Question 18.1

Last updated 29/04/2017 - 18:56
 Topic: Pharmacology and Toxicology
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A 62-year-old female is brought into hospital with suspected organophosphate poisoning.

a) List six acute clinical features associated with this condition.

b) List the antidotes indicated in this condition and the rationale for their use.

The following data are taken from this patient:

Parameter

Patient Value

Normal Adult Range

Cholinesterase

0.3 KU/L*

3.4 – 9.0

Cholinesterase mixing

33%*

100%

c)    What does the result of the mixing test indicate?

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College Answer

a)

  • Diarrhoea
  • Urination
  • Miosis
  • Bronchospasm
  • Bronchorrhoea
  • Emesis
  • Lachrymation
  • Salivation
  • Fasciculations
  • Tremor
  • Weakness
  • Respiratory muscle weakness
  • Bradycardia (tachycardia may be present)
  • Hypotension
  • Agitation
  • Coma
  • Seizures

b)

  • Atropine to control clinical features of cholinergic excess – anti-muscarinic. Large doses may be required
  • Pralidoxime to reactivate acetyl choline esterase – only effective before irreversible binding or “ageing” takes place

c)

  • This mixing test is suggestive of free organophosphate present in the blood OR inadequate dose of pralidoxime.

Discussion

The first part of the question asks the candidate to produce 6 features of the cholinergic toxidrome. This should be a piece of cake. One recalles the mnemonic SLUDGEM:

  • Salivation
  • Lacrimattion
  • Urination
  • Diarrhoea
  • Gastrointestinal upset
  • Emesis
  • Miosis

The college answer does not lend itself well to being so easily memorised, and has broken at least one anagram engine. However, Yun from Canberra has pointed out that it is taken directly from the Australian Toxicology Handbook. The first six points are DUMBBELS (the muscarinic features), and the rest are nicotinic.  

b)

Atropine and pralidoxime were asked for. The brevity of the college answer cannot be improved upon.

c)

In the mixing test, the patients serum and some random reference serum are both tested for plasma cholinesterase, and then a 50-50 mixture of the two is tested.

If there is enough pralidoxime being given, there will be little free organophosphate in the patient's sample, and the mixed sample will have a plasma cholinesterase level which is exactly between the patients sample and the reference sample.

If there is still free organophosphate present, then it will disable the plasma cholinesterase in the reference sample, and the cholinesterase level of the mixed sample will be surprisingly low.

References

Brian Kloss from LITFL has a superb cartoon to illustrate the horrors of the cholinergic toxidrome.

Sungur, Murat, and Muhammed Güven. "Intensive care management of organophosphate insecticide poisoning." Critical care 5.4 (2001): 211.

Kamanyire, R., and L. Karalliedde. "Organophosphate toxicity and occupational exposure." Occupational Medicine 54.2 (2004): 69-75.

Jr, Bailus Walker, and Joseph Nidiry. "Current concepts: organophosphate toxicity." Inhalation toxicology 14.9 (2002): 975-990.

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