidyl, are another important class of medications used to mitigate the motor symptoms of Parkinson’s disease. By using these drugs in the early progression of the disease, the need for Levodopa can be prolonged. While the exact mechanism of action is unknown, it is said that anticholinergic drugs are competitive antagonists of muscarinic receptors; thus, inhibiting disproportionate acetylcholine action from the basal ganglia, specifically involuntary muscle movement. These drugs are taken orally and range from 30-70% bioavailable. After taken, they are rapidly absorbed (with the exception of benztropine mesylate) into the brain and produce a high volume of distribution, then biotransforming via N-dealkylated and hydroxylated metabolites. The drug clearance appears to be low in comparison to hepatic blood flow, which reduces the chances of first pass effect. Excretion of the parent drug and metabolite are through the kidneys. With these things being said, there is very little information on the pharmacokinetic information for anticholinergic drugs.
As for dosage, the suggested amount of this class of drugs is between 6-20 mg daily; however, there is a specific anticholinergic phenothiazine compound that is to be taken from 50-600 mg daily. The half life of anticholinergic drugs is between 4 hours to 24 hours, with Diphenhydramine being on the shorter range and Biperiden being on the higher range.
Each medication has its own particular side effects; however common adverse effects of anticholinergic drugs include memory problems, drowsiness, constipation, sedation, urinary retention, blurred vision, tachycardia, and delirium. Increased side effects are typically seen in the elderly, when compared with younger adults. As a physical therapist, these are all things to consider, especially when treating your elderly patients. Future studies must be performed to get a better understanding of why elderly patients tolerate this drug less.
- Brocks, D. R. Anticholinergic drugs used in Parkinson's disease: An overlooked class of drugs from a pharmacokinetic perspective. J Pharmaceut Sci. https://sites.ualberta.ca/~csps/JPPS2(2)/D.Brocks2/anticholinergic.htm. August 22, 1999. Accessed November 5, 2018