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pharm > 11. Muscle relaxants > Flashcards

11. Muscle relaxants Flashcards

1
Q

Muscle relaxants

A

-drugs that decrease skeletal muscle tone
-used to treat muscle hypertonicity (central muscle relax) or decrease physiological tone of skeletal muscle (anesthesiology)
-2 groups->.central vs peripheral acting

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2
Q

central muscle relaxants

A

-used for muscle hypertonicity
-affects nerve excitement EARLIER THAN ON THE NMJ

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3
Q

MoA of central muscle relaxants

A

-varies depending on the representative
-inhibits polysynaptic signals at INTRANEURONAL SPINAL CORD LEVEL
-potentitate inhibition-> main inhibitory neurotransmitter in CNS -> GABA
-attenuate excitation -> main excit NT-> GLUTAMATE

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4
Q

how are the central muscle relaxants classified

A

benzos vs non benzos

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5
Q

what are the benzos

A

Diazepam

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6
Q

what are the non benzos

A

baclofen
tolperisone
tizanidine
thiocolchicoside
orphenadrine
guaifenesin
mephenoxalone
Cannabis sativa with defined content of THC and CBD (cannabidiol)

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7
Q

Diazepam -properties

A

muscle relaxant
anticonvulsant
anxiolytic
sedative
hypnotic

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8
Q

Diazepam action

A

-potentiated inhibition - (increased GABA at inhib synapse) -> anticonvuls and muscle relax

-increased gaba leads to attenuated excitation -Glut-> anxiolytic and hypnosedative

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9
Q

benzodiazepine receptors

A

BZD1 rc- anxiolytic and hypnosedative
BZD2- anticonvuls, muscle relax

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10
Q

Baclofen

A

-structural analogue of GABA
-agonist of GABA rcp- acts on level of spinal cord
-reduces monosynaptic and polysynpatic reflex transmissions in spinal cord by stimulating GABA B receptors
-inhibits release of excitatory amino acids
-acts mainly presynaptically -> reduces excitability of motorneuron

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11
Q

Tolperison

A

-similar chem structure to lidocaine
inhib action at level of reflex spinal pathway
-stabilising effect on cell membranes-reduces electrical excitability of motor neurons
-inhibits influx of Na+ membrane isolated nerve cells -> reduces amplitude and frequency of action potentials
-inhib action of ca2+ voltage gated channels-> reduces NT release
-weak alpha antag and antimusc properties

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12
Q

Tizanidine

A

-acts on spinal cord -> inhibits polysynaptic signals at interneuronal level-> reduces muscle tone
- inhibits release of excitatory amino acids stimulating NMDA receptors by stimulating presynaptic alpha receptors
-shows a mild analgesic effect
-high individual variability

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13
Q

Thicolchicoside

A
  • a colchicine analog with muscle relaxant pharm activity
    -acts as an agonist of GABA A receptors
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14
Q

orphenadrine

A

-block M and NMDA rcp in CNS
-affects the transmission in nerve impulses from spinal cord to muscle -> muscle relaxation
-shows locally anaesthetic and weak antihistamine properties

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15
Q

guaifenasin

A

-antagonises NMDA recep
-causes anxiolytic and expectorant effects
risk of overuse

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16
Q

mephenoxalone

A

-inhibits of neuronal transmission at level of reflex arc

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17
Q

Delta 9 tetrahydrocannabinol( THC )and cannabidiol (CBD)

A

from cannabis sativa
oral spray
used to improve symps in MS (mild to moderate spasticity)
for pts who have improved after an initial trial treatment in spasticity

18
Q

How are peripheral muscle relaxants classified

A

-by their action
-direct mechanism (botulinum toxin) vs indirect mechanism (non depolarising vs depolarising)

19
Q

what is the moa of non depolarising peripheral muscle relaxants ?

A

competitive antagonism at NM rcp. of
neuromuscular junction → Na+ channels will NOT
open → depolarization will NOT occur → muscle
contraction will NOT occur

20
Q

do non depolarising p.m relax have antidote

A

yes- ache inhibitors abolish the action

21
Q

what is the moa of depolarising peripheral muscle relaxants ?

A

non-competitive agonism at NM rcp.of
neuromuscular junction → Na+ channels open →
depolarization occurs → muscle contraction occurs
briefly but Na+ channels remain LONG inactive
state, agonist is degraded longer than ACh → rcp.
are blocked, new stimulation is not possible which
leading to relaxation

There is NO antidote- Ache inhibitors slow down the degradation and therefore increase the effect

22
Q

what are the depolarising peripheral muscle relaxants

A

suxamethonium

23
Q

what are the non depolarising peripheral muscle relaxants

A

pipecuronium
atracurium
rocuronium
mivacurium

24
Q

Pk of peripheral muscle relaxants

A

NOT ABSORBED ORALLY
ONLY INJECTION
does not cross BBB-> consciousness not affected

25
Q

clinical use of peripheral muscle relaxants

A

General anaesthesia
-application until the introduction
CONTROLLED LUNG VENTILATION NEEDED ( diaphragm will also relax)
-muscle relaxation before intubation (urgent in injuries and accidents)

26
Q

Succinylcholine=suxamethonium

A

-the only depolarising muscle relaxant used
fast onset , short effect (intubation and short term intervention

27
Q

what are the AE of suxamethonium

A

bradycardia
increased intraocular pressure and intracranial pressure
increased K+
malignant hyperthermia
prolonged paralysis

28
Q

CI of suxamethonium

A

bradycardia - bradycardia
crrush syndrome -(because of increased K+)
glaucoma -increased ICP and IOP
history of malig hyperthermia (malignant hyperthermia)

29
Q

Tubocurarine

A

-arrow poison
-rapid onset
short half life
long acting
AE- sudden histamine release, sudden BP drop , bronchospasm-> so it is replaced with a better representative with shorter duration of action

30
Q

long acting non depolarising p.m relaxant

A

pipercuronium - has a fast onset

31
Q

medium acting non depolarising p.m. muscle relaxant

A

rocuronium - fast onset , indication: INTUBATION

vercuronium

32
Q

short acting non depolarising p.m. muscle relaxant

A

mivacurium -> degraded by cholinesterase

33
Q

what are the AE of non depolarising peripheral muscle relaxants ?

A

Resemble an allergic reaction:

―histaminoliberation
―hypotension
―bronchospasm
―bronchial secretion and salivation
―myopathy (in accumulation)
―ganglion blockade contributes to
postoperative atony of the GIT and urinary tract

34
Q

Agents used to reverse the non depolarising peripheral muscle relaxants

A

sugammadex
neostigmine
dantrolene

35
Q

sugammadex

A

-causes the cancellationn of the rocuronium induced neuromuscular blockade
-binds selectively to steroid muscle relaxant-> forms an inactive plasma complex-> which is excreted unchanged in the urine
-causes fast cancellation of muscle relaxation and fewer. side effects than using NEOSTIGMINE

36
Q

neostigmine

A

an acetylcholinesterase
-used to antagonise the non depolarising periph muscle relax effect

37
Q

dantrolene mechanism of action and indication

A

moa - direct, by binding to ryanodine rcp. 1 of the sarcoplasmic reticulum blocks the
release of Ca2+ into the cytosol → prevents contraction directly in the myocyte

indication -malignant hyperthermia and malig neuroleptic syndrome

-must be given before all Ca2+ is released

38
Q

what is malignant hyperthermia

A

-rare congenital AE with high mortality rate
-caused by mutation in the Ca2+ channel of the sarcoplasmic reticulum (ryanodine receptors) -> leads to intense muscle cramps
-leads to sudden increase in body temp after admin of certain substances

39
Q

what is the most common cause of malignant hyperthermia

A

suxamethonium

40
Q

how is malignant hyperthermia treated

A

-dantrolene

  • a substance that inhibits muscle contractions by preventing the release of Ca2+ from sarcoplasmic reticulum

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