8 – Rodenticides

Question 1

Rodenticides

Answer 1

• Common problem in vet med
• Related to human actions
  o Inappropriate storage
  o Off-label use
  o Delayed removal of poisoned rodents
  o Malicious use
• Many different ones used
• Baits are typically bright coloured (cannot distinguish based on colour)

Question 2

What is secondary poisoning?

Answer 2

• RELAY TOXICITY
• *carcass of a poisoned animal poisons the animal that consumes it
  o Dogs at greatest risk
• Some have a very HIGH risk of secondary poisoning
  o Strychnine
  o Fluoroacetate
  o Bromethaline
  o Second generation ACRs

Question 3

What are some neurotoxic rodenticides? (3)

Answer 3

• Strychnine
• Bromethalin
• Fluoracetate

Question 4

Strychnine: ‘use’

Answer 4

• Recently banned in Canada (often used for gophers)

Question 5

How does strychnine poisoning occur?

Answer 5

• Consumption of strychnine-laced bait
• Consumption of strychnine poisoned animal
• Malicious poisoning

Question 6

Strychnine: species susceptibility, toxicity and target

Answer 6

• ALL species susceptible
  o *dogs most frequently poisoned
• Target: CNS
• Toxicity: extremely!! (*exam question)

Question 7

Strychnine: mechanism of action

Answer 7

• Glycine ANTAGONIST at post-synaptic receptors in spinal cord and medulla
  o Disinhibition of motor neurons
  o All skeletal muscles affected
• *Results in UNCONTROLLED STIMULATION OF MOTOR NEURONS (similar to tetanus)

Question 8

Strychnine: onset

Answer 8

• Within minutes=peracute

Question 9

Strychnine: clinical features

Answer 9

• Behavioural
• Neuromuscular
• *responsive to external stimuli (clap=seizure)
• Cyanosis
• Dilated pupils
• Sudden death possible
• *no specific PM or histological lesion=rapid rigor mortis

Question 10

Strychnine: behavioral

Answer 10

• Apprehension
• Anxiety
• Agitation

Question 11

Strychnine: neuromuscular

Answer 11

• Generalized muscle spasms
  o *severe extensor rigidity
  o *tonic clonic seizures

Question 12

Strychnine: management

Answer 12

• NO specific antidote
  o Aggressive decontamination and support care
• If asymptomatic: activated charcoal
• Seizure control: diazepam, GA
• Respiration intubation and mechanical ventilation
• IV fluid diuresis
• *manage of consequences of seizures: hyperthermia, rhabdomyolysis, hypoxia, acidosis

Question 13

Strychnine: key clinical exam findings

Answer 13

• Sudden onset of neurological signs
• Extensor rigidity
• Seizures that are responsive to external stimuli
• Lack of GI signs
• *presence of it in stomach contents, vomit, urine, liver or bait

Question 14

Strychnine: prognosis

Answer 14

• Poor to grave
  o If animal can survive 24-48hrs=prognosis improves

Question 15

Strychnine: DDx

Answer 15

• Rodenticides: fluroacetate, bromethalin
• Metaldehyde
• Tetanus
• High dose stimulates
• Anatoxin-a
• Water hemlock
• OP/carbamate insecticides
• Non-toxic: brain disease, hepatic encephalopathy, severe hypoglycemia, rabies

Question 16

Strychnine in Western Canada

Answer 16

• Typically seen in spring (try to get it in the gopher holes before they emerge)
  o More likely due to the animals getting into the bai and not a malicious poisoning
• *has decreased: still highest in dogs

Question 17

Bromethalin

Answer 17

• Widely available in home and garden stores
  o Emerged in response to warfarin resistant rodents
• Bait concentration varies
• *extremely to highly toxic
  o *cats=most sensitive species

Question 18

Bromethalin: mechanism of action

Answer 18

• 2 major
  o Uncoupled oxidative phosphorylation in mitochondria=decreased ATP production=impaired Na/K ATPase=loss of oncotic control in brain
  o Oxidative stress: cerebral lipid peroxidation
• **culminates in CEREBRAL EDEMA
  o Histological lesion: intramyelinic edema (good for PM)

Question 19

Bromethalin: toxicokinetics

Answer 19

• Bioactivation
  o Guinea pig=relatively resistant as it is unable to metabolize
• Highly lipophilic
• Long elimination half-life
  o Enterohepatic recirculation = will need to treat for a long period of time

Question 20

Bromethalin: high dose exposure in dogs, clinical features

Answer 20

• CONVULSANT SYNDROME
  o Asymptomatic for a few hours
  o Muscle tremors
  o Hyperesthesia
  o Agitation/hyperexcitability
  o Running fits
  o Seizures responsive to external stimuli
  o Obtundation
  o Death due to respiratory paralysis

Question 21

Bromethalin: low dose exposure in dogs and any dose in cats, clinical features

Answer 21

• PARALYTIC SYNDROME
  o Delayed onset
  o *hindlimb paresis, ataxia, decreased proprioception (‘ascending’ like botulism)
  o *cats: abdominal distension
• Progression to
  o Loss of deep pain sensation
  o UMN bladder (difficult to express)
  o CNS depression
  o Decerebrate posture
  o Obtundation
  o Seizure

Question 22

Bromethalin: clinical pathology

Answer 22

• Few changes on blood work: mild hyperglycemia
• Increased CSF pressure
• Normal CSF cytology: no inflammation, normal specific gravity and protein

Question 23

Bromethalin: management

Answer 23

• No antidotes
• Early GI decontamination is KEY
  o Activated charcoal + emesis
  o **hypernatremia
• Related to dose ingested and time since ingestion
• Low renal excretion: IVF diuresis not helpful
• Try ILE?

Question 24

Bromethalin management for a symptomatic patient

Answer 24

• Management of cerebral edema
• Seizure control
• Supportive care

Question 25

Bromethalin: diagnosis

Answer 25

- Antemortem: history of exposure and compatible clinical signs - Confirmation: detection of desmethylbromethalin in fat, serum, brain, kidney, liver - PM: characteristic histology (intramyelinic edema)

Question 26

Bromethalin: differentials

Answer 26

- Convulsant syndrome: strychnine, fluoracetate, zinc, etc. - Paralytic syndrome: botulism, tick paralysis, IVDD

Question 27

Bromethalin: prognosis

Answer 27

- Guarded to grave: some can recover - Symptomatic + decontamination =good - Mild symptoms = guarded - Symptomatic with neuro signs = poor

Question 28

Fluoroacetate (compound 1080)

Answer 28

- Sodium monofluoracetate - Found in many plants - Use in Canada (Alberta): livestock anti-predator collars - Exposure: stockpiled and malicious poisoning - *high risk of secondary poisoning and tertiary poisoning

Question 29

Fluoroacetate (compound 1080): mechanism

Answer 29

- Inhibits key enzymes in Krebs cycle o Inhibits energy production + binds to calcium - *target organs: CNS, heart

Question 30

Fluoroacetate (compound 1080): toxicity

Answer 30

- Extreme - *dogs are most sensitive species

Question 31

Fluoroacetate (compound 1080): onset

Answer 31

- Within 30ins to multiple hours after ingestion - *sudden death w/o clinical signs is possible

Question 32

Fluoroacetate (compound 1080): clinical features

Answer 32

- GI: vomiting, salivation, urination, defecation - CNS: hyperesthesia, frenzied, convulsions with extensor rigidity, running fits o Cats: vocalization - Cardiorespiratory: profound tachycardia, dyspnea, cyanosis, ventricular fibrillation possible - Death from cardiorespiratory failure

Question 33

Fluoroacetate (compound 1080): clinical pathology

Answer 33

- Hyperglycemia, hyperammonemia - Metabolic acidosis, hyperlactatemia - Hypocalcaemia - Elevated citrate

Question 34

Fluoroacetate (compound 1080): management

Answer 34

- Not readily available or practical antidote o Acetamide in 5% dextrose - Supportive care: seizure management, fluids, correction of electrolyte derangements

Question 35

Fluoroacetate (compound 1080): prognosis

Answer 35

- Poor to grave

Question 36

Fluoroacetate (compound 1080): diagnosis

Answer 36

- Antemortem: history and compatible clinical signs - Confirmation: detect it in bait, stomach contents, vomit, urine - Non specific PM/histo lesions: o Congestion and hemorrhage o Myocardial necrosis (in sheep)

Question 37

Fluoroacetate (compound 1080): DDx

Answer 37

- Same as strychnine and bromethalin