Nearly every prescription written to treat Parkinson's psychosis -- a common psychiatric side effect of Parkinson's disease -- is for medications that have not been shown to improve the condition, a new study finds.
The study also found that about three of every 10 prescriptions are for drugs that can actually harm patients.
"For ninety-eight percent of prescriptions there is no clear proof that they improve psychosis symptoms in Parkinson patients, other than clinician experience," said Dr. Daniel Weintraub, the lead author of the study and an associate professor of psychiatry at the Hospital of the University of Pennsylvania and a physician at the Philadelphia Veterans Affairs Medical Center.
Just one drug, clozapine, is known to improve psychotic symptoms in Parkinson's patients, but only two percent of prescriptions are for clozapine, Weintraub and his colleagues report in the Archives of Neurology.
Parkinson's disease affects nerve cells in the brain that help control muscle movement. As many as six of every 10 people with the condition develop Parkinson's psychosis at some point in their lives. It includes hallucinations and sometimes delusional thinking. One of the major contributors is thought to be the drugs used to treat the physical symptoms of Parkinson's disease.
The researchers tallied up the prescriptions for about 2,500 patients who were treated for Parkinson's psychosis at Veterans Affairs facilities in 2008.
About half of the patients received medication for their psychosis. Two thirds of prescriptions were for quetiapine, which goes by the brand name Seroquel. It's approved by the Food and Drug Administration to treat schizophrenia, which is another type of psychosis.
"Quetiapine became such a dominant medication," Weintraub said, yet "none of the efficacy studies show that it's beneficial" for Parkinson's psychosis.
In four studies, quetiapine didn't worsen patients' muscle problems but it also didn't help their psychosis, said Dr. Joseph Friedman, the director of the Parkinson's Disease and Movement Disorders Center at NeuroHealth, a medical center in Rhode Island.
Still, Friedman and Weintraub support the use of quetiapine, and prescribe it to their own patients.
"It's a peculiar sort of thing, because we pride ourselves on using evidenced-based medicine," Friedman, who was not involved in this study, told Reuters Health. But doctors have found, in their own personal -- and unscientific -- experience, that quetiapine appears safe and useful in patients with Parkinson's psychosis, he added.
Doctors often order medications that are tested and approved for a condition other than the one they are treating, a practice called "off-label prescribing." It lets physicians treat diseases for which there might not be a formally approved drug.
Of concern to Friedman was the finding that the second most popularly prescribed drug was risperidone, another schizophrenia medication that is marketed as Risperdal.
About 17 of every 100 patients treated with a drug for Parkinson's psychosis received risperidone.
Risperidone and another drug, olanzipine, are thought to worsen the symptoms of Parkinson's disease.
Olanzipine, whose brand name is Zyprexa, was prescribed 11 out of every 100 times.
Use of these two drugs shows "ignorance" on the part of physicians who prescribe them without keeping up to date on new studies about their safety, Friedman said of the results.
He encouraged doctors to learn more about the drugs. "The patients shouldn't be asked to read the literature."
Clozapine, the one drug with good results in clinical studies, was "grossly underutilized," Friedman said. It was used for just two of every 100 prescriptions.
The reason clozapine is rarely used, explained Weintraub, is that it requires regular blood testing to monitor for a serious but rare side effect. "It makes it somewhat impractical and a burden to the patients," Weintraub said.
He said the best approach to treating psychosis is to first try and limit, if possible, the Parkinson's medications that might be contributing to the hallucinations or delusions. If that fails, Weintraub then turns to quetiapine or clozapine for treatment.
He said medications should be used very cautiously for patients who also have dementia, because there is an association between anti-psychotic drugs and an increased risk of early death among people who have Parkinson's and dementia.
His study, which was funded by the National Institute of Mental Health, found that of the Parkinson's patients who were treated for psychosis, nearly a third had dementia and more than half of those patients were prescribed an anti-psychotic drug.
Physicians should keep in mind the potential complications of the drugs among Parkinson's patients with dementia, Weintraub said. "Medications should be used only when necessary and not indefinitely."