Forensic Applications of Gas Chromatography - Forensic Applications of Gas Chromatography - page 98

8.3.2 Routes of Administration
For drugs and other poisons to have any effect on an individual they first have
to enter the body. There are various routes, called routes of administration,
which these compounds can take to enter the body (with the main routes
explained next). For the purposes of conciseness, this chapter will focus only
on drugs of abuse. The field of toxicology covers many different compounds
that can be found in biological matrices; for more information on the field of
toxicology and the broad range of compounds encountered see the Further
Reading section at the end of this chapter. When a drug enters the body, it
will eventually reach the bloodstream. The bloodstream is the mode of trans-
port for the drug to move around the body and thus to cause an effect. The
first point to consider is how a drug enters the human body. The following are
the common routes of administration:
Intravenous administration: This involves the injection of a compound
in liquid form, through a vein and into the bloodstream. This is one
of the fastest routes of administration since the drugs directly enter
the bloodstream.
Inhalation: Drugs are absorbed by entering and travelling down the
trachea and on into the lungs for absorption into the bloodstream.
This is a relatively speedy route of administration.
Oral/swallowing: Oral administration of a drug involves the introduc-
tion of the compound into the mouth, through the oesophagus, and
down the gastrointestinal tract and into the stomach. Some of the
drugs will be absorbed through the stomach wall while some will
move through the digestive system into the intestines and will be
absorbed there. For some drugs, such as morphine, first-pass metab-
olism may occur through this route. This is where the concentration
of a drug is greatly reduced before entering the bloodstream. This
reduction of concentration usually occurs when a drug is adminis-
tered orally and enters the digestive system and then the hepatic por-
tal system. A large proportion of the original concentration of active
drug will travel through the portal vein directly to the liver where it
will be metabolised before being absorbed into the body.
Intramuscular administration: This is an injection of the drug directly
into a muscle and then into the bloodstream. How well and how
quickly a particular drug will enter the bloodstream depends upon
the chemistry of the compound.
Subcutaneous: This type of administration involves the introduction
of the drug, by injection, into the fatty tissue just below the skin.
The drug will enter the lymphatic or blood vessels before entering