post mortem toxicology and biochemistry

 

Bayer heroin bottle

Source: Wikipedia

 

An essential component of many medicolegal autopsies is toxicological analysis, the aim of which is to identify the presence of any substance relevant to the death. Post mortem biochemical analysis may also be of value in a proportion of sudden deaths, particularly those involving alcoholics and diabetics.

The following pages in this section provide an outline of the main toxicological/ biochemical topics of relevance to forensic pathology.

 

when to take samples for toxicology

 

Post-mortem toxicological analysis should be considered in all deaths in which there is a possibility of an overdose, in alcoholics, in cases of intoxication, where there is a duty of care owed (for example, in a nursing home), where machinery or vehicles have been used for example, during the course of work, or in cases where there may be suspicions that behaviour may have been impaired.

It should be remembered that there is a duty to retain material having a bearing on the cause of death in the Coroner’s rules, Rule 9.

 

some definitions

 

Drug

  • any substance that affects physical/mental functioning

Drug-related death

  • deaths where underlying cause is poisoning, drug abuse, or drug dependence, and where any of the substances listed is included in the Misuse of Drugs Act 1971

The Wales Assembly Government definition of a drug-related death 

  • “where it is probable that a direct or delayed consequence of the non-therapeutic taking or administration of any drug or volatile substance (excluding alcohol alone) to a person, was a causative or contributory factor in his/her death" (See their website for annual reports on drug-related deaths in Wales)

categories of drugs of abuse

 

cocaine toothache drops - advertisement 1885

Source: Wikipedia

 

Stimulants

Depressants

Drugs that alter perception

Volatile substances

Routes of administration

  • nasal
  • inhalation
  • ingestion
  • injection.

legal classification of drugs of abuse in England & Wales - Misuse of Drugs Act 1971

 

Class A

Morphine/heroin, methadone, cocaine, MDMA, LSD, injected amphetamine.

Class B

Non-injected amphetamine.

Class C

Benzodiazepines, cannabis.

relative merits of post mortem toxicology samples

 

 

SPECIMEN

 

 

ADVANTAGES

 

Blood/plasma/serum

Preferred specimen (recent use with respect to death)

 

Bile

Morphine, buprenorphine, tramadol, benzodiazepines, MDMA, paracetamol

 

Bone/bone marrow

Qualitative-morphine, benzodiazepines, amphetamine

 

Fat

THC (but little data); volatiles after increased post-exposure period

 

Gastric contents

 

Orally administered drugs and poisons

 

Hair

All substances especially basic/most metals

 

Muscle

Most drugs (little data) – qualitative only (good for drugs with increased Vd (greater than 2L per kilogram) and in decomposition

 

Pleural effusion

 

Most drugs (difficult to interpret)

 

Vitreous

Ethanol, some biochemistry, glucose, electrolytes

 

Liver

 

TCA, phenothiazine neuroleptics

 

Lung (small pieces)

 

Volatiles/anaesthetics

 

Kidney

 

Heavy metals

 

Faeces

 

Porphyria

 

Brain

 

Volatiles

(Drummer 2004)

 

Heavy metal analysis can also be undertaken on small +/- large bowel contents.

Complex molecules break down post-mortem to simple ones, and go down concentration gradients that were maintained in life by energy.  Drugs are released from binding sites post-mortem and the pH falls.

 

For a full-sized version of this infographic see Information is beautiful

typical toxicology laboratory screening

 

  • Chemically basic drugs (i.e. the majority of the British National Formulary - BNF)
  • Neutral substances
  • Acidic substances (e.g. anti-diabetic medications)
  • Drugs of abuse
  • Alcohol

 

Screening is undertaken by means of immunoassays, GC-MS, LC-MS-MS etc.

The toxicology screening analysis won’t usually include GHB, BHB, paraquat, ethylene glycol etc.

Positive findings on screening are confirmed with a second complimentary technique, and then quantified using 4 – 5 calibration standards for example:

deadliest drugs - infographic

 

 

see the full-sized versions of these infographics at the Guardian 'Datablog'

medical complications of the misuse of drugs

 

 

opium smokers in China 1902

Source: Wikipedia

fatal mechanisms in drug-related deaths

 

The finding of elevated levels of substances in an individual’s body might provide an explanation for how that individual got into, or could not get out of, a potentially lethal situation.

Potential mechanisms of interest in drug-related deaths include disease, trauma, and drug-specific toxicity (modified by the naiveté of the user, the potency of the substance, the route in which the individual took the substance, and including where the substance has been “smuggled” into a country via condoms filled with drugs in the gastrointestinal system – body packers), or hypersensitivity reactions.

Typical mechanisms include:

The question of whether an individual has developed a “tolerance” to the effects of the substance identified at post-mortem is almost impossible to assess, but one may get an indication from evidence of chronic/long-term use of that substance (for example following hair/nail analysis).

seizures and illicit drug use

 

  • Focal, generalised and status
  • Usually acute intoxication of cocaine, amphetamine, opiates (unlike alcohol, benzodiazepines, barbiturates when seizures occur on withdrawal)
  • Could be associated with cerebral oedema
  • May be a prelude to fatal intoxication
  • It is unclear whether cocaine provokes seizures, or reduces the threshold to seizure in epileptics.  It is also possible that cocaine leads to seizures following stroke

strokes and illicit drug use

 

  • Most common cause of stroke in those under 35 years of age
  • Cocaine increases the risk of stroke by 7 times, and may be primary or secondary to aneurysms or av malformation.  Cocaine causes a transient increase in blood pressure, vasoconstriction and platelet activation
  • Amphetamine raises the risk of stroke by 7 times
  • Heroin may be related to ischaemic and haemorrhagic stroke, and there may be changes in arterial border zones, and hypoxic/ischaemic lesions in the globus pallidus, cerebellum and cortex
  • Phencycladine (PCP)
  • LSD
  • Cannabis (ischaemic)

rhabdomyolysis and illicit drug use

 

  • Cocaine – vasoconstriction/intramuscular vascular vasoconstriction, and agitation, increased activity and hyperthermia
  • Amphetamine
  • PCP
  • MDMA

problems in interpretation

 

  • Lack of fatal range data
  • Drug tolerance (especially alcohol and opiates)
  • Pharmacogenetics (fast or slow metabolisers, and abnormally high levels)
  • Drug stability in sample at post-mortem (for example benzodiazepines, diltiazem, cocaine, phenothiazine)
  • Post-mortem production (alcohol, GHB)
  • Post-mortem redistribution

post mortem drug redistribution (Pounder and Jones 1990)

 

Post-mortem drug concentrations can vary considerably depending on the anatomical site, some of this difference being due to arterial-venous differences, or the nature of post-mortem blood.

The main post-mortem toxicological problem is that of redistribution, which represents the diffusion of drugs along concentration gradients, from high concentrations in solid organs to low concentrations in the blood.  Examples of this include from the liver and lungs to pulmonary vessels, and then to the cardiac chambers and inferior vena cava.  Redistribution is a multi-factorial phenomenon, but is mainly due to diffusion.

Blood “movement” post-mortem is due to the development of rigor mortis and putrefaction.  The distribution of drugs in life, however, is due to lipophilicity, pKa, molecular size and affinity for tissues.  After cell death, the cell membrane integrity is lost, and no energy-dependent concentration gradient maintenance occurs. 

Due to the phenomenon of post-mortem drug redistribution, interpretation of analytical results requires knowledge of the origin of the sample (for example femoral blood versus cardiac blood), and whether apparently fatal concentrations quoted in the literature refer to the same site as that which the post-mortem sample of interest has been taken.

One can’t easily estimate an ante-mortem concentration or dose of a particular substance from a post-mortem sample.  Drugs with high central-to-peripheral ratios also have a high post-mortem to ante-mortem ratio or parent to metabolite ratio (Cooke 2000).

questions likely to be raised at drug-related death inquests

 

  • How much was taken (but too many pharmacokinetic etc. variables)
  • When was the substance taken (may be able to tell from morphine ratios etc.)
  • Did the deceased have any tolerance to the substance taken (tolerance persists for longer for drugs with very long half-life , for example methadone)
  • Was there any affect of pre-existing liver or kidney disease (kidney disease may be more important)

 

Paracelsus (1493-1541 - the 'father of toxicology')

Source: Wikipedia

histopathology and drug abuse (see Passarino 2005)

  • Blood-bourne infection – HIV in 17%, HBV/ACV in 65%
  • Brain – intracerebral haemorrhage/microhaemorrhages frequent (? trauma, alcohol, cocaine/amphetamines, or viral-induced liver damage with clotting problems); cerebral infection rare
  • Heart effects – lymphocytic inflammatory heart lesions in HIV/Aids also associated with pericardial effusions/pericarditis; right ventricular hypertrophy; opportunist infection; kaposy sarcoma; endocarditis (non-bacterial); myocardial fibrosis (especially heroin); wavy fibres are common
  • Kidney effects – interstitial nephritis (women more than men), possibly due to urinary tract infection with reduced immunity; glomerular sclerosis (especially in older individuals, and those who are HIV positive, possibly due to ischaemia)
  • Lung effects – bronchitis/pneumonia (in 12%); pulmonary haemorrhage, and pulmonary granulomas are common; aspiration; congestion (especially heroin); perivascular lymphocytes are common
  • Liver effects – steatosis (in 66%); hepatitis (in 64%), with acute hepatitis more prevalent in women than men, and chronic hepatitis more prevalent in older individuals, and those in whom there is concomitant viral infection; cirrhosis (more prevalent in older drug users, those with concomitant viral infection, and in concomitant alcohol misuse).

references

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