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….
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
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
4
Q
What are features of Gas Chromatography Mass Spectrometry in forensic toxicology?
A
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)
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
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
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
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
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)
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)
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)
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)
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
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
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
