Transcript Past, Present, and Future of Neuromuscular Reversal Agents

PAST, PRESENT, AND
FUTURE OF
NEUROMUSCULAR
REVERSAL AGENTS
Jennifer Bradley, BS, BSN, SRNA
OBJECTIVES
• Review anticholinesterase agents: history, mechanism
of action, dosing
• “When” to reverse: TOF monitoring, adequate return of
muscular function, acceleromyography
• Discuss issues with current reversal agents
• Review of Sugammadex: mechanism of action, current
research, impact on future practice , update of FDA
approval status
HISTORY
• Physostigmine (prototype)- derived from the Calabar bean
of the physostigma veneosum plant in West Africa
• 1864-The pure alkaloid (physostigmine) was isolated by
Jobste and Hesse
• 1877-First therapeutic drug use was to treat glaucoma
• 1900- A physiologist in Vienna performed experiments on
dogs paralyzed with curare-observed respiratory recovery
with physostigmine
HISTORY
• Physostigmine (prototype)- derived from the Calabar bean
of the physostigma veneosum plant in West Africa
• 1864-The pure alkaloid was isolated by Jobste and Hesse and
named physostigmine
• 1877-First therapeutic drug use was to treat glaucoma
• 1900- A physiologist in Vienna performed experiments on
dogs paralyzed with curare-observed respiratory recovery
with physostigmine
HISTORY
• 1931-Neostigmine was introduced into therapeutics for GI
tract stimulation and symptomatic treatment of myasthenia
gravis
• 1946-Neuromuscular blocking agents (NMBA) were
established in England’s anesthesia practiceanticholinesterases were only suggested
• 1950’s (mid)-Incomplete surgical recovery and high
incidence of morbidity/mortality led to use of reversal agents
in anesthesia
CHOLINESTERASE INHIBITORS
(BASIC PRINCIPLES)
• Currently the primary clinical use of cholinesterase inhibitors is
to reverse nondepolarizing muscle blockade
• Acetylcholine (ACh) is the neurotransmitter for the:
•
•
•
•
entire parasympathetic nervous system
parts of the sympathetic nervous system
select neurons in the central nervous system
somatic nerves innervating skeletal muscle
• Neuromuscular transmission is blocked when nondepolarizing
muscle relaxants (NDMR) compete with acetylcholine to
bind to nicotinic cholinergic receptors
MECHANISM OF ACTION
• The cholinesterase inhibitors indirectly increase the amount of
acetylcholine available to compete with the NDMR by
reversibly binding to inactivate the acetylcholinesterase
enzyme
• Acetylcholinesterase is responsible for the rapid hydrolysis of
the neurotransmitter (ACh) acetylcholine to choline and
acetic acid
• Neostigmine, physostigmine, pyridostigmine, and
edrophonium follow this generic mechanism; increasing the
availability of acetylcholine at the neuromuscular junction
(NMJ) to compete with the NDMR
MECHANISM OF ACTION
CONTINUED
• The mechanism of action of these drugs not only increases
neuromuscular transmission but elicits muscarinic side effects
• Cellular goal of reversing the neuromuscular blockade:
• maximize nicotinic transmission
• minimize muscarinic side effects
• Reversal of blockade depends on:
• Pharmacokinetics-of the NDMR and the anticholinesterase
MUSCARINIC SIDE EFFECTS
OF CHOLINESTERASE
INHIBITORS
Organ System
Muscarinic Side Effects
Cardiovascular
Decreased heart rate,
bradyarrhythmias
Pulmonary
Bronchospasm, bronchial
secretions
Cerebral
Diffuse excitation
Gastrointestinal
Intestinal spasm, increased
salivation, nausea
Genitourinary
Increased bladder tone
Ophthalmological
Pupillary constriction
Unwanted muscarinic side effects are minimized by prior or
concomitant administration of anticholinergic medications,
such as atropine sulfate or glycopyrrolate(Robinul)
STRUCTURES
PHYSOSTIGMINE
• Structure: Tertiary amine, a carbamate group. but no
quaternary ammonium. Lipid soluble and the only clinically
available cholinesterase inhibitor that freely passes the
blood-brain barrier
• Dosing: The recommended dosage is 0.01-0.03 mg/kg.
• Physostigmine (0.04 mg/kg) has been shown to be effective in
preventing postoperative shivering
• Packaging: Packaged as a solution containing 1 mg/mL
• Effects: Onset, 1-2min with the duration of action 45-60min
• Metabolism: Plasma esterases
PHYSOSTIGMINE
• Anticholinergic Choice: Not typically needed. Bradycardia is
infrequent in the recommended dosage range, but atropine
should be immediately available
• Other Factors: Ability to antagonize morphine-induced
respiratory depression
• Effective in the treatment of central anticholinergic toxicity
caused by overdoses of atropine or scopolamine
• Reverses some of the CNS depression and delirium
associated with use of benzodiazepines and volatile
anesthetics
NEOSTIGMINE
• Structure: Consists of a carbamate moiety (covalent
bonding) and a quaternary ammonium group (lipid
insoluble) to prevent passage through the blood brain barrier
(BBB)
• Dosing: Most potent: 0.03-0.08 mg/kg (up to 5 mg in adults)
• Packaging: Most commonly packaged in a 10 mL vial of a 1
mg/mL solution ( although 0.5 mg/mL and 0.25 mg/mL
concentrations are also available)
• Effects: 5-7 min, peak at 10 min, BUT may take 15-30 minutes
for full effect Duration: >1 hr
• Metabolism: 50% hepatic, ~ 25% Renal ~ 25% plasma
esterases
NEOSTIGMINE
• Anticholinergic choice: Glycopyrollate’s onset and duration
(0.2 mg glycopyrrolate per 1 mg of neostigmine) is similar to
that of neostigmine and is associated with less tachycardia
than is experienced with atropine (0.4 mg of atropine per 1
mg of neostigmine)
• Factors to consider: The duration of action is prolonged in
geriatric patients
• Reported that neostigmine crosses the placenta, resulting in
fetal bradycardia
• Neostigmine is also used to treat myasthenia gravis, flaccid
bladder, and paralytic ileus
PYRIDOSTIGMINE
• Structure: Pyridostigmine is similar to neostigmine but the
quaternary ammonium is incorporated into the phenol ring.
Pyridostigmine shares neostigmine’s covalent binding to
acetylcholinesterase and its lipid insolubility
• Dosing: 20% as potent as neostigmine and may be
administered in doses up to 0.25 mg/kg (up to a total of 20
mg in adults)
• Packaging: It is available as a solution of 5 mg/mL
• Effects: Slowest onset of action(10-20 minutes) and longest
duration (>2 h)
• Metabolism: 75% hepatic
PYRIDOSTIGMINE
• Anticholinergic choice: Glycopyrollate (0.05 mg per 1 mg of
pyridostigmine) or atropine (0.1 mg per 1 mg of
pyridostigmine) to prevent bradycardia
• Glycopyrrolate is preferred because its slower onset of action
better matches that of pyridostigmine, and results in less
tachycardia
EDROPHONIUM
• Structure: Lacks a carbamate group, therefore it relies on
noncovalent bonding to the acetylcholinesterase enzyme.
The quaternary ammonium group limits lipid solubility
• Dosing: Less than 10% as potent as neostigmine. The
recommended dosage is 0.5-1 mg/kg
• Packaging: Available as a solution containing 10 mg/mL; it is
available with atropine as a combination drug (Enlon-Plus; 10
mg edrophonium and 0.14 mg atropine per 10mLvial). Max
40mg
• Effects: Most rapid onset of action (30-60s) and the shortest
duration of action of all the cholinesterase inhibitors (20-40
minutes)
• Metabolism: 30% Hepatic, ~ 70% Renal
EDROPHONIUM
• Anticholinergic Choice: Edrophonium’s rapid onset is well
matched to atropine (0.014 mg of atropine per 1 mg of
edrophonium)(preferred)
• Glycopyrrolate (0.007-0.1 mg per 1 mg of edrophonium) can
also be used, but it should be given several minutes prior to
edrophonium
• Facts: Reduced doses should not be used, longer acting
muscle relaxants may outlast the effects of edrophonium
• In equipotent doses, muscarinic effects of edrophonium are
less pronounced – approximately 50% less dose of
anticholinergic typically needed
ANTICHOLINESTERASES
Dose
(mg/kg)
Peak
Antagoni
sm
(min)
Duration of
Antagonis
m (min)
Dosage of
Atropine
(mcg/kg)
Dose of
Robinul
(mcg/kg)
Metabolism
and
Comments
Edrophonium
(Tensilon)
0.5-1.0
30-60s
40-60
7-14
7-10
30%
hepatic*
Neostigmine
(Prostigmin)
0.030.08
(up to
5mg)
5-7
55-75
14-40
1-2
50%
hepatic**
Pyridostigmine
(Mestinon)
0.25
10-15
80-130
15-20
10
75%
hepatic***
Agent
ANTICHOLINESTERASES
DOSING
Usual Dose of
Anticholinergic
per 1 mg of
Cholinesterase
Inhibitor
Cholinesterase
Inhibitor
Usual Dose of
Cholinesterase
Inhibitor
Neostigmine
0.04-0.08 mg/kg Glycopyrrolate
0.2 mg
Pyridostigmine
0.1-0.25 mg/kg
Glycopyrrolate
0.05 mg
Edrophonium
0.5-1 mg/kg
Atropine
0.014 mg
Physostigmine
0.01-0.03 mg/kg
Usually not
necessary
NA
Recommended
Anticholinergic
ADDITIONAL INFO
• In excessive doses, acetylcholinesterase inhibitors can
potentiate a nondepolarizing neuromuscular blockade
• These drugs also prolong the depolarization blockade of
succinylcholine
• Prolonged action of a nondepolarizing muscle relaxant from
renal or hepatic insufficiency will likely be accompanied by a
corresponding increase in the duration of action of a
cholinesterase inhibitor
ADDITIONAL INFO
• The time required to fully reverse a nondepolarizing block
depends on several factors:
• choice and dose of cholinesterase inhibitor administered
• the muscle relaxant being antagonized
• the extent of the blockade before reversal
• Recommended: A reversal agent should be routinely given
to patients who have received NDMR- unless full reversal can
be demonstrated or the postoperative plan includes
continued intubation
FACTORS THAT POTENTIATE
NEUROMUSCULAR
BLOCKADE
Drugs
•Volatile anesthetics
•Antibiotics: Aminoglycosides
• clindamycin,
• neomycin
• polymyxin B
• tetracycline
•,Dantrolene
•Verapamil
•Furosemide
•Lidocaine
Electrolytes and acid-base disorders
•Hypermagnesemia
•Hypocalcemia
•Hypokalemia
•Respiratory acidosis
Temperature
•Hypothermia
HALF-WAY VIDEO
REVERSAL
CONSIDERATIONS:
MONITORING BLOCKADE
• Monitoring the depth of paralysis when using NDMR is an
important part of standard practice when considering
reversal
• Train-of-Four (TOF) stimulation was introduced in 1970 by Ali
and colleagues
• There are different patterns of stimulation possible with the
TOF monitor
TOF MONITORING BASICS
• Single Stimulus: Simplest-single impulse every 10seconds
• TOF stimulation: 4 impulses over 2 seconds ( at 2Hz) and
relating the ratio of the last twitch (T4) to the first twitch (T1)
• Tetanic Stimulation: 50hz ( 50 stimuli per second) or 100Hz for
5 seconds
• Post-tetanic facilitation (PTC): 50Hz stimulus for 5 seconds
followed in 3 seconds by repetitive single twitches at 1 Hz
• Double Burst: Initial burst of 2 (0.2-ms) impulses at 50 Hz
followed by an identical stimulation in 750ms
TOF MONITORING
• Optimal placement: black electrode (-) closest proximity to
the nerve, red (+) electrode distal monitoring to reach
maximum twitch height
• Most commonly monitored nerve is the ulnar contraction
of the adductor pollicis muscle of the thumb (extubating
conditions)
• Opthalmic branch of the facial nerve contraction of the
orbicularis occuli (intubating conditions)
• Peroneal nerve (near the fibular head)dorsiflection of the
ankle
• Posterior tibial nerve (behind knee)plantar flexion of the big
toe
APPROPRIATE TIME TO
REVERSE BASED ON NERVE
STIMULATION
• Neuromuscular blockade can be reversed when there is at
least ONE twitch with TOF stimulation-but the
recommendation is a MINUMUM of 2 TOF twitches
• It is important to remember that only ONE of the alpha
subunits of the post-junctional receptor needs to be
occupied by NDMB to inhibit function and TWO Ach
molecules are required to stimulate the receptor
Tests of Return of Neuromuscular Function
Test
Results
Percentage of
Receptors Occupied
Tidal Volume
>5 ml/kg
80
Single twitch*
Return to baseline
75-80
Train of four (4/4)
No fade
70-75
Sustained tetanus
(50 Hz, 5 seconds)**
No fade
70
Vital capacity
>20 ml/kg
70
Double-burst stimulation
No fade
60-70
Sustained tetanus
(100 Hz, 5 seconds)**
No fade
50
Inspiratory force
>-40 cm H20
50
Head lift
Sustained 5 seconds
50
Hand grip
Return to baseline
50
Sustained bite
Sustained clenching of
a tongue depressor
50
RETURN OF
NEUROMUSCULAR
FUNCTION
• In general, the higher the frequency of stimulation, the
greater the sensitivity of the test (100-Hz tetany > 50-Hz
tetany>TOF > single-twitch height)
• Clinical signs of adequate reversal also vary in sensitivity
(sustained head lift/ hand grip > inspiratory force > vital
capacity > tidal volume)
• The suggested end points of recovery are sustained tetanus
for 5 sec in response to a 100-Hz stimulus in anesthetized
patients or sustained head or leg lift in awake patients
• Other methods for assessing recovery from neuromuscular
blockade, such as acceleromyography, may help reduce
the incidence of residual blockade
ACCELEROMYOGRAPHY
• Easy to use, relatively inexpensive and provides more
quantitative information regarding TOF ratio
• The device is usually attached to the tip of the thumb and a
digital readout is obtained (TOF ratio)
• The setup is sensitive to inadvertent displacement of the
thumb and careful positioning and placement of the hand is
important
• The operating concept is the knowledge that acceleration is
measured by the TOF
• According to Newton's law, acceleration is proportional to
force if mass remains unchanged
ACCELEROMYOGRAPHY
• Studies addressing post op residual blockade have begun to
look at the potential benefit using acceleromyography
• Acceleromyography studies have shown a significant
decrease in the incidence of TOF <0.9
• In a 2011 study that looked at 115 post-op patients 14.5% of
those measured with acceleromyography had residual
blockade versus 50% of patients monitored with the
conventional TOF monitor
ISSUES ENCOUNTERED
WITH REVERSAL
• Residual paralysis remains a serious clinical concern despite
intermediate acting NMBA
• Studies have shown that after a single dose of NMBA 37% of
patients have shown residual paralysis
• It is estimated that approximately 30%-60% of PACU patients
have a TOF<0.9
• Remember: There is an upper limit to the amount of
acetylcholinesterase inhibition that is possible at the
neuromuscular junction
ISSUES ENCOUNTERED
WITH REVERSAL
• Clinically evident events have occurred in 1%-3% of patients
with TOF< 0.9
• 0.8-6.9% of these events result in serious respiratory
complications
• In a case control study of 42 critical respiratory events in the
PACU, patients with mean TOF <0.62 accounted for 74% of
the adverse events (P<0.0001)
• Remember: muscles of the hypoglossal area are among the
last to recover, which also increases the aspiration risk in
these patients
ISSUES ENCOUNTERED
WITH REVERSAL
• Think of the patients: muscle weakness due to residual
blockade can be uncomfortable/frightening
• Unwanted events may also occur during transport between
the OR and PACU
• Ultimately, patients with residual blockade may have longer
PACU stays or require re-intubation
PROBLEMS WITH NEOSTIGMINE/
GLYCOPYRROLATE
COMBINATIONS
• Ineffective at reversing profound blockade
• Cardiac arrhythmias
• Combination of two powerful cardiovascular drugs
• Is the calculated reversal appropriate for each patient
• Errors?
• Inability to appropriately match two drugs
CHARACTERISTICS OF AN
IDEAL REVERSAL AGENT
• Quickly and completely reverses NDMB regardless of the
depth of blockade
• Achieve reversal without side effects (minimal)
• Provides the possibility to continue full paralysis until the end
of the procedure
• Serve as an alternative to succinylcholine for rapid sequence
induction
• Has the potential to decrease the incidence of post-op
residual blockade
SELECTIVE RELAXANT
BINDING AGENT
• Sugammadex (Bridion)-first in class using a novel mechanism
of action
• Approved in the European Union in 2008
• Currently approved in >50 countries, with >5million vials sold
• Awaiting approval from US FDA
SUGAMMADEX
• Sugammadex is in the family of cyclic dextrose units used as
solubilizing agents since 1953
• Modfied gamma-cyclodextrine-comprised of 8 sugar
molecules that form a rigid ring with a central lipophilic
cavity
• Initially discovered when a compound was needed to
increase the solubility of rocuronium in a specific media
• Observed permanent binding of the rocuronium molecule to
the center of the sugammadex molecule in a 1:1 ratio
MECHANISM OF ACTION
• Hydrophobic interactions trap the drug in the cyclodextrine
cavity forming a tight a water-soluble complex in a 1:1 ratio
(encapsulation)
• A concentration gradient is created with no free unbound
NMBA in the plasma as compared to the extravascular
compartment
• Favors movement of NDMB (rocuronium or veuronium) into
the plasma where they are rapidly encapsulated
• Terminates the NDMR’s action and restrains the drug in
extracellular fluid where it cannot interact with nicotinic
acetylcholine receptors
MOA VIDEO
GENERAL FINDINGS
• Extensive research and numerous clinical trials have
evaluated the safety, efficacy, and usefulness of
sugammadex
• A metaanalysis including 18 randomized controlled trials
(RTC’s) demonstrated that sugammadex can reverse
rocuronium induced blockade faster than neostigmine at all
levels of blockade in a dose dependent manner
• In trials of immediate reversal sugammadex (16mg/kg) was
administered 3 minutes after profound blockade by
rocuronium and showed faster recovery than patients who
underwent spontaneous recovery from succinylcholine
DOSING
Available: 2mL or 5mL vials (100mg/mL)
Elimination: 24h clearance unchanged via kidneys
Dose Sugammadex
Indication
Mean Recovery
time to TOF 0.9
16mg/kg
Immediate Reversal 1.5 minutes
after 1.2 mg/kg
rocuronium
4mg/kg
Routine reversal of
deep
neuromuscular
block (PTC 1-2)
2mg/kg
Routine reversal of
2 minutes
moderate block (T2
appearance)
3 minutes
RESEARCH FINDINGS
• In a 2012 RCT by Geldner et al, researchers evaluated 140
patients randomized into neostigmine versus sugammadex
groups to evaluate blockade recovery time
• Found that those who received sugammadex recovered 3.4
times faster (CI:95%)
• 94% of sugammadex patients recovered within 5 minutes versus
20% of the neostigmine patients
• In a 2011 RCT by Kadoi et al, researchers evaluated recovery
times of ECT patients who received succinylcholine for
muscle relaxation versus rocuronium and sugammadex
• Found that sugammadex 16mg/kg administered 3 minutes after
rocuronium showed faster return to TOF 0.9 and faster return to
respirations (CI 99%)
• Sugammadex 8mg/kg showed recovery times equivalent to
succinylcholine
• Sugammadex 4mg/kg showed slower recovery times
compared to succinylcholine
DRAWBACKS
• Hypersensitivity reactions: variable from rashes,
bronchospasm, hypotension, to anaphylactic reaction
• Cyclodextrines are prominent molecules with daily
exposures, leading to the possibility of cross sensitivity
• Case reports have shown allergic reactions in patients who
have received sugammadex for the first time
• Reviews of published approval studies and retrospective
data have shown the incidence to be < 1%
• The British Journal of Anesthesia discussed three case reports
of suspected hypersensitivity and reported occurrence of 13500 to 1-13,000 cases
DRAWBACKS
• Inability to reverse benzylquinolones
• Recurrence of neuromuscular blockade (when inadequate
dose used)
• Small risk of QT prolongation, nausea, prolonged bleeding
times (with use of 16mg/kg dose)
• Not suggested to use when a patient is taking fusidic acid or
toremifene ( potential for delayed recovery )
• Not to be used in patients with highly impaired renal function:
dialysis or creatinine clearance <30mL/min
FUTURE PRACTICE
• Sugammadex has the potential to allow full blockade to
remain until the “last stich” and ensure complete reversal
even at post-tetanic counts
• Importance in Can’t Intubate Can’t Ventilate cases where a
difficult airway was unrecognized and rocuronium or
vecuronium was used at induction
• Ability to replace succinylcholine in rapid sequence
inductions and ECT’s
• New research showing its efficacy in patients who are
typically not candidates for neuromuscular blockade
• Safer cardiac profile-concurrent administration of
anticholinergic is not required
FDA APPROVAL STATUS
• Since its approval in 2008 for use in the European Union,
Merck has sought US FDA approval
• Sugammadex was denied approval in 2008 and was resubmitted to the FDA for approval in January 2013
• September 2013 the FDA requested the Merck researchers to
“re-do” their hypersensitivity trials
• Currently Merck is conducting new hypersensitivity trials with
hopes for approval in January 2015
• Final Obstacle: Cost $$
SUMMARY
• Anesthesia is a continually evolving field with new standards,
monitoring techniques, medications, and management
styles
• To improve current standards we must understand our
current methods and recognize areas that can be improved
upon
• Though sugammadex is not yet available in the US, it is on the
horizon
• Sugammadex carries the potential to impact our practice
and provide choice with reversal agents
REFERENCES
• Duke, James. "Chapter 13 Muscle Relaxants AndMonitoring of Relaxant Activity."
Anesthesia Secrets. Philadelphia, PA: Mosby/Elsevier, 2011. 95-104. Print.
• Geldner, G., M. Niskanen, P. Laurila, V. Mizikov, M. Hübler, G. Beck, H. Rietbergen, and
E. Nicolayenko. "A Randomised Controlled Trial Comparing Sugammadex and
Neostigmine at Different Depths of Neuromuscular Blockade in Patients Undergoing
Laparoscopic Surgery*." Anaesthesia 67.9 (2012): 991-98. Print.
• Godai, K., M. Hasegawa-Moriyama, T. Kuniyoshi, T. Kakoi, K. Ikoma, S. Isowaki, A.
Matsunaga, and Y. Kanmura. "Three Cases of Suspected Sugammadex-induced
Hypersensitivity Reactions." British Journal of Anaesthesia 109.2 (2012): 216-18. Print.
• Kadoi, Yuji, Hiroko Hoshi, Akiko Nishida, and Shigeru Saito. "Comparison of Recovery
times from Rocuronium-induced Muscle Relaxation after Reversal with Three Different
Doses of Sugammadex and Succinylcholine during Electroconvulsive Therapy." Journal
of Anesthesia 25.6 (2011): 855-59. Print
• Kirkland, Matt L., John J. Nagelhour, and Mark D. Welliver. "Deep Neuromuscular
Blockade: Exploration and Perspectives on Multidisciplinary Care." AANA Journal (2013):
2+. Print.
• "Merck Sharp & Dohme Limited." Bridion 100 Mg/ml Solution for Injection. MSD, 25 Oct.
2013. Web.
https://www.medicines.org.uk/emc/medicine/21299/SPC/Bridion+100+mg+ml+solution
+for+injection/ 10 Mar. 2014,
REFERENCES
• Chapter 12. Cholinesterase Inhibitors & Other Pharmacologic Antagonists to
Neuromuscular Blocking Agents. In: Butterworth JF, IV, Mackey DC, Wasnick JD. eds.
Morgan & Mikhail's Clinical Anesthesiology, 5e. New York: McGraw-Hill; 2013.
http://accessanesthesiology.mhmedical.com/content.aspx?bookid=564&Sectionid=42
800543.Accessed March 10, 2014.
• Murphy, Glen S., Joseph W. Szokol, Michael J. Avram, Steven B. Greenberg, Jesse H.
Marymont, Jeffery S. Vender, Jayla Gray, Elizabeth Landry, and Dhanesh K. Gupta.
"Intraoperative Acceleromyography Monitoring Reduces Symptoms of Muscle
Weakness and Improves Quality of Recovery in the Early Postoperative Period." Survey
of Anesthesiology 56.3 (2012): 150-51. Print.
• Sadleir, P.H.M, T. Russell, R.C. Clarke, E. Maycock, and P.R. Platt. "Intraoperative
Anaphylaxis to Sugammadex and a Protocol for Intradermal Skin Testing." Anesthesia
Intensive Care 42 (2014): 93-96. Web
• Schaller, Stefan J., and Heidrun Fink. "Sugammadex as a Reversal Agent for
Neuromuscular Block: An Evidence Based Review." Core Evidence: Dove Medical Press,
Ltd 8 (2013): 57-67. Print.
• Taylor P. Chapter 10. Anticholinesterase Agents. In: Brunton LL, Chabner BA, Knollmann
BC. eds. Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e. New
York: McGraw-Hill; 2011.
http://accessanesthesiology.mhmedical.com/content.aspx?bookid=374&Sectionid=41
266216. Accessed March 10, 2014.
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