Muscle relaxants

Question 1

Mechanism of skeletal muscle contraction

Answer 1

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

Question 2

Drug targets

Answer 2

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

Question 3

Skeletal muscle reflex arc

Answer 3

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

Question 4

GABA

Answer 4

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

Question 5

Muscle spasm

Answer 5

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

Question 6

Chronic muscle spasms can result in

Answer 6

muscle atrophy

Question 7

Muscle spasticity

Answer 7

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

Question 8

Skeletal muscle relaxants are used to

Answer 8

decrease muscle spasms or spasticity, selective for skeletal muscles

Question 9

Central acting muscle relaxants mostly work by

Answer 9

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

Question 10

Skeletal muscle relaxant drugs

Answer 10

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

Question 11

Baclofen (Lioresal) MOA

Answer 11

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

Question 12

Baclofen (Lioresal) clinical uses

Answer 12

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

Question 13

Baclofen (Lioresal) ADRs

Answer 13

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

Question 14

Baclofen (Lioresal) boxed warning

Answer 14

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

Question 15

Baclofen (Lioresal) Pearls (5)

Answer 15

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

Question 16

Cyclobenzaprine (Flexeril) MOA

Answer 16

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

Question 17

Cyclobenzaprine (Flexeril) Clinical uses

Answer 17

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

Question 18

Cyclobenzaprine (Flexeril) ADRs

Answer 18

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

Question 19

Cyclobenzaprine (Flexeril) Pearls (4)

Answer 19

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

Question 20

Tizanidine (Zanaflex) MOA

Answer 20

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

Question 21

Tizanidine (Zanaflex) clinical uses

Answer 21

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

Question 22

Tizanidine (Zanaflex) ADRs

Answer 22

drowsiness, hypotension, dry mouth, constipation

Question 23

Carisoprodol (Soma) MOA

Answer 23

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

Question 24

Carisoprodol (Soma) clinical uses

Answer 24

Acute management of musculoskeletal pain (2-3 weeks)

Question 25

Carisoprodol (Soma) ADRs

Answer 25

drowsiness, sedation!!, dizziness

Question 26

Carisoprodol (Soma) Pearls (6)

Answer 26

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

Question 27

Metaxalone (Skelaxin) MOA

Answer 27

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

Question 28

Metaxalone (Skelaxin) clinical use

Answer 28

muscle spasms/discomfort

Question 29

Metaxalone (Skelaxin) ADRs

Answer 29

CNS depression, dizziness, drowsiness, sedation

Question 30

Metaxalone (Skelaxin) pearls (4)

Answer 30

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

Question 31

Methocarbamol (Robaxin) MOA

Answer 31

CNS depression

Question 32

Methocarbamol (Robaxin) ADRs

Answer 32

bradycardia

Question 33

Methocarbamol (Robaxin) Pearls (6)

Answer 33

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

Question 34

Dantrolene (Dantrium) MOA

Answer 34

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

Question 35

Dantrolen (Dantrium) clinical use

Answer 35

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

Question 36

Dantrolen (Dantrium) ADRs

Answer 36

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

Question 37

Other skeletal muscle relaxants

Answer 37

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

Question 38

Neuromuscular blockers types

Answer 38

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

Question 39

NMBs cause

Answer 39

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

Question 40

Succinylcholine (Anectine) MOA

Answer 40

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

Question 41

Succinylcholine (Anectine) clinical use

Answer 41

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

Question 42

Succinylcholine (Anectine) ADRs

Answer 42

hyperkalemia, bradycardia, malignant hyperthermia

Question 43

Non-depolarizing NMBs MOA

Answer 43

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

Question 44

Non-depolarizing NMBs clinical uses

Answer 44

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

Question 45

Non-depolarizing NMBs ADRs

Answer 45

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

Question 46

Non-depolarizing NMBs Pearls (6)

Answer 46

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

Question 47

Rocuronium (Zemuron) Pearls (3)

Answer 47

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

Question 48

Vecuronium/Pancuronium avoid in

Answer 48

pt with renal failure

Question 49

Which has active metabolites that make DOA variable

Answer 49

Vecuronium

Question 50

Cisatracurium (Nimbex) pearls

Answer 50

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

Question 51

NMB consideration

Answer 51

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!