BNF for Children 2011-2012

192 4.6 Drugs used in nausea and vertigo BNFC 2011–20124 Central nervous system4.6 Drugs used in nausea andvertigoAntiemetics should be prescribed only when the causeof vomiting is known because otherwise they may delaydiagnosis. Antiemetics are unnecessary and sometimesharmful when the cause can be treated, such as indiabetic ketoacidosis, or in digoxin or antiepileptic overdose.If antiemetic drug treatment is indicated, the drug ischosen according to the aetiology of vomiting.Antihistamines are effective against nausea and vomitingresulting from many underlying conditions. There isno evidence that any one antihistamine is superior toanother but their duration of action and incidence ofadverse effects (drowsiness and antimuscarinic effects)differ.The phenothiazines are dopamine antagonists and actcentrally by blocking the chemoreceptor trigger zone.They may be considered for the prophylaxis and treatmentof nausea and vomiting associated with diffuseneoplastic disease, radiation sickness, and the emesiscaused by drugs such as opioids, general anaesthetics,and cytotoxics. Prochlorperazine, perphenazine, andtrifluoperazine are less sedating than chlorpromazine;severe dystonic reactions sometimes occur with phenothiazines(see below). Some phenothiazines are availableas rectal suppositories, which can be useful inchildren with persistent vomiting or with severe nausea;for children over 12 years prochlorperazine can also beadministered as a buccal tablet which is placed betweenthe upper lip and the gum.Droperidol is a butyrophenone, structurally related tohaloperidol, which blocks dopamine receptors in thechemoreceptor trigger zone.Other antipsychotic drugs including haloperidol andlevomepromazine (section 4.2.1) are also used for therelief of nausea in palliative care (see p. 19 and p. 20).Metoclopramide is an effective antiemetic and itsactivity closely resembles that of the phenothiazines.Metoclopramide also acts directly on the gastro-intestinaltract and it may be superior to the phenothiazinesfor emesis associated with gastroduodenal, hepatic, andbiliary disease. In postoperative nausea and vomiting,metoclopramide has limited efficacy. For the role ofmetoclopramide in cytotoxic-induced nausea and vomitingsee section 8.1.Acute dystonic reactionsPhenothiazines and metoclopramide can all induceacute dystonic reactions such as facial and skeletalmuscle spasms and oculogyric crises; children (especiallygirls, young women, and those under 10 kg) areparticularly susceptible. With metoclopramide, dystoniceffects usually occur shortly after startingtreatment and subside within 24 hours of stoppingit. An antimuscarinic drug such as procyclidine (section4.9.2) is used to abort dystonic attacks.Domperidone acts at the chemoreceptor trigger zone; ithas the advantage over metoclopramide and the phenothiazinesof being less likely to cause central effects suchas sedation and dystonic reactions because it does notreadily cross the blood-brain barrier. For the role ofdomperidone in cytotoxic-induced nausea and vomitingsee section 8.1. Domperidone is also used to treatvomiting due to emergency hormonal contraception(section 7.3.5).Granisetron and ondansetron are specific 5HT 3 -receptorantagonists which block 5HT 3 receptors in thegastro-intestinal tract and in the CNS. They are ofvalue in the management of nausea and vomiting inchildren receiving cytotoxics and in postoperativenausea and vomiting.Nabilone is a synthetic cannabinoid with antiemeticproperties. It may be used for nausea and vomitingcaused by cytotoxic chemotherapy that is unresponsiveto conventional antiemetics. Side-effects such as drowsinessand dizziness occur frequently with standarddoses.Dexamethasone (section 6.3.2) has antiemetic effects.For the role of dexamethasone in cytotoxic-inducednausea and vomiting see section 8.1.Vomiting during pregnancyNausea in the first trimester of pregnancy is generallymild and does not require drug therapy. On rare occasionsif vomiting is severe, short-term treatment with anantihistamine, such as promethazine, may be required.Prochlorperazine or metoclopramide may be consideredas second-line treatments. If symptoms do notsettle in 24 to 48 hours then specialist opinion shouldbe sought. Hyperemesis gravidarum is a more seriouscondition, which requires intravenous fluid and electrolytereplacement and sometimes nutritional support.Supplementation with thiamine must be considered inorder to reduce the risk of Wernicke’s encephalopathy.Postoperative nausea and vomitingThe incidence of postoperative nausea and vomitingdepends on many factors including the anaestheticused, and the type and duration of surgery. Other riskfactors include female sex, a history of postoperativenausea and vomiting or motion sickness, and intraoperativeand postoperative use of opioids. Therapy toprevent postoperative nausea and vomiting should bebased on the assessed risk. Drugs used include 5HT 3 -receptor antagonists, droperidol, dexamethasone,some phenothiazines (e.g. prochlorperazine), and antihistamines(e.g. cyclizine). A combination of two ormore antiemetic drugs that have different mechanismsof action is often indicated in those at high risk ofpostoperative nausea and vomiting or where postoperativevomiting presents a particular danger (e.g. in sometypes of surgery). When a prophylactic antiemetic drughas failed, postoperative nausea and vomiting should betreated with one or more drugs from a different class.Opioid-induced nausea and vomitingCyclizine, ondansetron, and prochlorperazine are usedto relieve opioid-induced nausea and vomiting; ondansetronhas the advantage of not producing sedation.