Nausea is an unpleasant sensation often accompanied by the urge to vomit.
Vomiting is the forceful expulsion of gastric contents through the mouth.
Although nausea and vomiting often occur together, they are separate symptoms.

Recommended medicine: Metoclopramide
Recommended formulations:
Injection: 5 mg (hydrochloride)/mL in 2‐mL ampoule
Oral liquid: 5 mg/5 mL
Tablet: 10 mg (hydrochloride)

Scope
- Management of nausea and vomiting comprises identification and, wherever possible, treatment of possible underlying cause or causes.
- Most cancer chemotherapy is highly emetogenic. Appropriate management of chemotherapy-induced nausea and vomiting depends on the chemotherapy regime.
- Mechanisms of postoperative nausea and vomiting are likely to be different to nausea and vomiting in palliative care.
- Symptomatic management of nausea and vomiting should not be deferred until the underlying cause of the nausea and vomiting has been identified and treated, but should be initiated without delay. Pharmacological management is the mainstay of treatment of nausea and vomiting, however non-pharmacological measures, — including avoidance of precipitants and the use of acupressure — may have a role.

Overview of management options
- Pharmacological management based on knowledge of the most important pathophysiological mechanisms for emetogenesis and the relevant neurotransmitters is suggested for optimum management of nausea and vomiting, but the evidence to support this approach has been questioned.
- Unfortunately it is not always possible to identify the precise mechanism(s) underlying the presence of nausea and vomiting. A pragmatic approach addressing the most likely mechanism is indicated, differentiating for example between toxic or metabolic nausea and retention vomiting.
- Antiemetics should be prescribed regularly and as required.
- If a single first-line antiemetic does not relieve nausea and vomiting the antiemetic regime should be reviewed to ensure that:
o the likely pathophysiological mechanisms underlying nausea and vomiting are being targeted,
o the patient is receiving the medication and that it is being absorbed, and
o the dose is appropriate
- If necessary, a second antiemetic with a complementary mechanism of action may be added. Combinations of antiemetics with antagonistic actions should be avoided.
- Alternatively the first-line antiemetic can be changed to a single second-line antiemetic with a more appropriate or broader spectrum of action.
- Where the enteral route is unavailable or absorption is not reliable, an alternative route of administration, either rectal or subcutaneous (or intravenous if long-term central venous access is available), is required.
- Antiemetic administration via subcutaneous bolus injections or continuous subcutaneous (or intravenous if long-term central venous access is available) infusion is the route of choice where the enteral and rectal routes are unavailable and regular dosing is required.

Classes of drugs appropriate for pharmacological management of nausea and vomit
• Neuroleptics: haloperidol, levomepromazine, chlorpromazine, prochlorperazine
• Antiemetic antihistamines: cyclizine, promethazine
• 5HT3 antagonists: ondansetron
• Corticosteroids: dexamethasone
• Prokinetic antiemetics: metoclopramide, domperidone

Antiemetics in palliative care
Metoclopramide
- It is a D2-receptor antagonist with mixed 5-HT3 receptor antagonist/ 5-HT4 receptor agonist and prokinetic properties.
- Its action is antagonized by antimuscarinics.
- It can cause extrapyramidal side effects.
- Oral bioavailability: 50-80%
- Duration of action following single dose: 1-2 hours
- It is recommended for the first-line management of nausea and vomiting associated with delayed gastric emptying.
- Regurgitation suggests gut hypomotility, which responds to a gastrokinetic antiemetic, such as metoclopramide.

Recommendations
- If cause of emesis established, the choice of first-line agent should correlate with this cause. For effective control, a combination of antiemetics with complementary actions may be necessary.
- In palliative care, the most common cause for vomit is gastric stasis, which responds well to metoclopramide.
- Most of the evidence base for pharmacological treatment of nausea and vomiting in palliative and terminal care is weak. Two recent reviews on antiemetic therapy in palliative care patients indicate a moderate evidence of the effectiveness of metoclopramide.
- The moderate to weak evidence from clinical trials is supported by clinical expertise. Expert opinion strongly supports the use of metoclopramide in palliative care patients with nausea or vomiting.
- Availability of a combination of antiemetics with different mechanisms of action is recommended to ensure appropriate first- and second-line management for each underlying pathophysiological mechanism. For patients with chemotherapy- or radiation therapy-related nausea, 5HT3 antagonists might be preferable. Neuroleptics were more effective than metoclopramide in some trials, but their side effects have to be considered.
- In the absence of any data showing greater efficacy of one agent over another, the choice of antiemetics is likely to be determined by other factors, such as availability of suitable formulations, route of administration, pharmacokinetics, cost effectiveness, and potential for other roles in palliative care.

Adapted from Radbruch L et al. Essential medicines in palliative care - An application for the 19th WHO Expert committee on the selection and use of essential medicines. Kindle Edition, 135 pp. Published on June 5, 2013 by IAHPC Press. Available at https://www.amazon.com/Essential-Medicines-Palliative-Care-Application-ebook/dp/B00D7S2D0C