L15: Spamolytics & Skeletal muscle relaxants

Sudden involuntary contractions of one or more muscle groups

Muscle spasm

State of increased muscular tone with exaggeration of the tendon reflexes associated with illnesses such as multiple sclerosis, stroke, and spinal cord injury

Spasticity

Spasmolytics

• act on brain, spinal cord, muscles to relieve spasm

• Decrease musculoskeletal pain and spasm from different disease states

• Indication

  • Lower back / neck pain

  • Fibromyalgia

  • Tension HA

  • Myofacial pain syndrome

Neuromuscular blockers

• Interfere with transmission at the neuromuscular end plate (autonomic)

• Used in surgical procedures & emergency medicine to cause temporary paralysis

Baclofen (Lioresal, Kemstro) MOA

• Act like GABA → blocks activity of nerves within brain that controls the contraction & relaxation of skeletal muscle

• Activates GABA(B) receptor → increased K+ conductance

• Hyperpolarization reducing Ca++ influx & reduce the release of neurotransmitter in the brain & spinal cord

Baclofen (Lioresal, Kemstro) indication & AEs

• Multiple schlorisis related muscle Sx

• Sedation, dizzy, hypotension, nausea

Diazepam (Valium)

• MOA

  • facilitates GABA

  • Reducing spasticity mediated in spinal cord

  • Effective in patients with cord transection

• Indication

  • Treats Anxiety, Alcohol withdrawal, Seizures

• AEs

  • drowsy, fatigue, constipation, ataxia

Tizanidine

• MOA

  • Alpha 2 adrenoceptor agonist (hyperpolarization)

  • Presynaptic inhibition of motor neuron hyperactivity in spinal cord

  • Inhibits nociceptive transmission in spinal dorsal horn

• Indication

  • Antispasmodic & Antispastic

• AEs

  • Sedation, Drowsy, Hypotension

Dantrolene (Dantrium IV)

• MOA

  • Binds to Ryanodine receptor (RyR) channel

  • Interferes with Ca++ release through Sarcoplasmic reticulum Ca channel

• Indication

  • Treat spasticity or muscle spasms in spinal cord injuries, stroke, multiple sclerosis, cerebral palsy

  • Malignant hyperthermia

• AEs

  • Liver toxicity

Cyclobenzaprine (Flexeril, Amrix)

• MOA

  • Tricyclic antidepressant by inhibiting 5-HT & NE reuptake

  • Relieve muscle spasms & symptoms

• Indication

  • Fibromyalgia muscle pain

• AEs

  • Anticholinergic

  • Do NOT take with monoamine oxidase inhibitor → hyperpyretic crisis / death

  • High fiver, convulsions

Carisoprodol (Soma)

• MOA

  • Blocks inter neuronal activity

  • Decreases transmission of polysynaptic neurons in spinal cord

  • Metabolized in liver, excreted in kidneys

  • Meprobamate, active anxiolytic metabolite

• Indication

  • Used with rest, physical therapy, & other Tx

• AEs

  • CNS depression, sedation, dizzy

Chlorzoxazone (Paraflex, Parafon)

• MOA

  • Prevent histamine & inflammatory leukotriene release

  • Decrease polysynaptic reflexes in spinal cord

• Indication

  • Used with rest, physical therapy, & other Tx

• AEs

  • GI irritation, red/orange urine, liver toxicity in elderly

Metaxalone (Skelaxin)

• Adjuvant to physical therapy for painful muscle conditions

• AEs

  • Less drowsy/dizzy compared to other muscle relaxants

  • Respiratory depression with concurrent use of other relaxants

Orphenadrine (Norflex)

• MOA

  • Muscarinic receptor antagonist

  • Anti-histamine activity

• Indication

  • Relieves stiffness, pain & discomfort from HA strains, Sprains or other muscle injuries

  • Orphenadrine hydrochloride → Parkinson’s

  • Orphenadrine citrate → muscle pain

• AEs

  • Caution elderly, avoid in glaucoma