Lesson B8 - Pharmacology Flashcards
The major reason for the extensive use and abuse of
alcohol is
its ready availability and the permissive attitudes of society
alcohol is an old drug. It was the first sedative-hypnotic drug to be used by
ancient physicians. The use of fermented beverages can be traced back to 8000 B.C., when mead was
prepared from honey.
Traditionally, alcohol has been used for three major purposes.
In medicine as a sedative and hypnotic.
∙ For religious and other occasions, e.g. sacramental use by Christians and Jews.
∙ Recreational purposes.
The terms “alcohol” and “ethanol” are used
interchangeably
Ten to 13 ml of absolute alcohol is the amount metabolized by
the liver each hour.
Ethanol is absorbed rapidly from the
stomach and the upper small intestine (the major site of
absorption).
The overall absorption rate for a given dose of ethanol is affected by:
(a) Stomach-emptying time, or the time required for the alcohol to reach the small intestine.
(b) Ethanol concentration in the G.I. tract.
Ethanol distributes throughout the total body water and readily distributes across the
blood-brain barrier.
In pregnant women who drink alcoholic beverages, ethanol is readily transferred across the
placenta and distributes throughout the total body water of the fetus.
Over 95% of ethanol in the body is eliminated by biotransformation, primarily in the
liver
The remaining 5% is excreted in the
breath, urine and sweat.
Aldehyde dehydrogenase (ADH) converts alcohol to acetaldehyde, and in turn aldehyde dehydrogenase converts acetaldehyde (ALDH) to
acetic acid. Acetic acid is then further
metabolized by a number of tissues. Disulfiram and calcium carbimide (drugs used to treat
alcohol abuse) inhibit aldehyde dehydrogenase, and as a result, acetaldehyde accumulates and
the individual will feel ill and presumably stop abusing alcohol to stop the adverse effects of
acetaldehyde.
The metabolism of alcohol is unusual as it occurs at a constant rate, irrespective of the blood
alcohol concentration. A constant amount of alcohol is metabolized each hour. This is because
ADH becomes rate-limiting or saturated at 20 mg of alcohol per 100 ml of blood (saturation is a
term used when a process is running at full capacity)
Ethanol is classified as a general central nervous system (CNS)
depressant.
Acute use of ethanol
more obviously affects the CNS, whereas
chronic, high-dose use affects many organ systems of
the body including the CNS, cardiovascular system, gastrointestinal tract and liver.
Chronic,
maternal use of high-dose ethanol can adversely affect the
fetus, including teratogenesis, which
can manifest as the fetal alcohol syndrome or fetal alcohol effects.
Ethanol produces dose-dependent depression of CNS function:
disinhibition → sedation → hypnosis → general anesthesia →
coma
Low dose: Disinhibition (inhibition of an inhibitory pathway in the CNS).
This is usually manifested by increased social
interaction, e.g
talking
High dose: Sedation → hypnosis → general anesthesia → coma →
death
A change in sleep pattern often occurs. The changes are an increase in slow-wave sleep and a
decrease in rapid-eye-movement sleep. A reduction in rapid-eye-movement sleep is associated with a feeling of having “slept poorly”.
The mechanism of action of alcohol is not understood. At high concentrations of alcohol, it was believed that the drug acted as a
general anesthetic