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Anti-emetics

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Authors

Michele Butler, MmedSci, BSc, RGN, RNT, CertED (FE), senior lecturer in clinical science, School of Biological and Molecular Science, Oxford Brookes University. Molly Courtenay, PHD, MSc, Cert Ed, RNT, RGN, lecturer, Southampton University.

Article

Independent nurse prescribers working in palliative care are able to prescribe a number of products from the Nurse Prescribers’ Formulary that may relieve nausea and vomiting associated with cancer and chemotherapy treatment. Treatment will depend on the cause, with 80% of cases resulting from gastric stasis, intestinal obstruction, drugs and biochemical factors. Raised intracranial pressure accounts for less than 5% of cases.

Vomiting involves two functionally distinct medullary centres: the vomiting centre and the chemoreceptor trigger zone. The act of vomiting is integrated by the vomiting centre and this orchestrates a complex series of events that results in nausea and vomiting. The chemoreceptor trigger zone (CTZ) is located on the floor of the fourth ventricle, where it is exposed to both blood and cerebrospinal fluid. This zone is considered to be outside the blood-brain barrier and is able to detect blood-borne drugs and toxins that are emetogenic. The vomiting centre may receive stimuli from the gastrointestinal tract and other organs, the cerebral cortex, the vestibular apparatus and the CTZ.

Medications

Preparations for the management of nausea and vomiting comprise the following: cyclizine injection, domperidone tablets, suspension and suppositories, levomepromazine (methotrimeprazine) tablets and injection and metoclopramide tablets, oral solution, syrup and injection.

The first-line anti-emetic for gastritis, gastric stasis and functional bowel obstruction is metoclopramide. For most chemical causes of vomiting, haloperidol is prescribed. This, however, is not available to the nurse prescriber, but metoclopramide may also be effective.

Cyclizine should be prescribed for organic bowel obstruction, raised intracranial pressure and motion sickness. Second-line drugs include levomepromazine. Cyclizine is an antihistamine and acts directly on H1-receptors in the vomiting centre by antagonising the action of histamine. Its effect appears to be on the vestibular pathway of the vomiting reflex and hence, it is particularly useful when motion causes symptoms of nausea and vomiting.

Domperidone is used to relieve nausea and vomiting, especially when associated with cytotoxic drug therapy. It does not readily cross the blood-brain barrier and therefore has an advantage over metoclopramide of being less likely to cause central nervous system effects.

Metoclopramide and domperidone antagonise dopamine receptors in the chemoreceptor trigger zone which are involved in the vomiting reflex. In addition they are both prokinetic anti-emetics, as they increase the rate of gastric emptying and peristalsis. They also decrease the sensitivity of receptors in the pharynx and upper gut to noxious stimuli.

Levomepromazine (methotrimeprazine) is an antipsychotic (neuroleptic) drug belonging to the group called phenothiazines. It antagonises dopamine receptors in the central nervous system, depressing the cerebral cortex, hypothalamus and limbic system. The clinical effects produced by this action include a depressant action on conditioned responses and emotional responsiveness, a sedative action useful for the treatment of restlessness and confusion, an anti-emetic effect through blockade of the chemoreceptor trigger zone - which is useful to treat vomiting - and antihistamine activity.

Contraindications

Metoclopramide should not be used in gastro-intestinal obstruction, perforation or haemorrhage. Domperidone has no contraindications listed. Cyclizine is contraindicated in hypersensitivity. Levomepromazine (methotrimeprazine) is contra-indicated in hypersensitivity, comatose states, central nervous system depression and phaeochromocytoma. It should be avoided in pregnancy.

Side-effects

Metoclopramide may produce extrapyramidal effects, hyperprolactinaemia, drowsiness, diarrhoea, depression, rashes, pruritus and oedema. Domperidone may also cause hyperprolactinaemia, galactorrhoea and gynaecomastia.

Cyclizine can cause drowsiness, dizziness, restlessness, insomnia, tachycardia, constipation, urinary retention, dry mouth and blurred vision.

Side-effects of levomepromazine (methotrimeprazine) include agranulocytosis, leucopenia, haemolytic anaemia, jaundice, drowsiness, apathy, insomnia, depression, extrapyramidal symptoms, dry mouth, constipation, rashes, nasal congestion, blurred vision, hypotension, tachycardia and arrhythmias.

The most likely cause of the nausea and vomiting should be determined before an anti-emetic is prescribed. Correctable causes should be treated and the most appropriate first-line anti-emetic prescribed. However, if there is little or no benefit an alternative first-line anti-emetic should be provided or a second-line anti-emetic added. Due to the limited choice of anti-emetics available to nurse prescribers, they may need to refer the client back to the physician.

This article is based on a book by Courtney, M. and Butler, M. (2002). Essential Nurse Prescribing. London: Greenwich Medical Media.

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