CNS Depressants & Muscle Relaxants

Drugs that have an inhibitory effect on the CNS to the degree that they reduce nervousness, excitability, or irritability

Sedatives

Drugs that cause:

• Sleep

• Much more potent effect on CNS than sedatives

• A sedative can become a hypnotic if it is given in large enough doses

Hypnotics

A sedative drug can become a hypnotic if

It is given in large enough doses

• Are dose dependent

• Low doses: calm the CNS without inducing sleep

• High doses: calm the CNS to the point of causing sleep

Sedative-hypnotics

CNS depressants

Barbs, benzos, ORAs, non-benzo sedative hypnotics

Prodrug of barbiturates

Phenobarbital

Common suffix for barbiturates

-barbital

Barbiturate MOA

• Binds to and stimulates GABA receptor (increase time channel is open)

• Inhibits the CNS

Barbiturate indication

• Obsolete for most uses

• Treatment of seizure disorders (status epilepticus, generalized tonic-clonic)

• May be used IV as general anesthetics

Drugs may be used IV as general anesthetics

Barbiturates 

Caution use w/ barbiturates due to

• High risk for addiction (schedule II-IV)

• NTI → high r/o OD

Prodrug of benzos

Diazepam (Valium)

Common suffix for benzos

–lam/–pam (midazolam, temazepam)

Benzos MOA

• Binds to GABA receptors (increase frequency)

• Enhances the inhibitory effect of GABA

Low dose benzos =

Relieves anxiety (acute/short-term anxiety relief)

Increased dose benzos =

Induce sleepiness → treat insomnia

Very high dose benzos =

Used for anesthesia

Benzo indication

• Anxiety (acute/short-term)

• Preprocedural/preoperative sedation

• Insomnia

• Seizures

• Alcohol withdrawal

• Serotonin syndrome/NMS management

Scheduling of benzos

Schedule IV

• Judicious monitoring

• Consider alternate drug therapy if possible due to widespread drug abuse

• CNS depressant

  • sedation, confusion, memory impairment (anterograde amnesia)

  • Impaired manual skills & coordination (ataxia)

  • Shallow breathing

• Low HR & BP

• Paradoxical effects → increased anxiety, agitation, and restlessness in elderly

Benzos SE/AE

Benzo antidote

Flumazenil → reverse CNS depression; may cause withdrawal symptoms (withdrawal is preferrable)

ABUSED (S&S of benzo OD)

A – AMS (stupor, coma)

B – Bradycardia

U – Unable to walk/coordinate movements (ataxia)

S – Slurred or garbled speech

E – Eyes → blurred/double vision

D – Decreased symptoms

Prodrug of nonbenzo sedative-hypnotics

• Eszopiclone (Lunesta)

• Zolpidem (Ambien)

Nonbenzo sedative-hypnotics MOA

Act on the GABA receptors at or close to the benzodiazepine receptors

Nonbenzo sedative-hypnotic indication (EZZ)

• Used for insomnia

  • Zolpidem, zaleplon → short-term (7-10 days) for insomnia

  • Eszopiclone → FDA approved for long-term insomnia treatment; > 6 months but no more than 12 months

Nursing implications of nonbenzo sedative-hypnotics (EZZ)

• Schedule IV controlled substance

• Caution w/ use in elderly (Beers list)

Nonbenzo sedative-hypnotics SE/AE (EZZ)

• Dizziness, lightheadedness, ataxia

• Paradoxical effects → aggression or bizarre behavior

• Monitor worsening depression/suicidal ideation

• Hallucinations

• Anterograde amnesia

• BBW for sleepwalking and other sleep related activities that can result in serious injury or death → accident/falls, confusion

Drug that can cause worsening depression or suicidal ideation

Nonbenzo sedative-hypnotic; BBW for antidepressants

Nonbenzo sedative-hypnotic BBW (EZZ)

Drug can cause sleepwalking and other sleep related activities that can result in serious injury or death → accident/falls, confusion

Prodrug of (ORAs)

Suvorexant (Belsomra)

ORAs MOA (suvorexant)

Blocks/antagonize orexin receptors (these receptors promote wakefulness) → induce sleep

ORAs indication (suvorexant)

• Sleep induction

• For patient who cannot tolerate benzos or nonbenzo sedative-hypnotics

Nursing considerations for ORAs

• SEs more common in females

  • Drowsiness, HA, dizziness, dry mouth, increased cholesterol

• 12 hr half-life (quite long) → concerns about daytime somnolence/drowsiness

Drugs that have 12 hr half-life

ORAs (suvorexant) → cause daytime drowsiness/somnolence 

Common muscle relaxants

• Baclofen (Lioresal)

• Cyclobenzaprine (Flexeril)

• Dantrolene (Dantrium)

MOA of muscle relaxants (baclofen, cyclobenzaprine, dantrolene)

• Majority are centrally acting

  • Similar in structure and action to other CNS depressants (stimulate GABA)

• Direct acting muscle relaxants

  • Act directly on skeletal muscle

Muscle relaxant indication (baclofen, cyclobenzaprine, dantrolene)

• Useful for relief of painful musculoskeletal conditions

  • Muscle spasms

  • Management of spasticity of severe chronic disorders (multiple sclerosis, cerebral palsy)

  • IV Dantrolene used to treat malignant hyperthermia & NMS

Nursing considerations for muscle relaxants (baclofen, cyclobenzaprine, dantrolene)

• Work best when used alongside physical therapy

• Caution with other CNS depressants

  • Avoid benzos & alcohol

• SE are common:

  • Dizziness

  • Fatigue

  • Weakness 

• These effects decrease over time as patient grows more tolerant to med

SE of muscle relaxants (baclofen, cyclobenzaprine, dantrolene)

Dantrolene MOA

Direct-acting muscle relaxant; works directly on skeletal muscle