Forensic Biochemistry Flashcards
What are the forensic diciplines?
- 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….
How is sample prepared for Forensic Toxicology?
- 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
What are advantages and disadvantages of immunoassay used for Forensic Toxicology?
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
What are features of Gas Chromatography Mass Spectrometry in forensic toxicology?
What are advantages and disadvantages of Gas Chromatography Mass Spectrometry used for Forensic Toxicology?
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)
What are advantages and disadvantages of HPLC-DAD used for Forensic Toxicology?
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
What are advantages and disadvantages of LCMS/MS used for Forensic Toxicology?
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
What is Accurate Mass (Q-TOF / Orbitrap)?
- 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
How is Routine Screening Conducted in Clinical Toxicology?
- 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
What isn’t covered by routine analysis?
- 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)
What are drugs used in practice for Clinical toxicology?
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)
Which drugs are linked with suicidal ideation?
- 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)
Which drugs can contribute to Opiate Toxicicty?
- 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)
Which drugs can contribute to Lamotrigine Toxicicty?
- 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
Which heart complications can occur from drugs?
- 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