2
b. Lungs
c. Plasma
d. Muscles
e. Kidneys
(c) procaine is an ester; esters are metabolized predominately
by pseudocholinesterases in the plasma.
10. Which of the following is local anesthetic subject to inactivation by
plasma esterases?
a. Lidocaine
b. Prilocaine
c. Tetracaine
d. Mepivacaine
e. Bupivacaine
(c) esters are metabolized by plasma esterases - tetracaine is
the only ester listed, all the rest are amides
11. The activity of procaine is terminated by
a. Elimination by the kidney
b. Storage in adipose tissue
c. Metabolism in the liver only
d. Metabolism in the liver and by pseudocholinesterase in the
plasma
(d) remember #9 above? see the word "mainly"? same
question, but worded a little differently to throw you off. Again,
procaine is an ester; esters are metabolized predominately by
pseudocholinesterases in the plasma, but also to some extent
by esters in the liver.
12. All of the following factors are significant determinants of the duration
of conduction block with amide-type local anesthetics EXCEPT the
a. pH of tissues in the area of injection
b. Degree of vasodilatation caused by the local anesthetic
c. Blood plasma cholinesterase levels
d. Blood flow through the area of conduction block
e. Concentration of the injected anesthetic solution
(c) the word "EXCEPT" should alert you that this is basically a
true-false type question with 4 true statements and 1 false
statement; you just have to figure out which one! In this case,
you just have to remember that plasma cholinesterase levels
are only important for the duration of action of ester-type LAs,
not amides, which are metabolized in the liver. All the other
statements are variables which affect duration of the block, but
apply to both esters and amides.
13. Which of the following is contraindicated for a patient who had an
allergic reaction to procaine six months ago?
a. Nerve block with lidocaine
b. Topical application of lidocaine
c. Topical application of tetracaine
d. Infiltration with an antihistamine
(c) again, just another question that requires you to be able to
pick out an ester or an amide from a list. Since procaine is an
ester, only another ester LA would be cross-allergenic. In this
list the only ester listed is tetracaine.
14. Bupivacaine (Marcaine ) has all of the following properties relative to
lidocaine (Xylocaine ) EXCEPT bupivacaine
a. Is more toxic
b. Is an ester-type local anesthetic
c. Has a slower onset of action
d. Has a longer duration of action
(d) According to textbooks, local anesthetics fall into the
following classes in terms of duration of action: short: procaine;
moderate: prilocaine, mepivacaine, lidocaine; long: bupivacaine,
tetracaine, etidocaine. Statements (a), 3, and 4 would be true if
the question was comparing mepivacaine to bupivacaine, which
are structurally similar; but the comparison is to lidocaine. The
only difference that applies is duration of action ((d)),
bupivacaine is longer. (b) is wrong, both are amides.
15. Amide-type local anesthetics are metabolized in the
a. Serum
b. Liver
c. Spleen
d. Kidney
e. Axoplasm
(b) don't forget: esters in plasma; amides in liver
15. The duration of action of lidocaine would be increased in the presence
of which of the following medications?
a.
Prazosin
b.
Propranolol
c.
Hydrochlorothiazide
d.
Lisinopril
e.
Digoxin
(b) this is an interaction I tested you on several times – now you
know why! Propranolol interacts with lidocaine in two ways.
By slowing down the heart via beta receptor blockade, blood
delivery (and lidocaine) to the liver is reduced, thus lidocaine
remains in the systemic circulation longer, and can potentially
accumulate to toxic levels. Propranolol and lidocaine also
compete for the same enzyme in the liver, thus metabolism of
lidocaine can be reduced.
16. Severe liver disease least affects the biotransformation of which of
the following?
a. Lidocaine
b. Procaine
c. Prilocaine
d. Mepivacaine
(b) Answer is (b)- You should be able to recognize that all of
these drugs are local anesthetics. Local anesthetics are of one
of two types, either esters or amides. Ester types are subject to
hydrolysis in the plasma and thus have short half lives. Amides
are metabolized primarily in the liver and have longer half lives.
Thus the biotransformation (e.g., metabolism; again, the rats are
using a different word to confuse you, even though they are
asking the same basic question) of an amide type local
anesthetic would be the most altered in the presence of sever
liver disease. The key word here is "least". Of the drugs listed,
only procaine is an ester. The rest are amides.
Questions regarding toxicity:
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