Prepared by M.L. Thompson, Ph. D., Dept. of General Dentistry, Tufts Dental School
C:\Documents and Settings\mthomp01\Desktop\pharm2007 shortcuts\Boards2005.doc
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the neuron - the positively charged ion blocks nerve conduction.
33. The more rapid onset of action of local anesthetics in small nerves is
due to
a.
The slightly lower pH of small nerves
b.
The greater surface-volume ratio of small nerves
c.
The increased rate of penetration resulting from depolarization
d.
Smaller nerves usually having a higher threshold
Who knows? Who cares? probably the answer is (b) - the theory
goes that there is a size dependent critical length of
anesthetic exposure necessary to block a given nerve. Small
fibers will be blocked first because the anesthetic
concentration to h critical length in a small fiber will be reached
faster than the critical length in a larger fiber. You have to
block three nodes of ranvier, and they are farther apart in
larger fibers than they are in small diameter fibers. Make
sense?
34. Which of the following statements are true regarding onset, degree
and duration of action of local anesthetics?
a. The greater the drug concentration, the faster the onset and the
greater the degree of effect
b. Local anesthetics block only myelinated nerve fibers at the nodes
of Ranvier
c. The larger the diameter of the nerve fiber, the faster the onset of
effect
d. The faster the penetrance of the drug, the faster the onset of
effect
i.
(a), (b), and (c)
ii.
(a), (b) and (d)
iii.
(a) and (c) only
iv.
(b), (c) and (d)
(ii) if you knew the fact above about small nerves, then this
question basically becomes a true false type thing, and (c) is the
false statement. (a) and (d) make logical sense so you are
stuck picking between (b) and (c). You have your pick of
memorizing the small nerve thing or the myelinated nerve nodes
of ranvier thing.
And now, for those of you that complained in class “do we really
have to know this stuff?”
35. A dentist administers 1.8 ml of a 2% solution of lidocaine. How many
mg of lidocaine did the patient receive?
a. 3.6
b. 9
c. 18
d. 36
e. 180
(d) 2% solution = 20 mg/ml X 1.8 ml = 36 mg lidocaine. And
you thought you would never have to do this stuff again!
36. Three ml of a local anesthetic solution consisting of 2% lidocaine with
1:100,000 epinephrine contains how many milligrams of each?
a. 6 mg. lidocaine, 0.3 mg. epinephrine
b. 6 mg. lidocaine, 0.03 mg. epinephrine
c. 60 mg. lidocaine 0.3 mg. epinephrine
d. 60 mg. lidocaine 0.03 mg epinephrine
e. 600 mg lidocaine, 0.3 mg. epinephrine
f. 600 mg. lidocaine, 0.03 mg. epinephrine
(d) 2% lidocaine = 20 mg/ml x 3 = 60 mg lidocaine
1:100,000 epi = 0.01 mg/ml x 3 = 0.03 mg epi
37. The maximum allowable adult dose of mepivacaine is 300 mg. How
many milliliters of 2% mepivacaine should be injected to attain the
maximal dosage in an adult patient?
a. 5
b. 10
c. 15
d. 20
e. 25
(c) 2% mepivacaine = 20 mg/ml, so 300 mg / 20 mg/ml = 15 ml
38. A recently introduced local anesthetic agent is claimed by the
manufacturer to be several times as potent as procaine. The product
is available in 0.05% buffered aqueous solution in 1.8 ml. cartridge.
The maximum amount recommended for dental anesthesia over a 4-
hour period is 30 mg. The amount is contained in approximately how
many cartridges?
a.
1-9
b.
10-18
c.
19-27
d.
28-36
e.
Greater than 36
(d) 0.05% = 0.5 mg/ml . To give 30 mg, you have to give
30mg/0.5 mg/ml or 60 ml. 1 cartridge = 1.8 ml, thus 60ml /1.8ml
= 33.3 cartridges. - first express the percentage of solution as a
fraction of 100, then add the units gm/ml. 0.05% equals 0.5 or
1/2 gms per 100 ml. The cartridge is 1.8 ml which you can
round off to almost 2 mls total. In this 2 ml you would have 1 gm
of the local anesthetic. You need to give 30 gms, which would
require 30 cartridges. The alternative that meets this answer is
(d). Don't get tricked by the placement of the decimal point-
many people read the 0.05% as being the same as 5 gms
rather than 0.5 gms.
39. According to AHA guidelines, the maximum # of carpules of
local anesthetic containing 1:200,000 epinephrine that can be used
in the patient with cardiovascular disease is
a. 1
b. 2
c. 3
d. 4
e. 11
(d) the AHA limit is 0.04 mg, compared to 0.2 mg in the healthy
patient. 1:200,000 equals 0.005 mg/ml or 0.009 per 1.8 ml
carpule. 4 carpules would thus contain 0.036 mg, which is just
below the 0.04 mg limit
Antibiotics
1. The most frequently asked type of question requires you to be able to
compare various penicillin antibiotics in terms of potency against
certain bugs, allergenicity, drug of choice against certain conditions,
etc. For example:
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