Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Mercury Pharmaceuticals Ltd, Capital House, 85 King William Street, London, EC4N 7BL, UK
Pharmacotherapeutic group: Antipsychotics, Phenothiazines with piperazine structure
ATC code: N05AB04
Prochlorperazine belongs to the phenothiazine group which have a piperazine group at position 10 of the phenothiazine molecule. This entails a greater risk of inducing extrapyramidal side effects but less tendency to produce sedation or autonomic side effects such as hypotension, unless unusually large doses are employed.
At therapeutic doses, prochlorperazine is mainly dopamine antagonist but it also has anticholinergic and anti-adrenoceptor blocking activity. Its actions on dopamine receptors in the medulla chemoreceptor trigger zone probably accounts for its anti emetic effects. Unwanted effects results from the drugs dopamine and adrenoceptor antagonism. Dystonias and dyskinesias and parkinsonism in the elderly can occur with prolonged use or high dosage. Postural hypotension and excessive sedation are risks, especially in the elderly.
The pharmacokinetics of prochlorperazine in man have been little studied because of its difficulty to assay. The low and variable bioavailability is largely due to extensive metabolism of the drug in the gut wall and liver, to sulphoxide.
Parenteral (intramuscular) administration can increase the availability of the active drug by four to ten times. There is a marked interindividual variation in pharmacokinetics following intravenous administration but no evidence of dose dependent pharmacokinetics; mean terminal half life is of the order of 6.85 hours. A few generalisations can be made. The phenothiazine group of drugs to which prochlorperazine belongs is highly lipophilic, highly membrane or protein bound and will accumulate in the brain, lung and other tissues with a high blood supply; it also enters the foetal circulation quite easily. This apparent high volume of distribution would confirm that the liver is not the only site of metabolism.
No further relevant information other than that which is included with other sections of the Summary of Product Characteristics.
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