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Anti-emetics

Nausea and vomiting

Anti-emetics are drugs that take away nausea and vomiting (N&V), and are a mainstay of treatment in all hospital wards.  Not only is N&V unpleasant for the patient, but it has been shown to increase hospital stay following an operation by four days (unpleasant for the bed manager!).

 

Why is N&V so prevalent in our hospitals?  Because we are responsible for most of it!  The majority of cases are caused by the drugs doctors prescribe without thinking of their emetic effects (see table below).

 

Causes of nausea and vomiting

Treatment of N&V

Vomiting is a very complex physiological process (just think about all the CNS centres involved!) and as such is difficult to treat.  Research has identified several neurotransmitters involved in the process, and drugs in general use target four of these (see table below).    However, anti-emetic treatment is often a trial and error process – what has worked for a patient on one occasion does not always work on another, and similarly what has worked for one patient does not always work for another.  It is vital to review progress regularly to ensure effective management of symptoms.

 

The main anti-emetics currently in use.

*NNT: Number needed to treat – an epidemiology term describing the number of patients one needs to treat to control one patient’s nausea adequately.  It is a measure of the effectiveness of a drug.

 

How to choose an anti-emetic

Firstly, identify the cause of the N&V, and tackle it if possible.  It is important to investigate the underlying pathology as the choice of drug depends on it.

 

The anti-emetic ladder shown below shows how you should proceed when prescribing.  Always refer to local guidelines if available, and take into account drug interactions and side effects.  For example, in cancer patients who are also suffering from anorexia, dexamethasone may be indicated as first line to improve appetite and general wellbeing.  Also, there is a higher rate of extrapyramidal side effects with the dopamine agonists in children and teenagers than in adults, so these should be avoided in these age groups.

 

Formulation

It is important to think about how you are going to give your anti-emetic - it may seem obvious, but doctors actually do prescribe oral anti-emetics to patients who cannot keep anything down!  In a hospital setting IM/IV/SC drugs can be used easily, and some are even administered via a syringe driver.  In the community buccal preparations may be preferred.

 

The anti-emetic ladder.

More obscure anti-emetics

  • NK1 receptor antagonists – currently in development
  • Cannabinoids – obviously cannabis is illegal, but some synthetic analogues are available/in development
  • Ginger
  • Peppermint
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