Forensic Pharmacology
Page 3
concentration of drug X would be approximately 3% of the initial
value. To maintain therapeutic levels of drug X, you might require
taking a dose every three hours. Knowledge of excretion patterns
of a chemical and of its metabolites is important for determining
treatment schedules as well as for determining, in criminal or
civil matters, when a drug had been taken or administered.
PHARMACODYNAMICS
Pharmacodynamics is the study of the mechanisms of drug
action. How does a chemical cure disease, stimulate or inhibit
the nervous system, change behavior, influence our digestive
system, or induce a toxic reaction? The body itself is made up
of chemicals, and when drugs (chemicals) are taken, the drugs
interact with the body’s chemicals and these interactions result
in biochemical and physiological effects. While there are many
different mechanisms of drug action that account for the dif-
ferent effects of diverse drugs, in this book we will restrict our
discussion to those reactions that explain the effects of drugs
of abuse. Drugs of abuse bring about their effects by interacting
with cell receptors or by influencing the levels of various neu-
rotransmitters, outlined below.
Pharmacokinetics and Pharmacodynamics
19
Cell Receptors
A receptor is a macromolecule on or in a cell with which a drug
can interact and begin a sequence of events eventually leading
to an effect. There are many receptors, some specific to a tissue
or organ and others that are found more generally. Receptors
include enzymes, regulatory proteins, and DNA-binding pro-
teins. Often, the first reaction between chemical and recep-
tor brings about a chain of reactions before the final effect is
The Science of Anatomy
The study of anatomy was original y restricted to animals. In
the fourteenth century, an Italian named Mondino de’ Liucci
performed human dissection and published his findings. Leon-
ardo da Vinci, born in the fifteenth century, was recognized
as a painter, a scientist, and an engineer. His most famous
paintings are the Mona Lisa and The Last Supper. Da Vinci
was also interested in human anatomy and published the
first textbook on human anatomy. Andreas Vesalius, a physi-
cian, was influenced by da Vinci’s work. Vesalius published a
seven-volume collection detailing the human body entitled De
Humani Corporis Fabrica. In the eighteenth century, medical
students were al owed to perform human dissection. In Eng-
land, in 1858, Dr. Henry Gray published his first book, entitled
Anatomy, Descriptive and Surgical. Today, many people know
this book as Gray’s Anatomy. In 1989, Frank H. Netter, a physi-
cian and medical illustrator, published his extremely detailed
anatomical drawings in ful color, termed Atlas of Human
Anatomy.
20 Forensic Pharmacology
produced. Drugs that bring about effects are called agonists.
Chemicals that can block effects are termed antagonists.
Neuronal Signaling
At the end of each neuron are stores of chemicals called neu-
rotransmitters that can be released to stimulate adjacent neu-
rons (Figure 2.2). There are many different neurotransmitters,
dependent on location and specific function in the nervous sys-
tem. Generally, once a neuron is stimulated, the stimulus travels
along the neuronal axon until it reaches the end of the neuron
from which a neurotransmitter is released. The neurotrans-
Figure 2.2 In this il ustration of neuronal signaling, an electrical
impulse causes the release of neurotransmitters from vesicles in the
axon terminal of a neuron. The neurotransmitters cross the synapse (also
known as the synaptic cleft) and bind to receptors on a receiving neuron.
Pharmacokinetics and Pharmacodynamics
21
mitter enters a space between the neuron it was released from
and adjacent neurons. This space is called a synapse. The neu-
rotransmitter diffuses across the synapse and excites a recep-
tor on an adjacent neuron. Any chemical that has not attached
itself to the surrounding neurons can either be destroyed by
enzymes or be taken back up into the original neuron. Drugs
can affect the function of the nervous system in several ways.
They can stimulate or inhibit release of neurotransmitter, block
its effects or affect its metabolism, prevent reuptake of the neu-
rotransmitter, or mimic the effects of a neurotransmitter. Some
examples of neurotransmitters in the CNS affected by drugs of
abuse include gamma-aminobutyric acid (GABA), norepineph-
rine and dopamine, serotonin, endorphins, dynorphins, and
enkephalins, and glutamate.
● Gamma-aminobutyric acid (GABA), is present in many
areas of the brain, and is inhibitory. GABA can influ-
ence sensation of pain and affects memory, mood,
and coordination. GHB and benzodiazepines increase
GABA activity.
● Norepinephrine and dopamine are stimulants and
increase mental alertness. Amphetamines activate nor-
epinephrine receptors and also release norepinephrine
and dopamine from storage; cocaine blocks the reup-
take of dopamine.
● Serotonin (5HT) affects sleep, temperature, sexual
behavior, sensory perception, appetite, and mood.
There are many serotonin receptors, and activation of
each brings about different effects. LSD and psilocybin
activate serotonin receptors.
● Endorphins, dynorphins, and enkephalins are natu-
ral peptide neurotransmitters that activate the opioid
22 Forensic Pharmacology
receptors and affect sensation of pain, and induce
euphoria, a feeling of well-being or elation.
● Glutamate activates the N-methyl-D-aspartate (NMDA)
receptor. Glutamate is involved in perception of pain,
sensory input, and memory. PCP and dextrometho-
rphan block this receptor.
● The enzyme MAO metabolizes some of the neurotrans-
mitters affected by some drugs of abuse, namely epi-
nephrine, norepinephrine, dopamine, and serotonin.
Dangerously high levels can result if an inhibitor of this
enzyme, or monoamine oxidase inhibitor (MAOI), is
used along with the drug of abuse.
Figure 2.3 Many drugs of abuse act on the brain’s reward center,
which is illustrated above. The drugs cause neurons in the ventral
tegmental area to release dopamine. The dopamine, in turn, initiates
a chain of events that results in feelings of enjoyment and pleasure.
Pharmacokinetics and Pharmacodynamics
23
Many of the effects of drugs of abuse have been localized to
what is termed the brain’s reward center (Figure 2.3). The
drugs increase the concentration of the neurotransmitter
dopamine in the mesolimbic dopaminergic system. This sys-
tem includes those areas of the brain designated as the ventral
tegmental area (VTA), which transmits signals to the nucleus
accumbens, prefrontal cortex, and other area
s of the brain.
All together these are considered the reward and drug seeking
areas of the brain.
SUMMARY
The cell membrane is a complex structure of lipid, protein,
and carbohydrate and regulates chemical passage via several
mechanisms. Chemicals can interact with cell membranes or
be absorbed into a cell to exert their pharmacologic effects.
Chemicals reach their target via the bloodstream, and intracel-
lular concentration is dependent on the extent of plasma protein
binding. Most chemicals undergo some form of metabolism
to be either activated or inactivated, or, in some cases, both.
Lipid-soluble molecules tend to be deposited in fat cells and are
released slowly over time. Eventually, chemicals are eliminated,
most often via urine and feces. Drugs of abuse bring about their
effects by interacting with cell receptors or by influencing the
levels of various neurotransmitters.
3
Drug Analysis
One role of the forensic scientist is to help determine whether
drugs caused the behavior, illness, injury, or death of an indi-
vidual. To do this with some scientific basis, the scientist must
determine whether a drug or active metabolite is present in
bodily fluids and tissues, and, if so, its concentration. It is the
concentration of drug in blood and inside the cell that relates
to pharmacologic effects (dose-response relationship), and the
concentration inside the cell closely approximates the concen-
tration in blood. Thus, analysis of a sample of blood, plasma,
or serum (the liquid part of the blood remaining after clotting)
is best for establishing a direct connection. While a drug or
metabolite may be detected in urine, such evidence is indicative
of prior exposure to the drug, but the concentration may not be
related to the observed effects.
When dealing with deceased individuals, the forensic patholo-
gist (usually the medical examiner) will provide samples of blood
taken from both the heart and the leg’s femoral vein. The results
will be compared to avoid reaching an incorrect conclusion of
drug concentration for those drugs that exhibit postmortem
redistribution, which is when substances that were concentrated
24
Drug Analysis
25
in heart and adjacent organs leak back out into the blood and
produce abnormally high values. The forensic scientist may also
receive samples of urine, bile, vitreous humor, and tissue from
various organs such as liver, kidney, lung, heart, and brain, as
well as stomach contents, to determine if large amounts of a drug
had been ingested. Analysis of these tissues could give a clearer
picture of whether any drugs present had a direct connection to
the manner of death, whether it be natural, suicide, homicide, or
accidental.
Analysis of tissues such as nails, hair, and bone, where chemi-
cals are deposited but not readily released (Figure 3.1), is useful
to determine whether an individual had ever been exposed to a
particular chemical, but is of less value in determining recent
exposure and causation.
ANALYTICAL TESTS
The forensic scientist has multiple analytic techniques available.
Some are screening tests that may not absolutely identify the
chemical in question but narrow the number of possibilities.
Subsequently, the analyst will perform confirmatory tests in
which the chemical is positively identified. It is important to
remember that even though the analysis may reveal the presence
of a drug, there may be a legitimate reason for such a finding. We
will discuss such examples in individual chapters.
There are two types of analysis: qualitative and quantitative.
Qualitative analysis determines which chemical is present, while
quantitative analysis determines the concentration of a chemi-
cal. Concentration means an amount of chemical per unit of
sample, for example, 100 micrograms (μg) of morphine per
liter (L) of blood (100 μg/L); or the amount of pure chemical
per weight of material, such as 1 gram of heroin per 10 grams of
white powder.
26 Forensic Pharmacology
Figure 3.1 A hair sample from a suspected drug user is prepared
for forensic analysis. As hair grows, it incorporates small amounts of
chemicals that are produced when drugs are broken down in the body.
To identify these drugs, the hair is first cut into pieces and soaked in a
liquid solvent. The solvent removes the traces of drug metabolites from
the hair so that they can be identified by chromatography and mass
spectrometry.
Drug Analysis
27
Important considerations in any type of test include specificity
and sensitivity. Specificity refers to the ability of a test to detect
only the compound in question and not mistakenly identify other
compounds in the sample (which is known as a false positive).
Sensitivity refers to how reliably a test will detect the compound
in question when it is present in a sample. A less sensitive test will
sometimes fail to detect the presence of a compound.
When samples are received in the laboratory, they are often
first treated by various extraction procedures to separate any
chemicals from the original fluid or tissue. The extract is then
analyzed by screening or confirmatory procedures.
On occasion it becomes necessary to dig up, or exhume, a
body and to test for the presence of drugs. Such analysis presents
special problems for the forensic scientist. First, the blood has
been displaced with embalming fluid, and blood levels are not
obtainable; second, the drug may have decomposed in air or
moisture or been chemically altered by the embalming fluid or
by bacteria growing on decomposing tissue; and third, the tis-
sues may have completely decomposed. Although teeth, bone,
or nails may be present, death may have occurred too soon for
the drug to have accumulated in these tissues. Interpretation of
data and any conclusions drawn using exhumed samples must
be done with caution.
A notable case involving exhumation is that of Dr. X. In 1976,
Dr. Mario E. Jascalevich, known as Dr. X before his true identity
was revealed, was accused of murdering five patients 10 years
earlier at Riverdell Hospital in Oradell, New Jersey, by adminis-
tering curare, a muscle relaxant. The five bodies were exhumed,
and toxicology results were presented at trial that lasted 34 weeks.
A key argument between the prosecution and defense expert
witnesses was whether curare was in fact detected in the bodily
samples. The prosecutor could not prove that curare was present,
and Dr. Jascalevich was eventually acquitted.
28 Forensic Pharmacology
There are several screening tests available. One commonly
used test for drugs in urine is the enzyme multiplied immunoas-
say technique (EMIT). This test is based on an immunological
principle of antibody-antigen reaction. An antibody to the drug
> (antigen) being tested for is added to the urine sample. Also
added to the sample is a known amount of the drug being ana-
lyzed with an enzyme attached to it, so that enzymatic activity can
be measured. If the urine sample contains a large amount of drug,
the drug will bind to the antibody and, by competition, prevent
binding of the enzyme-drug complex to the antibody. Thus, more
of the free enzyme can be measured. If little drug is present in the
urine sample, then more of the enzyme-drug complex will bind
to the antibody, and enzyme activity will be less. The more drug
in a person’s urine, the greater the amount of measurable enzyme
activity. There are many variations of this antibody-antigen type
testing. Since chemicals or metabolites of drugs with structures
similar to the drug of interest may cross-react with the antibody
and falsely indicate a positive result (a false positive), this test is
considered a screening test. Subsequent tests must be done to
positively identify the chemical in the urine sample and to deter-
mine its concentration. If something in the sample prevents the
drug from reacting with the antibody, the result would appear
negative (a false negative). Although the EMIT test cannot deter-
mine accurately the amount of chemical present, the analysis is
very sensitive and can detect quantities of drug in the nanogram
(ng) range, one-billionth of a gram or 1 × 10-9 gram.
Another screening procedure for detecting drugs is based on
the drug reacting with a reagent to produce a characteristic color.
Color tests are simple and quick and require small amounts of
sample. Items found at a crime scene may be analyzed for the
presence of drugs and urine samples and tissue extracts may be
screened for some drugs using color tests. Any positive result
must be confirmed using gas chromatography (GC), gas chro-
Drug Analysis
29
matography/mass spectrometry (GC/MS), high-performance
liquid chromatography (HPLC), or infrared spectrometry.
CHROMATOGRAPHY
The application of chromatography is widely used for detecting
drugs. Chromatography can separate a mixture of chemicals
from one another so that each can be identified and quanti-
fied. The principle of separation is based on the fact that differ-
ent chemicals have different affinities for a particular material,