Mosby items and derived items © 2005, 2002 by Mosby, Inc. CHAPTER 12 Central Nervous System Depressants and Muscle Relaxants.

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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 Effects

CNS Drowsiness, lethargy, vertigo, mental depression, coma

Respiratory Respiratory depression, apnea, bronchospasms,cough

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Barbiturates: Side Effects (cont'd)

Body System Effects

GI Nausea, vomiting, diarrheaconstipation

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 sedative-hypnotics

• 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

• baclofen (Lioresal)

• cyclobenzaprine (Flexeril)

• dantrolene (Dantrium)

• metaxalone (Skelaxin)

• tizanidine (Zanaflex)

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Muscle Relaxants: Nursing Implications

• See others listed for CNS depressants