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Centrally Acting
Antispastic Drugs
Introduction
A muscle relaxant is a drug which affects skeletal muscle function and
decreases the muscle tone
used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia.
Muscle Relaxants classified as:
1.Neuromuscular Junction Blockers
1.1. depolarizing
1.2. Nondepolarizing muscle relaxant
2.Spasmolytics
1.Neuromuscular Junction Blockers
Can be;
1.1. Depolarizing
1.2. Nondepolarizing Muscle Relaxants
Neuromuscular blockers act by interfering with transmission at the
neuromuscular end plate and have no central nervous system (CNS) activity.
Important for induction of muscle paralysis as part of preoperative general
anesthesia.
2.Spasmolytics
 Spasmolytics, also known as "centrally acting" muscle relaxants
 Used to alleviate musculoskeletal pain and spasms and to reduce spasticity
 Both neuromuscular blockers and spasmolytics are often called muscle
relaxants
 It is often associated with cerebral palsy, multiple sclerosis, and stroke.
 The generation of the neuronal Signals in motor neurons that cause muscle
contractions are dependent on the:
 balance of synaptic excitation and
 inhibition the motor neuron receives
What is muscle spasm?
 Muscle spasms is defined as an involuntary muscular
contraction
 A painful muscle spasm is typically referred to as a
muscle cramp
 Spasticity is defined as a muscle tone disorder
characterized by hyperactive tonic stretch reflexes
 thought to arise from an imbalance of excitatory and
inhibitory neurotransmitters
 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 GABA
 The mechanisms underlying clinical spasticity appear to involve not only the
stretch reflex arc itself but also
 Higher centers in the central nervous system (ie, upper motor neuron lesion),
with damage to descending pathways in the spinal cord resulting in
hyperexcitability of the alpha motoneurons in the cord.
Centrally Acting Antispastic Drugs
Baclofen
Baclofen has commonly been used for its muscle relaxant effects in the treatment of
spasticity
 Baclofen is as effective as diazepam in reducing spasticity
 Causes much less sedation
Mechanism Of Action
 Acts as a GABA agonist at GABAB receptors in the brain and spinal cord
Potassium Ion Conductance
Hyperpolarization
calcium ion influx
Release of excitatory neurotransmitters
substance P
 Baclofen also inhibits neural function presynaptically
 Reducing the in both the brain and spinal cord
 It may also reduce pain in patients by inhibiting the release of substance P in
the spinal cord, as well
 Studies have confirmed that intrathecal administration of baclofen can control
severe spasticity and muscle pain that is not responsive to medication by
other routes of administration
 Partial tolerance to the effect of the drug may occur after several months of
therapy, but can be overcome by upward dosage adjustments to maintain the
beneficial effect
Pharmacokinetics
 Metabolized in the liver and excreted in the urine
 Baclofen can be administered orally as well as intrathecally
 Baclofen is rapidly and effectively absorbed after oral administration
 It is lipophilic and able to penetrate the blood-brain barrier
 Approximately 35% of the drug is excreted unchanged in the urine and feces
side effects
 Common are weakness, sedation, and dizziness
 At higher doses, baclofen can cause seizures, ataxia, and hallucinations
 Abrupt withdrawal should be avoided because it can precipitate
seizures and hallucinations
Diazepam
 The benzodiazepines, such as diazepam, interact with
the GABAA receptor in the central nervous system
 Its action in reducing spasticity is at least partly mediated
in the spinal cord because it is somewhat effective in
patients with cord transection
 While it can be used in patients with muscle spasm of
almost any origin
 Produces sedation in most individuals at the doses
required to reduce muscle tone
Tizanidine
 Clonidine and other imidazoline compounds have also been shown to reduce
muscle spasms by their central nervous system activity.
 Tizanidine is an agonist at α2 adrenergic receptor
 Reduces spasticity at doses that result in significantly less hypotension
than clonidine
 Neurophysiologic studies show that it depresses excitatory feedback from
muscles that would normally increase muscle tone, therefore minimizing spasticity
 Several clinical trials indicate that tizanidine has a similar efficacy to other
spasmolytic agents, such as diazepam and baclofen, with a different spectrum of
adverse effects
 Tizanidine is a centrally acting muscle relaxant that, through its alpha-2
adrenergic agonist properties
 Thought to prevent the release of excitatory amino acids by suppressing
polysynaptic excitation of spinal cord interneurons
 Even though tizanidine’s pharmacologic effect is similar to another alpha-2
agonist like clonidine, but
 It possesses only a fraction of its blood pressure–lowering effect
OTHER CENTRALLY ACTING - SPASMOLYTIC DRUGS
Gabapentin
 An antiepileptic drug that has
shown considerable promise as
 a spasmolytic agent in several
studies involving patients with
multiple sclerosis
Pregabalin
 is a new analog of gabapentin that
may also prove useful
Progabide and glycine
 Have also been found in
preliminary studies to reduce
spasticity
 Progabide is a GABAA and GABAB
agonist and has active metabolites,
including GABA itself
Glycine
 Is another inhibitory amino acid neurotransmitter
 It appears to possess pharmacologic activity when given orally and readily
passes the blood-brain barrier
Idrocilamide and riluzole
 Newer drugs for the treatment of amyotrophic lateral sclerosis
 Have spasm-reducing effects, possibly through
 Inhibition of glutamatergic transmission in the CNS
Spasmolytic Drugs
Side Effects
 Because of the enhancement of inhibition in the CNS
most spasmolytic agents have the side effects
 Sedation
 Drowsiness and
 Dependence with long-term use
Several of these agents also have abuse potential, and their prescription is
strictly controlled!!!
 The most commonly used muscle relaxant for non spasticity-related
muscle pain
 Structurally, it resembles tricyclic anti-depressants(TCAs)
 Its therapeutic effect is centrally mediated and carries no direct peripheral
action on the affected muscles
 Its main pharmacologic action occurs at the brainstem and spinal cord
levels and is partially explained by a depressant effect on the descending
serotonergic neurons
Cyclobenzaprine
Methocarbamol
 It is a centrally acting muscle relaxant that suppresses spinal polysynaptic
reflexes and has no direct effect on skeletal muscle
Orphenadrine
 Structurally related to diphenhydramine and carries relativelystronger
anticholinergic and weaker sedative properties
 Its exact mechanism of action is unknown
 Common side effects include drowsiness and dizziness, followed by other
central nervous system effects such as agitation, hallucinations, and euphoria
Quinine
 Antimalarial, antipyretic, analgesic, and muscle relaxant effects
 Prescribed for the Rx of nocturnal leg muscle cramps
 Increase the refractoriness of muscle and to decrease the excitability of the
neuromuscular endplate
Metaxalone
 Metaxalone is a centrally acting muscle relaxant with an unknown mechanism
 It is metabolized in the liver and excreted through the kidneys in the form of
metabolites
Carisoprodol
 Carisoprodol is still a commonly prescribed muscle relaxant that should
caution owing to the
 Potentially addictive properties of its main metabolite, meprobamate
 Carisoprodol produces its muscle relaxant effect by depressing the
interneuronal activity at the
 Spinal cord level aswell as in the descending tracts of the reticular
formation
 It is not recommended in the pediatric age population
These neurotoxins exert their pharmacologic effect at the
neuromuscular junction (NMJ)
Prevent the calcium-dependent release of acetylcholine
Producing a state of temporary drug-induced denervation
The therapeutic effect can take up to 1 week to take place fully and can
last up to 3 months, at which point repeat injections can be considered
Caution should be exercised in using appropriate botulinum dosing to
avoid functionally limiting muscle weakness
 Diazepam has commonly been used in the treatment of muscle spasm
especially in the acute setting
 It belongs to a group of compounds called benzodiazepines
 known for their potent anxiolytic, sedative, as well as muscle
Mechanism of action
 Their main mechanism of action is through central potentiation
 of the inhibitory g-aminobutyric acid (GABA) effect through presynaptic
 Facilitation of GABA release
 Antispastic drugs are principally used for the treatment of spasticity observed
in disease states with upper motor neuron pathology such as
 Stroke
 Spinal cord injury
 Traumatic brain injury, and
 Multiple sclerosis
 All but two of these agents exert their clinical effect through centrally mediated
mechanisms
 Dantrolene reduces muscle spasms by inhibiting the release of calcium
from the sarcoplasmic reticulum and does not directly affect the CNS
 Because dantrolene tends to produce greater muscle weakness than
baclofen,
 It should not be the first-line agent for patients who are capable of
ambulation
Centrally Acting Antispastic Drugs
Centrally Acting Antispastic Drugs

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Centrally Acting Antispastic Drugs

  • 2. Introduction A muscle relaxant is a drug which affects skeletal muscle function and decreases the muscle tone used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. Muscle Relaxants classified as: 1.Neuromuscular Junction Blockers 1.1. depolarizing 1.2. Nondepolarizing muscle relaxant 2.Spasmolytics
  • 3. 1.Neuromuscular Junction Blockers Can be; 1.1. Depolarizing 1.2. Nondepolarizing Muscle Relaxants Neuromuscular blockers act by interfering with transmission at the neuromuscular end plate and have no central nervous system (CNS) activity. Important for induction of muscle paralysis as part of preoperative general anesthesia.
  • 4. 2.Spasmolytics  Spasmolytics, also known as "centrally acting" muscle relaxants  Used to alleviate musculoskeletal pain and spasms and to reduce spasticity  Both neuromuscular blockers and spasmolytics are often called muscle relaxants  It is often associated with cerebral palsy, multiple sclerosis, and stroke.  The generation of the neuronal Signals in motor neurons that cause muscle contractions are dependent on the:  balance of synaptic excitation and  inhibition the motor neuron receives
  • 5. What is muscle spasm?  Muscle spasms is defined as an involuntary muscular contraction  A painful muscle spasm is typically referred to as a muscle cramp  Spasticity is defined as a muscle tone disorder characterized by hyperactive tonic stretch reflexes  thought to arise from an imbalance of excitatory and inhibitory neurotransmitters
  • 6.  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 GABA  The mechanisms underlying clinical spasticity appear to involve not only the stretch reflex arc itself but also  Higher centers in the central nervous system (ie, upper motor neuron lesion), with damage to descending pathways in the spinal cord resulting in hyperexcitability of the alpha motoneurons in the cord.
  • 8. Baclofen Baclofen has commonly been used for its muscle relaxant effects in the treatment of spasticity  Baclofen is as effective as diazepam in reducing spasticity  Causes much less sedation Mechanism Of Action  Acts as a GABA agonist at GABAB receptors in the brain and spinal cord Potassium Ion Conductance Hyperpolarization calcium ion influx Release of excitatory neurotransmitters substance P
  • 9.  Baclofen also inhibits neural function presynaptically  Reducing the in both the brain and spinal cord  It may also reduce pain in patients by inhibiting the release of substance P in the spinal cord, as well  Studies have confirmed that intrathecal administration of baclofen can control severe spasticity and muscle pain that is not responsive to medication by other routes of administration  Partial tolerance to the effect of the drug may occur after several months of therapy, but can be overcome by upward dosage adjustments to maintain the beneficial effect
  • 10. Pharmacokinetics  Metabolized in the liver and excreted in the urine  Baclofen can be administered orally as well as intrathecally  Baclofen is rapidly and effectively absorbed after oral administration  It is lipophilic and able to penetrate the blood-brain barrier  Approximately 35% of the drug is excreted unchanged in the urine and feces side effects  Common are weakness, sedation, and dizziness  At higher doses, baclofen can cause seizures, ataxia, and hallucinations  Abrupt withdrawal should be avoided because it can precipitate seizures and hallucinations
  • 11. Diazepam  The benzodiazepines, such as diazepam, interact with the GABAA receptor in the central nervous system  Its action in reducing spasticity is at least partly mediated in the spinal cord because it is somewhat effective in patients with cord transection  While it can be used in patients with muscle spasm of almost any origin  Produces sedation in most individuals at the doses required to reduce muscle tone
  • 12. Tizanidine  Clonidine and other imidazoline compounds have also been shown to reduce muscle spasms by their central nervous system activity.  Tizanidine is an agonist at α2 adrenergic receptor  Reduces spasticity at doses that result in significantly less hypotension than clonidine  Neurophysiologic studies show that it depresses excitatory feedback from muscles that would normally increase muscle tone, therefore minimizing spasticity  Several clinical trials indicate that tizanidine has a similar efficacy to other spasmolytic agents, such as diazepam and baclofen, with a different spectrum of adverse effects
  • 13.  Tizanidine is a centrally acting muscle relaxant that, through its alpha-2 adrenergic agonist properties  Thought to prevent the release of excitatory amino acids by suppressing polysynaptic excitation of spinal cord interneurons  Even though tizanidine’s pharmacologic effect is similar to another alpha-2 agonist like clonidine, but  It possesses only a fraction of its blood pressure–lowering effect
  • 14. OTHER CENTRALLY ACTING - SPASMOLYTIC DRUGS Gabapentin  An antiepileptic drug that has shown considerable promise as  a spasmolytic agent in several studies involving patients with multiple sclerosis Pregabalin  is a new analog of gabapentin that may also prove useful Progabide and glycine  Have also been found in preliminary studies to reduce spasticity  Progabide is a GABAA and GABAB agonist and has active metabolites, including GABA itself
  • 15. Glycine  Is another inhibitory amino acid neurotransmitter  It appears to possess pharmacologic activity when given orally and readily passes the blood-brain barrier Idrocilamide and riluzole  Newer drugs for the treatment of amyotrophic lateral sclerosis  Have spasm-reducing effects, possibly through  Inhibition of glutamatergic transmission in the CNS
  • 16. Spasmolytic Drugs Side Effects  Because of the enhancement of inhibition in the CNS most spasmolytic agents have the side effects  Sedation  Drowsiness and  Dependence with long-term use Several of these agents also have abuse potential, and their prescription is strictly controlled!!!
  • 17.  The most commonly used muscle relaxant for non spasticity-related muscle pain  Structurally, it resembles tricyclic anti-depressants(TCAs)  Its therapeutic effect is centrally mediated and carries no direct peripheral action on the affected muscles  Its main pharmacologic action occurs at the brainstem and spinal cord levels and is partially explained by a depressant effect on the descending serotonergic neurons Cyclobenzaprine
  • 18. Methocarbamol  It is a centrally acting muscle relaxant that suppresses spinal polysynaptic reflexes and has no direct effect on skeletal muscle Orphenadrine  Structurally related to diphenhydramine and carries relativelystronger anticholinergic and weaker sedative properties  Its exact mechanism of action is unknown  Common side effects include drowsiness and dizziness, followed by other central nervous system effects such as agitation, hallucinations, and euphoria
  • 19. Quinine  Antimalarial, antipyretic, analgesic, and muscle relaxant effects  Prescribed for the Rx of nocturnal leg muscle cramps  Increase the refractoriness of muscle and to decrease the excitability of the neuromuscular endplate Metaxalone  Metaxalone is a centrally acting muscle relaxant with an unknown mechanism  It is metabolized in the liver and excreted through the kidneys in the form of metabolites
  • 20. Carisoprodol  Carisoprodol is still a commonly prescribed muscle relaxant that should caution owing to the  Potentially addictive properties of its main metabolite, meprobamate  Carisoprodol produces its muscle relaxant effect by depressing the interneuronal activity at the  Spinal cord level aswell as in the descending tracts of the reticular formation  It is not recommended in the pediatric age population
  • 21. These neurotoxins exert their pharmacologic effect at the neuromuscular junction (NMJ) Prevent the calcium-dependent release of acetylcholine Producing a state of temporary drug-induced denervation The therapeutic effect can take up to 1 week to take place fully and can last up to 3 months, at which point repeat injections can be considered Caution should be exercised in using appropriate botulinum dosing to avoid functionally limiting muscle weakness
  • 22.  Diazepam has commonly been used in the treatment of muscle spasm especially in the acute setting  It belongs to a group of compounds called benzodiazepines  known for their potent anxiolytic, sedative, as well as muscle Mechanism of action  Their main mechanism of action is through central potentiation  of the inhibitory g-aminobutyric acid (GABA) effect through presynaptic  Facilitation of GABA release
  • 23.  Antispastic drugs are principally used for the treatment of spasticity observed in disease states with upper motor neuron pathology such as  Stroke  Spinal cord injury  Traumatic brain injury, and  Multiple sclerosis  All but two of these agents exert their clinical effect through centrally mediated mechanisms
  • 24.  Dantrolene reduces muscle spasms by inhibiting the release of calcium from the sarcoplasmic reticulum and does not directly affect the CNS  Because dantrolene tends to produce greater muscle weakness than baclofen,  It should not be the first-line agent for patients who are capable of ambulation