Chapter 25 Muscle relaxants agents Flashcards
Centrally Acting Skeletal Muscle Relaxants MEDS
Baclofen (Lioresal)
Carisoprodol (Soma)
Chlorzoxazone (generic) Cyclobenzaprine (Amrix)
Metaxalone (Skelaxin)
Methocarbamol (Robaxin) Orphenadrine (generic)
Tizanidine (Zanaflex)
Diazepam (Valium) (also used for anxiety but has muscle relaxant properties)
MOA central acting muscle relaxants
These drugs inhibit spinal and subcortical neurons, reducing muscle hyperactivity and reflexes.
Tizanidine acts as an alpha- adrenergic agonist, increasing presynaptic motor neuron inhibition.
Some drugs enhance gamma-aminobutyric acid (GABA) neurotransmission, increasing muscle relaxation.
They work centrally, rather than directly affecting skeletal muscles
Indications of central acting
Relief of discomfort associated with acute, painful musculoskeletal conditions.
Adjunct to rest, physical therapy, and other pain management strategies.
Baclofen is specifically used for spinal cord injuries and central spasticity
Pharmacokinetics central acting
Absorption: Most drugs in this class are rapidly absorbed orally.
Metabolism: Primarily liver metabolism, except baclofen, which is not metabolized.
Excretion: Mostly through the urine.
Available Forms:
- Baclofen: Oral and intrathecal
pump.
- Cyclobenzaprine: Controlled release for sustained action
- Methocarbamol : Oral and
injectable forms
CI central acting
Allergy to these drugs.
Skeletal muscle spasms due to rheumatic disorders (as they won’t provide benefits).
Baclofen should not be used if spasticity contributes to posture, locomotion, or function—blocking spasticity can lead to functional loss.
Use with caution in:
- Epilepsy (may worsen seizures).
- Cardiac dysfunction (risk of
muscle weakness and
cardiovascular depression).
- Hepatic/renal dysfunction
(especially metaxalone and tizanidine, which are metabolized in the liver and excreted renally).
- Pregnancy/lactation (use only if benefits outweigh risks)
AE central acting
CNS Depression: Drowsiness, fatigue, weakness, confusion, headache, insomnia.
Gastrointestinal (GI) Effects:
Nausea, dry mouth, constipation, anorexia.
Cardiovascular Effects:
Hypotension, arrhythmias.
Urinary Effects: Urinary urgency, frequency, enuresis (involuntary urination).
Unique Side Effects:
- Chlorzoxazone may cause
orange to purplish-red urine discoloration (patients should be warned).
- Tizanidine has been linked to liver toxicity and hypotension
DDI central acting
Other CNS depressants (opioids, alcohol, benzodiazepines):
- May increase sedation,
confusion, and
respiratory depression.
- Patients should avoid
alcohol.
Baclofen should be tapered off gradually to prevent psychosis and hallucinations
Nursing interventions central acting
Assessment:
- Check for contraindications, including renal/hepatic dysfunction, epilepsy, cardiac conditions, pregnancy/lactation.
- Monitor CNS effects, including drowsiness, confusion, and reflex impairment.
- Assess cardiovascular status, including blood pressure, pulse, and ECG.
- Evaluate bowel sounds and urinary function.
Interventions:
- Educate about drowsiness risk and caution against
driving or hazardous activities.
- Encourage fluid intake and fiber to prevent
constipation.
- Monitor liver function with tizanidine use.
- Ensure the patient voids before taking the drug to
prevent urinary retention.
- If using baclofen intrathecally, educate patients on
proper pump use and monitoring.
- Taper baclofen gradually to avoid severe withdrawal
symptoms.
Patient Teaching:
- Take exactly as prescribed.
- Avoid alcohol and CNS depressants
Report any severe side effects, such as hallucinations, confusion, or jaundice (liver dysfunction).
- Increase fluid intake to reduce constipation risk.
- Do not abruptly stop taking these medications
Direct acting muscle relaxant MEDS
Dantrolene (Dantrium) OnabotulinumtoxinA (Botox, Botox Cosmetic)
IncobotulinumtoxinA (Xeomin) RimabotulinumtoxinB (Myobloc)
MOA direct acting
Dantrolene:
Interferes with calcium release from the sarcoplasmic reticulum, which prevents muscle contraction.
Does not affect neuromuscular transmission or the central nervous system (CNS).
Botulinum Toxins
(OnabotulinumtoxinA, IncobotulinumtoxinA, RimabotulinumtoxinB): Block acetylcholine release at the neuromuscular junction, paralyzing muscle fibers.
Effects are localized and can spread beyond the injection site
Indications direct acting
Dantrolene:
Chronic spasticity from upper motor neuron disorders (e.g., spinal cord injury, multiple sclerosis, cerebral palsy).
Prevention and treatment of malignant hyperthermia.
Botulinum Toxins:
Muscle spasticity (e.g., cerebral palsy, stroke, dystonia).
Chronic migraines.
Cervical dystonia, excessive sweating, strabismus, overactive bladder, cosmetic wrinkle reduction.
Pharmacokinetics direct acting
Dantrolene:
Half-life: ~9 hours (oral), 4-8 hours (IV).
Metabolized in the liver, excreted in urine.
Botulinum Toxins:
Injected locally, effects last 3-6 months.
Not systemically absorbed.
CI direct acting
Dantrolene:
-Liver disease (high risk of hepatotoxicity).
- Cardiac or respiratory dysfunction
(may worsen muscle weakness).
Pregnancy and lactation (use only if benefits outweigh risks).
Botulinum Toxins:
-Active infections at the injection site.
-Neuromuscular diseases (e.g., myasthenia gravis) due to increased weakness.
AE direct acting
Dantrolene:
- Liver toxicity (black box warning) – monitor liver function tests.
- CNS effects: Drowsiness, dizziness, weakness, fatigue.
- Gastrointestinal (GI) effects: Diarrhea, nausea.
- Cardiovascular effects: Tachycardia, transient blood pressure changes.
Botulinum Toxins:
- Localized muscle weakness (can spread beyond the injection site).
- Dysphagia, difficulty breathing
(if effects spread).
- Flu-like symptoms, headache.
DDI direct acting
Dantrolene + Estrogens: Increased risk of hepatotoxicity (especially in women over 35).
Dantrolene + CNS depressants (opioids, benzodiazepines, alcohol): Enhanced sedation and CNS depression.
Botulinum Toxins + Neuromuscular blockers or aminoglycosides: Increased paralysis risk.
Nursing interventions direct acting
Assessment:
- Monitor liver function (AST, ALT, bilirubin) before and during dantrolene therapy.
- Assess for respiratory and cardiac function to prevent complications.
- For botulinum toxins, assess for muscle weakness and swallowing difficulties.
Interventions:
- Discontinue dantrolene if liver dysfunction occurs (nausea, fatigue, jaundice).
- Periodically stop dantrolene therapy for 2-4 days to evaluate effectiveness.
- Monitor IV access for extravasation (dantrolene is highly irritating to tissues).
- Avoid administering botulinum toxin in infected areas.
- Educate patients about muscle weakness risks and
caution against hazardous activities.
Patient Teaching:
- Report any signs of liver toxicity (yellow skin, dark urine, nausea).
- Dantrolene may cause drowsiness—avoid driving and operating machinery.
- Botulinum toxins can take 2 weeks to work and last 3-6 months.
- Report any difficulty swallowing or breathing immediately.
