Forensic Toxicology

Question 1

How does the preliminary breath test for alcohol work?

Answer 1

Chemical oxidation using potassium dichromate

2 K2Cr2O7 + 3 C2H5OH + 8 H2SO4 -> 2 Cr2(SO4)3 + 3 CH3COOH + 11 H2O

Question 2

What method is used for measuring alcohol in the blood?

Answer 2

GC - high specificity, accurate quantitative analysis and ease of automation -> headspace alcohol injected into GC air = air withdrawn from blood in bail and injected

Question 3

Define Henry’s law

Answer 3

Law or chemistry that governs the equilibrium between a volatile substance in solution and in gas phase = alcohol present in breath is equal to conc in the blood

Question 4

What are the 3 pharmacokinetic methods of alcohol?

Answer 4

1. absorption
   - rate of absorption depends on nature of drink, rate/speed of drinking and stomach contents
2. Distribution
   - circulates rapidly and distributes proportionally to the water content
3. Elimination
   - metabolism = converts ethyl alcohol to acetic acid
   - liver = breaking down alcohol

Question 5

What are two confirmatory tests to detect drugs?

Answer 5

1. EMIT

2. TLC

Question 6

What are the 2 preliminary immunoassay tests used?

Answer 6

1. Enzyme multiplied immunoassay test (EMIT)
   - rabbit injected with drug in question and then produces antibodies to it = serum removed and immediately binds to antibodies if present in the body
2. Radioimmunoassay (RIA)
   - similar to EMIT but antigens are radioactively labelled

Question 7

What is the preliminary test used to detect drugs?

Answer 7

SCREENING TESTS - indicates a drug may be present but not confirm the present of a specific drug

1. Chromatographic
2. immunoassay

Question 8

What 2 methods are used to extract drugs from the body?

Answer 8

1. Liquid phase
   - pH range of drug must be known = dictates method of extraction
2. Solid phase
   - coated wife extracts drug from the matrix

Question 9

Define the terms ‘synergism’ and ‘tolerance’

Answer 9

SYNERGISM - when drugs work together to magnify their effects or create effects that would not have occurred otherwise

TOLERANCE - the body’s system adapts to the drug = taking ever-increasing doses to achieve equivalent effects

Question 10

Define the terms ‘agonist’ and ‘antagonist’ drugs

Answer 10

AGONIST - binds to a receptor and causes it to exert its function on the cell

ANTAGONIST - binds to a receptor and doesn’t cause it to exert the action on the cell

Question 11

What are the 4 methods of pharmacokinetics in drugs?

Answer 11

1. Absorption
   - passage of the drug through a tissue barrier and into the bloodstream
2. Distribution
   - drugs distributed via bloodstream = reaches every cell in the body
3. Metabolism
   - changing a drug chemically into another substance = metabolites to eliminate and deactivate the drug
4. Elimination
   - removal through urination and some via perspiration

Question 12

Define the terms ‘pharmacokinetics’ and ‘pharmacodynamics’

Answer 12

PHARMACOKINETICS - how drugs move into and out the body

PHARMACODYNAMICS - how drugs act in the body (agonist and antagonist)