Central Nervous System Depressants and Muscle Relaxants (Vocabulary)

Vocabulary flashcards covering key terms, mechanisms, indications, adverse effects, interactions, and case-study concepts from CNS depressants and muscle relaxants.

Sedatives

Drugs that depress CNS activity to reduce nervousness, excitability, and irritability.

Hypnotics

CNS depressants that induce sleep; more potent than sedatives and require higher doses to cause sleep.

Sedative-hypnotics

CNS depressants whose effects are dose dependent: low doses sedate without sleep, high doses induce sleep; main groups are barbiturates and benzodiazepines.

REM sleep

Rapid eye movement sleep; a sleep stage within the sleep cycle associated with dreaming.

Non-REM sleep

Sleep stages without REM; include the deeper stages of sleep in the cycle.

REM rebound

Increase in REM sleep after REM sleep has been suppressed.

Barbiturates

Old class of CNS depressants that potentiate GABA in the brainstem; have a low therapeutic index and were largely replaced by benzodiazepines.

Benzodiazepines

Class of CNS depressants that enhance GABA activity at GABA-A receptors; used for anxiety, sleep, seizures, and muscle relaxation.

GABA

Gamma-aminobutyric acid; main inhibitory neurotransmitter in the CNS; benzodiazepines enhance its effect.

Benzodiazepines: Mechanism of Action

Potentiate GABA, increasing inhibitory effects on CNS neurons; tend to have less REM suppression compared with barbiturates.

Benzodiazepines: Indications

Sedation, sleep induction, skeletal muscle relaxation, anxiety relief, and related conditions.

Benzodiazepines: Contraindications

Drug allergy, narrow-angle glaucoma, pregnancy.

Benzodiazepines: Adverse Effects

Mild effects such as headache, drowsiness, dizziness, cognitive impairment, vertigo, lethargy; fall risk in older adults; daytime ‘hangover’ effect.

Benzodiazepines: Toxicity and Overdose

Somnolence, confusion, coma, diminished reflexes; treated with flumazenil as an antidote.

Benzodiazepines: Interactions

Interactions with other CNS depressants and certain drugs (e.g., antifungals, macrolide antibiotics, calcium channel blockers, grapefruit juice) that can increase effects.

Nonbenzodiazepines

Hypnotic-type sleep aids (e.g., zolpidem) that are not benzodiazepines and generally have lower daytime sedation.

Kava

Herbal product used for anxiety and sleep; can cause skin and eye disturbances, hepatotoxicity; interactions with CNS depressants; inform provider about use.

Valerian

Herbal product used for anxiety and insomnia; can cause CNS depression, hepatotoxicity, GI upset; numerous drug interactions.

Diazepam (Valium)

Prototype benzodiazepine; uses include anxiety, procedural sedation, anticonvulsant therapy, and skeletal muscle relaxation; available orally, rectally, and injectably.

Midazolam (Versed)

Short-acting benzodiazepine used preoperatively for sedation and amnesia; high-alert medication; commonly given by injection.

Zolpidem (Ambien)

Nonbenzodiazepine hypnotic with rapid onset; Ambien CR has extended release and two drug reservoirs; watch for sleepwalking (somnambulation).

Flumazenil

Benzodiazepine receptor antagonist used to reverse benzodiazepine overdose or excessive sedation.

Barbiturates: Low therapeutic index

Barbiturates have a narrow safe dosage range; toxicity can occur easily, and dependence is a concern.

Barbiturates: Mechanism of Action

Act on the brainstem reticular formation and potentiate GABA to inhibit nerve impulses; more profound CNS depression than benzodiazepines.

Barbiturates: Indications

Ultrashort-acting (anesthesia induction), short-acting (sedation/control of convulsions), intermediate (sedation), long-acting (prophylaxis of seizures).

Barbiturates: Contraindications

Drug allergy; pregnancy; significant respiratory difficulties; severe kidney or liver disease; caution in older adults.

Barbiturates: Adverse Effects

Cardiovascular: vasodilation and hypertension; CNS: drowsiness, lethargy; respiratory depression; GI: N/V; hematologic effects; hypersensitivity; Stevens-Johnson syndrome; reduced REM sleep.

Barbiturates: Toxicity/Overdose

Respiratory depression and CNS depression; management is supportive; maintain airway and consider urine alkalization to hasten elimination; interactions with MAOIs and enzyme inducers can complicate effects.

Pentobarbital (Nembutal)

Long-acting barbiturate used for preoperative anxiety/sedation and certain seizure conditions; not commonly used as a hypnotic.

Phenobarbital

Long-acting barbiturate used for seizure prevention and certain neonatal conditions; rarely used as a hypnotic.

OTC Hypnotics

Nonprescription sleep aids such as doxylamine and diphenhydramine; often contain acetaminophen/diphenhydramine or melatonin; can cause CNS depression and respiratory risk with alcohol.

Muscle Relaxants (General)

Drugs used to relieve skeletal muscle spasms; most are centrally acting with some direct-acting options on skeletal muscle.

Centrally Acting Muscle Relaxants

Act on the CNS to reduce muscle spasm and pain; examples include baclofen, cyclobenzaprine, tizanidine, methocarbamol, carisoprodol, chlorzoxazone.

Direct-Acting Muscle Relaxants

Act directly on skeletal muscle to reduce contraction; include agents like dantrolene.

Baclofen (Lioresal)

Centrally acting muscle relaxant; sometimes available as an injectable for intrathecal pump therapy.

Cyclobenzaprine (Flexeril)

Centrally acting muscle relaxant; commonly causes marked sedation.

Dantrolene (Dantrium)

Direct-acting muscle relaxant; used in malignant hyperthermia and some spasticity conditions.

Metaxalone (Skelaxin)

Centrally acting muscle relaxant with sedative effects.

Tizanidine (Zanaflex)

Centrally acting muscle relaxant; alpha-2 adrenergic agonist that reduces spasticity.

Carisoprodol (Soma)

Centrally acting muscle relaxant with sedative properties.

Chlorzoxazone (Paraflex)

Centrally acting muscle relaxant with sedative effects.

Methocarbamol (Robaxin)

Centrally acting muscle relaxant with sedative properties.

Amrix (Cyclobenzaprine Extended-Release)

Extended-release form of cyclobenzaprine; centrally acting muscle relaxant with potential marked sedation.

Nursing implications: safety with CNS depressants

Monitor for increased sedation, ensure fall prevention, keep side rails up, and monitor breathing and mental status when combined with other CNS depressants.