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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