Tox clinical cases

Question 1

Methemoglobinemia

about

causes

effect

Test

Answer 1

• Oxidative damage of iron within hemoglobin
  
  • loss of an electron
  • inability to transport oxygen
• MetHgb occurs with
  
  • inc oxidant exposure
  • MetHgb reductase deficiency (uncommon congen defect)
    
    • should be on ddx list for young animals
• Effect
  
  • Dec oxygen transport (NOT HEMOLYSIS)
  • chocolate syrum brown blood
• Test
  
  • filter paper sport test (or white paper towels)
  • at least 10% metHgb causes positive test

Question 2

Case 1 problem list

1) facial edema
2) Lacrimation
3) Methemoglobinemia associated with

• cyanosis
• prolonged CRT
• tachycardia
• tachypnea

4) Heinz bodies
5) Eccentrocytes

Answer 2

MetHgb:

• cardiac signs at 20%
• death at 80%

DDX

• acetaminophin toxicity
• Benzocaine (local topical anesthetic)
• Phenazopyridine (urinary analgesic)

Question 3

dDx MetHgb

Large animals

Answer 3

• Horses/camelids: red maple leaf toxicity
• Sheep & goats: copper toxicity
  
  • copper can be in foot baths
• Ruminants: fertilized nitrate-accumulating plants and action of rumen microorganism generates nitrites
  
  • nitrate/nitrite poisoning

Question 4

Signs of Acetaminophen Intoxication

Answer 4

• Edema of face and paws
• Lacrimation
• Pruritus
• MetHgb & cyanosis within 24 hours
  
  • document low PaO2 by pulse oximetry
• Heinz body hemolytic anemia
  
  • perform blood film with new methylene blue

Question 5

Answer 5

• Heinz bodies stained in new methylene blue
• Blue dot is oxidized hemoglobin

Question 6

3 targets in RBC for oxidative damage

Answer 6

• 1) Globin portion of hemoglobin
  
  • heinz bodies
• 2) Membranes of erythrocytes
  
  • eccentrocytes and pyknocytes
• 3) Iron portion of hemoglobin
  
  • methemoglobin

Question 7

Heinz Bodies in cats

Answer 7

• up to 10% can be normal
• Usually small and infrequent
• more -SH groups per globin molecule
• Non-sinusoidal spleen
  
  • doesn’t pull out heinz bodies as well as other spleens

Question 8

Acetaminophen Intoxication

Answer 8

• Toxic dose
  
  • Canine: > 100 mg/kg
  • Feline: 10-40 mg/kg
    
    • 2 reg strength 325 mg tabs w/in 24 hours can be lethal
    • ferrets similar to cats
• Happens when glucuronidation and sulfation are exceeded => NAPQI
  
  • cats => hematologic changes
  • dogs=> hepatocellular necrosis
    
    • dogs will have inc liver enzymes

Question 9

Initial Tx for acetaminophen toxicity

Answer 9

• Oxygen cage
• Emesis/charcoal
• Osmotic cathartics
• Get antidote
  
  • N-Acetylcysteine (replentishes depleted glutathione)
  • Ascorbic acid
  • Supportive care for liver failure (PRN)

Question 10

AST origin

Answer 10

• Muscle
• Liver
• Red blood cells

Question 11

Ionophore toxicosis

Clinical signs

Answer 11

• Partial to complete anorexia
• diarrhea
• colic
• ataxia
• muscle weakness/tremors
• tachycardia
• recumbency
• intermittent profuse sweating
• cardiac disease and heart failure

Question 12

Ionophores

Answer 12

• Polyether antibiotics isolated from bacteria
• Used to prevent coccidiosis
  
  • beef, dairy, poultry
• Bloat prevention in cattle
• Species variability
  
  • Monensin in horses has an LD₅₀ 1/100th that of ruminants

Question 13

Common Ionophores

Answer 13

• Monensin (Coban, Rumensin)
• Lacsalocid (Avatec, Bovatec)
• Salinomycin (Bio-cox, Sacox)
• Narasin (Monteban, Maxiban)
• Maduramicin (Cygro)
• Laidlomycin (Cattlyst)
• Semduracmicin (Aviax)

Question 14

Ionophore toxicoses

MOA

Answer 14

• Form lipid-soluble, dynamically reversible complexes with cations
• Causes abnormal movement of ions into muscle cells
  
  • sodium
  • potassium
  • calcium ions
• Movement of these into cells causes
  
  • myocyte osmolar imbalance
  • mitochondria dysfunctoin
    
    • myocardial necrosis

Question 15

Ionophore tox tx

Answer 15

• supportive care
  
  • fluids
  • antioxidants (Vit C)
  • thiamine
  • selenium
  • pain management
• ionophore screening of gastric contents and heart muscle can confirm toxicity