14 – Anti-Infectives

Question 1

Metronidazole

Answer 1

• Antibacterial and antiprotozoal
• Toxicity: high dose for a number of days
• *hallmark: vestibular signs
  o Head tilt, circling, nystagmus
  o Central vestibular disease

Question 2

Metronidazole: management

Answer 2

• *D/C (discontinue) metronidazole
  o Symptoms should resolve rapidly
• Could give diazepam: speed recovery
• *excellent prognosis

Question 3

Metronidazole: diagnosis

Answer 3

• History
• If use unknown: differentiate from other things that cause vestibular disease
  o Blood work
  o Chest rads
  o Advanced imaging

Question 4

Metronidazole: clinical signs

Answer 4

• *Most common was cerebellovestibular ataxia (wide based stance)
• *Nystagmus
• Spread of other signs point to brain, cerebellum and vestibular system

Question 5

What are DDx of vestibular signs?

Answer 5

• Otitits media/interna
• Intracranial neoplasia
• Idiopathic vestibular disease
• Lead poisoning

Question 6

Ivermectin

Answer 6

• ML: broad spectrum
• Pastes, liquids, tablets
• Genetic polymorphism: ABCB1 mutation dogs=more susceptible
  o *intraspecies differences: border collies, Australian shepherd, etc.)

Question 7

Ivermectin: exposure scenarios

Answer 7

• Dermal or oral
• Administration of products with ivermectin: overdose
• Accidental exposure to large animal ivermectin
• Ingestion of feces of treated livestock

Question 8

Ivermectin: target organ

Answer 8

• *CNS
• Any species can be poisoned

Question 9

Ivermectin: mechanism

Answer 9

• Potentiation of glutamate and GABA-gated chloride channels
  o *CNS depression
  o ABCB1 polymorphism dogs: defective p-glycoprotein
• turtles also very susceptible

Question 10

Ivermectin: onset

Answer 10

• Several hours or days (dose-dependent)

Question 11

Ivermectin: clinical features

Answer 11

• Lethargy, depressed/dull mentation
• Disorientation, ataxia
• Vomiting, hypersalivation
• *mydriasis (huge pupils)
• *blindness
• Severe intoxications: seizures, obtundation, respiratory depression, death
• Non-specific bloodwork findings

Question 12

Ivermectin-induced blindness

Answer 12

• *underlying pathology=retinal edema +/- folds and separation
• Exact mechanism unknown
• Absent menace, sluggish-to-absent PLRs
• In acutely blinded animal: fundic exam and maybe electroretinography (ERG)
• Cannot be detected postmortem (can’t fixed edema with formalin)

Question 13

Ivermectin: management

Answer 13

• No specific antidote
• Decontamination if not contraindicated (ex. dermal)
• Symptomatic and supportive care
  o Monitor blood gas
  o Prolonged monitoring and treatment may be required
  o Animals generally regain their sight slowly
• Reports of successful treatment with IVLE

Question 14

Ivermectin: diagnosis

Answer 14

• History of exposure, compatible clinical signs

Question 15

What are some DDx for ivermectin?

Answer 15

• CNS depressants
• Barbiturates
• Opiates
• Tremorgenic mycotoxins
• Nicotine
• Benzodiazepines

Question 16

Ivermectin: prognosis

Answer 16

• Generally good with appropriate supportive care
  o Severely affected=prolonged care often required

Question 17

Pyrethrins and Pyrethroids

Answer 17

• Derived from chrysanthemum flower
• Flea and tick products
• High potency against insects vs. mammals
• *exposure scenario: application of flea/tick products meant for dogs applied to cats

Question 18

Pyrethroids: target organ

Answer 18

• *CNS

Question 19

Pyrethroids: mechanism

Answer 19

• Prolonged Na channel opening in nerves=repetitive AP firing
• **CNS excitation

Question 20

Pyrethroids: toxicity

Answer 20

• Generally low in mammals
  o Exception: CATS or animals with liver damage

Question 21

Pyrethroids: prominent clinical sings

Answer 21

• *tremors, twitching, muscle fasciculations
• Vomiting, diarrhea
• Depressed mentation or hyperexcitable
• Mydriasis
• Hypersalivation
• Ataxia
• Severe cases: seizures, coma
  o Can be fatal if seizures cannot be controlled

Question 22

Pyrethroids: management

Answer 22

• NO specific antidote
• Decontamination if not contraindicated (dermal or GI)
  o Ensure cat cannot groom itself
• *tremor control: METHOCARBAMOL
• Supportive care
  o IVFT
  o Thermoregulation
  o Close monitoring of neurological status and CV system

Question 23

Pyrethroids: diagnosis

Answer 23

• History of application meant for dogs
• Dog recently treated with topical product in a house with a cat
• Usually a clinical diagnosis

Question 24

What are DDx for CNS excitation?

Answer 24

• Strychnine
• Fluoroacetate
• Metaldehyde
• OP/carbamate insecticides
• Organochlorine insecticides
• Stimulant drugs
• Bromethalin
• Salt
• Tremorgenic mycotoxins
• Lead

Question 25

Pyrethroids: prognosis

Answer 25

• Good with early and aggressive treatment
  o Status epilepticus: poor