Forensic Biochemistry Flashcards

1
Q

What are the forensic diciplines?

A
  • Crime scene examination
  • Fingerprints (comparison, enhancement of latent)
  • Biological material screening / examination (e.g. microscopy)
  • Blood pattern analysis
  • Archaeology
  • Digital forensics (e.g. hard drive imaging, mobile phone tracing)
  • Fire arms (classification, ballistics, discharge residue)
  • Drug analysis / toxicology
  • Footwear impressions
  • Forensic pathology
  • DNA analysis
  • Others….
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2
Q

How is sample prepared for Forensic Toxicology?

A
  • Automated – no prep.
  • Any thing else, must get your drug out of the matrix!
  • Simple – dilute and shoot (urine, oral fluid), protein precipitation
  • Liquid-liquid extraction
  • Solid phase extraction / suspended liquid extraction
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3
Q

What are advantages and disadvantages of immunoassay used for Forensic Toxicology?

A

Advantages

  • Easily automatable
  • Cheap (depending on situation)
  • LOTS of literature (easy implementation)
  • Excellent for large volume screening for routine drug screening

Disadvantages

  • Class based antibodies = not definitive answer
  • Must confirm positive findings
  • Reports may look confusing
  • Can prove expensive (especially for user…)
  • One test per group
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4
Q

What are features of Gas Chromatography Mass Spectrometry in forensic toxicology?

A
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5
Q

What are advantages and disadvantages of Gas Chromatography Mass Spectrometry used for Forensic Toxicology?

A

Advantages

  • Excellent seperation of compounds (e.g. BHB vs. GHB, amfetamine isomers)
  • Cheap(ish) (vs. LC-MS/MS)
  • LOTS of literature (gold standard)
  • Universal ionisation (EI) = reliable library matches

Disadvantages

  • Long run times (~20 mins, especially scanning)
  • May need to derivatize compounds
  • Require carrier gas (e.g. Helium)
  • Specialist technical and interpretative skills
  • Manual sample prep
  • ? Sensitive enough (Scan)
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6
Q

What are advantages and disadvantages of HPLC-DAD used for Forensic Toxicology?

A

Advantages

  • Good seperation of compounds
  • Cheap(ish) (vs. LC-MS/MS)
  • Sensitive
  • Good for common prescription / OTC drugs
  • Short run times possible
  • No carrier gas required (stand alone)

Disadvantages

  • Specialist technical and interpretative skills
  • Manual sample prep (normally concentration step)
  • ? Sensitive enough
  • Not all compounds may be detected (THC, morphine)
  • Problems with co-elution
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7
Q

What are advantages and disadvantages of LCMS/MS used for Forensic Toxicology?

A

Advantages

  • Very sensitive
  • Baseline seperation not (necessarily) required
  • Isotope dilution – minimal matrix effects
  • Minimal sample prep (sometimes)
  • Multiplex analysis
  • Short run times possible

Disadvantages

  • Specialist technical and interpretative skills
  • Not looking for it = won’t find it!
  • Expensive equipment
  • Consider ionisation mode (positive / negative)
  • Maintenance costs
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8
Q

What is Accurate Mass (Q-TOF / Orbitrap)?

A
  • Accurate mass together with structural MS/MS data can give HUGE amount of information
  • Comparison with chemical databases possible for total unknown screening (i.e. no libraries) BUT CRM would have to be used for confirmation and quantitation
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9
Q

How is Routine Screening Conducted in Clinical Toxicology?

A
  • Full Toxicology Screen performed by Liquid Chromatography Time of Flight Mass Spectrometry (LC QTof-MS) plus other methods if needed (HPLC-DAD, GC-MS and LC-MS/MS)
  • Uses 50 µL of blood/serum or 200 µL urine in semi-automated sample extraction
  • Very sensitive (limit of detection ~ 1 µg/L for most drugs)
  • Full retrospective data analysis
  • Will cover the vast majority of drugs of interest
  • Ethanol by HS-GC will also be performed
  • Quantitative analysis of any drugs of interest
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10
Q

What isn’t covered by routine analysis?

A
  • BHB / GHB (and related compounds)
  • Toxic alcohols (ethylene glycol etc.)
  • Metals (inc. lithium)
  • Synthetic cannabinoids
  • Some fentanyl analogues
  • Insulin / C-peptide
  • MetHb / COHb (lithium heparin blood please)
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11
Q

What are drugs used in practice for Clinical toxicology?

A

Most drugs commonly associated with death in OD are those associated with risks of CNS/respiratory depression, cardiac issues, convulsions

  • Opiates, stimulants (e.g. amfetamine), antidepressants, antipsychotics, ethanol, cocaine, Z-drugs, barbiturates, paracetamol
  • Other drugs unlikely to cause death on their own but can enhance toxicity of other drugs (e.g. benzodiazepines, gabapentoids, ethanol)
  • Other drugs unlikely to be an issue (e.g. levetiracetam, atorvastatin)
  • Not to say other drugs can’t be involved but need a suspicion to measure them (e.g. metformin, gliclazide, propranolol)
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12
Q

Which drugs are linked with suicidal ideation?

A
  • Antidepressants and suicidal ideation. 1 in every 200 people will attempt suicide, 3 times higher than placebo1
  • Suicidal ideation on come down from drug
  • Acute mania at time of taking drug
  • PM toxicology alone may not tell you that much (e.g. tolerance)
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13
Q

Which drugs can contribute to Opiate Toxicicty?

A
  • Deaths due to opiate use typically due to respiratory depression. Any other drug which can exacerbate that depression could be potentially contributory
  • Ethanol, benzodiazepines, other opiates, anti-depressants (e.g. TCAs) etc.
  • Alcohol concentrations, even those associated with mild intoxication appear to lower the amount of heroin (and also methadone) required to fatally OD
  • Other substances did not show same characteristics (e.g. diazepam)
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14
Q

Which drugs can contribute to Lamotrigine Toxicicty?

A
  • Effective first line anticonvulsant
  • Carbamazepine, phenytoin and phenobarbitone upregulate enzymes which metabolise lamotrigine (potential risk of seizure)
  • Valproate inhibits metabolism – risk of increased circulating concentration
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15
Q

Which heart complications can occur from drugs?

A
  • Arrhythmia (irregular rhythm)
  • QTc prolongation (ECG)
  • Tachycardia / bradycardia
  • Myocardial infarction
  • Cardiac arrest
  • Lots of non-drug causes for these and
  • Occurrence of cardiac events not necessarily related to blood drug concentration
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16
Q

What are features of Synthetic Cannibinoids?

A
  • ‘Spice’ or ‘Mamba’ is not a single compound but a generic name for a group of compounds which have changed rapidly over the past 7/8 years
  • Highly lipophilic (partition into adipose)
  • Very low concentrations in blood (< 1 µg/L)
  • Extensively metabolised (i.e. often no parent drug in urine)
17
Q

Why are synthetic cannabinoids so toxic?

A
  • Manufacturers guess the amount to add and often not homogenous mixture – ‘hot pockets’
  • Products change all the time – may not be taking same drug as last week!
  • Very selective, potent, full agonist of CB1 receptor (c.f. THC)
  • Active metabolites
18
Q

What are Benzodiazepines?

A
  • USed to treat anxiety and insomnia
  • One of most widely prescribed drugs – Valium (diazepam) in UK and Xanax (alprazolam) in US
  • Often not potent on own but contribute to CNS / respiratory depression with other drugs
  • Potent NPS benzodiazepines keep appearing
19
Q

What is Alcoholic Ketoacidosis?

A
  • Typically occurs after alcohol binge & vomiting
  • Alcohol and food not consumed for period of time (e.g. 24 h)
  • Vomiting may continue and abdominal pain develops – patient seeks medical attention
  • In death – often BAC < 10 mg/dL with signs of excess alcohol consumption / vomiting at property
20
Q

What is Diabetic Ketoacidosis?

A
  • Ketoacidosis is very rare in T2DM (typically state of insulin resistance). Need to diagnose HHS – vitreous U/E and glucose.
  • Glucose will fall rapidly in PM vitreous (even if in FlOx tube) so quick measurement crucial
  • Measurement of Na and K not possible in FlOx tube.
21
Q

What are the issues with disorders of Glucose?

A
  • BHB typically very high in cases of fatal DKA (+ acetone)
  • DKA does not occur in patients with T2DM
  • HHS – demonstrate hypernatraemia and hyperglycaemia (vitreous)
  • Glucose unstable in vitreous – analyse quickly!
  • Insulin measurement unreliable in haemolysed samples, must be separated and frozen ASAP following collection
  • Low vitreous glucose with high insulin and low C-peptide = ? Insulin OD
22
Q

What are some other causes of Beta-hydroxybutyrate?

A

Hypothermia

Starvation

Presence of acetone in absence of BHB

  • Putrefaction
  • Ingestion of acetone
  • Ingestion of IPA. IPA intercoverting to Acetone
23
Q

What is Post Mortem Redistribution?

A
  • Movement of drug after death along a concentration gradient e.g. post overdose high concentration in stomach causes elevated concentrations in nearby tissue
  • Occurs for drugs which are highly protein bound, basic with a Vd > 3L/Kg (e.g. TCAs, propoxyphene, chloroquine)
  • Occurs within 1 h of death and continues as the PM interval increases (most important 24 h)
  • Increases will be greater in central sites (e.g. vessels near major organs) hence peripheral sites typically used
24
Q
A