QUESTIONS

1. How do these compounds kill insects?
    
2. So what would be some typical signs of a pyrethroid poisoned pet?
    
3. If the LD50 of permethrin is about 2 gm/kg (pretty high), what's the big deal using DEFEND EXSPOT in cats?
    
4. This is from a real case on the toxicology board.  A 2 lb yorkie was dipped in vet kem pyrethrin dip diluted 50%.  It seemed normal when it was put in the cage with a drier before anyone knew what had happened it was dead.  temp was 108 degrees & the belly had large eccymotic hemorrhages.  CPR was unsuccessful. The DVM suspects pyrethrin intoxication in this tiny dog. What do you think?
    
5. Pyrethrins are an effective & relatively safe natural insecticide.  They are extracts from pyrethrum flowers (chrysanthymum relatives).  Approximately how long have they been in use as insecticides?
    
6. What determines whether a pyrethroid is Type 1 or Type 2?
   
   
   
   
    

ANSWERS

1. Pyrethrin-type insecticides kill bugs by altering the sodium channels of nerves so that the channel is open longer than it is supposed to .  As a result there are elevated afterpotentials that result in repeated nerve firing.  You need to know that there are type 1 & type 2 pyrethroids & the type group also kill by antagonizing the action of GABA.
   
   
   
   
    
2. Typical signs would include drooling, & tremors progressing to ataxia.  (unfortunately, these signs can mimic OP toxicosis.)
   
   
   
   
    
3. DEFEND EXSPOT is 65% permethrin or so.  Most permethrin sprays & such are in the 1% or less range.  The mallinkrodt people tell me the exspot technology will never be available in the cat because such high percentages of insecticide are needed to cover the whole body with one application.
   
   
   
   
    
4. Feeling on the boards was that heat stroke from the drier followed by DIC was more plausible based on the rapid death, high temp & bruises.
   
   
   
   
    
5. We've been using pyrethrins in the war against insects for about 120 years.
   
   
   
   
    
6. This classification is based on what type of toxic signs the pyrethroid in question produces in rats.  Note, some of these products are so safe that they had to be injected into the rat's actual brain to get toxic signs for the sake of classification.
   
   Type 1:  aggressive sparring behavior & sensitivity to external stimuli then tremors & hyperthermia.
   
   Type 2:  Progressive increase in burrowing behavior, drooling, tremors, abnormal rear end locomotion, writhing & then seizures.