Pharmacology for Anaesthesia and Intensive Care

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Section IVOther important drugs

Uses

Droperidol has been shown to be effective in the prevention and treatment of PONV

at doses from 0.25 to 5 mg, although the incidence of side effects increases with dose.

Itis also used in neurolept analgesia and in the control of mania.

Mechanism of action

Droperidol antagonizes central dopamine (D 2 )receptors at the CTZ.

Effects

These are similar to those seen with phenothiazines.


Central nervous system – sedation is more pronounced compared to the phenoth-

iazines. The true incidence of extrapyramidal effects is unknown but increases with

higher doses. They may develop more than 12 hours after administration and up

to 25% of patients may experience anxiety up to 48 hours after administration. In

sufficient dose it induces neurolepsis.


Metabolic – it may cause hyperprolactinaemia.


Cardiovascular – hypotension resulting from peripheralα-adrenoceptor blockade

may occur.

Kinetics

Droperidol is usually given intravenously although it is absorbed readily after intra-

muscular injection. It is highly plasma protein bound (approximately 90%) and

extensively metabolized in the liver to products that are excreted in the urine, only

1% as unchanged drug.

Domperidone

This D 2 antagonist is less likely to cause extrapyramidal effects as it does not cross the

blood–brain barrier. Its use in children is limited to nausea and vomiting following

chemotherapy or radiotherapy. It also increases prolactin levels and may cause galac-

torrhoea and gynaecomastia. The intravenous preparation was withdrawn following

serious arrhythmias during the administration of large doses. It is only available as

tablets or suppositories.

Benzamides

Metoclopramide

Uses

Metoclopramide is used as an antiemetic and a prokinetic. Approximately half of the

clinical studies have demonstrated placebo to be as effective as metoclopramide as

an antiemetic. However, metoclopramide appears to be most effective when 20 mg

is given at the end of anaesthesia rather than at induction.