and codeine to morphine, exhiditing higher activity
than the respective parent drugs; others are at least
as active as, or less active than, the parent drugs
(diazepam to nerdiazepam and temazepam, and then
to oxazepam; fluoxetine to norfluoxetine; ami-
triptyline to nortriptyline). Cn the other hand, drug
metabolites are also physiclogicaily inactive, but
some of them may be chemically reactive, ¢.g., N-
acetyi-p-benzoquinone imine (NAPQI), imminium
ions, arene oxide and aliphatic epoxide intermedi-
ates, and free radicals; reactive metabolites have a
strong potential to chemically react with macromol-
ecules causing cei] death and tumorigenesis.
Benzoylecgonine of cocaine, azacycionol of
terfenadine, and !1-nor-9-carboxy-A’-tetrahydre-
cannabinol (1 1-nor-9-carboxy-A®-THC) of A°-THC
are examples of physiologically inactive metabo-
lites; they are act considered reactive metabolites.

The enzyme systems responsible for metabolism
of foreign compounds are integral parts of the
smooth endoplasmic reticulum. The reactions cata-
lyzed by these enzyme systems can be classified
into Phase I and Phase II (Williams, 1959). Phase I
reactions consist of oxidation, reduction, and hy-
drolysis, whereas Phase II reactions include conju-
gations of molecules containing suitable polar
groups with endogenous groups or substances, such
as glucuronidation, acetylation, glycine, sulfate and
glutathione (GSH) conjugations, and transsulfuration.
The oxidation reaction is the major pathway for
biotransformation of xenobiotics. Almost ali
xenobiotic oxidations are carried out by the enzymatic
machinery mixed function oxygenases system (MFO),
aiso referred to as the cytochrome P-450 containing
monooxygenases. During the oxidation reaction,
equivalent amounts of O,, NADPH (nicotinamide
adenine dinucleotide phosphate - reduced form),
and a drug are utilized (Gillitte and Jollow, 1974;
Neal, 1980). There are several agents that can alter
the MFO activity, and thereby the metabolism of
an agent. Phenobarbital, ethanol, 3-methytcholan-
threne, DDT, toxaphene, and 1-phenylcyclohexene
(PC) are examples of MFO inducers, while SKF-
525A, piperonyl butoxide, cobaltous chloride, CCI,
and a-naphthylisothiocyanate are of MFO inhibitors.
Effects of these agents on the MFO are generally stud-

ied by ix vitro metabolism of drugs/chemicals, like
phenacetin, aniline, amidopyrine, and
benzo{a}pyrene; and by the determination of hepatic
cytochrome P-450 levels (Abe and Watanabe, 1982;
Chaturvedi and Kuntz, 1988; Chaturvedi et al.,
1991; Omure and Sato, 1964a; 1964b; Overton et
al., 1985). In experimental animals, alterations in
the MFO activity can be measured by changes in
the sleep time induced by the short acting barbitu-
tate pentobarbital (Chaturvedi, 1993); the barbitu-
rate is primarily metabolized by the MFO, and its
metabolites are weaker in action. The induction in
the MFO activity is further supported by the in-
crease in liver/body weight ratio and proliferation,
along with dilatation and fragmentation of the en-
doplasmic reticulum in the liver (Hu et al., 1984;
Kuntz et al., 1990). Liver pathological conditions
also alter biotransformation of drugs; drug metabo-
lism decreases during hepatic necrosis and cirrho-
sis, while it increases during the active regeneration
of hepatic cells following a toxicant-caused liver
injury (Sipes and Gandolfi, 1991).

Chemical structure of a drug plays a key part in
biotransformation. A slight change in drug melecules
may alter their metabolism—for example, esters are
hydrolyzed at a faster rate than the corresponding
amides. Procaine, cocaine, and pentobarbital are
quickly metabolized in the body. The ester procaine
has a lower half-life than the amide procainamide.
Determination of benzoylecgonine in the urine will
be more feasible than the ester cocaine, since co-
caine is extensively biotransformed and excreted
unchanged only up to 9% in the urine (Baselt and
Cravey, 1989). Different to the termination of
pentobarbital action through its hepatic metabolism,
effects of barbital are predominanily terminated by
its excretion through the kidneys; barbitai is ex-
creted in the urine unchanged.

Lipophilic compounds are present in very low
concentrations in the urine. The lipophilic A°-THC
is metabolized to the hydrophilic 11-nor-9-carboxy-
4°-THC via 11-hydroxy-A°-THC, which, like the
parent compound, is short-lived in the body. There-
fore, the presence of 11-nor-9-carboxy-A?-THC in
a suitable sample would indicate a possible abuse
of marihuana (Foltz et al., 1980). It is known that

ARR ARRAN A


have been successful in the identification and
quantitation of metabolites. Knowledge of drug
metabolism can assist in developing safe drugs and
in recommending proper treatments in the event of
possible intoxication. Additionally, demonstrating
the presence of metabolites, including parent drugs,
provides compelling evidence for exposure to the
parent drug and facilitates interpretation of toxico-
logical findings and accident investigation.

REFERENCES

Abe T, Watanabe M (1982). Genetic differences in
the induction of aryl hydrocarbon hydroxylase
and its components by 3-methylcholanthrene in
liver and lung microsomes among four strains
of guinea pigs. Biochem. Pharmacol., 31,2077-
2082.

Bailey DN (1994). Studies of cocaethylene
(ethylcocaine) formation by human tissues in
vitro. J. Anal. Toxicol., 18, 13-15.

Baselt RC, Cravey RH (1989). Disposition of Toxic
Drugs and Chemicals in Man, 31d edn., Year
Book Medical Publishers, Inc., Chicago, IL.

Canfield DV, Flemig J, Hordinsky JR, Veronneau
SJH (1994). Unreported medications used in in-
capacitating medical conditions found in fatal
civil aviation accidents. Aviat. Space Environ.
Med., 65, 455.

Chaturvedi AK (1993). Biochemical and toxicologi-
cal studies on the mixtures of three commonly-
used herbicides in mice. Arch. Environ. Contam.
Toxicai., 24, 449-454.

Chaturvedi AK, Kuntz DJ (1988). Interaction be-
tween phencyclidine and its pyrolysis product,
1-phenylcyclohexene. Pharmacel. Biochem.
Behav., 30, 1035-1043.

Chaturvedi AK, Kuntz DJ, Rao, NGS (1991). Meta-
bolic aspects of the toxicology of mixtures of
parathion, toxaphene and/or 2,4-D in mice. J.
Appl. Toxicol., 11, 245-251.

Chaturvedi AK, Rao NGS, Hurley MP? (1983a).
Toxicological findiags in a multi-drug death in-
volving propoxyphene, ceffcine, phenacetin, ac-
etaminophen and salicylate. Forensic Sci. Int.,
23, 255-264.

Chaturvedi AK, Rao NGS, McCoy FE (19836). A
multi-chemical death involving caffeine, nico-
tine and malathion. Forensic Sci. Int, 23, 265-
275.

Dean RA, Harper ET, Dumaual N, Stoeckel DA,
Bosron WF (1992). Effects of ethanol on cc-
caine metabolism: Formation of coceethylene
and norcocaethlyene. Toxicol. Appl. Pharmacol.,
117, 1-8.

Dieterle W, Faigle JW (1583). Preparative liquid-
chromatographic methods in drug metabolism
studies. In Drug Metabolite Isolation and De-
termination, Reid E, Leppard JP, eds., pp. 13-
32. Plenum Press, New York, NY.

Evans MA, Baseit RC (1981). Principles of toxic
disposition. Ir Introduction to Forensic Toxi-
cology, Cravey RH, Baselt RC, eds., pp. 41-68.
Biomedical Publications, Davis, CA.

Finkle BS, McCloskey KL, Kiplinger GF, Bennett
IF (1976). A national assessment of pro-
poxyphene in postmortem medicolegal inves-
tigation, 1972-1975. J. Forensic Sci., 21,
706-742.

Foitz RL, Fentiman, Jr., AF, Foltz RB (1980). GC/
MS Assays for Abused Drugs in Body Fluids.
National Institute on Drug Abuse Research
Monograph 32, US Department of Health and
Human Services, Rockville, MD.

Freeman AS, Martin BR (1981). Quantification of
phencyclidine in mainstream smoke and iden-
tification of phenylcyclohex-1-ene as pyroly-
sis product. J. Pharm. Sci., 70 1002-1004.

Gillette JR, Joliow DJ (1974). Drug metabolism in
liver. In The Liver, Part A, Becker FF, ed., pp.
165-201. Marcel Dekker, Inc., New York, NY.



Role of Metabolites in Aviation Forensic Toxicology

INTRODUCTION

Although drugs are aormally taken for medica!
reasons, exposures to drugs could also be acciden-
tal, recreational, suicidal, or even homicidal. Mood
altering drugs impair performance and may coatrib-
ute to accidents, but accidents could also be attrib-
uted to medical conditions for which a drug is
prescribed. During aeromedical accident investiga-
tions, postmortem biological specimens from air-
craft victims are analyzed for drugs, volatiles, and
primary fire gases (Canfield et al., 1994; White et
al., 1992). The presence of drugs in the biological
samples indicates exposures to the drugs and sug-
gests possible associated medical conditions for
which they might have been taken. Such analytical
findings are instrumental in establishing the cause
of aviation accidents.

Metabolic studies are essential for evaluating the
safety and efficacy of drugs. Such types of studies
provide a better understanding of a drug’s mode of
action, toxicity, and interaction with other medica-
tions; they also elucidate the biochemical reaction
mechanisms that are involved in the biotransfor-
mation and toxicity of drugs (Nelson, 1982). In fo-
rensic toxicology, the knowledge of metabolic
principles is of significance in making the proper
choice of a biological specimen for analysis, in
understanding the possible metabolites of a drug,
and in interpreting the analytical data for toxico-
logical investigations (Evans and Baselt, 1981).
Demonstrating the presence of drug metabolite(s)
in postmortem samples becomes prima facie evi-
dence for exposure to the parent drug, particularly
when those in vivo biotransformed metabolic enti-
ties ase otherwise not avaiiable as drugs for com-
mon usage. Contrary to general forensic toxicology
cases usually encountered in coroner and medical
examiner systems, drugs in aviation forensic toxi-
cology cases are mostly found in therapeutic to
subtherapeutic levels (White et al., 1992); normal
drug pharmacokinetics patterns in the former situ-
ations are altered because of the involvement of the
toxic/lethal doses of drugs. At therapeutic or

subtherapeutic doses, drugs in biclogica! samples
are generally present in very low levels, but their
primary metabolites might exist in higher concen-
trations in 2 suitable sample type. Determination
of metabolites becomes more prudent with those
drugs which are efficacious at low doses/concen-
trations and/or undergo extensive first pass
biotransformation (diltiazem, terfenadine, and
triazolobenzodiazepines). The relative low drug
concentrations usually experienced in aviation cases
warrant the need for identification and determina-
tion of possible drug metabolites. Such qualitative
and quantitative analyses of metabolites, along with
parent drugs, in multispecimens, further facilitate
aeromedical accident investigation and authenticate
its conclusion.

DRUG METABOLISM

Once foreign chemicals enter the body by inges-
tion, injection, inhalation, and/or absorption through
skin, they are eliminated into the urine, feces, bile,
perspiration, vomitus, milk, hair, and/or expired air.
The elimination largely depends upc « their hydro-
philicity; lipophilic compounds have a tendency to
eccumuiste in adipose tissues. There is a variety of
enzymes in the body that metabolize xenobiotics
into more water aoluble forms, thereby enhancing
their elimination and diminishing their bioiogical
response (Zimmerman, 1978). The enzymes respon-
sible for metabolizing foreign compounds are pri-
marily found in the liver. Howeves, metabolism in
other tissues, such as brain, kidneys, and intestine,
afso occurs, but to a jesser degree than in the liver.
Metabolism is a biological process that alters the
chemical structure of parent drugs; there may be
one or more metabolites of « drug, and drug me-
tabolites may further be biotransformed into other
chemical entities. It is not always true that atl me-
tabolites are biologically inactive. Some drugs are
biotransformed into active forms, such as primidone
to phenobarbital, flurazepam to N-desatkylflurazepam,

ADA299212


phencyclidine (PCP) is an abused drug (Petersen
and Stillman, 1978), and one of its major routes of
administration is smoking (Henderson, 1982). Dur-
ing smoking, about 50% PCP pyrolizes into PC
(Freeman and Martin, 1981). Therefore, the pres-
ence of PCP and PC and their metabolites will sug-
gest the PCP abuse by smoking, as PCP does not
metabolize into PC.

DISCUSSION

Demonstrating the presence of drug metabolites
in suitable biological samples facilitates toxicologi-
cal investigations, since this acts as convincing evi-
dence for exposures to the parent drugs. The levels
of the parent compound and its active metabolites
help in establishing the extent of intoxication, as
well. Finding the relative concentration of the par-
ent drug and metabolite can assist in determining
the approximate time of parent drug exposure, as
demonstrated with A°-THC and 11!-nor-9-carboxy-
A°-THC (Huestis et al., 1992). Levels of both
amitriptyline and nortriptyline, codeine and mor-
phine, ephedrine and phenylpropanolamine,
imipramine and desipramine, isopropyl alcohol and
acetone, methamphetamine and amphetamine,
phenacetin and acetaminophen, or propoxyphene
and porpropoxyphene will be indicative of the pos-
sible exposure to the respective parent compound.
Since metabolites may also be available as medi-
cations, their presence may not necessarily suggest
exposures to the corresponding parent drugs only;
it could also imply exposures to the parent drug and/
or the metabolite drug. In spite of this, their con-
centrations in specific bio-samples will be of sig-
nificance in establishing the degree of drug
intoxication. Certainly, if metabolites—for example,
benzoy!ecgonine of cocaine, azacyclonol of
terfenadine, and 11-nor-9-carboxy-A’-THC of
4*-THC-are not available as drugs for common us-
age, exhibiting the metabolite presence in the
samples will support exposures to the parent drugs
because the metabolites were formed in the body.
In the presence of ethanol, the cocaine metabolism is
altered leading to the bio-formation of cocaethylene,

a pharmacologically active cocaine analog (Bailey,
1964; Dean et al., 1992). Therefore, the presence
of cocaine, cocacthylene, and benzoylecgonine
along with ethanol would suggest
exposure to the stimulant cocaine and ingestion of
ethanol; this information will be crucial in forensic
accident investigations.

There are some limitations for analysis of me-
tabolites. Major metabolites of drugs are not always
feasible to characterize because reference standards
are nct easily available; the possibility to detect or
identify minor metabolites is hardly high. However,
detection and characterization of metabolites can
effectively be achieved by applying the basic prin-
ciples of biochemical metabolic reactions and us-
ing sensitive and selective analytical techniques.
Gas liquid chromatography/mass spectrometry and
capillary ges liquid chromatography utilizing flame
ionization, nitrogen phosphorus, electron capture,
Fourier transform infrared, and atomic emission
detectors have been instrumental in the identifica-
tion and/or quantification of drugs and their me-
tabolites. Derivatization of extracted metabolites is
recommended for gas-chromatographic analyses,
but sometimes, interferences are reported because
of endogenous materials. High pressure liquid chro-
matography equipped with mass spectrometry has
been found to be suitable in the identification of
metabolites; this technique has been used for study-
ing metabolism of drugs, particularly those of high
relative molecular masses and polar metabolites
(Skellern, 1983). Preparative liquid chromato-
graphic methods in drug metabolism studies have
been reported (Dieterie and Faigie, 1983). Radio-
immunoassays and/or enzyme immunoassays for
various drugs, such as A’-THC and diazepam, have
routinely been utilized in forensic laboratories.
Although lacking specificity and precision, these
assays do offer an advantage over other methods.
The advantage is due to the cross reactivity between
the parent compound (e.g., A’- THC) and its metabo-
lites and related analogs (other cannabinoids;
Petersen, 1980). The cross reactivity is a clear-cut
indication for the presence of the parent drug and/
or structurally related molecule(s) in the sample.

ANANDQANDAIYD


Henderson G (1982). Phencyclidine, a widely
abused but little understood psychotomimitic
agent. Trends in Pharmacol. Sci., 3, 248-250.

Hu CY, Choudhuri MSK, Berg IE, Rao NGS,
Chaturvedi AK (1984). Toxicity of 1-
phenylcyclohexene and its interaction with
phencyclidine. Taxicol. Appl. Pharmacoi., 76,
405-413.

Huestis MA, Henaingfield JE, Cone EJ (1992).
Blood cannabinoids. II. Models for the predic-
tion of time of marijuana exposure from plasma
concentrations of A°-tetrahydrocannabinol
(THC) and 11-nor-S-carboxy-A’- rocan-
nabinol (THCCOOH). J. Anal. Toxicol., 16,
283-289.

Kuntz DJ, Rao NGS, Berg IE. Khattree R,
Chaturvedi AK (1990). Toxicity of parathion,
toxaphene and/or 2,4-D in mice. J. Appl.
Toxicol., 10, 257-266.

McBay AJ (1978). Propoxyphene. In Methodology
for Analytical Toxicology, Sunshine I, ed., pp.
322-324. CRC Press, Inc., West Palm Beach,
FL.

McBay AJ, Turk RF, Corbett BA, Hudson P (1974).
Determination of propoxyphene in biological
materials. J. Forensic Sci., 19, 81-89.

Neal RA (1980). Metabolism of toxic substances.
in Toxicology: The Basic Science of Poisons,
Doull J, Klaassen CD, Amdur MO, eds., pp. 56-
69. Macmillan Publishing Co., Inc., New York,
NY.

Nelson SD (1982). Metabolic activation and drug
toxicity. J. Med. Chem., 25, 753-765.

Omura T, Sato R (19642). The carbon monoxide-
binding pigment of liver microsomes: I. Evi-
dence for its hemoprotein nature. J. Biol. Chem.,
239, 2370-2378.

Omure T, Sato, R (1964b). The carbon monoxide-
binding pignent of liver microsomes: II. Solu-
bilization, purification, and properties. J. Biol.
Chem., 239, 2379-2385.

Overton M, Hickman JA, Threadgill MD, Vaughan
K, Gescher A (1985). The generation of poten-
tially toxic reactive iminium ions from the oxi-
dative metat-tism of xenobiotic N-alkyl
compounds. Biochem. Pharmacol., 34, 2055-
2061.

Petersen RC (1980). Marihuana Research Find-
ings:1980. National Institute on Drug Abuse
Research Monograph 31, US Department of
Health and Human Services, Rockville, MD.

Petersen RC, Stillman RC (1978). Phencyclidine
(PCP) Abuse: An Appraisal. National Institute
on Drug Abuse Research Monograph 21, US
Department of Health and Human Services,
Rockville, MD.

Sipes 1G, Gandolfi AJ (1991). Biotransformation
of toxicants. In Cesarett and Doull’s Toxicol-
ogy: The Basic Science of Poisons, 4th edn.,
Amdur MO, Doull J, Klaassen CD, eds., pp. 88-
126. Pergamon Press, New York, NY.

Skeliern GG (1983). Strategies centered on HPLC.
In Drug Metabolite Isoiation and Determina-
tion, Reid E, Leppard JP, eds., pp. 3-11. Ple-
num Press, New York, NY.

White VL, Canfield DV, Hordinsky JR (1992). The
identification and quantitation of triamterene in
blood and urine from a fatal aircraft accident.
US Department of Transporiation/Federal Avia-
tion Administration, Washington, DC. Publica-
tion No. DOT/FAA/AM-92/23. Available from
Nationai Technical Information Service,
Springfield, VA 22161.

Williams RT (1959). Detoxification Mechanisms,
Wiley, New York, NY.

Zimmerman Hi (1978). Hepatic metabolism of for-
eign compounds. In Hepatotoxicity: The Ad-
verse Effects of Drugs and Other Chemicals on
the Liver, Chapter 2, pp. 11-31. Appleton-Cen-
tury-Crofts, New York, NY.

AUS, COVEROMENT PEINTING OPPICE: 1995 . sen-ecv2e823


DOT/FAA/AM-95/26

Office of Aviation Medicine
Washington, D.C. 20591

19950919 362

Role of Metabolites
in Aviation Forerisic

Toxicology

Arvind K. Chaturvedi
Dennis V. Canfield

Civil Aeromedical Institute
Federsl Aviation Administratic:.

Accesion For

NTIS CRA&I

OTIC TAB
Unannounced Oo
Justification

By
Distribution |

Avaitability Codes

. Avail and! or
Dist Special

Oklahoma City, Oklahoma 73125 Al- ! |

August 1995

Final Report

This document is available to the public
through the National Tech: ‘<al Information
Service, Springfield, Virginia 22161.

@

ry
U.S. Department ps0 QUALITY rePECIED

of Transportation

Federal Aviation
Administration


Although isolation of conjugate metabolites of
drugs establishes their metabolic routes, it also dem-
onstrates exposures to the parent drug in forensic
toxicology situations. Acid or enzymatic bydroly-
sis of conjugates improves the yield of a parent drug
and/or its Phase I metabolites. Therefore, the de-
tection becomes easier. Protein precipitants are used
with tissue homogenates. Some precipitants react
with chemical entities in question, thus interfering
with assay procedures. Consequently, precipitants
should be carefully selected. Do levels of a drug
and its metabolites after the hydrolysis or depro-
teinization really correlate with the true drug tox-
icity or the drug-induced impairment? Such levels
could be misleading, as only the free drug contrib-
utes to a phermacological response; bound or con-
jugated drugs and metavolites are generally
considezed ineffective. Regardless, their presence
would indicate possible exposure to the drug and
potentially incapacitating medical conditions. Some
analytical procedures do not distinguish metabolites
from the parent drugs. The UV spectrophotometric
method for propoxyphene (McBay, 1978; McRay
etal., 1974) determines both propoxyphene and its
metabolite norpropoxyphene (Finkle et al., 1976),
and it does not distinguish propoxyphene from
norpropoxyphene. Thus, the observed levels reflect
the inclusion of the metabolite giving an aggregate
concentration value for propoxyphene (Chaturvedi
et 2!., 1983a). In multi-drug (or chemical) deaths,
the levels of those drugs should be carefully inter-
preted, as there may be interaction among the drugs,
leading to the rapid onset of toxicity of a greater
intensity (Chaturvedi et al., 19832; 1983b).

Reactive metabolites irreversibly bind to mac-
romolecules, causing permanent cell toxicity. In the
acetaminophen toxicity, the reactive intermediate
NAPQI is primarily responsible for the liver ne-
crosis. This intermediate undergoes electrophilic
reaction with GSH, a detoxification route. Induc-
tion or inhibition of the cytochrome P-450 system
should influence the acetaminophen toxicity, but
this is not always true. Phenobarbital, an inducer
of the P-450 system, increases the toxicity of ac-
etaminophen in mice, but decreases its toxicity in
hamsters. In hamsters, phenobarbital induces

glucuronyltransferase, as well. Inhibition of the P-
450 system decreases the toxicity in both species.
On the basis of the metabolic princigles, two gen-
eral approaches can be used to decrease the toxic
reactions. These approaches are: (i) molecular
modification to block toxic metabolite formation
and (ii) coadministration of other agents, either to
promote the formation of nontoxic metabolites, or
to decrease reactive metabolite toxicity. N-Methy-
lation of acetaminophen lowers the formation of the
reactive metabolite p-quinone imine, but decreases
the analgesic activity and increases convulsant ac-
tivity (Nelson, 1982); introduction of the N-acetyl
moiety in procainamide lowers its toxicity. The ef-
fective use of SH-containing compounds to treat
acetaminophen overdose has been documented.
Administration of cysteine to maintain adequate
levels of GSH and of sodium sulfate to maintain
the sulfation reaction has been effective against the
acetaminophen toxicity.

Overall, the extensive knowledge of a drug’s
metabolism facilitates predicting its effects on bio-
logical systems and correlating those effects with
the amounts of the drug and/or its metabolites
present in the target tissue(s).

SUMMARY

Foreign compounds are primarily biotransformed
in the body by the microsomal! drug metabolizing
enzyme systems. Metabolites could be active, in-
active, and/or reactive. Most of the time, metabo-
lites are more polar than the parent compounds and
are thus more easily eliminated. Identification and
quantification of the metabolites are integral parts
of forensic toxicology. In seme cases, the concen-
trations of metabolites can be correlated with the
intoxication of a drug. Several selective and sensi-
tive techniques are available for the analysis of
xetabolites. Lack of metabolite reference standards,
interference with endogenous substances, and low
levels of metabolites in biological tissues/fluids may
pose difficulty in metabolite analyses. However,
proper modifications of the analytical procedures,
utilization of sophisticated instrumental techniques,
and application of biochemical metabolic principles

ANAND


NOTICE

cooument

tates

thereof.


Technical Report Documentation Page
T. Report Na. 2. Goverment Accession NO. ‘S. Recipront’s Catstog No.
DOT/FAA/AM-95/26
2. Tile ond Gubtivie 6. Report Dato
Role of Metabolites in Aviation Forensic Toxicology August 1995
6. Performing Orpanization Code
7. Authortsh “3. Performing Orgenizeton Report No.
Arvind K. Chaturvedi and Dennis V. Canfield
“D. Performing Organization Name and Address 70. Work Unt Ne. (RATS!
FAA Civil Aeromedical Institute
P. O. Box 25082
Oklahoma City, OK 73125-5066 "1. Contract or Grant No.
PTZ. Sponsoring Agency name and Address 13. Type of Report and Period Covered
Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, SW
Washington, DC 20591 14. Sponsoring Agency Code
"TS. Supplemental Notes
1S. Abstract

In aviation accident investigations, specimens from fatal aircraft victims are analyzed for drugs. Their
presence indicates exposure to drugs and suggests possible associated medical conditions for which they
might bave been taken. As drugs are mostly present in therapeutic to subtherapeutic levels in aviation
forensic toxicology cases, determination of parent drugs and their metabolites in multispecimens is of
significance. Although chemically reactive metabolites are difficult to detect, physiologically active and
inactive metabolites can be analyzed. Selective and setsitive techniques are available, but unavailability of
metabolite reference standards, endogenous substance interference, and low tissue metabolite levels limit
the anslyses. However, the majority of primary metabolites can be effectively characterized/quantitated.
Demonstrating the presence of drug (e.g., terfenadine, cocaine, THC) metabolites provides a compelling
evidence for exposure to the parent drug and facilitates interpretation of results, particularly when the
metabolites are active. Such analyses are not as helpful if the metabolites are also available as drugs (e.g.,

diazepam, temazepam, oxazepam).

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