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2014-01-30 12:01:17
Vet Med

Module 4 - Infectious Agents - Toxicity
Show Answers:

  1. What is a lethal dose?
    A dose that will kill an animal
  2. What is the LD50?
    The dose that will kill 50% of test animals
  3. What is the ED50?
    The dose that will be effective in 50% of test animals
  4. What is the therapeutic index?
    The ratio between LD50 and ED50.  It tells you how safe the drug is.
  5. How safe is a drug if it has an a) high or b) low TI?
    • a) relatively safe
    • b) less safe
  6. What are the five basic routes of intoxication?
    • Ingestion
    • Cutaneous
    • Inhalation
    • Injection
    • Ocular
  7. If you are not sure how to treat a poisoned animal, where can you get help?
    VPIS - veterinary poisons information service
  8. What are some of the most common enquires to the VPIS?
    • NSAIDS
    • Anti-coagulent rodenticides
    • Chocolate
    • Paracetamol
    • Pemethrin
    • Metaldehyde
    • Lilies
    • Grapes etc
    • Batteries
    • Adder bites
  9. How is a poisoned animal treated?
    • Breathing, heart rate and temperature stabilised
    • Information is gathered from the owner
    • Continued absorption of the poison is prevented
    • Elimination of the absorbed poison is attempted
    • An antidote may be given
    • Symptomatic and supportive care is given
  10. How can you prevent continued absorption of a poison?
    • Wash
    • Gastric evacuation
    • Gastric lavage
    • Adsorbent
    • Elimination
  11. How can you stimulate gastric evacuation in an animal? (What areas do you stimulate?)
    • You can stimulate the vomiting centre in the brain.  Also the Medullary chemoreceptor trigger zone (MCTZ).
    • You can also stimulate the vagal and sympathetic afferents int he GI tract to trigger emesis
  12. What are some household/emergency remedies to induce emesis?
    Salt solution, mustard, washing soda, sticking a finger down the back of the animals throat
  13. What is the drug commonly used to trigger emesis in cats?
  14. What is the drug commonly given to dogs to induce emesis?
  15. When would you not want to induce emesis in an animal?
    • If the animal is:
    • having seizures
    • in depression/coma
    • loss of gag reflex
    • hypoxia
    • species unable to vomit
    • ingestion of corrosives/volatile petroleum products
    • recent abdominal surgery
  16. What is gastric lavage?
    Washing out the stomach contents
  17. Give an example of an adsorbent
    • Activated charcoal
    • Fullers earth
  18. What is activated charcoal?
    Charcoal that has been treated with oxygen to open up pores; these pores can bind to the toxins.
  19. How do adsorbents work?
    There is no chemical reaction between a toxin and adsorbent.  Once the toxin is 'stuck' to the adsorbent they can move through the GI tract to be eliminated from the body
  20. What are cathartics?
    Substances that help to increase the motility of the GI tract (to help things move through faster)
  21. Give examples of cathartics
    • Sodium or magnesium salts
    • Sorbitol (which is often used in activated charcoal formulations as activated charcoal itself causes constipation whilst sorbitol draws water into the GI tract)
  22. What are chelating agents?
    Agents that bind metal ions only. The bound ions are chemically inert and so this prevents poisoning
  23. Give an example of a chelating agent
    • EDTA
    • Desferrioxamine
  24. How do anticoagulant rodenticides act as a poison?
    They are vitamin K antagonists (reversible) and so interfere with the production of clotting factors.  This leads to haemorrhages.
  25. What are the clinical signs of anticoagulant rodenticide poisoning?
    • Depression and anorexia (even before bleeding)
    • In acute ingestion of very high doses - vascular collapse
    • Repeated intake - haemorrhage (either internal or external) and the symptoms of this e.g. weakness
  26. What is the treatment for anticoagulant poisoning?
    An oral dose of vitamin K1 will act as an antidote, this overcomes the antagonism of the drug
  27. What are the clinical signs of chocolate poisoning?
    • Vomiting
    • Excitability
    • Ataxia
    • Tachycardia
  28. What type of chocolate is most poisonous?
    Dark > milk > white
  29. What is the treatment for chocolate poisoning?
    There is no antidote for chocolate poisoning, so you must stabilise the animal and provide supportive care
  30. Why are cats and dogs susceptible to paracetamol poisoning?
    Paracetamol is normally removed by conjugation.  However, dogs have an inability to conjugate things to sulphate and cats have an inability to conjugate things to glucuronide (missing the enzymes).  This means in cats and dogs paracetamol is made into a toxic intermediary.
  31. What are the symptoms of paracetamol poisoning?
    • Facial/pulmonary odema
    • cyanosis
    • Liver damage - haemolysis, jaundice
  32. What is the treatment for paracetamol poisoning?
    • You can give N-acetylcysteine (a glutathione precursor) to increase glutathione levels in the body.  This helps as when the toxic intermediary reacts with glutathione it makes mercapturic acid which is not toxic and can be eliminated in the urine.
    • You can also give a sodium sulphate to act as an alternative substrate for the reaction.
  33. What is the main source of ethylene glycol poisoning?
    Antifreeze mixtures
  34. Why is ethylene glycol poisonous?
    The metabolites are toxic
  35. What are the clinical signs of ethylene glycol poisoning?
    • Early clinical signs (1-2hrs):
    • weakness, vomiting, incoordination
    • Delayed signs (24-96hrs):
    • thirst, inhibition of urine production, blood in urine, convulsions, death
  36. What is the treatment for ethylene glycol poisoning?
    Ethanol acts as an alternative substrate - give 20% ethanol IV slowly over a long period of time