Study Guide for Final (The most recent stuff) Flashcards
Toxicology
the study of the adverse effects of a chemical, physical, or biological agent on living organisms and the ecosystem, including the prevention of such adverse effects in
- Occupational settings
- Environmental settings
- Ecological settings
Toxicity
the ability of a material to damage a biological system, cause injury, or impair function.
-The dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals all effect the degree of toxicity.
Hazard
ability of an agent to cause toxicity;
-depends on the inherent properties of the agent & exposure liability.
Risk
the expected frequency of exposure to a hazardous agent.
-quality & suitability of the -dose-response data used for extrapolation limits risk assessment accuracy
Route of exposure
- Route of entry into the body;
- inhalation, transdermal, oral, mucosal, etc.
Duration of Exposure
- May effect selection of treatment.
- Acute vs Chronic
ADME
The Adsorption, Distribution, Metabolism, and Excretion of toxic substances and their metabolites.
Clearance
1st vs 0 order clearance
measure of the plasma cleared per unit time;
-sum of both the renal and hepatic contributions
When exposed to very high concentrations (toxic doses), normal kinetic properties can change:
- under normal conditions, elimination of most drugs/chemicals is proportional to their plasma concentration (1st order kinetics)
- When plasma levels become very high, protein binding and normal metabolism can both become saturated and the rate of elimination can become fixed (zero order kinetics) and more drug will be delivered into the circulation in unbound fraction.
- This is why at toxic doses of a drug or a toxin, normal kinetics may be altered to reflect prolonged a half-life and increases toxicity (larger, unbound free fractions)
Volume of Distribution
more difficult to remove a substance with a large Vd than one with a small Vd
apparent volume into which a substance is distributed in the body
- A large Vd implies a substance will not be easily accessible to purification attempts (e.g., hemodialysis***);
- Examples include antidepressants, antipsychotics, antimalarials, and opioids
- A small Vd, better candidates;
- Examples include salicylates, ethanol, and phenobarbital.
phenyotin follows 0 order kinetics
Bioaccumulation
accumulation of an toxic agent when the uptake of the agent exceeds the organism’s ability to metabolize/excrete it.
-in large exposures, capacity of 1st pass metabolism can be overwhelmed resulting in increased levels in blood and/or kidney.
Bioaccumulation refers to accumulation of higher and higher amounts of material within one specificorganism’s body such as one fish where as biomagnificationrefers to acquiring increasing levels of a substance in bodies of higher trophic-level organisms such as fish, seal, bear.
Biomagnification
increases in the relative amount of a contaminant in a biological system as it passes up the food chain.
-polychlorinated biphenyls (PCB’s) in exposed plankton eaten by fish; fish eaten by people
Acquisition of increasing levels of a substance in bodies of higher trophic-level organisms such as fish, seal, bear as you go up the food chain.
Biocompatibility
the ability of a material to elicit an appropriate biological response in a given application in the body.
- Should not be harmful to pulp or soft tissues
- Should not contain toxic diffusable substances that may be released and absorbed into the circulatory system to cause systemic toxicity
- Should be free of potentially sensitizing agents that may cause allergic reactions
- Should have NO carcinogenic potential
What defines some metals as “heavy”?
Naturally occurring elements defined as “heavy” due to their high atomic weight and having a density at least five times greater than that of water (i.e., specific density >5 g/cm3).
The most toxic substances are
lead (#1), mercury (#2) and arsenic (#3)
Heavy metals (high atomic weight), interfere with normal biological processes by
competing with normal substrates
The shorter the t1/2 the more
effective is the use of chelators to remove the heavy metal
Lead
( has no physiological value):
What are the primary exposure sources? for lead
These include building materials/construction, batteries, lead pipes, paint etc.
Why is lead exposure particularly detrimental to young children?
Their bodies absorb because Pb competes with Ca, and growing bodies require considerable Ca. Children absorb >50% consumed whereas adults absorb ~10-15%
They often eat or suck on things that contain Pb, such as things covered with Pb-containing paint, dirt etc.
What do we know about its toxicokinetics? of lead
t1/2 = 1-2 months
What do we know about its symptomology? of lead
Headaches, neurocognitive deficits, kidney damage, etc.
Lead
What is the main repository in the body for its lead burden?
What are Burtonian lines?
What is the mechanism of lead’s toxicity?
What is the treatment regimen for lead toxicity, particularly the recommended chelators?
- It substitutes for Ca++ in bone
- Lead lines causing a darkening of the gingiva
- Interferes with Ca++ use
- Causes anemia Causes immunosuppression
- Remove exposure
- Administer a chelator such as EDTA (edetate calcium disodium). It removes Pb from bone slowly and requires multiple chelating treatments
Mercury (quicksilver) :
- Properties?
- What are the primary exposure sources?
- What is the mechanism of mercury toxicity?
-liquid at room temperature -primarily used in the methylHg form
- Found in fish
- Amalgam (no CDC-recognized evidence that it is a problem in dentistry)
- thermometers
- Reacts with selenium (necessary for reducing oxidized Vitamin C and E)
- Can cause gingivostomatitis
Mercury quicksilver
What do we know about its toxicokinetics?
What do we know about its symptomology?
Explain the phrase “Mad as a hatter.”
What is the treatment regimen for mercury toxicity, particularly the recommended chelators?
Why is dimercaprol contraindicated in chronic mercury intoxication scenarios?
highly reactive with selenium, an essential dietary element required for thioredoxin reductase to prevent & reverse oxidative damage.
- Can cause neurological, psychiatric problems
Mad hatter means mercury was used in process of curing pelts used in hats making it impossible for hatters to avoid inhaling mercury fumes given off the hat making process. They suffered poisoning..causing conufsed speech, vision and neuro damage
Dimercaprol, succimer
Chronic use of dimercaprol can cause serious renal toxicity
• What do we know about its symptomology?
Arsenic
- Fatigue, anemia, renal failure, hyperpigmentation
- Carcinogenic in lungs, skin and bladder
- Hemolytic on RBC
• What do we know about its toxicokinetics? (arsenic)
-absorbed through respiratory mucosa and GI tract, but so much through the skin
Arsenic primay exposure sources
-industrial contamination from the production of semiconductors, wood preservatives, alloys, glass, insecticidals, veterinary-grade antibacterials,
groundwater contamination by natural arsenic containing mineral deposits;
Arsenite (As3+): used in chemotherapeutics for various forms of leukemia.
Arsenic mechanism
-absorbed via respiratory & GI tract,
poor absorption through skin;
**binds to sulfhydryl groups in keratinized tissues (hair, nails, skin) where it acts a depot;
excreted primarily through kidney, but small amounts also in lost in sweat and feces.
• How does the treatment regimen, including the use of chelators, differ for each of the following conditions:
o acute arsenic intoxication
o chronic arsenic intoxication
o acute arsine gas intoxication
Treatment:
Decontamination & supportive care
Chelation with Unithiol (i.v.) or Dimercaprol (i.m.) for 4-6 hours;
If exposure is even suspected, empiric chelation should be started
Treatment:
supportive care,
dietary supplementation with folate promotes methylation & excretion,
chelators offer no therapeutic benefit since chronic arsenosis leads to irreversible damage to several vital organs and is an established carcinogen.
Treatment: Blood exchange hemodialysis and transfusions, aggressive hydration, chelators of no benefit
- How do chelators work on heavy metals?
- How does the half-life of the heavy metal effect the ability of a chelator to remove it from a target organ?
- Is it better to treat with chelators quickly or take a wait and see approach when an exposure has occurred?
- They render heavy metal ions unavailable for covalent interactions
- The longer the t1/2, the less effective is the chelator
-Generally, most effective if administered A.S.A.P. after exposure.
So expose chelator quick
Dimecaporol
• FDA-approved for which heavy metal poisonings as a monotherapy?
- Can be administered with CaNa2-EDTA for severe, chronic poisoning with what heavy metal?
- Why should it not be given as a monotherapy after chronic exposure to lead?
Water soluble?
• What is its only route of administration?
• How does its therapeutic index compare to succimer or unithiol?
FDA approved:
Monotherapy for acute arsenic and/or mercury poisoning
Combination therapy with edetate calcium disodium (CaNa2-EDTA) for severe LEAD poisoning
note:Contraindicated for use alone after chronic exposure to lead, since it redistributes larger doses of lead to CNS.
• It pulls Pb from bone and it goes to brain and causes toxicity
- Not water-soluble (cannot be given orally)
- Administered via i.m. route only
• It can be very toxic, especially on kidneys—succimer has for most part replaced dimercaprol
• What is the mechanism of arsenic toxicity? Acute
Acute Intoxication: abrupt gastroenteritis, hypotension, metabolic acidosis, cardiac dysfunction, pancytopenia, and peripheral neuropathy
Treatment:
Decontamination & supportive care
Chelation with Unithiol (i.v.) or Dimercaprol (i.m.) for 4-6 hours;
If exposure is even suspected, empiric chelation should be started
• What is the mechanism of arsenic toxicity? Chronic
fatigue, anorexia, anemia, weakness, GI complaints, peripheral neuropathy (dyesthesia); hyperpigmentation & hyperkeratoses of the skin of hands and feet, prolonged QT interval, cancer of lung, skin, bladder
Treatment:
supportive care,
dietary supplementation with folate promotes methylation & excretion,
chelators offer no therapeutic benefit since chronic arsenosis leads to irreversible damage to several vital organs and is an established carcinogen.
• What is the mechanism of arsenic toxicity? Acute arsine gas intoxication
causes hemolysis, headache, nauseau, vomitting, diarrhea, dypsnea, abdominal pain, jaundice and renal failure 1-3 days later.
Treatment: Blood exchange hemodialysis and transfusions, aggressive hydration, chelators of no benefit
