As a first-generation antipsychotic, prochlorperazine mainly blocks D2 dopamine receptors in the brain. It can also block histaminergic, cholinergic and noradrenergic receptors. One study also found that prochlorperazine inhibits the P2X7 receptor in human macrophages, but not in mouse cells, preventing a calcium ion influx. This mechanism was independent of dopamine antagonism.
Prochlorperazine can be administered orally, parenterally, intramuscularly and rectally. All four routes can be given to control nausea and vomiting. For nausea and vomiting pre- and post-surgery, the intramuscular and parenteral routes are both viable options. For psychiatric conditions, the administration can be via both intramuscular and oral routes. For headaches, parenteral is the route used.
As a first-generation antipsychotic, prochlorperazine can cause a variety of adverse effects. Significant extrapyramidal symptoms including acute dystonia, tardive dyskinesia, Parkinsonism, akathisia, and neuroleptic malignant syndrome. Anticholinergic side effects include anorexia, blurred vision, constipation, dry mucosa and urinary retention. Antihistaminic side effects (blockage of H1) include sedation. Prochlorperazine can also lower the seizure threshold. It can also lead to prolonged QT interval and cause other cardiac conduction abnormalities. Antiadrenergic effects (blockage of alpha1-adrenergic receptor) can lead to orthostatic hypotension. Due to dopamine blockage in the tuberoinfundibular tract, hyperprolactinemia, amenorrhea, breast enlargement and sexual dysfunction may also occur.
Leukopenia, agranulocytosis, cholestatic jaundice and fatty liver are other possible but rare side effects. A rare but very severe condition that can result from any antipsychotic use is the neuroleptic syndrome. Symptoms occur over a period of 24-72 hours and present with elevated vitals, agitation, confusion, severe muscle rigidity, increased white blood cell count, increased creatinine phosphokinase concentrations, abnormal liver function tests, myoglobinuria and acute renal failure.
Prochlorperazine may also have a negative effect on melanocytes. In one in-vitro study, the presence of the drug was associated with decreased cell viability as well as reduced melanin content and tyrosinase activity.
Prochlorperazine may have significant adverse effects in children. One study from 2009, examining treatment modalities for pediatric nausea and vomiting, noted that side effects of prochlorperazine are high in children; therefore, patients under two years of age should not use it and patients over two years old should consider alternatives such as ondansetron (5-HT3 antagonist). A review/meta-analysis from 2016 examined 49 previous studies and recorded pediatric side effects from dopamine antagonist use. Sedation and extrapyramidal symptoms were the most common whereas serious adverse effects such as seizure, tardive dyskinesia, neuroleptic malignant syndrome and autonomic failure were rare. Therefore, healthcare providers should exercise caution when prescribing prochlorperazine to children.
It is important to note that geriatric patients with dementia have a higher risk of death when treated with an antipsychotic including prochlorperazine.
It is not recommended that patients who are pregnant take prochlorperazine. Antipsychotics are generally not recommended in pregnant patients. Also, there is a lack of evidence to suggest that prochlorperazine is clinically effective in treating nausea and vomiting during pregnancy nor are the side effects completely understood.
For patients who take prochlorperazine on a short-term basis, there are no recommendations for monitoring. However, for patients with chronic mental illnesses who take the drug long-term, some monitoring parameters are recommended. Every physician visit should record the patient's weight, height, and BMI. Patients who are overweight or have other diabetes risk factors should have fasting plasma glucose, or hemoglobin A1C measured four months after starting an antipsychotic and then annually. Lipid plasma concentrations should are indicated once every two years, and once every six months if LDL-C > 130 mg/dl.
The concentration of prochlorperazine in the blood is not typically measured. When performed in cases such as suspected overdose, high-performance liquid chromatography/tandem mass spectrometry may be performed. The limit for quantification of the metabolite in the plasma is estimated to be around 0.20 ng/ml. Oral prochlorperazine has high first-pass metabolism and poor absorption so the exact concentration present in the body can be variable.
Oral prochlorperazine is metabolized by the cytochrome P450 system, so it is essential to monitor a patient's full list of medications. If the patient takes medications which stimulate or inhibit cytochrome P450, then the healthcare provider should consider adjusting the dose of prochlorperazine. One study examined the effects of three cytochrome P450 genotypes (CYP2C19, CYP2D6, and CYP3A5) and its effects on the concentrations of prochlorperazine and its metabolites; the authors found no significant differences amongst the three.
There are varying treatments that can be given for extrapyramidal symptoms. Parkinsonism can be treated with benztropine or amantadine. Acute dystonia can be treated with benztropine or diphenhydramine. Akathisia can be treated with beta-blockers, benztropine or benzodiazepines. Tardive dyskinesia is treatable by switching to atypical antipsychotics such as clozapine. Tetrabenazine can also be offered. For neuroleptic malignant syndrome, the healthcare provider should immediately discontinue prochlorperazine and give dantrolene (0.8 to 2.5 mg/kg given four times per day; up to 10 mg/day may be given). Also, monitor white blood cell count and vitals, and cool and hydrate the patient as much as possible.
Prochlorperazine is a medication which can present with numerous side effects and drug-drug interactions. Therefore, close interprofessional coordination amongst physicians, nurses, pharmacists, and other healthcare providers is necessary to monitor for signs and symptoms related to the above. Working together with both team members and the patient is also essential to determine if prochlorperazine is clinically indicated and to increase medication compliance.
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