Monday, 14 September 2015

Paracetamol as an anti-emetic

Now that children have returned to school you may have notice something new in your consulting room: the smell of stale vomit.  I think that I have a fairly protected professional life but puke is not one of those things that I mention when extolling the virtues of my (eventually) chosen career.  As winter approaches, the number of children with viral gastritis and gastroenteritis will go up and up until one day before Christmas, I will have a loved one ask me to shower before supper so that I can be in polite company.

Perhaps there is one good thing to come out of all this though.  I think that all these vomiting children have taught me something that not everyone else knows: For the child with viral vomiting who will not drink, paracetamol is an accidental anti-emetic.  (I am also fairly sure that there is no medical evidence for it, having done a literature search.)
Anti-emetics are traditionally avoided in  viral vomiting due to the possibility of side effects which might complicate what should be a self-limiting illness.  In the UK, most children with viral gastritis/ gastroenteritis do not become significantly unwell. However it is unpleasant and occasionally causes a child to become severely unwell.

I know that I can’t prove my belief but I can tell you this: I frequently see children who seem unwilling to drink and incapable of appropriate onwards gastric peristalsis (AOGP, as well as a new acronym, happens to be the sound made just before an almighty puke).   Parents bring their children in the hope that we will help.  These children seem beyond simple measures and yet almost without fail, an hour after a dose of paracetamol they are drinking, soon to be followed by appropriate discharge.

Why haven’t they been give paracetamol already?  That’s easy.  It is counter-intuitive to give slimy medicine to a child who vomits every few minutes.  It stand to reason that it will come straight back or precipitate a puke.  The child may not be febrile and even if they are it seems a waste of good medicine.

When I sit down to write these posts, I enjoy the fact that FOAMed allows the writer to be free of the normal constraints of traditional forms of publications.  I am keen, however to make sure that I don’t write anything that is dangerous or wrong.  As mentioned above, I really did do a literature search on this.  You may have noticed that I never sport a serious disclaimer.  This is for two reasons.  Firstly, a disclaimer is no defence against wrongness.  Secondly a lack of a disclaimer is no excuse for you to go and jump off a bridge just because I said so.  We have an understanding, you and I.  I will make this as good as I can make it and you will be professional, question my advice and apply what you get from it in the context of everything else that you know about clinical medicine.  That said, paracetamol really is an anti-emetic when a child has viral gastritis.

In the absence of a randomised controlled trail (that will probably never be done) one needs a plausible explanation for one's claim.  It works like this: When you feel unwell and have abdominal pain you do not want to drink.  Pain and malaise are both emetic in their own right.  Paracetamol reduces pain and feelings of malaise, helping a child to vomit less and drink more.


There are two caveats with this.  Firstly, I would be against giving repeated doses paracetamol too readily to a child who is dehydrated.  Secondly, remember that many paracetamol suspensions contain sugar substitutes which are hyper-osmolar.  Sugar is preferable in vomiting children since they need to energy and don’t need the diarrhoea that can be made worse by sugar free suspensions. 

I know that just because it makes sense doesn't mean it is true, nor does an observed association prove causation. (1)  In this case I have been convinced of an association because it seems to work and it makes sense.  If that’s good enough for you, then great.   There are plenty more like this to come in future posts.

Edward Snelson
Statistical Sceptic when it suits me
@sailordoctor

Disclaimer: Were you even paying attention?  I covered this.



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