Lash - Toxicology III Flashcards
What is a pesticide?
General classification that includes rodenticides, insecticides, herbicides, fungicides and fumigants; designed to kill various pests (plants and animals)
o Selective toxicity of pesticides exist, but all capable of some sort of toxicity in humans
o Exposures generally occur at home (oral) or at work (inhalation, dermal exposure)
Chlorinated Hydrocarbon Insecticides: Properties (4)
Fat-soluble (low water-solubility; concentrates in adipose tissue)
- Capable of crossing placenta
Low-molecular weight
Stable
Poor biodegradability (half life= 10 years) resulting in BIOACCUMULATION o Persist in the environment
Chlorinated Hydrocarbon Insecticides: mechanism of human toxicity
Interferes with inactivation of Na channel (alters transport of Na and K across axonal membranes)
Causes rapid, repetitive firing in most neurons after a single stimulus
Chlorinated Hydrocarbon Insecticides:
Treatment
Example
Treatment:
o No specific regimen
o Provide support of physiologic function
Example: DDT (use now restricted)
Clinical characteristics of organochlorine (chlorinated hydrocarbon) insecticides
Nausea, vomiting Paresthesias of tongue, lips, and face Restlessness Apprehension, irritability Tremor Convulsions Hypersusceptibility to stimuli Coma Respiratory failure Death
Organophosphorous Insecticides: Properties
Carcinogenic potential vs. toxicity
What pesticide is most frequently involved in fatal poisoning?
Absorbed by:
Excreted by:
Persist in the environment (negative environmental impact), but do not bioaccumulate
Extremely low carcinogenic potential but high acute toxicity
Parathion pesticide most common pesticide involved in fatal poisoning
All readily absorbed by the skin, GI tract and respiratory tract
Readily metabolized and hydrolyzed metabolites excreted in the urine
Organophosphorous Insecticides mechanism of Toxicity:
Signs/symptoms
What may it also cause?
Inhibition of AChE by phosphorylation of esteratic site; some may also have direct cholinergic activity
Signs/symptoms therefore related to persistent ACh hyperstimulation
- Muscarinic, nicotinic and CNS effects
May also cause delayed neurotoxicity by phosphorylating another enzyme in neural tissue (neurotoxic esterase)
Carbamate Insecticides: Mechanism of Toxicity: (3)
Inhibition of AChE by carbamoylation of esteratic site
Signs/symptoms similar to organophosphorous insecticides (due to ACh hyperstimulation)
Do not bioaccumulate (little negative environmental impact)
Carbamate Insecticides differences from Organophosphorus Insecticides: (4)
Readily dissociate from AChE
Shorter duration of action
Less toxic
Non-persistent in the environment (little negative environmental impact
Herbicide examples (3)
o 2,4-Dicholophenoxyacetic Acid (2,4-D)
o 2,4,5-Trichlorophenoxyacetic Acid (2,4,5-T)
o TCDD
Herbicide properties (3)
Used to control many broad-leaf woody plants (act as growth hormones in plants)
Do no accumulate in animals
Slowly metabolized but readily excreted in the urine
Herbicide: Mechanism of toxicity
Animals that have died due to massive ingestion of herbicides believed to be due to ventricular fibrillation
Herbicide examples (3)
o 2,4-Dicholophenoxyacetic Acid (2,4-D)
o 2,4,5-Trichlorophenoxyacetic Acid (2,4,5-T)
o TCDD
Polychlorinated Biphenyls (PCBs): Use and properties (4)
Use: Widely used, but use terminated in 1977. Still very persistent in the environment.
Properties:
- Very lipophilic
- Highly stable
- Poorly metabolized
- Resistant to environmental degradation (bioaccumulate in the food chain)
Polychlorinated Biphenyls (PCBs): source and safety
Source: contaminated food
Safety: considered a major problem but have not been shown to be very hazardous to health unless food with extremely high levels is consumed
Coumarin poisoning
Similar structure to vitamin K and functions as an anti-coagulant (OD leads to hemorrhage)
Also used as a rodenticide (D-con)
Treat by removing coumarin and administering vitamin K (competes for same substrates)
Paraquat: mechanism of toxicity
Undergoes redox cycling in cells to generate large amount of reactive oxygen species (Superoxides and others)
Generation of oxidative stress causes changes in the regulation of cellular function and ultimately cell necrosis
Effects of Two Chemicals Together: (4)
Additive: of individual responses (2+3=5)
o Most common: unless there is evidence otherwise, normally assumed that the effects of a mixture of chemicals is additive
Synergistic: together produce much more effect than would be expected based on mathematical sum of individual actions (2+2=20)
Potentiation: one may potentiate the other (ie. has no effect alone but may increase toxicity of another chemical; 2+0=14)
Antagonism: one may antagonize the other (10 + 0=2, 10 + (-4)=0); desirable and serve as basis for antidotes
Polychlorinated Biphenyls (PCBs): source and safety
Source: contaminated food
Safety: considered a major problem but have not been shown to be very hazardous to health unless food with extremely high levels is consumed
Physiological Antagonism
Drugs that stimulate antagonistic physiological mechanisms
May be of little clinical value and may even decrease survival
o Difficult to titrate the effect of one drug against another when 2 drugs act on opposing systems
o Duration of action of poison an antidote may differ, thereby producing poisoning by antidote
Physiological Antagonism examples
CNS stimulants reverse respiratory depression
o May cause seizures/convulsions
o Mechanical support of respiration preferred
Mechanisms of DDIs:(6)
- Physical interaction
- Plasma protein binding
- Competition at receptor sites
- Induction of drug metabolizing enzymes
- Inhibition of drug metabolizing enzymes
- Competition for renal tubular transport
Overlooked DDIs
Alcohol, caffeine, tobacco
Interactions due to alcohol:
Chronic use results in:
Competitive substrate for:
Potentiating:
o Chronic use results in INDUCTION of some liver cytochromes P450 enzymes (ie. CYP2E1) –> increasing metabolism of certain drugs and DECREASED effects
o Can be a competitive substrate for some P450s –> inhibiting metabolism of some drugs POTENTIATING their effects
o CNS effects of alcohol and many other drugs
Interactions due to caffeine:
o Inducer AND a substrate for microsomal drug metabolizing enzymes o Potential harm via interaction with many common medications: - Benzodiazepines - Oral contraceptives - Cimetidine - MAO inhibitors - Phenothiazines - Theophylline
Interactions due to tobacco:
- Interactions due to tobacco: o Inducer of some drug metabolizing enzymes o Decreases effects of commons drugs: - Acetaminophen - Antidepressants - Benzodiazepines - Cimetidine - Oral contraceptives - Estrogens - Insulins - Propanolol - Theophylline
Paraquat: Basics:
Non-selective herbicide used to destroy plant tissue on contact
Primary sites of damage in humans are lungs, liver and kidneys
Widespread proliferation of fibroblasts in the lung
Prompt removal of from digestive tract is important
