Drugs used in nausea and vertigo

4.6 Drugs used in nausea and vertigo

Antiemetics should be prescribed only when the cause of vomiting is known because otherwise they may delay diagnosis, particularly in children. Antiemetics are unne- cessary and sometimes harmful when the cause can be treated, such as in diabetic ketoacidosis, or in digoxin or antiepileptic overdose.

If antiemetic drug treatment is indicated, the drug is chosen according to the aetiology of vomiting.

Antihistamines are effective against nausea and vomi- ting resulting from many underlying conditions. There is no evidence that any one antihistamine is superior to another but their duration of action and incidence of adverse effects (drowsiness and antimuscarinic effects) differ.

The phenothiazines are dopamine antagonists and act centrally by blocking the chemoreceptor trigger zone. They are of considerable value for the prophylaxis and treatment of nausea and vomiting associated with dif- fuse neoplastic disease, radiation sickness, and the eme- sis caused by drugs such as opioids, general anaes- thetics,

and cytotoxics.

Prochlorperazine,

perphenazine, and trifluoperazine are less sedating than chlorpromazine; severe dystonic reactions some- times occur with phenothiazines, especially in children. Other antipsychotic drugs including haloperidol and levomepromazine (methotrimeprazine) are also used for the relief of nausea (see Palliative Care, p. 17). Some phenothiazines are available as rectal suppositories, which can be useful in patients with persistent vomiting or with severe nausea; prochlorperazine can also be administered as a buccal tablet which is placed between the upper lip and the gum.

Metoclopramide is an effective antiemetic and its activity closely resembles that of the phenothiazines. Metoclopramide also acts directly on the gastro-intes- tinal tract and it may be superior to the phenothiazines for emesis associated with gastroduodenal, hepatic, and biliary disease. In postoperative nausea and vomiting, metoclopramide in a dose of 10 mg has limited efficacy. High-dose metoclopramide injection is now less com- monly used for cytotoxic-induced nausea and vomiting. As with the phenothiazines, metoclopramide can induce acute dystonic reactions involving facial and skeletal muscle spasms and oculogyric crises. These dystonic effects are more common in the young (especially girls and young women) and the very old; they usually occur shortly after starting treatment with metoclopramide and subside within 24 hours of stopping it. Injection of an antiparkinsonian drug such as procyclidine (section

4.9.2) will abort dystonic attacks. Domperidone acts at the chemoreceptor trigger zone; it

is used for the relief of nausea and vomiting, especially when associated with cytotoxic therapy. It has the advantage over metoclopramide and the phenothi- azines of being less likely to cause central effects such as sedation and dystonic reactions because it does not readily cross the blood-brain barrier. In Parkinson’s disease, it is used to prevent nausea and vomiting during treatment with apomorphine and also to treat nausea caused by other dopaminergic drugs (section 4.9.1). Domperidone is also used to treat vomiting due to emergency hormonal contraception (section 7.3.5).

Dolasetron, granisetron, and ondansetron, are speci- fic 5HT antagonists which block 5HT receptors in the gastro-intestinal tract and in the CNS. They are of value in the management of nausea and vomiting in patients receiving cytotoxics and in postoperative nausea and vomiting. Palonosetron is licensed for prevention of nausea and vomiting associated with moderately or highly emetogenic cytotoxic chemotherapy.

Dexamethasone (section 6.3.2) has antiemetic effects and it is used in vomiting associated with cancer chemo- therapy. It can be used alone or with metoclopramide, prochlorperazine, lorazepam, or a 5HT antagonist (sec- tion 8.1).

Aprepitant and fosaprepitant are neurokinin 1 recep- tor antagonists licensed for the prevention of acute and delayed nausea and vomiting associated with cisplatin- based cytotoxic chemotherapy; they are given with dexamethasone and a 5HT antagonist.

Nabilone is a synthetic cannabinoid with antiemetic properties. It may be used for nausea and vomiting caused by cytotoxic chemotherapy that is unresponsive to conventional antiemetics. Side-effects such as drow- siness and dizziness occur frequently with standard doses.