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Drugs acting on the central and peripheral nervous systems
alter the metabolism and excretion of the drugs
; and
with renal stones,
which could be exacerbated by the
effects of some of these agents.
Adverse effects
The most frequently occurring adverse effects associ
ated with the drugs used for partial seizures relate to the
CNS depression that results. The following conditions
may occur: drowsiness, fatigue, weakness, confusion,
headache and insomnia; GI depression, with nausea,
vomiting and anorexia; and upper respiratory infec
tions. These antiepileptics can also be directly toxic to
the liver and the bone marrow, causing dysfunction. The
exact effects of each drug vary.
People with renal dysfunction are more likely to
experience toxic effects of levetiracetam, and the dose
for these individuals needs to be decreased accordingly.
The adverse effects most commonly seen with
pregabalin are related to CNS depression—tremor,
dizziness, somnolence and visual changes. This drug
does have a controlled substance rating as Category V.
It can cause feelings of wellbeing and euphoria. Because
of this, its use should be limited in people who have a
history of abuse of medications or alcohol.
A reduced dose of topiramate is recommended for
people with renal impairment. The drug has also been
associated with marked CNS depression. Tiagabine has
also been associated with serious skin rash.
Clinically important drug–drug interactions
If any of these drugs is taken with other CNS depressants
or alcohol, a potential for increased CNS depression
exists. Caution people to avoid alcohol while taking
drugs for partial seizures or to take extreme precautions
if such combinations cannot be avoided.
In addition, numerous drug–drug interactions are
associated with carbamazepine. Always consult a drug
reference whenever a drug is added or withdrawn from
a carbamazepine-containing regimen. Dose adjustments
may be necessary.
Oxcarbazepine is an inhibitor of CYP2C19. There
fore, interactions could arise when co-administering
high doses of
Trileptal
with medicinal products that
are metabolised by CYP2C19 (e.g. phenobarbitone,
phenytoin).
Prototype summary: Carbamazepine
Indications:
Treatment of seizure disorders, including
partial seizures with complex patterns; tonic–clonic
seizures; mixed seizures; trigeminal neuralgia.
Actions:
Inhibits polysynaptic responses and
blocks post-tetanic potentiations; mechanism of
action is not understood; related to the tricyclic
antidepressants.
Pharmacokinetics:
Route
Onset
Peak
Oral
Slow 4–5 hours
Extended release oral
Slow 3–12 hours
T
1/2
:
25 to 65 hours, then 12 to 17 hours;
metabolised in the liver, excreted in the urine and
faeces.
Adverse effects:
Drowsiness, ataxia, dizziness,
nausea, vomiting, CV complications, hepatitis,
haematological disorders, Stevens–Johnson
syndrome.
Care considerations for people receiving
drugs to treat partial seizures
Assessment: History and examination
■
■
Assess for contraindications and cautions:
any known allergies to these drugs
to avoid
hypersensitivity reactions
; history of bone
marrow suppression or renal stones,
which could
be exacerbated by these drugs
; history of renal
or hepatic dysfunction
that might interfere with
drug metabolism and excretion
; and current
status of pregnancy or breastfeeding,
which are
contraindicated or require caution when using
these drugs
.
■
■
Perform a physical assessment to establish baseline
data for determining the effectiveness of therapy
and the occurrence of any
potential adverse
effects.
■
■
Inspect the skin for colour and lesions
to determine
evidence of possible skin effects
; assess pulse and
blood pressure and auscultate heart
to evaluate for
possible cardiac effects
; assess level of orientation,
affect, reflexes and bilateral grip strength
to evaluate any CNS effects
; monitor bowel
sounds and urine output
to determine possible
gastrointestinal or genitourinary effects.
■
■
Obtain a baseline electroencephalogram if
appropriate
to evaluate brain function.
■
■
Assess the person’s renal and liver function,
including renal and liver function tests,
to
determine the appropriateness of therapy and
determine the need for possible dose adjustment.
■
■
Monitor the results of laboratory tests such as
urinalysis and FBC with differential
to identify
changes in bone marrow function.
