principles of toxicology SDL

Question 1

define toxicology

Answer 1

The study of harmful properties, actions and effects of chemicals on biological systems.

Question 2

define toxin

Answer 2

a substance produced by a living organism (as a bacterium) that is very poisonous to other organisms and that usually causes antibody formation

Question 3

define toxicant

Answer 3

Any toxic substance, usually man made or a product of man made activities

Question 4

define poison

Answer 4

a substance that is capable of causing the illness or death of a living organism when introduced or absorbed.

Question 5

define venom

Answer 5

A poisonous substance/secretion containing one or more toxins secreted by an animal, usually injected into prey or aggressor by biting or stinging

Question 6

define toxicity

Answer 6

The extent to which something is poisonous or harmful.

Question 7

define xenobiotic

Answer 7

A chemical substance within an organism that is not naturally expected or foreign

Question 8

define toxicosis

Answer 8

a pathological condition caused by the action of a poison or toxin.

Question 9

define developmental toxicity

Answer 9

Adverse toxic effects to the developing embryo or foetus. Toxicant exposure to either parent before conception or to the mother and the developing embryo-foetus.

Question 10

what are the possible effects of toxicity

Answer 10

• cell replacement such as fibrosis
• damage to an enzyme system
• disruption of protein synthesis
• production of reactive chemicals in cells
• DNA damage

Question 11

when does a chemical become toxic

Answer 11

Xenobiotic (foreign) compound enters the body and absorption exceeds elimination

Question 12

What is LD50?

Answer 12

the lethal dose required of a substance that kills 50% of the test population
- Lower LD50 = more toxic

Question 13

what questions are important to ask in a case of suspected poisoning

Answer 13

• WHAT? What is the animal doing? (Clinical signs)
• WHAT? What is the suspected poison?
• WHEN? When did the poisoning happen? How many hours have passed
• WHO? Did anyone see what happened?
• WHO ELSE? Are there any other animals or humans who have/could access the poison and are in danger?
• HOW? How did it get the poison? E.g swallowed, injected, bitten, touched.
• HOW? How did it come into contact with the poison in the first place?
• HOW? How much poison has the animal received?

Question 14

list ways in which toxicants are absorbed

Answer 14

• GI tract (ingestion)
• skin (absorption/contact)
• inhaled
• mucous membranes
• uterus
• injection

Question 15

describe how toxicants get distributed around the body

Answer 15

• may have effect locally OR
• travel via the blood
• toxin deposited in tissue depends on receptor types
• ease of distribution affected by toxin solubility (fat vs water)

Question 16

where do toxicants go once they have been distributed around the body

Answer 16

• lipid soluble chemicals tend to accumulate in fatty tissue
• where the toxin is stored is not necessarily the site of toxcitity

Question 17

outline how the body gets rid of toxins

Answer 17

• metabolised to a less or more (lethal synthesis) toxic metabolite
• most toxins excreted via kidneys but can also be excreted via milk or sweat

Question 18

Describe the metabolic pathway for elimination of fat soluble toxicants

Answer 18

1. Lipophilic toxin binds to lipoproteins in the blood
2. Undergoes metabolism in liver
3. Phase I metabolism:
   - oxidation
   - reduction
   - hydrolysis
4. Phase II metabolism:
   - synthetic conjugation
5. Increased water solubility
6. Excreted in bile or urine

Question 19

what factors effect toxicity

Answer 19

• Dose
• Duration + frequency of exposure
• Age and health of patient
  route of exposure
• Environmental factors
• Inability to vomit
• Seasonal or climatic changes
• Isomer of toxin

Question 20

what is chronicity factor?

Answer 20

ratio of the acute to chronic LD50 dose
example: a compound may have a low acute toxicity, but if it accumulates in the tissue, it can lead to chronic toxicity = cumulative poisons
A CF of >2 suggests a drug is relatively cumulative
- gives an indication of cumulative danger

Question 21

what is acute toxicosis

Answer 21

refers to effects during the first 24-hour period.

Question 22

what is chronic toxicosis

Answer 22

Effects produced by prolonged exposure (≥3 months) are referred to as chronic toxicosis.

Question 23

what is tolerance in terms of toxicity

Answer 23

ability to show less response to a specific dose with repeat exposure - an acquired response, not innate response

Question 24

how does tolerance to toxin develop

Answer 24

• repeated binding between receptor and substance desensitises receptor
• increase in degradation enzymes reduces amount of substance reaching target tissue

Question 25

what is resistance

Answer 25

is development of the ability to withstand the previously destructive effect of a drug by microorganisms

Question 26

how can resistance develop

Answer 26

• Antibiotic inactivation or modification
• Alteration of target or binding site
• Bypassing metabolic inhibition
• Preventing antibiotic accumulation

Question 27

What are the possible methods of reducing further absorption of toxin?

Answer 27

• wash off if possible
• induce emesis if possible (unless would damage esophagus)
• lavage stomach?
• gastro-protectants or absorbant meds (charcoal)

Question 28

what supportive treatment is needed in toxicosis

Answer 28

Supportive therapy is often necessary until the toxic agent can be metabolized and eliminated. The type of support required depends on the animal’s clinical condition. Supportive efforts may include:
- control of convulsive seizures
- maintenance of respiration
- treatment for shock
- correction of electrolyte imbalance and fluid loss
- control of cardiac dysfunction
- alleviation of pain.