330
P A R T 4
Drugs acting on the central and peripheral nervous systems
■■
The SSRIs prevent the reuptake of serotonin into
the presynaptic nerve, leading to an accumulation
of these biogenic amines in the synaptic cleft. This
accumulation causes increased stimulation of the
postsynaptic nerve and may be responsible for the
antidepressant effects of these drugs.
■■
The SSRIs are not associated with many of the CNS,
CV and anticholinergic effects of other antidepressants.
OTHER ANTIDEPRESSANTS
Some other effective antidepressants do not fit into any
of the three groups that have been discussed in this
chapter. These drugs have varying effects on noradrena
line, 5HT and dopamine. Although it is not known how
their actions are related to clinical efficacy, these agents
may be most effective in treating depression in people
who do not respond to other antidepressants. They may
even be used before MAO inhibitors or TCAs, which
have many more adverse effects. As with the other anti
depressants, these drugs have a black box warning to
be alert for the possibility of increased suicidality, espe
cially in children and adolescents, whenever the drugs
are used. Other antidepressants include the following
(see Table 21.5 for usual indications):
• Agomelatine (
Valdoxan
) (not available in New
Zealand) is a melatonergic antidepressant used in the
treatment of major depressive disorder. The drug is
KEY POINTS
metabolised in the liver and excreted through urine.
A substantial increase in selegiline bioavailability (up
to threefold) occurs when selegiline is administered
with food high in fat. The drug does cross the
placenta and enters breast milk, so it should only be
used during pregnancy and breastfeeding if the benefit
outweighs the potential risk to the neonate. This drug
is associated with CNS effects, as well as GI effects
including nausea, dry mouth and abdominal pain.
• Bupropion (
Prexaton
) weakly blocks the reuptake of
noradrenaline, 5HT and dopamine. At lower doses,
this drug is effective in smoking cessation. It is well
absorbed from the GI tract, metabolised in the liver
and excreted in the urine. Zyban tablets should be
swallowed whole and not crushed or chewed as
this may lead to an increased risk of adverse effects
including seizures. There are no adequate studies done
in pregnancy, and the drug should be used during
pregnancy only if the benefits to the mother clearly
outweigh the potential risks to the fetus. Bupropion
does enter breast milk and should not be used by
breastfeeding women. The drug is available in a
sustained-release formulation which some people find
to be more convenient.
• Desvenlafaxine (
Pristiq
) (not available in New
Zealand) is the newest of the SSRIs. It blocks the
reuptake of noradrenaline and 5HT. It is readily
absorbed from the GI tract, reaching peak levels in
7.5 hours. It is metabolised in the liver and excreted
through urine within about 72 hours. It passes into
breast milk and should not be used by breastfeeding
Provide support and reassurance to help D.J. deal with drug
effects (4-week delay in full effectiveness).
Provide teaching regarding drug dosage, adverse effect
conditions to report and the need to use barrier
contraceptives.
Evaluation
Evaluate drug effects: relief of signs and symptoms of
depression.
Monitor for adverse effects: sedation, dizziness, insomnia;
respiratory dysfunction; GI upset; GU problems; rash.
Monitor for drug–drug interactions.
Evaluate effectiveness of teaching program.
Evaluate effectiveness of comfort and safety measures.
TEACHING FOR D.J.
• The drug that has been prescribed is called a selective
serotonin reuptake inhibitor or SSRI. SSRIs change the
concentration of serotonin in specific areas of the brain.
An increase in serotonin level is believed to relieve
depression.
• The drug should be taken once a day in the morning.
If your dosage has been increased or if you are having
stomach upset, the dose may be divided.
• It may take as long as 4 weeks before you feel the full
effects of this drug. Continue to take the drug every day
during that time so that the concentration of the drug in
your body eventually reaches effective levels.
• Common side effects of SSRIs include the following:
•
Dizziness, drowsiness, nervousness and insomnia:
If these
effects occur, avoid driving or performing hazardous or
delicate tasks that require concentration.
•
Nausea, vomiting and weight loss:
Small frequent meals
may help. Monitor your weight loss; if it becomes
excessive, consult your healthcare provider.
•
Sexual dysfunction and flu-like symptoms:
These effects
may be temporary. Consult with your healthcare
provider if these conditions become bothersome.
• Report any of the following conditions to your healthcare
provider:
rashmania, seizures and severe weight loss
.
• Tell your doctors, nurses and other healthcare providers
that you are taking this drug. Keep this drug and all
medications out of the reach of children and pets.
Do not take this drug during pregnancy because severe
fetal abnormalities could occur. The use of barrier
contraceptives is recommended while you are taking this
drug. If you think that you are pregnant or would like to
become pregnant, consult with your healthcare provider.
