A progressive, degenerative neurological disorder, Parkinson's disease causes muscle tremors, muscle stiffness and difficulty with movement. The symptoms result due to damage to the brain areas that produce the chemical messenger dopamine, a critical signal between nerves and muscles. When the damage affects 60 percent to 80 percent of dopamine-producing cells, symptoms start to appear, according to the National Parkinson's Foundation. Factors that increase the rate of damage or interfere with dopamine regulation worsen the symptoms of Parkinson's disease.
Gene Mutations
As outlined in Johns Hopkins University's Online Mendelian Inheritance in Man, Parkinson's disease has a genetic component, and people who inherit one faulty copy of particular dominant genes are at very high risk for developing the disease. People with two faulty copies of other recessive genes can have an increased risk for developing Parkinson's disease, an earlier age of onset of symptoms or a more severe course of the disease compared with people without the faulty gene copies. In addition to these genes that reside in the cell's nucleus, evidence suggests that alterations in genes specific to the mitochondria, the energy factories of cells, can contribute to Parkinson's disease.
Antipsychotics
According to The Merck Manual for Healthcare Professionals, certain drugs can cause or worsen the symptoms of Parkinson's disease. In particular, patients with Parkinson's disease should avoid typical or traditional antipsychotic medications such as phenothiazines, thioxanthines and butyrophenone, which are often prescribed to treat schizophrenia or other conditions when patients lose touch with reality. These antipsychotic drugs directly block dopamine receptors, exacerbating the decline in dopamine levels and counteracting the effects of Parkinson's medications such as levodopa or dopamine agonists that stimulate dopamine receptors. Unfortunately, many patients with Parkinson's disease develop psychosis as a result of their treatment, because increased levels of dopamine can lead to psychotic episodes. Hallucinations and delusions are a common side effect of Parkinson's medications. Medicating patients with Parkinson's disease to reduce muscle symptoms yet avoid hallucinations and delusions can become a delicate and ongoing balancing act, requiring frequent tweaking of drugs and dosages. According to the National Parkinson's Foundation, two newer atypical antipsychotic medications, clozapine and quetiapine, are considered safe to use by Parkinson's patients.
Other Drugs
The Merck Manual for Healthcare Professionals lists some drugs that can cause parkinsonism, a condition with symptoms similar to Parkinson's disease but due to a different cause. Patients with Parkinson's disease should avoid these drugs because they can worsen tremor and reduce muscle control by interfering with the action of dopamine in the basal ganglia, the movement center of the brain. Examples include methyldopa, meperidine, metoclopramide and long-term use of lithium.
References
- National Parkinson's Foundation: What is Parkinson's Disease
- Johns Hopkins University: Online Mendelian Inheritance in Man: Parkinson's Disease
- The Merck Manual for Healthcare Professionals: Parkinson's Disease
- The Merck Manual for Healthcare Professionals: Schizophrenia
- National Parkinson's Foundation: Parkinson's Disease and Psychosis
