topic 5: forensic toxicology

Question 1

what is forensic toxicology?

Answer 1

Qualitativeandquantitativedeterminationofbiologicalspecimensforthepresenceof
alcohol,drugs,and/orpoisonsandtheircorrespondingmetabolites
that mayhavecontributedtoorcauseddeath.

Question 2

what is the difference between pharmacologists and forensic toxicologists?

Answer 2

-Pharmacologistsdealwiththeexperimentationand
synthesisoftherapeutic drugs.
-Forensictoxicologists examinetheeffectsoftoxinswhenacrimeorpoisoning
hasbeencommitted, inordertoaidalegalinvestigation indeterminingthecauseandmannerofdeath
(natural,accidental,suicide,orhomicide)

Question 3

what are the 3 main sub-desciplines of forensic toxicology? (PHF)

Answer 3

• post mortemforensictoxicology,
• humanperformance toxicology
• forensic drugtesting.

Allofthesesub‐disciplines measuresubstancesinbiologicalmatricesfor
agivenpurpose.

Question 4

when is forensic toxicology analysis required? what is the most common type of cases forensic toxicologist deal with?

Answer 4

Morethanhalfofthecases receivedbyforensictoxicologistsinvolve
drinkingalcoholanddriving.

Question 5

who is the father of forensic toxicology?

Answer 5

-M.J.B.Orfila‐Thefatherofforensictoxicology Mainlyfocusedonarsenic;thepoisonofchoiceintheearly19th century.Itwasreadilyavailableinratpoison. Thefirstmodernforensictestimonyinapoisoningcase.
(marie lafarge)

Question 6

what is a poison?

Answer 6

“Allsubstancesarepoisons,thereisnonewhichisnotapoison.
Therightdosedifferentiates a poison fromaremedy.”

“Thedifferencebetweenapoisonandamedicineisthedose”
even water can be poison!

Question 7

what is a drug?

Answer 7

Adrugisasubstance,wheningested,iscapableofinducing
aphysiologicalchange.
Alldrugsaretoxic.
Itisthedose thatdifferentiatesatherapeuticdrugfrompoison.

Question 8

what are the 3 classifications of poison? briefly describe them and give eg.

Answer 8

1. Systemicpoisons:
   materialsthataretoxictospecificorgansororgansystemsasaresultofexposure.
   Thesetoxichazardscanbegroupedincategoriesbasedontheorganorsystemtheyaffect.
   Systemicpoisonsaretoxicsubstanceswhoseeffectisnotlocalizedinonespotbutspreadsto
   otherbodyorgansandsystemsinvaryingdegrees.
   Themajoreffectsareusuallymanifestedinoneortwoorgans.
   e.g cyanide, carbon monoxide, morphine, coniine, arsenic
2. Toxins
   anypoisonoussubstancesthatarenaturallyproduced byanorganisms,
   be it animal, plants, fungi, micro-organisms
3. Xenobioticis
   achemicalwhichisfoundinanorganismbutwhichisnotnormallyproduced
   orexpectedtobepresentinit
   (synthetic/foreignchemicalstohumanbody).
   e.g nicotine, caffiene, snti biotics, legal and illegal drugs.

Question 9

what is a route of administration? what are the 4 types of routes of drug administration. Briefly describe each. (OIIS)

Answer 9

pathbywhichadrug,fluid,poison,orothersubstanceistakenintothebody.
•Oraladministration(absorbedthroughdigestivetract;easy,painless)
•Inhalation(rapidlyvia therespiratorytract) •Intravenous(directlyintotheveinusinganeedleortube,efficient)
•Sublingual(placement of drug under tongue, oftenfastandefficient)

Question 10

describe the metabolism of alcohol.

Answer 10

• > 90%ofalcoholiseliminatedbytheliver;
• 2‐5%isexcretedunchangedinurine,sweat,orbreath.

1st Step oxidationbyalcoholdehydrogenasetoacetaldehyde(highlyreactiveandtoxicsubstance).
2nd Step‐ItisoxidisedrapidlybyAcetaldehyde dehydrogenasetoharmlessaceticacid.

Theaceticacidiseventuallyconvertedinthecellintocarbondioxideandwater.

Question 11

what is a breath analyser used in field testing?

Answer 11

Aportable,handheld,roadsidebreathanalyser/testermaybeusedtodetermineapreliminarybreath‐alcoholcontent.
Usesachemicalreactioninvolvingalcoholthatproducesacolourchange.

Question 12

what is a breath intoxilyzer used in field testing? what is its principal?

Answer 12

Aportable,handheld,roadsidebreathanalyser/testermaybeusedtodetermineapreliminarybreath‐alcoholcontent.

Principleofinfraredabsorption. Degreeoftheinteractionofthelightwithalcoholinthecapturedbreathsample ConcentrationbasedonBeer’sLaw. Moresensitive,withlowerdetectionlimitascomparedtobreathanalyser. S

Question 13

what is commonly used in the lab to test for blood alcohol levels? what is its advantage?

Answer 13

GC
offersthetoxicologistthemostwidelyusedapproachfordeterminingalcohol
levelsinbloodaccurately.
Muchmoresensitiveascomparedtofieldanalysers
i.e.breathanalyser&breathintoxilyzer.

Question 14

how is toxicity measured? (2 ways) describe what each method means

Answer 14

Dose‐Response/Exposure–ResponseRelationship Describesthemagnitudeoftheresponseofanorganism,
asafunctionofexposuretoastimulusorstressorafteracertainexposuretime.

Measuringtoxicity: LD50
Lethaldosefor50percent
Amountofchemicalrequiredtokillhalf ofthetestpopulation.

Question 15

how does accuracy of LD50 vary?

Answer 15

Varyaccordingtoadministrationof poison: Oraladministrationvsdirect injection

Dependonspeciesusedfor testing
Typicallymiceor rats,assumesimilarLD50valuesfor humans.

Question 16

what are some factors affecting LD50? (SASDP)

Answer 16

Size(mg/kg)
Age‐metabolismchangeswithage
StateofHealth‐especiallyconditionoftheliver
DrugHistory‐buildupoftoleranceandlossoftolerance,e.g.heroinaddict
Paradoxicalreactions‐rarebutknown
Effectofachemicalsubstance,mostlyamedicaldrug,causedunexpectedserioussideeffect.
Anexampleofa paradoxicalreaction ispaincausedbyapainreliefmedication.

Question 17

explain the phenomenon of asian flush

Answer 17

Most Asians have an inactive variant of the liver enzyme acetaldehyde dehydrogenase;

acetaldehyde takes a much longer to clear from their blood and this causes reddening of the face, sweating and palpitations.