The human body must be prepared for a daily onslaught
of thousands of chemicals. Some will be food materials that are absorbed and
metabolized because cells have membrane channels and enzymes to recognize and
deal with these compounds. Other compounds may or may not enter the cells of
the body. If they do, then the body can recognize such compounds and must deal
with them appropriately to prevent deleterious effects. It is not always
successful in this aim and many xenobiotics cause diseases and may be fatal if
a threshold dose is exceeded.
Toxicology is the study of
the adverse effects of chemicals on organisms, thatis the study of poisons,
where a poison can be defined as any substance that causes injury, illness or
death. Toxicology covers the study of the adverse effects of chemicals
including drugs, chemicals acquired from the environment and toxins, which are
defined here as harmful substances produced by other organisms, often derived
meaning ‘stranger to life’, are substances that do notoriginate in the body but
are pharmacologically, endocrinologically or toxicologically active. Thus, they
might be drugs or synthetic chemicals or a substance produced in one organism
and introduced into another where they would not normally occur. An example
would be a compound produced by a plant and ingested as food. Equally, it might
be a compound that has been completely synthesized chemically and have harmful
effects, for example a poison or a carcinogen, or it could be beneficial, such
as a medicinal drug.
Drugs are xenobiotics that are used to achieve
certain effects. For example, paracetamol alleviates headaches and aspirin
controls inflammatory responses. Alternatively, a drug may also be a compound
with pharmacological activity used for ‘recreational’ purposes or taken by an
addict. The body has to deal with these drugs and eventually get rid of them.
An overdose may exceed the body’s capacity to detoxify these compounds, with
potentially disastrous effects. However, if the body inactivates the drug too
quickly, then its effects will be short-lived. These are all considerations
that pharmaceutical companies need to address when developing a new drug.