Organophosphate poisoning

Here’s some notes taken mainly from this paper (can’t remember who linked to it… sorry):

Eddleston M, Buckley NA, Eyer P, Dawson AH. Management of acute organophosphorus pesticide poisoning. Lancet. 2008 Feb. 16;371(9612):597–607. PMC2493390

And also from the excellent Toxicology Handbook:

Murray L, Daly F, McCoubrie D, Cadogan M. Toxicology Handbook. Elsevier; 2011.

WHERE WILL WE SEE IT?

• lots of this is Asia based as they see so much of it. The paper quotes 200000 deaths a year
• mainly pesticides, mainly intentional

TOXICOLOGY

• big pathophys is inhibition of acetylcholinesterase
• overstimulation of ACh receptors in autonomic nervous system and at skeletal NM junction
• mainly parasympathetic syndrome but can have a sympathetic form as their are some Ach receptors there too.
• the assays used to make a diagnosis seem a bit complicated and redundant to be honest

WHAT TO EXPECT

• everything’s wet, from the underwear to bronchi
• wheezy as hell
• altered mental status
• muscle weakness

TREATMENT

• supportive, blah, blah, blah but really they’ll likely need a tube to stop them drowning in their secretions
• atropine +++: the review and the Handbook suggest a dose doubling regime every 5mins (starting at 1-3mg) until HR>80 and BP>80)
  • This may well mean colossal amounts of atropine so speak to your pharmacy

• the atropine is for the real killer effects – the drowning in your own secretions, it’s not going to fix motor weakness so they will likely still need ventilation
• an AChEsterase reactivator (an oxime) mainly pralidoxime. Some evidence in RCTs in early 90s showing harm. Cochrane showed no clear evidence of benefit or harm. One RCT since (n = 200) that showed good benefit (8% v 1% mortality in moderately sick pts).
  • The Tox Handbook that it hasn’t been shown to improve outcomes so here’s the link to that RCT so you can make up your own mind (I haven’t read it yet so it may be nonsense)
  • Look up the dose is what I’ll do.
• gastric decontamination can be done but not charcoal and as usual no real evidence for it and it’s a problem if it gets in the way of atropine and oxygen

Seeing as it’s a post on tox I have to include a chemical structure for you. Not relevant to organophosphates mind you…

UPDATE:

Here’s a couple of links from people who know a lot more about this than me!

1) From a guy who’s studied this pretty significantly. @trainthetrainer

2) From Bipin: a yahoo group discussion on the topic by docs in India who do this everyday.