Download Pharmacology and the Nursing Process, 4th ed. Lilley/Harrington

CHAPTER 12
Central Nervous System
Depressants and Muscle
Relaxants
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CNS Depressants
Sedatives or Hypnotics
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CNS Depressants
Sedatives
• Drugs that have an inhibitory effect on the
CNS to the degree that they reduce:
– Nervousness
– Excitability
– Irritability without causing sleep
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CNS Depressants (cont'd)
Hypnotics
• Calm or soothe the CNS to the point that they
cause sleep
• A sedative can become a hypnotic if it is
given in large enough doses
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CNS Depressants (cont'd)
Sedative-hypnotics—dose dependent
• At low doses, calm or soothe the CNS
without inducing sleep
• At high doses, calm or soothe the CNS to the
point of causing sleep
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Sleep
• Normal sleep is cyclic and repetitive
• A sleeping person is unaware of sensory
stimuli within the immediate environment
• Rapid eye movement (REM)
• Non–rapid eye movement (non-REM)
• Sleep stages
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Table 12-2 Stages of Sleep
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Sedative-Hypnotics: Barbiturates
• First introduced in 1903; standard
agents for insomnia and sedation
• Habit forming
• Only a handful commonly used today
due in part to the safety and efficacy of
benzodiazepines
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Barbiturates: Four Categories
• Ultrashort
– mephobexital, thiamylal, thiopental
• Short
– pentobarbital, secobarbital
• Intermediate
– butabarbital
• Long
– phenobarbital, mephobarbital
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Therapeutic Index
• Dosage range within which the drug is
effective but above which is rapidly toxic
• Barbiturates have a very narrow
therapeutic index
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Table 12-3 Barbiturates: Onset and Duration
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Barbiturates:
Mechanism of Action
• Site of action
– Brainstem (reticular formation)
• By inhibiting GABA, nerve impulses
traveling in the cerebral cortex are also
inhibited
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Barbiturates: Drug Effects
• Low doses: sedative effects
• High doses: hypnotic effects (also
lowers respiratory rate)
• Notorious enzyme inducers
– Stimulate liver enzymes that cause the
metabolism or breakdown of many drugs
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Barbiturates: Indications
• Hypnotic
• Sedative
• Anticonvulsant
• Anesthesia for surgical procedures
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Barbiturates: Side Effects
Body System
CNS
Effects
Drowsiness, lethargy,
vertigo, mental depression,
coma
Respiratory
Respiratory depression,
apnea, bronchospasms,
cough
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Barbiturates: Side Effects
(cont'd)
Body System
GI
Effects
Nausea, vomiting, diarrhea
constipation
Other
Agranulocytosis,
vasodilation, hypotension,
Stevens-Johnson syndrome
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Barbiturates: Side Effects
(cont'd)
• Reduce REM sleep, resulting in:
– Agitation
– Inability to deal with normal stress
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Barbiturates:
Toxicity and Overdose
• Overdose frequently leads to respiratory
depression, and subsequently, respiratory
arrest
• Overdose produces CNS depression (sleep
to coma and death)
• Can be therapeutic
– Anesthesia induction
– Uncontrollable seizures: “phenobarbital coma”
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Barbiturates:
Drug Interactions
• Additive effects
– ETOH, antihistamines, benzodiazepines,
narcotics, tranquilizers
• Inhibited metabolism
– MAOIs will prolong effects of barbiturates
• Increased metabolism
– Reduces anticoagulant response, leading
to possible clot formation
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Common Barbiturates
•
•
•
•
butabarbital (Butisol)
pentobarbital (Nembutol)
phenobarbital (Luminal)
secobarbital (Seconal)
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CNS Depressants:
Benzodiazepines
Most frequently prescribed sedativehypnotics
• Most commonly prescribed drug classes
• Favorable side effect profiles
• Efficacy
• Safety
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Benzodiazepines:
Classification
• Classified as either:
– Sedative-hypnotic
– anxiolytic (medication that relieves anxiety)
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Benzodiazepines:
Sedative-Hypnotic Types
• Long acting
– estazolam (Prosom), quazepam (Doral)
• Short acting
– flurazepam (Dalmane), temazepam
(Restoril)
– triazolam (Halcion)
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CNS Depressants:
Nonbenzodiazepine Hypnotics
Zalepion (Sonata) and zolpidem (Ambien)
• Share many characteristics of
benzodiazepines
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Benzodiazepines:
Mechanism of Action
• Depress CNS activity
• Affect hypothalamic, thalamic, and limbic
systems of the brain
• Benzodiazepine receptors
• Do not suppress REM sleep as much as
barbiturates do
• Do not increase metabolism of other drugs
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Benzodiazepines:
Drug Effects
• Calming effect on the CNS
• Useful in controlling agitation and
anxiety
• Reduce excessive sensory stimulation,
inducing sleep
• Induce skeletal muscle relaxation
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Benzodiazepines:
Indications
•
•
•
•
•
Sedation
Sleep induction
Skeletal muscle relaxation
Anxiety relief
Treatment of alcohol withdrawal
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Benzodiazepines:
Indications (cont'd)
•
•
•
•
Agitation
Depression
Epilepsy
Balanced anesthesia
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Benzodiazepines: Side Effects
Mild and infrequent
•
•
•
•
•
•
•
Headache
Drowsiness
Dizziness
Vertigo
Lethargy
Paradoxical excitement (nervousness)
“Hangover effect”
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CNS Depressants:
Nursing Implications
• Before beginning therapy, perform a thorough
history regarding allergies, use of other
medications, health history, and medical
history
• Obtain baseline vital signs and I&O, including
supine and erect BPs
• Assess for potential disorders or conditions
that may be contraindications, and for
potential drug interactions
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Nursing Implications
• Give 15 to 30 minutes before bedtime for
maximum effectiveness in inducing sleep
• Most benzodiazepines (except flurazepam)
cause REM rebound and a tired feeling the
next day; use with caution in the elderly
• Patients should be instructed to avoid alcohol
and other CNS depressants
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Nursing Implications
• Check with physician before taking any other
medications, including OTC medications
• It may take 2 to 3 weeks to notice improved
sleep when taking barbiturates
• Rebound insomnia may occur for a few nights
after a 3- to 4-week regimen has been
discontinued
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Nursing Implications
• Safety is important
– Keep side rails up or use bed alarms
– Do not permit smoking
– Assist patient with ambulation (especially
the elderly)
– Keep call light within reach
• Monitor for side effects
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Nursing Implications
• Monitor for therapeutic effects
– Increased ability to sleep at night
– Fewer awakenings
– Shorter sleep-induction time
– Few side effects, such as hangover effects
– Improved sense of well-being because of
improved sleep
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Muscle Relaxants
• Act to relieve pain associated with skeletal
muscle spasms
• Majority are central acting
– CNS is the site of action
– Similar in structure and action to other CNS
depressants
• Direct acting
– Acts directly on skeletal muscle
– Closely resembles GABA
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Muscle Relaxants: Indications
• Relief of painful musculoskeletal
conditions
– Muscle spasms
– Management of spasticity of severe
chronic disorders
– Multiple sclerosis, cerebral palsy
• Work best when used along with
physical therapy
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Muscle Relaxants: Indications
(cont'd)
• dantrolene
– Malignant hyperthermia crisis
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Muscle Relaxants: Side Effects
• Extension of effects on CNS and
skeletal muscles
– Euphoria
– Lightheadedness
– Dizziness
– Drowsiness
– Fatigue
– Muscle weakness
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Common Muscle Relaxants
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•
•
•
•
baclofen (Lioresal)
cyclobenzaprine (Flexeril)
dantrolene (Dantrium)
metaxalone (Skelaxin)
tizanidine (Zanaflex)
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Muscle Relaxants:
Nursing Implications
• See others listed for CNS depressants
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