Forensic Pharmacology:

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Forensic Pharmacology

• the relevance of medicines and drugs to some
  criminal cases

How can the pharmacologist help the legal team to
maximize the value of the evidence?
Academic Consultancy Services Ltd
Professor Nicholas J. Birch
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Forensic Pharmacology

• Basic tenet of pharmacology
• there is always an ordered relationship between
  the concentration of a drug acting in the body
  and the magnitude of its effect

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Effects of alcohol on behaviour
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Forensic Pharmacology

• There are always TWO sets of considerations

• Pharmacodynamics

• Pharmacokinetics

Professor Nicholas J.Birch
Academic Consultancy Services Ltd
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Pharmacodynamics response of the body to the
presence of a drug

• The actions of a drug at a receptor or receptors

response proportional to drug concentration at
receptor
Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Drug effects and toxicity
Phenytoin target blood concentration range
Useful dose range
Increasing toxicity
Ineffective
Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Drug response may be influenced by

• naturally occurring substances present at
  receptor
• e.g. neurotransmitters, hormones

• other drugs or xenobiotics present at receptor

• factors affecting number, structure or function
  of receptors
• disease, exercise, abnormal environment,
  starvation, obesity dehydration, age, sex,
  previous drug or dietary history

• genetic variability

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Drug Dosage Regimen

• Objective To prescribe a dose, the size and
  timing of which will provide the maximal
  THERAPEUTIC effect at the minimal cost in ADVERSE
  effects

• Assumes Orderly relationship between Dose Rate
  and both Therapeutic and Toxic effects

• Boundaries Ineffective Effective Toxic

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Phenytoin dosage
Professor Nicholas J.Birch
Academic Consultancy Services Ltd
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Size does matter

• Dose depends on
• Body size
• Age dependent factors
• Gender dependent factors
• Current physiological state

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Volume of distribution
Total body water is approximately 60 of lean
body mass
Weight 14.5 kg (3yr)
56kg 70 kg

• Total water
• 8.7 l 33.6 l
  42 l

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Pharmacokinetics movement of drug to and from
the locality of the receptor
ABSORPTION

• DISTRIBUTION

• METABOLISM

• EXCRETION

ADME controls the concentration of drug present
at the receptor at any precise time
Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Drug distribution kinetics
log10 concentration vs time linear

• concentration vs time
• exponential

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Professor Nicholas J.Birch
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Half life is the time taken for the blood
concentration to decline to one-half of its
present value
t½

• characteristic range of values for each drug

• long-acting drugs have long half-life

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Multiple doses

• Equilibrium occurs between four and five Half-
  Lives after first dose

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Phenytoin marginal overdose
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Fluoxetine pharmacokinetics
Effects of additional dose?
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Drug kineticsMurder Attempted Murder in which
it was alleged that the victims had been drugged
prior to lethal assault with machete
Blood sample Recalcd to give body load
Blood sample
Alleged time of dose
Professor Nicholas J.Birch
Academic Consultancy Services Ltd
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Drug interactions

• Drugs may interact
• Pharmacodynamically
• affect each others response at the same
  receptors
• block or modify biochemical action of receptor
• Pharmacokinetically
• alter rate of absorption or distribution
• prevent access to receptors
• alter each others metabolism or excretion

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Drug interactions

• Pharmacokinetic interaction between Prozac and
  diazepam (Valium)
• these drugs are both metabolised in the liver by
  a single enzyme, cytochrome P450-cyp2D6.
• presence of Prozac will cause the rate of removal
  of Valium to be decreased and vice versa
• Valium effects will be prolonged
• Prozac effects will be prolonged

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Pharmacological issues in criminal cases

• Those in which the drug is the main issue

• Illicit drugs, possession or dealing

• Driving offences

• Alcohol by definition, Other drugs by implication

• Those in which drug effects are related to the
  offence

• Behaviour alleged to be modified by presence of
  drug

• Intent, memory, ability to comprehend, ability to
  perform

• Behaviour triggered by drug

• Aggression, Confusion, Amnesia, Consent,
  Unconsciousness

Professor Nicholas J.Birch
Academic Consultancy Services Ltd
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Psychopharmacology

• Drugs affecting the mind are the most widely
  prescribed of all drugs

• About 50 of all GPs consultations have a
  psychiatric component

• 10 of the population will be treated for
  serious psychiatric disease at some stage in
  their life

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Common psychotropic drugs

• Hypnotics sleeping tablets
• Anti-anxiety drugs (anxiolytics)
• Antidepressants
• Antipsychotics
• Major tranquilizers

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Other drugs which may also have psychiatric
effects

• Alcohol
• Anaesthetics
• Antihistamines
• Calcium channel blockers
• Anticonvulsants
• Drugs leading to dependence
• analgesics, stimulants, hallucinogens, solvents

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Psychotropic drugs and crime

• Drugs may be used in the performance of criminal
  acts e.g. murder, abduction
• Drugs may be themselves the main issue of the
  crime e.g. drink driving, drug dealing
• Drugs may precipitate the criminal act e.g.
  psychiatric patient who commits theft whilst
  confused, drug interaction leading to
  uncharacteristic disinhibition

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Forensic Pharmacology How can a pharmacologist
assist the legal team?

• Pharmacologist can
• interpret drug actions

• evaluate the likely interplay between drugs and
  related disease processes

• evaluate potential interactions between drugs

• make estimates of the timescale of events based
  on the properties of drugs involved

• confirm other evidence by providing collateral
  data

Academic Consultancy Services Ltd
Professor Nicholas J.Birch
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Contact details

• Professor Nicholas J. Birch

• Tel/ Fax
• 01902 844679
• Email
• N.J.Birch_at_btinternet.com
• Postal address
• Rowanshiel, Histons Hill,
• Codsall, Staffordshire,
• WV8 2ER

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