Muscle Relaxants
 Nerves and movement
o Spasticity—damages to CNS neurons may cause this permanent start of muscle contraction—as a result of loss of
nerves that help to maintain balance in controlling muscle activity
o Posture, balance, & movement are the result of a constantly fluctuating sequence of muscle contraction & relaxation—
influenced by
 Cerebellum (associated w/ conscious muscle movements)
 Basal ganglia (associated w/ unconscious muscle movement)
o Spinal Reflexes
 Simple—involving an incoming sensor neuron & outgoing motor neuron
 Spindle gamma loop system
o Simple reflex arcs that involve sensory receptors in the peripheral that respond to stretch &
spinal motor nerves & cause muscle fiber contraction: responsible for maintaining muscle tone &
keeping an upright position against the pull of gravity
 Complex—involving interneurons that communicate w/ the related centers in brain, not muscles or glandes
o Brain Control
 Pyramidal tract
 Fibers w/in CNS that control precise, intentional movement
 Extrapyramidal tract
 Cells from the cortex and subcortical areas, including the basal ganglia & the cerebellum, which
coordinate unconsciously controlled muscle activity
 Allows the body to make automatic adjustments in posture or position & balance
 Neuromuscular Abnormalities
o Muscle spasm
 Result from injury to the musculoskeletal system
 Ex: overstretching a muscle, wrenching a joint, or tearing a tendon or ligament
 Injuries cause violent & painful involuntary muscle contraction

The contraction cuts off blood flow to the muscle fibers in the injured area, causing lactic acid to accumulate &
resulting in pain
o Muscle Spasticity
 Result of damage o neurons w/in the CNS rather than injury to peripheral structures
 Condition is permanent bc of damage in CNS
 Result from an ↑ in excitatory influences or ↓ in inhibitory influences w/in CNS
 Hypertonia—state of excessive muscle response & activity
 S/s of cerebral palsy & paraplegia are rt the disruption in nervous control of muscles
Centrally Acting Skeletal Muscle Relaxants
P: Baclofen
Therapeutic/ indications
*Work in the CNS to interfere
w/ the reflexes that are causing
the muscle spasm
*Spasmolytic—lyse or destroy
spam
*thought to involves actions in
the upper or spinal interneurons
*Tizanidine—alpha-adrenergic
agonist, thought to ↑ inhibition
or presynaptic motor neuron in
CNS
*indicated for relief of
discomfort associated w/ acute,
painful musculoskeletal
conditions as an adjunct to rest,
physical therapy, & other
measures
Kinetics
* Baclofen—oral &
intrathecal forms & can be
administered via a delivery
pump for the treatment of
central spasticity
Contraindication and Cautions
*allergy
*Cyclobenzaprine—
controlled release oral
form for continual control
of discomfort w/o repeated
dosing
*baclofen—spasticity that contribute
to locomotion, upright position, or ↑
function—blocking results in loss of
these function
*Methocarbamol—oral &
parenteral forms
*skeletal muscle spasms resulting
from rheumatic disorder—would not
benefit
All centrally should be caution w/:
*history of epilepsy—CNS
depression & imbalance may
exacerbate
*M: liver (except baclofen)
*Cardiac dysfunction—muscle
function is depressed
*any condition marked by muscle
weakness—make worse
Adverse Effect
*CNS depression—
drowsiness, fatigue,
weakness, confusion,
headache, insomnia
Drug-drug
*CNS depressant
or alcohol
*GI may be linked to CNS
depression of the
parasympathetic reflexes—
nausea, dry mouth, anorexia,
constipation
*hypotension & arrhythmias
*urinary frequency, enuresis
(involuntary urination), &
feeling of urinary urgency
*Chlorzoxaxone—discolor
urine orange to purplish-red
*Tizanidine—liver toxicity &
hypotension
*hepatic or renal dysfunction
 Interventions
o Baclofen—taper drug slowly over 1-2 weeks to prevent development of psychoses & hallucinations
 Other measures
o Rest of the affects muscles, heat application to ↑ blood flow to the area to remove the muscle to normal tone and
activity, & anti-inflammatory agents (if underlying problem is rt injury or inflammation)
Direct-Acting Skeletal Muscle Relaxants
P: Dantrolene
Therapeutic/ indications
*enter muscle to prevent
muscle contraction directly
*Dantrolene—prevent
peripheral muscle contraction
by interfere w/ the release of
calcium from the muscle
tubules
*Botulinum toxins A & B—
bind directly to the receptor
sites of motor nerve terminal
& inhibit the release of Ach,
leading to local muscle
paralysis
*Rimabotulinumtoxin B—
reduce the severity of
abnormal head position &
neck pain associated w/
cervical dystonia (Involuntary
muscle contractions that cause
repetitive or twisting
movements)
Kinetics
* Dantrolene—
oral and
parenteral
-M: liver & E:
urine
-cross placenta
& milk
*botulinum no
kinetic
information
Contraindication and Cautions
Dantrolene
*allergy
*spasticity that contribute to locomotion,
upright position, or ↑ function—blocking
results in loss of these function
Adverse Effect
Dantrolen
*CNS depression—drowsiness,
fatigue, weakness, confusion,
headache, insomnia, visual
disturbance
*hepatic or renal disease—known for liver
toxicity
*GI direct irritation from calcium
effects—irritation, diarrhea,
constipation, cramps
-Caution
*women & all pts > 35—potentially fatal
hepatocellular disease
*direct hepatocellular damage &
hepatitis
*history of liver disease—more susceptible
*urinary frequency, enuresis, &
to toxicity
feeling of urinary urgency, crystalline
*Cardiac disease—cardiac muscle depression urine w/ pain or burning on urination
Botulinum
*allergy
*active infection at the site of injection—
aggravate infection
-Caution
*any peripheral neuropathic disease
*neuromuscular disorders
*acne, abnormal hair growth, rashes,
photosensitivity, abnormal sweating,,
chill, myalgia
Botulinum
*Anaphylactic reaction
*headaches, dizziness, muscle pain,
paralysis
*Onabotulinumtoxin A—
*Incobotulinumtoxin A—
*children-nothing reported
*known cardiac disease—potential changes
in tissue perfusion & systemic absorption
*redness & edema at injection side
Drug-drug
*Dantrolene
combined w/
estrogen the
incidence of
hepatocellular
toxicity ↑
*botulinum w/
other drugs that
interfere w/
neuromuscular
transmission or
w/
aminoglycosides
↑ additive effects