8 – Rodenticides Flashcards
1
Q
Rodenticides
A
- 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)
2
Q
What is secondary poisoning?
A
- 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
3
Q
What are some neurotoxic rodenticides? (3)
A
- Strychnine
- Bromethalin
- Fluoracetate
4
Q
Strychnine: ‘use’
A
- Recently banned in Canada (often used for gophers)
5
Q
How does strychnine poisoning occur?
A
- Consumption of strychnine-laced bait
- Consumption of strychnine poisoned animal
- Malicious poisoning
6
Q
Strychnine: species susceptibility, toxicity and target
A
- ALL species susceptible
o *dogs most frequently poisoned - Target: CNS
- Toxicity: extremely!! (*exam question)
7
Q
Strychnine: mechanism of action
A
- 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)
8
Q
Strychnine: onset
A
- Within minutes=peracute
9
Q
Strychnine: clinical features
A
- Behavioural
- Neuromuscular
- *responsive to external stimuli (clap=seizure)
- Cyanosis
- Dilated pupils
- Sudden death possible
- *no specific PM or histological lesion=rapid rigor mortis
10
Q
Strychnine: behavioral
A
- Apprehension
- Anxiety
- Agitation
11
Q
Strychnine: neuromuscular
A
- Generalized muscle spasms
o *severe extensor rigidity
o *tonic clonic seizures
12
Q
Strychnine: management
A
- 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
13
Q
Strychnine: key clinical exam findings
A
- 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
14
Q
Strychnine: prognosis
A
- Poor to grave
o If animal can survive 24-48hrs=prognosis improves
15
Q
Strychnine: DDx
A
- Rodenticides: fluroacetate, bromethalin
- Metaldehyde
- Tetanus
- High dose stimulates
- Anatoxin-a
- Water hemlock
- OP/carbamate insecticides
- Non-toxic: brain disease, hepatic encephalopathy, severe hypoglycemia, rabies
16
Q
Strychnine in Western Canada
A
- 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
17
Q
Bromethalin
A
- 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
18
Q
Bromethalin: mechanism of action
A
- 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)
19
Q
Bromethalin: toxicokinetics
A
- 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)
20
Q
Bromethalin: toxicokinetics
A
- 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
21
Q
Bromethalin: high dose exposure in dogs, clinical features
A
- 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
22
Q
Bromethalin: low dose exposure in dogs and any dose in cats, clinical features
A
- 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
23
Q
Bromethalin: clinical pathology
A
- Few changes on blood work: mild hyperglycemia
- Increased CSF pressure
- Normal CSF cytology: no inflammation, normal specific gravity and protein
24
Q
Bromethalin: management
A
- 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?
25
Q
Bromethalin management for a symptomatic patient
A
- Management of cerebral edema
- Seizure control
- Supportive care
26
Q
Bromethalin: diagnosis
A
- Antemortem: history of exposure and compatible clinical signs
- Confirmation: detection of desmethylbromethalin in fat, serum, brain, kidney, liver
- PM: characteristic histology (intramyelinic edema)
27
Q
Bromethalin: differentials
A
- Convulsant syndrome: strychnine, fluoracetate, zinc, etc.
- Paralytic syndrome: botulism, tick paralysis, IVDD
28
Q
Bromethalin: prognosis
A
- Guarded to grave: some can recover
- Symptomatic + decontamination =good
- Mild symptoms = guarded
- Symptomatic with neuro signs = poor
29
Q
Fluoroacetate (compound 1080)
A
- 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
30
Q
Fluoroacetate (compound 1080): mechanism
A
- Inhibits key enzymes in Krebs cycle
o Inhibits energy production + binds to calcium - *target organs: CNS, heart
31
Q
Fluoroacetate (compound 1080): toxicity
A
- Extreme
- *dogs are most sensitive species
32
Q
Fluoroacetate (compound 1080): onset
A
- Within 30ins to multiple hours after ingestion
- *sudden death w/o clinical signs is possible
33
Q
Fluoroacetate (compound 1080): clinical features
A
- 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
34
Q
Fluoroacetate (compound 1080): clinical pathology
A
- Hyperglycemia, hyperammonemia
- Metabolic acidosis, hyperlactatemia
- Hypocalcaemia
- Elevated citrate
35
Q
Fluoroacetate (compound 1080): management
A
- Not readily available or practical antidote
o Acetamide in 5% dextrose - Supportive care: seizure management, fluids, correction of electrolyte derangements
36
Q
Fluoroacetate (compound 1080): prognosis
A
- Poor to grave
37
Q
Fluoroacetate (compound 1080): diagnosis
A
- 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)
38
Q
Fluoroacetate (compound 1080): DDx
A
- Same as strychnine and bromethalin
