29th December 2024

Nausea and vomiting

Nausea and vomiting are common but not always well managed. The underlying cause should always be considered. Mode of delivery is also key: a patient who is actively vomiting is unlikely to benefit from an oral antiemetic.

Main causes of nausea and vomiting, alongside clinical features and management options, are as follows:

Anxiety can also be a cause of nausea and vomiting. Management options include cognitive behavioural therapy, benzodiazepines and levomepromazine, and the decision depends very much on the specific clinical context.

Sometimes, the cause of the vomiting is unknown. In this case, levomepromazine is usually the first antiemetic to be trialled. Second-line options include metoclopramide, haloperidol and cyclizine. If these are ineffective, a trial of dexamethasone can be considered.

Pharmacology notes on antiemetics

There are a few things that might cause your pharmacist to come knocking regarding antiemetics.

Long QT: metoclopramide, haloperidol, levomepromazine and domperidone can all prolong the QT interval, increasing the risk of arrhythmias. This is a consideration, especially when a patient is on other medications that may also have this side effect. At the very end of life, the risks of this need to be balanced with the benefits gained from the medications.

Cancelling out: prokinetics (e.g. metoclopramide) and antimuscarinics (e.g. cyclizine) should not be prescribed together as the antimuscarinics will block the prokinetic effect.

Extrapyramidal side effects: avoid dopamine antagonists (in particular metoclopramide and haloperidol) in those at increased risk of extrapyramidal side effects, e.g. patients with Parkinson’s disease. Domperidone does not cross the blood-brain barrier and so is safe in patients with Parkinson’s disease.