Biomedical Engineering Reference
In-Depth Information
5.3.3
Pharmacokinetics
THC undergoes metabolic degradation in the liver, where it is hydroxylated to
11-hydroxy tetrahydrocannabinol (THC-11OH). The latter, still with psychoactive
activity, is oxidized to D 9 -THC-COOH, an inactive metabolite which is conjugated
as 11-nor-D 9 -tetrahydrocannabinol-9-carboxy-glucuronide ( D 9 -THC-COOH-glu),
more hydrophilic metabolite and therefore easily excreted in the urine [ 32 ] .
6
Biological Matrices for the Determination of Illicit Drugs
It is possible to select a biological matrix and a suitable analytical strategy depend-
ing on the aim of the analysis (clinical, medicolegal, epidemiological) and/or on the
availability of the sample or on which kind of information is needed.
The main biological matrices are the following:
￿
Plasma and urine, the most used and known for toxicological analysis.
￿
Hair and nails.
￿
Oral fl uid (OF) and sweat.
Each one has a specific time window and often specific target analyte; when an
analysis on more matrices is made, it is also possible to gather information on the
means of administration.
Blood (plasma, serum, or whole blood) and, with some limits, OFs give detailed
information about what is occuring at the time of testing; hair analysis demonstrates
the history of abuse, that could backdate several months.
As for correlation among the different biological fluids, Toennes et al. have dem-
onstrated that both OF and urine are able to predict the plasmatic positivity with
90 % of accuracy for most drugs, except for amphetamines, which have a detection
time in OF greater than in plasma [ 33 ] .
6.1
Blood, Plasma and Serum
Blood travels through the human body in more than 96,000 km of blood vessels and
it is full of marker molecules [ 34 ]. The physiological pH is usually 7.4 with a com-
plex buffer system (bicarbonate-carbonic acid, hemoglobinate-hemoglobin, phos-
phate buffer) [ 35 ] .
Plasma is the liquid part of blood that is about 93 % water and 7 % of organic
substances (proteins in suspension, nutrients such as glucose or lipids, hormones,
metabolic products) and inorganic (electrolyte, carbon dioxide, oxygen).
Serum is deprived of fibrinogen, but all the other proteins are the same as plasma;
the plasmatic proteins are the main problem for the analytical determination of
drugs, because they bind many molecules, including the drugs of abuse.
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