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Flashcards in Muscle relaxants Deck (51):
1

Mechanism of skeletal muscle contraction

initiation of impulse, release of acetylcholine, activation of nicotinic receptor at motor end plate, opening of ion channel, passage of Na depolarization of end plate, muscle contraction

2

Drug targets

neuromuscular blocking agents interfere with process of signal conduction, also by blocking muscle contraction even if the signal to contract is propogated along the neuron

3

Skeletal muscle reflex arc

increase in Ca causes muscle contraction, signal carried from spinal cord to muscle (efferent neurons), muscles to spinal cord (afferent neurons)

4

GABA

gamma aminobutyric acid inhibitory neurotransmitter in CNS that bind to GABA receptors and decrease efferent firing- stops reflex arc to prevent inappropriate contractions

5

Muscle spasm

a sudden, involuntary muscle contraction, initiated by trauma, tonic or clonic, painful (spasm-pain-spasm etc)

6

Chronic muscle spasms can result in

muscle atrophy

7

Muscle spasticity

increased muscle tone or contraction, stiff awkward movements, caused by nerve damage in CNS, usually permanent (cerebral palsy), not disease but a process

8

Skeletal muscle relaxants are used to

decrease muscle spasms or spasticity, selective for skeletal muscles

9

Central acting muscle relaxants mostly work by

decreasing signalling from the efferent neurons as opposed to directly inhibiting contraction

10

Skeletal muscle relaxant drugs

Baclofen (Lioresal), Cyclobensaprine (Flexeril), Carisoprodol (Soma), Metaxalone (Skelaxin), Methocarbamol (Robaxin), Chlorzoxazone (Parafon Forte), Dantrolene (Dantrium), Orphenadrine (Norflex)

11

Baclofen (Lioresal) MOA

centrally acting GABA agonist on efferent neurons, inhibits transmission of reflexes at spinal cord level, relieving muscle spasticity, also inhibits substance P in spinal cord

12

Baclofen (Lioresal) clinical uses

spasticity, migraine prevention, MS, spinal cord injury, usually long term

13

Baclofen (Lioresal) ADRs

CNS related, drowsiness, sedation, muscle weakness, hypotension, HA, *less sedating than others

14

Baclofen (Lioresal) boxed warning

severe withdrawal from abrupt d/c, causes altered mental status and rebound spasticity

15

Baclofen (Lioresal) Pearls (5)

TID, PO, can be given intrathecal route for spinal cord injury, MS, degenerative myelopathy, CA; caution with seizure pts, older drug

16

Cyclobenzaprine (Flexeril) MOA

centrally-acting, structurally and pharmacologically very similar to TCAs, reduces tonic somatic motor activity

17

Cyclobenzaprine (Flexeril) Clinical uses

muscle spasms associated w/ muscle injury or strain, short term use only, also good for low back spasms

18

Cyclobenzaprine (Flexeril) ADRs

drowsiness, dizziness, sedation, anticholinergic (no BPH, glaucoma, Alzheimer's)

19

Cyclobenzaprine (Flexeril) Pearls (4)

Only PO, immediate release or long acting (TID/daily), not for use in MS or cerebral palsy, caution in elderly, MAOI pts, or liver failure

20

Tizanidine (Zanaflex) MOA

alpha agonist, similar to clonidine, bu not lipophilic enough to penetrate BBB, causes presynaptic inhibition of motor neurons

21

Tizanidine (Zanaflex) clinical uses

PO and BID-TID, spasticity, unlabeled for tension HA, acute low back pain

22

Tizanidine (Zanaflex) ADRs

drowsiness, hypotension, dry mouth, constipation

23

Carisoprodol (Soma) MOA

not sure, but is CNS depressant, sedating/anxiolytic properties resulting in muscle relaxation

24

Carisoprodol (Soma) clinical uses

Acute management of musculoskeletal pain (2-3 weeks)

25

Carisoprodol (Soma) ADRs

drowsiness, sedation!!, dizziness

26

Carisoprodol (Soma) Pearls (6)

QID, PO only, result in addiction, caution in elderly/ pt with drug abuse, abrupt d/c= withdrawal, DEA controlled

27

Metaxalone (Skelaxin) MOA

not sure, but CNS depressant, breaks spasm-pain cycle, no direct effect on skeletal muscle

28

Metaxalone (Skelaxin) clinical use

muscle spasms/discomfort

29

Metaxalone (Skelaxin) ADRs

CNS depression, dizziness, drowsiness, sedation

30

Metaxalone (Skelaxin) pearls (4)

TID-QID, only PO, caution in renal AND hepatic failure, elderly, pts taking other sedatives and pt with anemia

31

Methocarbamol (Robaxin) MOA

CNS depression

32

Methocarbamol (Robaxin) ADRs

bradycardia

33

Methocarbamol (Robaxin) Pearls (6)

IV, PO, IM, IV contra in renal insufficiency, caution in pt with seizure disorders, usually for long-term

34

Dantrolene (Dantrium) MOA

unique in that it is not central acting, acts directly on skeletal muscle, interfering w/ excitation/contraction coupling to produce relaxation, decr amt of Ca released

35

Dantrolen (Dantrium) clinical use

acute management of malignant hyperthermia, neuroleptic malignant syndrome (short-term), and cerebral palsy or MS (long-term), Rare, IV and PO

36

Dantrolen (Dantrium) ADRs

euphoria, muscle weakness, drowsiness/sedation, hepatotoxic w/ chronic use

37

Other skeletal muscle relaxants

Chlorozoxazone (Parafon Forte) PO only and Orphenadrine (Norflex)- centrally acting, euphorigenic and analgesic properties

38

Neuromuscular blockers types

depolarizing (Succinylcholine, (Anectine)) and non-depolarizing (Pancuronium, Vecuronium (Norcuron), Rocuronium (Zemuron), Cisatracurium (Nimbex), Atracurium

39

NMBs cause

system-wide paralysis, are selective for skeletal muscle not smooth muscle

40

Succinylcholine (Anectine) MOA

depolarizing, acetylcholine agonist, binds nicotinic receptors to open the channels and cause immediate depolarization, leave channels open and unable to contract muscle

41

Succinylcholine (Anectine) clinical use

1x IVP dose for intubations, very fast onset, short duration

42

Succinylcholine (Anectine) ADRs

hyperkalemia, bradycardia, malignant hyperthermia

43

Non-depolarizing NMBs MOA

compete with acetylcholine at the nicotinic receptor sites of neuromuscular junction, will not see initial muscle contraction

44

Non-depolarizing NMBs clinical uses

intubation, and continuous paralysis in critically ill, paralysis during surgical procedures, in ICU for pts whose respiratory fnc is not improving while on mechaniclal ventilation

45

Non-depolarizing NMBs ADRs

hypotension, hyperkalemia (mostly in pts with burns, nerve damage, crush injuries, head injuries), CNS stimulation(Rocuronium), tachy (Pancuronium)

46

Non-depolarizing NMBs Pearls (6)

monitor with train of four (2/4), all given parenterally, short T1/2, always via continuous infusion, relative quick onset, not for combative or agitated pts

47

Rocuronium (Zemuron) Pearls (3)

fastest onset, avoid in liver failure, DOC in pt w/ renal failure

48

Vecuronium/Pancuronium avoid in

pt with renal failure

49

Which has active metabolites that make DOA variable

Vecuronium

50

Cisatracurium (Nimbex) pearls

$$$, unique metabolism (Hoffman eilimination) that results in spontaneous breakdown of drug

51

NMB consideration

T1/2 and duration dictate how that are used, do not use in management of seizures, reversed with acetylcholinesterase inhibitors (Physostigmine, neostigmine), always ensure pt is properly sedated w/ ample analgesia, high risk med!