Forensic toxicology

Last updated: Tuesday, 30, March, 2004

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Item Process
Specimen

Supervision of specimen collection and sealing of containers is mandatory to establish a chain of custody. The process must be fully documented.

Living patients: blood (10 mL in fluoride tube), urine, hair, faeces, gastric contents as appropriate.

Post mortem: as for living patients plus appropriate tissue especially liver, muscle, brain, fat.

Other materials: as appropriate.

Method

Drugs and organic chemicals - immunoassay, spectrophotometry, TLC, GC, HPLC. GCMS is usually required for confirmation.

Metals and some non-metals - atomic absorption spectrophotometry.

Reference Interval

Depends on the drug or poison in question and the circumstances of the case.

Multiple drug ingestions are more common than single drug ingestions and may lower the toxic thresholds of individual drugs.

See below for approximate upper therapeutic levels in plasma, consistent with therapeutic use and threshold levels for probable toxicity. Note that some toxic thresholds are close to, or identical with, the upper therapeutic level.

Therapeutic and toxic plasma levels of selected drugs. First amount shows upper therapeutic level mg/L, second amount shows toxic threshold mg/L

Anti-depressants:                          
Amitriptyline*  0.25, 0.5
Dothiepin*  0.2, 0.5
Doxepin* 0.25, 0.5
Fluoxetine 0.5, Not known
Imipramine*  0.3, 0.5
Mobenclamide 10.0, 30.0

Analgesics:
Morphine (total) 0.1, 0.2
Codeine (total) 0.4, 0.6
Pethidine 2.0,  2.0
Propoxyphene* 1.0, 1.0

Anti-psychotics:
Thioridazine* 1.5, 1.5
Chlorpromazine*  2.0, 2.0
Haloperidol 0.05, 0.1

Benzodiazepines:
Diazepam 2.0, 2.0
Oxazepam 2.0, 2.0
Temazepam 2.0, 2.0
Nitrazepam 0.2, 0.2
Flunitrazepam 0.05, 0.05

Application

Estimation of drugs or poisons in plasma, urine, gastric contents or tissues of suspected poisoning cases.

Detection of drugs of dependence in the urine of suspected or known drug addicts.

Interpretation

Consult pathologist.

Post-mortem drug concentrations may be elevated, compared to ante-mortem concentrations, due to redistribution (drugs marked with an asterisk* are most prone to this effect) - consult a forensic pathologist or toxicologist.

In some cases the significance of the results may have to be assessed by a court after expert evidence.

Reference

Baselt RC and Gravey RH. Disposition of Toxic Drugs and Chemicals in Man. 3rd ed. Year Book Medical Publishers 1989.

Cordner SM et al. Aust NZ J Med 1992; 22: 477-486.