310
P A R T 4
Drugs acting on the central and peripheral nervous systems
■■
Anxiety is a feeling of tension, nervousness,
apprehension or fear. In the extreme, anxiety may
produce physiological manifestations and may
interfere with activities of daily life. Anxiolytic drugs,
such as the benzodiazepines, depress the CNS to
diminish these feelings.
■■
CNS depressants, such as sedatives, block the
awareness of and reaction to environmental stimuli.
They induce drowsiness, as do hypnotic drugs,
which also depress the CNS and inhibit neuronal
arousal.
■■
Hypnotics react with GABA-inhibitory sites to
depress the CNS. They can cause drowsiness,
lethargy and other CNS effects.
BARBITURATES USED AS ANXIOLYTIC/
HYPNOTICS
The
barbiturates
were once the sedative/hypnotic
drugs of choice. Not only is the likelihood of sedation
and other adverse effects greater with these drugs
than with newer sedative/hypnotic drugs, but the risk
of addiction and dependence is also greater. For these
reasons, newer anxiolytic drugs have replaced barbitu-
rates in most instances. The only barbiturate used as an
anxiolytic/hypnotic in Australia and New Zealand is
phenobarbitone.
KEY POINTS
Therapeutic actions and indications
The barbiturates are general CNS depressants that
inhibit neuronal impulse conduction in the ascend-
ing RAS, depress the cerebral cortex, alter cerebellar
function and depress motor output (see Figure 20.1).
Thus, they can cause sedation, hypnosis, anaesthesia
and, in extreme cases, coma. In general, barbiturates
are indicated for the relief of the signs and symptoms of
anxiety and for sedation, insomnia, preanaesthesia and
the treatment of seizures (Table 20.2). Parenteral forms,
which reach peak levels faster and have a faster onset
of action, may be used for the treatment of acute manic
reactions and many forms of seizures (see Chapter 23).
Pharmacokinetics
The barbiturates are absorbed well, reaching peak levels
in 20 to 60 minutes. They are metabolised in the liver to
varying degrees, depending on the drug, and excreted
in the urine. The longer-acting barbiturates tend to be
metabolised more slowly and excreted to a greater degree
unchanged in the urine. The barbiturates are known to
induce liver enzyme systems, increasing the metabolism
of the barbiturate broken down by that system, as well
as that of any other drug that may be metabolised by
that enzyme system. People with hepatic or renal dys-
function require lower doses of the drug to avoid toxic
effects and should be monitored closely. Barbiturates are
lipid soluble; they readily cross the placenta and enter
breast milk.
TEACHING FOR P.P.
• The drug that has been prescribed for you is called
diazepam or
Valium
. It belongs to a class of drugs called
benzodiazepines, which are used to relieve tension
and nervousness. Exactly how the drug works is not
completely understood, but it does relax muscle spasms,
relieve insomnia and promote calm. Common side effects
of this drug include:
•
Dizziness and drowsiness:
Avoid driving or performing
hazardous or delicate tasks that require concentration if
these effects occur.
•
Nausea, vomiting and weight loss:
Small frequent meals
may help to relieve nausea. If weight loss occurs,
monitor the loss; if the loss is extensive, consult your
healthcare provider. Do not take this drug with antacids.
•
Constipation or diarrhoea:
These reactions usually pass
with time. If they do not, consult with your healthcare
provider for appropriate therapy.
•
Vision changes, slurred speech, unsteadiness:
These effects
also subside with time. Take extra care in your activities
for the first few days. If these reactions do not go away
after 3 or 4 days, consult your healthcare provider.
• Report any of the following conditions to your
healthcare provider:
rash, fever, sore throat, insomnia,
depression, clumsiness or nervousness.
• Tell any doctor, nurse or other healthcare provider
involved in your care that you are taking this drug.
• Keep this drug and all medications safely away from
children or pets.
• Avoid the use of over-the-counter medications or herbal
therapies while you are taking this drug. If you think
that you need one of these products, consult with your
healthcare provider about the best choice because many
of these products can interfere with your medication.
• Avoid alcohol while you are taking this drug.
Combining alcohol and a benzodiazepine can cause
serious problems.
• If you have been taking this drug for a prolonged time,
do not stop taking it suddenly. Your body will need time
to adjust to the loss of the drug, and the dosage will need
to be reduced gradually to prevent serious problems.
When discontinuing use of this drug, tell your healthcare
provider if the following occurs: trembling, muscle
cramps, sweating, irritability, confusion or seizures.
