Centrally acting muscle relaxants

1. CENTRALLY
ACTING MUSCLE
RELAXANTS
Dr. Mamta
Department of Pharmacy Practice

2. Definition
 These are the drugs which
affects skeletal muscle function and decreases
the muscle tone. It may be used to alleviate
symptoms such as muscle spasms, sprains &
pain and produce muscle relaxation without
loss of consiousness.
Muscle relaxants are of two major therapeutic
groups: neuromuscular blockers
and spasmolytics

3. Spasmolytics
Spasmolytics are used to alleviate
musculoskeletal pain, spasms and to reduce
spasticity in a variety of neurological
conditions. They are of three types
Centrally acting
Directly acting
Miscellaneous

4. Mechanism of centrally acting drugs
Spasmolytic agents generally work by either
enhancing the level of inhibition, or reducing the
level of excitation.
Inhibition is enhanced by mimicking or enhancing
the actions of endogenous inhibitory substances,
such as gamma-Aminobutyric acid (GABA).
GABA is the chief inhibitory neurotransmitter
in the mammalian central nervous system.
In humans, GABA is directly responsible for
the regulation of muscle tone.

5. Individual centrally acting drugs
Diazepam
– Facilitating the action of -aminobutyric acid
(GABA)
– Acts at all GABAA synapses
– Useful in muscle spasms of any origin
– sedation limits use.
– Used in patients with lesions of spinal cord and
cerebral palsy and also used in stiffness
syndrome.
– Drug of choice in spasms caused by tetanus
toxin.

6.  Tizanidine:
It has a cental Alpha2 adrenoreceptor action.
It acts by inhibiting the release of excitatory
aminoacids and by facilitating the inhibitory
transmitter glycine.
It also acts by inhibiting polysynaptic reflexes.
It reduces muscle tone and it decreases the
frequency of muscle spasms.
ADR: Drowsiness, hypotension, dry mouth, insomnia at
night and hallucinations.

7. Baclofen
– GABAB agonist. So, it decreases the release
of excitatory transmitter.
– Induce hyperpolarization and serve as presynaptic
inhibitory function
– Intrathecal administration effective in sever
spasticity.
– It is a powerful neuronal depressant and it
acts in the spinal cord on presynaptic
mechanisms.
– It improves bladder and bowel control in
patients with spinal lesions.
– ADR: drowsiness, blurred vision and
gastrointestinal disturbances.

8. Other centrally acting drugs used for local
muscle spasm
• Carisoprodol
• Chlorophenesin
• Chlorzoxone
• Cyclobezaprine
• Metaxalone
• Methocarbamol
• orphenadrine
•Most of them act as sedative at level of the spinal cord or brain
stem
•The main therapeutic use is in relief of acute temporary muscle
spasm cause by Local trauma or strain

9. Thank you