Insecticides Flashcards
When was the first organophosphate synthesized?
1854
What was one of the earliest OP insecticides?
Parathion
More toxic versions of parathion were developed when?
During WWII
Thousands of organophosphates have been synthesized in an attempt to do what?
Find species-selective compounds to reduce mammalian toxicity.
T/F: There are several types of organophosphates.
True
Name 3 organophosphates that have direct Acetylcholinesterase activity?
- Dichlorvos
- Monocrotophos
- Trichlorfon
Name 4 organophosphates that must be desulfurated before they become active.
- Bromophos
- Diazinon
- Fenthion
- Parathion
What is the average amount of time organophosphates persist in the environment?
2-4 weeks
Name 4 organophosphates that are subject to “storage activation”.
- Parathion
- Malathion
- Diazinon
- Coumaphos
What is storage activation?
If sealed & stored 1-2 years, becomes more toxic.
What “grade” of organophosphate is more toxic?
What are 2 reasons why?
- Technical grade.
- Heat isomeration, impurities
Which is more likely to be readily absorbed from the GIT, skin and mucous membranes or by inhalation: a toxin that is lipophilic or hydrophilic?
Lipophilic
What is the most common type of exposure for organophosphates?
Oral exposure (contaminated feeds)
What are 3 possible routes of exposure for organophosphates?
- Oral (contaminated feed)
- Dermal (dip/spray)
- Inhaled (recent aerial spray)
Are organophosphates well distributed throughout the body?
Yes
Can organophosphates affect the CNS?
Yes
Is there significant tissue accumulation with organophosphates?
No
What is an example of an organophosphate that is more lipophilic than average, meaning it can sequester more in fat and stay in the body longer?
Dichlorvos
Where are organophosphates metabolized?
Liver
Toxins that require desulfuration are activated by liver metabolism in a process known as what?
“Lethal synthesis”
Is “lethal synthesis” less toxic in young or old patients?
Why?
- Young
- Liver metabolism is not completely developed in the young.
Organophosphates that require desulfuration by the liver to be activated are made more toxic if what are present?
What is an example of one?
- Enzyme inducers
- Phenobarbital
Continued exposure to organophosphates can lead to what?
What are 3 reasons for this?
- Tolerance
- Enzyme induction, functional adaptation to decreased esterases, adaptation of ACh receptors to excessive amounts of ACh
Adaptation of ACh receptors to excessive amounts of ACh is known as what?
Receptor down-regulation
What is the mechanism of action for organophosphates?
Irreversible inhibition of cholinesterases
Do organophosphates increase or decrease ACh at all cholinergic sties?
Increase
Which receptors do organophosphates stimulate first?
Muscarinic receptors
Which receptors do organophosphates stimulate second?
Nicotinic receptors
What is the last receptor effect that organophosphates have?
Nicotinic blockade
What happens in a nicotinic blockade?
Eventually depolarizes to the point it can’t repolarize.
What is the cause of death with high exposure to organophosphates?
Respiratory failure/paralysis
What is another name for the delayed neurotoxicity possible with organophosphates?
OP induced delayed polyneuropathy
How quick is the onset of clinical signs seen with acute organophosphate toxicity?
15 mins - 1 hr
What is the initial clinical sign seen with organophosphate toxicity?
Muscarinic stimulation
Muscarinic stimulation can cause DUMBBELLS, which stands for what?
D - diarrhea U - urination M - myosis B - bronchoconstriction B - bradycardia E - emesis L - lacrimation S - salivation
Muscle fasciculation, tremors, twitching, spasm, hypertonicity and stiff gait can be seen with the stimulation of what kind of receptors by organophosphates?
Nicotinic receptors
Anxiety, restlessness, hyperactivity, may proceed to tonic-clonic seizures when what is stimulated?
CNS
Paralysis, CNS depression, coma, dyspnea and death due to respiratory failure can be cause by what type of blockade?
Nicotinic blockade
What can be seen with massive (malicious) doses of organophosphates?
OP induced intermediate syndrome
T/F: No muscarinic signs or muscle fasciculations are seen with OP induced intermediate syndrome.
True
What type of exposure can lead to OP induced intermediate syndrome?
Chronic exposure
What can occur if acute poisoning with an organophosphate happens?
OP induced delayed polyneuropathy
What are 3 signs of OP induced delayed polyneuropathy?
- Muscle weakness
- Ataxia
- Rear limb paralysis
How long does it take after exposure for OP induced delayed polyneuropathy to develop?
10-14 days
Distal degeneration of long/large diameter motor and sensory axons of peripheral nerves and spinal cord can occur with what?
OP induced delayed polyneuropathy
What species is most sensitive to OP induced delayed polyneuropathy?
Chickens
Are there any specific lesions with acute death associated with organophosphates?
No
Dogs exposed to more lipophilic organophosphates can have what condition develop?
Pancreatitis
How are organophosphates diagnosed?
Direct detection
Residues of which organophosphate may be seen in samples from fat or liver tissue?
Chlorpyrifos
What is something that can be tested antemortem to detect organophosphate toxicity?
Acetylcholinesterase activity level
How soon does a sample for organophosphate toxicity need to be assessed?
ASAP to preserve activity.
Less than what percentage of acetylcholinesterase activity is considered suspicious in suspected OP toxicity?
What percentage is considered diagnostic?
-
What are 3 things to be considered for clinical diagnosis of OPs?
- History of exposure
- Clinical signs
- Lab testing
If a strong response to a low dose (0.02mg/kg) of this drug is seen, then it is less likely to be OP toxicity.
Atropine
Should emesis be induced with OP toxicity?
Only if recent. Not if depressed or seizures.
What can be done with dermal exposure to OPs?
Wash gently with tepid, soapy water.
Can activated charcoal be used for OPs?
Yes
What are 4 things that should be avoided with OP toxicity?
- Phenothiazines
- Aminoglycosides
- Muscle relaxants
- Drugs that depress respiration (opioids)
What drug can be used to treat OP toxicity?
What is the MOA?
Doses?
- Atropine
- Specific physiologic antagonist
- SA/horses: 0.2 mg/kg
Food/LA: 0.5mg/kg
Give 1/4 dose IV then rest IM or SC, repeat 3-6 hr based on clinical response.
What is the most effective treatment of OP toxicity in acute cases?
Dose?
- 2-PAM (Pralidoxime, Protopam)
- 25-50 mg/kg 10% solution slow IV
Is 2-PAM effective against all OPs?
No
2-PAM may not be effective if what has occurred?
Aging
What is “aging”?
OP bound for a long time, changes chemically so that 2-PAM can no longer pull it off.
What is the main form of treatment with OP intermediate syndrome?
Supportive care
Is atropine more or less effective with OP intermediate syndrome compared to acute toxicity?
Less effective
With OP intermediate syndrome, 2-PAM should be reserved for what type of cases?
Severe cases
What is the treatment for OP induced delayed polyneuropathy?
Symptomatic therapy
Prognosis for OP toxicity is better if patient is what?
Alive
What are 2 determiners of prognosis for OP toxicity?
- Dose
- How long since exposure
Mild to moderate signs with OP toxicity are generally what?
Treatable
Acute cases of OP toxicity that respond to treatment can recover within what time frame?
24 hours
What is an example of a carbamate?
Carbaryl (Sevin)
What is something that carbamates do not undergo that OPs do?
Storage activation
Do carbamates require hepatic bioactivation?
No
Which has a faster onset: OPs or carbamates?
Shorter duration of action?
- Carbamates
- Carbamates
T/F: A low exposure to carbamates may recover without treatment.
True
Are carbamates metabolized slowly or rapidly?
Very rapidly
What is the MOA of carbamates?
Reversible inhibition of acetylcholinesterase
What can be tested in the lab when looking for carbamate toxicity?
Cholinesterase levels
What can happen if a sample for carbamate testing is not tested fast enough?
False negative due to reversible binding.
What drug is used to treat carbamates?
Atropine
Is 2-PAM a good choice for carbamates?
Why?
- No
- Reversible binding reduces benefit.
Which carbamate is 2-PAM contraindicated with?
Why?
- Carbaryl (Sevin)
- Can potentially increase carbamylation process.
What happens with a high dose exposure of carbamates?
Animal dies too quickly for treatment.
What happens with a low dose exposure of carbamates?
Animal may survive without treatment if signs are not severe.
What type of insecticide are Diphenyl aliphatics (DDT, methoxychlor?
Chlorinated hydrocarbon (Organochlorine)
What type of insecticide are aryl hydrocarbons (Lindane)?
Chlorinated hydrocarbon (Organochlorine)
What type of insecticide are cyclodienes (Aldrin, Toxaphene)?
Chlorinated hydrocarbon (Organochlorine)
What insecticide was banned in the USA in 2003?
Methoxychlor
Are chlorinated hydrocarbons lipophilic or hydrophilic?
Highly lipophilic
Are chlorinated hydrocarbons soluble in water?
No
The lipophilic nature of chlorinated hydrocarbons leads to what?
Bio-accumulation in the food chain.
What is the soil half-life of chlorinated hydrocarbons?
2-15 years
Which can survive longer in the environment: organophosphates or chlorinated hydrocarbons?
Chlorinated hydrocarbons
Which species is more sensitive to chlorinated hydrocarbons: dogs or cats?
Cats
Do chlorinated hydrocarbons generally have a low or high toxicity to mammals?
Low
Which animals are susceptible to chlorinated hydrocarbons?
All animals
Are chlorinated hydrocarbons readily absorbed?
Yes - highly lipophilic
Do chlorinated hydrocarbons cross into the CNS?
Yes
T/F: Chlorinated hydrocarbons undergo metabolism by liver microsomal enzymes.
True
Do the metabolites of chlorinated hydrocarbons undergo enterohepatic recycling?
Yes
What are 4 ways the metabolites of chlorinated hydrocarbons can be excreted from the body?
- Milk
- Feces
- Urine
- Bile
What is the half-life of chlorinated hydrocarbons?
Weeks to months
What can disrupt equilibrium and allow a large amount of chlorinated hydrocarbon metabolites to be released into the blood stream?
Weight loss
What is the main clinical sign for chlorinated hydrocarbon toxicity?
CNS stimulation
Some mammals can show what instead of typical CNS excitability with chlorinated hydrocarbon toxicity?
Intermittent or persistent depression
Which species may show depression, abnormal postures, apparent blindness and death with chlorinated hydrocarbon toxicity?
Birds
Which species can have seizures as a result of chlorinated hydrocarbon toxicity?
Cattle
Are there any specific pathological lesions for chlorinated hydrocarbons?
No
Acute chlorinated hydrocarbon toxicity can be confirmed if insecticide is in what 3 types of samples at significant concentrations?
- Blood
- Liver
- Brain
A diagnosis of chlorinated hydrocarbon toxicity is made with what 4 factors?
- History of exposure
- Clinical signs
- Lack of specific lesions
- Chemical analysis of tissues
Compared to cholinesterases, chlorinated hydrocarbon toxicity has less or more parasympathetic signs?
CNS stimulation?
- Less parasympathetic signs
- More severe CNS stimulation (convulsive seizures)
Is there any specific antidote for chlorinated hydrocarbon toxicity?
No
What are 3 forms of decontamination that can be used with chlorinated hydrocarbons?
- Induce emesis (if indicated)
- Wash soap/water if dermal exposure
- Activated charcoal (better) or mineral oil
What 2 drugs can be given to help control seizures caused by chlorinated hydrocarbon toxicity?
Diazepam or barbiturates