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P A R T 4
Drugs acting on the central and peripheral nervous systems
Therapeutic actions and indications
The CNS stimulants act as cortical and RAS stimulants,
possibly by increasing the release of catecholamines
from presynaptic neurons, leading to an increase in stim-
ulation of the postsynaptic neurons. The paradoxical
effect of calming hyperexcitability through CNS stimu
lation seen in attention-deficit syndrome is believed to
be related to increased stimulation of an immature RAS,
which leads to the ability to be more selective in response
to incoming stimuli.
The CNS stimulants are indicated, as part of a com-
prehensive treatment program, for the treatment of
attention-deficit syndromes, including behavioural syn-
dromes characterised by hyperactivity and distractibility,
as well as for narcolepsy and improvement of wakeful-
ness in people with various sleep disorders.
Pharmacokinetics
These drugs are rapidly absorbed from the GI tract,
reaching peak levels in 2 to 4 hours. They are metabo-
lised in the liver and excreted in the urine, with half-lives
ranging from 2 to 15 hours, depending on the drug.
Safety for use during pregnancy and breastfeeding has
not been established; during those periods, these drugs
should be used only if the benefit to the mother clearly
outweighs the potential risk to the fetus or neonate.
Contraindications and cautions
The CNS stimulants are contraindicated in the presence
of known allergy to the drug,
which could lead to
hypersensitivity reactions
. Other contraindications
include the following conditions: marked anxiety, agi-
tation or tension and severe fatigue or glaucoma,
which
could be exacerbated by the CNS stimulation caused
by these drugs
;
cardiac disease,
which could be aggra-
vated by the stimulatory effects of these drugs, making
it important to rule out congenital heart problems
;
and
pregnancy and breastfeeding
because of the potential
for adverse effects on the fetus or neonate.
Caution should be used in people with a history of
seizures,
which could be potentiated by the CNS stim-
ulation
; in people with a history of drug dependence,
including alcoholism,
because these drugs may result in
physical and psychological dependence
;
and in people
with hypertension,
which could be exacerbated by the
stimulatory effects of these drugs.
Adverse effects
The adverse effects associated with these drugs are
related to the CNS stimulation they cause. CNS effects
can include nervousness, insomnia, dizziness, headache,
blurred vision and difficulty with accommodation. GI
effects such as anorexia, nausea and weight loss may
occur. CV effects can include hypertension, arrhythmias
and angina. Skin rashes are a common reaction to some
of these drugs. Physical and psychological dependence
may also develop. Because CNS stimulants have this
effect, the drugs are controlled substances. Atomoxe-
tine, which does not show dependence development, is
not a controlled substance. The adverse effects asso-
ciated with this drug are mainly anticholinergic (dry
mouth, constipation, nausea, urinary hesitancy).
Clinically important drug–drug interactions
The combination of a CNS stimulant with a monoamine
oxidase (MAO) inhibitor leads to an increased risk of
adverse effects and increased toxicity and should be
avoided if possible.
In addition, the combination of CNS stimulants with
tricyclic antidepressants or phenytoin leads to a risk of
increased drug levels. People who receive such a combi-
nation should be monitored for toxicity.
Prototype summary: Methylphenidate
Indications:
Narcolepsy and attention-deficit
disorder.
Actions:
Mild cortical stimulant with CNS actions
similar to those of amphetamines.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
Varies
1–3 hours
4–6 hours
T
1/2
:
1–3 hours; metabolised in the liver; excreted in
the urine.
Adverse effects:
Nervousness, insomnia, increased or
decreased pulse rate and blood pressure, tachycardia,
loss of appetite, nausea, abdominal pain.
Care considerations for people receiving
central nervous system stimulants
Assessment: History and examination
■
■
Assess for
contraindications or cautions for the
use of the drug
, including any known allergies to
the drug; glaucoma, anxiety, tension, fatigue or
seizure disorder; cardiac disease and hypertension;
pregnancy or breastfeeding; a history of leukaemia;
and a history of drug dependency, including
alcoholism.
■
■
Assess temperature; skin colour and lesions;
CNS orientation, affect and reflexes; ophthalmic
examination; bowel sounds and reported output;
pulse, auscultation and blood pressure, including
orthostatic blood pressure; respiration rate
and adventitious sounds; and urinary output
