Prochlorperazine Levodopa

Vomiting is triggered in the chemoreceptor trigger zone of the medulla, and nearly all dopamine receptor agonists (e.g. bromocriptine), and agents that increase dopamine in the brain (e.g. levodopa), cause vomiting. Conversely, many dopamine receptor antagonists (e.g. metoclopramide, and phenothiazines, e.g. chlorpromazine and prochlorperazine) have antiemetic activity. 

Prochlorperazine may antagonize the therapeutic effect of bromocriptine on prolactin secretion it also may decrease the vasoconstricting effects of high-dose dopamine and may decrease effectiveness and increase toxicity of levodopa (by dopamine blockade). Prochlorperazine may inhibit metabolism and increase toxicity of phenytoin. 

Note that prochlorperazine should not be given if apomorphine is used for Parkinson s disease, as its dopamine antagonist actions can worsen the disease (see also Levodopa + Antiemetics , p.682). Because apomorphine is highly emetogenic at the doses required for the treatment of Parkinson s disease (1 to 4 mg/hour by subcutaneous infusion), patients with Parkinson s disease requiring apomorphine should be pretreated with domperidone 20 mg three times daily for at least 2 days. Rare reports of extrapyramidal adverse effects have been reported with ondansetron, which may be of relevance in patients with Parkinson s Disease. 

The manufacturer of APO-go specifically notes that there is a potential interaction between clozapine and apomorphine, although they say that clozapine may also be used to reduce the symptoms of neuropsychiatric complications of Parkinson s disease. See also prochlorperazine in (c) above, and Levodopa + Antipsychotics , p.683. 

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