Insecticides

Question 1

Permithrins

Answer 1

• from chrysanthemum flowers
• over-the-counter flea tx
• cats more sensitive to neurological effects
• most often from accidental application of K9 flea products or being in contact with treated dogs
• rapid absorption: 40-60% absorbed after oral exposure and >2% after dermal exposure
• Pyrethroids (synthetic analogues of permethrin)
• stored in the skin and released slowly over time
• They work by
• binding to membrane lipids phase of nerve cells
• slowing opening and closing of neural sodium channels = repetitive firing

Clinical signs:

• paresthesia
• hyperesthesia
• ear twitching
• tail flicking
• twitching of skin on the back
• can progress to tremors and seizures
• onset can be minutes to hours

Tx:

• decontamination by bathing in dish detergent
• thermal regulation and support: usually with high temperature that plummet once tremors are controlled, and shivering can worsen tremors
• muscle relaxants: methocarbimol (55-220mg/kg IV: give 1/3 to 1/2 dose, then to effect, not to exceed 2ml/min)
• AC not of any benefit
• IVF: to prevent myoglobinuric-induced renal failure, and manage hyperthermia
• hypoglycaemia secondary to increased muscle activity
• IV lipid therapy: results rapid and remarkable, with resolution of tremors within an hour of initiating lipid therapy
• symptoms can persist for 3-5 days (less if lipid therapy is used)

Question 2

Ivermectin

Answer 2

• broad-spectrum antiparasitic
• derived from bacterium Streptomyes avermitilis
• tx of endo and ectoparasites in dogs and cats
• liquid injection or oral administration and paste
• overdose:
• hyperpolarizing cell membranes and preventing neuronal depolarization
• results in flaccid paralysis
• progresses to ataxia to stupor and even coma and death
• animals lacking full expression of mdr-1 gene and P-glycoprotein synthesis = increased sensitivity to ivermectin
• absorption is rapid via SQ or oral routes
• half-life is 2 days in dogs
• toxic dose:
• dog=2.5mg/kg
• cats=1.3mg/kg
• clinical signs:
• ataxia
• agitation
• vocalization
• disorientation
• mydriasis (dilated pupils)
• blindness
• weakness
• bradycardia
• Severe clinical signs:
• seizures
• stupor or comatose

Tx:

• supportive care and decontamination
• multiple doses of AC (due to enterohepatic recirculation)
• anticonvulsant therapy: phenobarbital, propofol, etomidate
• mechanical ventilation
• IV lipids