Chapter 12 Central Nervous System Depressants and Muscle Relaxants Flashcards
Sedatives
-Drugs that have an inhibitory effect on the CNS to the degree that they reduce:
Nervousness
Excitability
Irritability
CNS Depressants: Benzodiazepines
-Formerly the most commonly prescribed sedative-hypnotic drugs
-Favorable drug effect profiles, efficacy, and safety
-Classified as either:
Sedative-hypnotic
Anxiolytic (medication that relieves anxiety)
Benzodiazepines: Mechanism of Action
-Depress CNS activity
-Affect hypothalamic, thalamic, and limbic systems of the brain
-Benzodiazepine receptors
Gamma-aminobutyric acid (GABA)
-Do not suppress rapid eye movement (REM) sleep as much as barbiturates do
-Do not increase metabolism of other drugs
Benzodiazepines: Drug Effects
- Calming effect on the CNS
- Useful in controlling agitation and anxiety
- Reduce excessive sensory stimulation, inducing sleep
- Induce skeletal muscle relaxation
Diazepam (Valium)
First clinically available benzodiazepine drug. It has varied uses, including treatment of anxiety.
Midazolam (Versed)
- Most commonly used preoperatively and for moderate sedation.
- Causes amnesia and anxiolysis (reduced anxiety) as well as sedation.
- Normally administered by injection in adults
- Liquid oral dosage form is also available for children.
Temazepam (Restoril)
- Intermediate-acting benzodiazepine
- One of the metabolites of diazepam
- Normally induces sleep within 20 to 40 minutes
- Long onset of action, so it is recommended that patients take it about 1 hour prior to going to bed
- Still an effective hypnotic; however, it has been replaced by newer drugs
Nonbenzodiazepine: Eszopiclone (Lunesta)
- First hypnotic to be FDA approved for long-term use
- Designed to provide a full 8 hours of sleep
- Considered a short- to intermediate-acting agent
- Patients should allot 8 hours of sleep time and should avoid taking hypnotics when they must awaken in less than 6 to 8 hours.
Nonbenzodiazepine: Ramelteon (Rozerem)
- Structurally similar to the hormone melatonin: works as an agonist at melatonin receptors in the CNS
- Technically, it is not a CNS depressant; used as hypnotic
- Not classified as a controlled substance
- Indicated for patients who have difficulty with sleep onset rather than sleep maintenance
Nonbenzodiazepine: Zaleplon (Sonata)
- Short-acting nonbenzodiazepine hypnotic
- Unique advantage of this drug stems from its very short half-life
- Patients whose sleep difficulties include early awakenings can take a dose in the middle of the night as long as it is at least 4 hours before they must arise.
Nonbenzodiazepine: Zolpidem (Ambien)
- Short-acting nonbenzodiazepine hypnotic
- Lower incidence of daytime sleepiness compared with benzodiazepine hypnotics
- Ambien CR is a longer acting form with two separate drug reservoirs
- Somnambulation
Herbal Products: Kava
- Used to relieve anxiety, stress, and restlessness and to promote sleep
- May cause temporary yellow skin discoloration (extended, continued intake) and visual disturbances
- Potential interactions with alcohol, barbiturates, and psychoactive drugs
- Contraindicated in liver disease, alcoholism, other conditions
- Patient should not operate heavy machinery during use.
Herbal Products: Valerian
- Used to relieve anxiety, restlessness, and sleep disorders
- May cause CNS depression, hepatotoxicity, nausea, vomiting, anorexia, restlessness, insomnia
- Many interactions, including with CNS depressants, -MAOIs, phenytoin, warfarin, and alcohol
- Contraindicated in cardiac and liver disease
- Patient should not operate heavy machinery during use.
Barbiturates
- First introduced in 1903; were the standard drugs for insomnia and sedation
- Habit forming; low therapeutic index
- Only a handful commonly used today partly because of the safety and efficacy of benzodiazepines
Barbiturates:Mechanism of Action
- Site of action: brainstem (reticular formation)
- By potentiating the action of GABA, nerve impulses traveling in the cerebral cortex are inhibited.
Barbiturates: Drug Effects
- Low doses: sedative effects
- High doses: hypnotic effects (also lower respiratory rate)
- Notorious enzyme inducers
- Stimulate liver enzymes that cause metabolism or breakdown of many drugs
- Result in shortened duration of action
Ultrashort acting Barbiturates
Anesthesia for short surgical procedures, other uses
Short Acting Barbiturates
Sedation and control of convulsive conditions
Intermediate Acting Barbiturates
Sedation and control of convulsive conditions
Long Acting Barbiturates
Sleep induction, epileptic seizure prophylaxis
Barbiturates: Adverse Effects
Cardiovascular Vasodilation, hypotension
CNS Drowsiness, lethargy, vertigo
Respiratory Respiratory depression, cough
Barbiturates: Adverse Effects (Cont.)
GI Nausea, vomiting, diarrhea, constipation
Hematologic Agranulocytosis, thrombocytopenia
Other Hypersensitivity reactions, Stevens-Johnson syndrome
Treatment of overdose for Barbiturates
- Symptomatic and supportive
- Maintain adequate airway
- Assisted ventilation or oxygen therapy
- Fluids
- Pressor support
- Activated charcoal
Inhibited metabolism
MAOIs prolong the effects of barbiturates.
Common Barbiturates
- Pentobarbital (Nembutol)
- Phenobarbital
Pentobarbital (Nembutal)
- Prototypical barbiturate
- Long-acting drug
- Uses: prevention of generalized tonic-clonic seizures and fever-induced convulsions, as well as treatment of hyperbilirubinemia in neonates
- Rarely used today as a sedative and is no longer recommended to be used as a hypnotic drug
Over-the-Counter Hypnotics
- Nonprescription sleeping aids often contain antihistamines, which have CNS depressant effect.
- Doxylamine (Unisom) and diphenhydramine (Sominex), acetaminophen/diphenhydramine (Extra Strength Tylenol PM)
- As with other CNS depressants, concurrent use of alcohol can cause respiratory depression or arrest.
Low therapeutic index
Drugs with a low therapeutic index have only a narrow dosage range within which the drug is effective; above that range, they are rapidly toxic. `
Muscle Relaxants
-Act to relieve pain associated with skeletal muscle spasms
-Majority are centrally acting
CNS is the site of action
Similar in structure and action to other CNS depressants
-Direct acting
Act directly on skeletal muscle
Closely resemble GABA
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
Muscle Relaxants: Adverse Effects
Extension of effects on CNS and skeletal muscles
- Euphoria
- Lightheadedness
- Dizziness
- Drowsiness
- Fatigue
- Muscle weakness, others
Nursing Implications
- Give hypnotics 30 to 60 minutes before bedtime for maximum effectiveness in inducing sleep (depends on drug’s onset).
- Most benzodiazepines cause REM rebound and a tired feeling the next day; use with caution in older adults.
- Rebound insomnia may occur for a few nights after a 3- to 4-week regimen has been discontinued
