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P A R T 4
Drugs acting on the central and peripheral nervous systems
Contraindications and cautions
These drugs are contraindicated with known allergy to
any component of the drug. The sulfonamides are also
contraindicated with known allergy to antibacterial
sulfonamides and thiazide diuretics
to avoid hypersen-
sitivity reactions.
When it is discontinued, zonisamide
should be tapered over 2 weeks because of a risk of precip
itating seizures. People who take this drug should be very
well hydrated
due to risk of renal calculi development.
Caution should be used in people with hepatic or
renal impairment,
which could alter metabolism and
excretion of the drug.
These drugs should not be used
during pregnancy or breastfeeding unless the benefit
clearly outweighs the risk to the fetus or neonate
because
of the potential for serious adverse effects on the baby.
Cross sensitivity between acetazolamide, sulfona
mides and other sulphonamide derivatives is possible.
Acetazolamide is contraindicated in individuals with
marked liver disease or impairment of liver function,
including cirrhosis, because of the risk of development
of hepatic encephalopathy.
Adverse effects
Sodium valproate is associated with liver toxicity.
All of these drugs cause CNS effects related to CNS
suppression—weakness, fatigue, drowsiness, dizziness
and paraesthesias. Acetazolamide and zonisamide may
cause rash and dermatological changes. Zonisamide is
associated with bone marrow suppression, renal calculi
development and GI upset.
Clinically important drug–drug interactions
Acetazolamide increases the serum levels of quinidine,
tricyclic antidepressants and amphetamines and may
increase salicylate toxicity when given with salicylates.
Sodium valproate can increase serum levels and potential
toxicity of phenobarbitone, ethosuximide, diazepam,
primidone and zidovudine. If any of these drugs are
used in combination, the person should be monitored
carefully and doses adjusted appropriately.
Breakthrough seizures have been reported when
sodium valproate is combined with phenytoin, and
extreme care should be taken if this combination must
be used.
Zonisamide levels and toxicity are increased if it is
combined with carbamazepine, and the person should
be monitored and zonisamide dose reduced as needed.
Care considerations for people receiving
drugs for treating generalised seizures
The information that follows primarily relates to
drug therapy with hydantoins and succinimides,
acetazolamide, sodium valproate and zonisamide.
See Chapter 20 for care considerations for people
receiving barbiturates or benzodiazepines.
Assessment: History and examination
■
■
Assess for contraindications or cautions
to the use
of hydantoins, including known history of allergy
to hydantoins
to avoid hypersensitivity reactions
;
cardiac arrhythmias, hypotension, diabetes, coma
or psychoses,
which could be exacerbated by
the use of the drug
; history of renal or hepatic
dysfunction
that might interfere with drug
metabolism or excretion
; and current status related
to pregnancy and breastfeeding.
■
■
Assess for contraindications or cautions
to the use
of succinimides, including any known allergies
to these drugs; history of intermittent porphyria,
which could be exacerbated by these drugs
; history
of renal or hepatic dysfunction
that might interfere
with drug metabolism or excretion
; and current
status related to pregnancy or breastfeeding.
■
■
Obtain a description of seizures, including onset,
aura, duration and recovery,
to determine type of
seizure and establish a baseline
.
■
■
Perform a physical assessment
to establish
baseline data for determining the effectiveness
of therapy and the occurrence of any potential
adverse effect.
■
■
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
;
and evaluate gums and mucous membranes
to
establish baseline and monitor changes associated
with adverse 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 appropriateness of therapy and
determine the need for possible dose adjustment.
Refer to the Critical thinking scenario for a full
discussion of care for a person who is being
prescribed antiepileptic drugs.
Implementation with rationale
■
■
Discontinue the drug at any sign of hypersensitivity
reaction, liver dysfunction or severe skin rash
to
limit reaction and prevent potentially serious
reactions.
