By: Matthew Clark, PharmD, PGY-2 Pharmacy Resident in Pain and Palliative
Care, Hospice of Southern Illinois
October is American Pharmacists Month and we present to you a series of
end-of-life topics throughout the month by our very own, Matthew Clark, PharmD,
PGY-2 Pharmacy Resident in Pain and Palliative Care! Our series will help
expand your understanding of the field and debunk some myths in the field of
Topic 2 : Best Agents for Psychosis Related to Parkinson’s
Parkinsonism is a disease that is prevalent across the elderly population. In fact, Parkinson’s affects 1% of patients above the age of 60 in the United States. The disease is due to an insufficiency of dopamine and dopamine receptors in the area of the brain called substantia nigra. The loss of dopamine leads to common symptoms associated with Parkinson’s disease such as: bradykinesia, shaking, tremors, and rigidity. In addition to
Parkinsonism, patients can develop psychosis during the late stages of the disease. As healthcare professionals, it is important to choose the most appropriate agent to treat psychosis without exacerbating Parkinson’s symptoms.
Appropriate Agents to Treat Psychosis
The use of atypical antipsychotics is preferred for the treatment of psychosis. This class of medications exerts their mechanism by binding to dopamine and serotonin receptors which help alleviate symptoms of psychosis. However, by blocking these receptors, antipsychotics can actually exacerbate Parkinson’s symptoms. The binding affinity of each medication to dopamine receptors determines the extent they can affect Parkinsonism. In other words, the stronger the antipsychotic agent binds to dopamine receptors, the more likely it will cause Parkinson-like symptoms called extrapyramidal
symptoms (EPS). The antipsychotics that bind tightly to dopamine receptors and
are more likely to cause EPS are olanzapine and risperidone. The agents preferred
for psychosis related to Parkinson’s are clozapine and quetiapine.
Despite clozapine and quetiapine being preferred agents for treating psychosis in patients with Parkinson’s disease, they are associated with unfavorable adverse reactions. Quetiapine can cause metabolic syndromes such as increased blood glucose and weight which may not be ideal for patients with hyperglycemia. On the other hand, clozapine can cause a fatal blood disorder called agranulocytosis. This is a decrease in white blood cells which can lead to life-threatening infections. In order to monitor for this
condition, routine blood tests must be conducted in order to track an absolute
neutrophil count (ANC). A drop in ANC below 1,000/mm3 in the blood constitutes discontinuation of clozapine.
Treating psychosis in patients with Parkinson’s disease can be quite a challenge given the adverse reactions associated with the use of antipsychotics. Clozapine and quetiapine are
preferred since they do not extensively exacerbate Parkinson’s symptoms. Despite the adverse effects that these two medications cause, appropriate monitoring can not only prevent these effects, but also optimally treat patients.
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