-insecticides : flea and tick spot- on treatments for cats and dogs
-pyrethrins are extracted from Chrysanthemum species
-pyrethroids are a synthetic version
-permethrin and etofenprox are two common examples
-available for public use without the supervision of a veterinarian
-extremely lipophilic drug
-allows it to cross the blood brain barrier
-causes prolonged opening of voltage-dependent sodium channels in the peripheral and central nervous system
-this results in prolonged influx of sodium and loss of the normal membrane charge; repeated firing degenerates to paralysis
-effects on the sodium channel are compounded by hypothermia
Most common: application of a canine 'spot on' product
Less common: contact with a 'spot on' treated dog
overdosing using a feline product
Absorbed rapidly by dermal route (lipophilic)
Increased absorption with hyperthermia (increased dermal blood flow)
Oral absorption (grooming) and inhalation exposure possible
Stabilize seizuring patient with diazepam (0.5-1mg/kg IV or rectally, however rectal absorption in cats is not as reliable as in dogs) and oxygen
Pyrethrins, Pyrethroids, Permethrins?
Pyrethrin Toxicity in Cats
Action of Toxicity
Route of Exposure
Products
Why cats??
-2nd most common reported toxicity in cats in 2009 UK study, topped only by Lily ingestion
-their high surface area to weight ratio means they are exposed to higher doses on a mg/kg basis
-the drug is excreted by oxidation & glucuronidation – cats are deficient in their glucuronidation ability
-some compounds are added to the insecticide to decrease the rate of metabolism in insects which also decreases metabolism in cats leading to toxic buildup
prognosis is good for mild cases and unlikely to have long term effects
for more severe cases the prognosis is good IF aggressive, early treatment with continuous supportive care is provided, this can be expensive and some cats are euthanized
seizure activity may be hard to control – another reason for euthanasia & some cats do die due to severity of clinical signs
recovery usually takes 2-3 days but can be as little as 3 hrs and as many as 7 days.
Clinical Signs
tremors/muscle fasiculations (86%)
twitching (41%)
hyperesthesia (41%)
seizures (33%)
pyrexia (29%)
ptylism (24%)
ataxia (24%)
mydriasis (19%)
temporary blindness (12%)
- appear quickly after exposure, but can possibly be delayed up to 72 hours
- history of exposure is important for diagnosis as there are no quick definitive diagnostic tests
- may initially see paresthesia in the area of application (ear twitching or twitching of cutaneous trunci; can resemble hyperesthesia syndrome in cats)
- oral consumption (grooming) leads to vomiting and hypersalivation
- occasionally see dyspnea due to diaphragm paralysis
- convulsions and tremors can last 38.9 hours on average (range of 2 hrs to 5 days)
Control tremors
- Although diazepam may initially be helpful for seizures, benzodiazepines are not usually helpful long term
- Propofol CRI can be administered @ (0.1 - 0.4 mg/kg/min) but be cautious of oxidative damage to RBC in cats
- Methocarbamol has been shown to the best at controlling muscle tremors
Specific Monitoring
Decontaminate
Wash the patient with warm water and hand or dish soap (the sooner the better and use copious water!)
- Shaving the area can help with decontamination
- Don't allow them to become hypothermic during washing, but avoid hyperthermia as well. Some patients will be hyperthermic due to prolonged muscle activity
Charcoal is likely not helpful as absorption is fast even orally and there is no significant enterohepatic circulation. It is also contraindicated in seizuring or tremoring patients who cannot swallow
Stop seizures
1. Good nursing and supportive care
2. IV fluids and hydration maintenance
3. Nutritional support if needed
4. Regulation of body temperature within a normal range
5. Regular turning of a laterally recumbent body
6. The bladder may need regular expressing
7. Ventilation may be needed in some cases
Other....
*monitor for myoglobinura and subsequent nephrotoxicity due to prolonged seizure activity and muscle tremors
*temperature (avoid hyper and hypothermia)
*monitor for hemolysis if using Intra-lipid and signs of heinz body anemia if using propofol CRI
Methocarbamol
20%Intra-lipid
- Centrally acting skeletal muscle relaxant; a carbamate of guaifenesin
- It can be difficult to obtain injectable drug in Canada
- The tablets can be crushed & administered as a slurry rectally or via stomach tube, it can also be given orally hidden in food once the cat is able to swallow and eat (remember diazepam is an appetite stimulant)
- Methocarbamol = Robaxin (500mg tabs); be cautious of Robaxacet which also contains acetaminophen
- Dose: 55-220 mg/kg IV or TID if orally/rectally (caution of respiratory depression if exceeding 330mg/kg/day).
- Some clinicians start with 100mg/kg TID (a common mistake is not being aggressive enough with treatment)
- Patients should be weaned off the methocarbamol slowly over the course of several weeks – should any tremoring be noted, the dose should be stepped up again.
Use 20% Intra-lipid IV to act as a lipid sink and assist with removal of the lipid soluble toxin
This lipid emulsion can be obtained from human hospitals, however as of late it has been very difficult to obtain due to a shortage
It provides significant calories as a benefit
Dose: Give a bolus of 1.5 ml/kg over 1 minute IV, then begin a CRI of 0.25ml/kg per minute for 30 minutes
There are reports of hemolysis in people given Intra-lipid, it is not clear why but free radical damage and changes to the RBC membrane are suspect. (Note that Intra-lipid is iso-tonic).
Treatment
Photo based on: 'horizon' by pierreyves @ flickr