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This is the second of seven pages which constitute a course in
local anesthetics. Each page stands on its own, however for a thorough
understanding of dental local anesthetics the reader is advised to read the
pages in order. <==Anesthetic
agents and their history
Toxicity and
dosage==>
Vasoconstrictors
  No
matter how quickly an anesthetic agent can enter a nerve, the local blood vessels
begin to absorb the unused anesthetic as soon as it is injected. In order
to slow this process down, manufacturers of these solutions add a substance
that in low concentrations acts to cause the local blood vessels to constrict,
or narrow down. This restricts the amount of blood and plasma entering and
leaving the site of the injection which has the net effect of slowing the
vascular absorption of the anesthetic solution. This keeps the unused
anesthetic solution in place longer and prolongs the action of the drug. The substance used to do this is called a vasoconstrictor
(vaso refers to blood vessels and constriction means to close down). The
vasoconstrictor used is the naturally  occurring hormone epinephrine or one of
its analogs called levonordefrin.
Epinephrine is an ideal
vasoconstrictor because it is manufactured naturally by the body as adrenaline, sometimes called the "fight or flight hormone". In
addition to causing a constriction of blood supply, if it
enters the general circulation it can cause an increased
heart rate and stronger heart beat, along with a feeling of nervousness. These side effects account for the
"rush" that some people feel after receiving an anesthetic shot.
The
downside to vasoconstrictors Most
anesthetic solutions are sold with added vasoconstrictor. Only two,
mepivicaine and
prilocaine are
sold with or without vasoconstrictor (prilocaine is sold under the trade name
Citanest®).
Mepivicaine and prilocaine have the advantage of producing only minor vasodilation and, though both are short acting without their
vasoconstrictor added, they still produce adequate anesthesia for short
procedures. The major advantage
of using an anesthetic without a vasoconstrictor is that there are virtually no
interactions with other drugs the patient may be taking. Vasoconstrictors
may not be used with certain types of blood pressure medications or tricyclic antidepressants. The use of vasoconstrictor does
carry one additional penalty for the practitioner. These naturally
occurring hormones are not very stable, and must be stabilized by the addition
of an acidic preservative. The presence of the preservative can lower the
PH of the anesthetic solution to the range of 3.8 to 5.0, thus reducing the
amount of the neutral basic radical (RN) and slowing the onset of action of the
anesthetic. This effect is, thankfully not especially significant,
and anesthesia with vasoconstrictor is far and away the most popular choice
among practitioners when other clinical considerations permit its use.
Carpules that do not contain vasoconstrictor do not contain preservatives
either. This is an important point, since it is most frequently
the preservatives, and not the anesthetics themselves which play a roll in
allergic
reactions. Vasoconstrictors
are also not used in any body area in which the blood supply must "double
back" on itself. This includes such blind ended appendages as the tip of
the nose, or the fingers or toes. In these areas, a vasoconstrictor may
block all blood flow to the appendage causing tissue necrosis (death of the
tissue). Finally, the preservatives necessary to stabilize
the vasoconstrictor are sulfides, and these can cause allergic reactions.
There has never been a documented case of allergy to the modern amine based
anesthetics themselves, however, many people are allergic to to the
preservatives associated with the vasoconstrictor. If you believe that
you are allergic to dental anesthesia, ask the dentist to use mepivicaine or
prilocaine without vasoconstrictor.
Vasoconstrictor concentrations The concentration of
vasoconstrictor in any given carpule of anesthesia is denoted by a ratio of
vasoconstrictor per mL of solution. For example, a solution may be labeled as
1:100,000. This concentration represents 1000mg/100,000mL or 0.01mg/mL, or 1
gram per 100 Liters. A 1:1000 solution translates to 1 mg vaoconstrictor
per mL of solution, or 1 gram per Liter. Here are some others:
| CONCENTRATION |
DOSAGE EQUIVALENCE |
PERCENT |
| 1:1,000 |
1mg/mL |
0.1% |
| 1:10,000 |
0.1mg/mL |
0.01% |
| 1:100,000 |
0.01mg/mL |
0.001% |
| 1:200,000 |
0.005mg/mL |
0.0005% |
Most anesthetic solutions contain the minimum amount of
anesthesia necessary to constrict local blood vessels and prolong the action of
the anesthetic. Some, however, contain a higher concentration of
vasoconstrictor for use in controlling bleeding for specific purposes, such as
periodontal surgery. For example, general purpose lidocaine contains
epinephrine in the amount of 1/100,000 for producing profound, prolonged
anesthesia. However, lidocaine also comes with epinephrine at twice the
normal concedntration (1/50,000) used mostly by periodontists who need to
control gingival bleeding during surgery.
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Indications and
contraindications for vasoconstrictor
Drugs and conditions of concern to the dentist
The use of vasoconstrictor in dentistry has been
shown over time to be very safe for almost all patients. In
fact, the use of vasoconstrictor is highly recommended due to the
increase in efficacy and longevity of dental anesthesia.
There are no absolute
contraindications to the use of vasoconstrictors in dental local
anesthetics, since epinephrine is an endogenously produced
neurotransmitter. In 1964, the American Heart Association and the
American Dental Association concluded a joint conference by stating
that “the typical concentrations of vasoconstrictors contained in
local anesthetics are not contraindicated with cardiovascular
disease so long as preliminary aspiration is practiced, the agent is
injected slowly, and the smallest effective dose is administered."
Still, there are a few
situations in which the use of vasoconstrictor should be reduced.
The California dental
association provided some of the following information:
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Conditions in which vasoconstrictor
should be avoided or kept to a minimum
-
Uncontrolled hypertension
-
Uncontrolled hyperthyroidism
-
Patients with angina
-
patients who have recently had a
myocardial infarction
-
Patients taking NON SELECTIVE
Beta Blockers (see table below)
-
Patients taking tricyclic
antidepressants (See table below)
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| Note that patients with hyperthyroidism or
hypertension who’s conditions are properly stabilized
with medication (except non selective beta blockers) may
be anesthetized with reasonable doses of anesthetic
solution containing vasoconstrictor. |
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The following is a
list of non selective beta blockers. If the
patient is taking one of these, vasoconstrictor
should be avoided
carteolol (Cartol)
carvedilol (Coreg)
labetolol (Normodyne, Trandate)
nadolol (Corgard)
penbutolol (Levatol)
pindolol (Visken)
**propranolol (Inderal)**
sotalol (Betapace)
timolol (Blocarden)
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The following is a
list of tri-cyclic antidepressants. If the patient
is taking one of these, the amount of vasoconstrictor
should be restricted to no more than 3 carpules of
1/100,000
amitriptyline (Elavil)
amoxapine (Asendin)
clomipramine (Norpramin)
doxepin (Sinequan)
imipramine (Tofranil)
nortriptyline (Aventyl, Pamelor)
protriptyline (Vivactil)
trimipramine (Surmontil) |
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| Cocaine
IS ALWAYS DANGEROUS WHEN COMBINED WITH A
VASOCONSTRICTOR. Patients strung out on
cocaine are at risk for fatal arrhythmias and must be
treated with extreme care. |
Vasoconstrictors are NOT
contraindicated (ie. they are acceptable within
accepted guidelines) if the patient is taking drugs within the
classifications below:
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Selective Beta blockers
acetutolol (Sectral)
atenolol (Tenormin)
betaxolol (Kerlone)
bisoprolol (Zebeta)
esmolol (Brevibloc)
metoprolol (Lopressor)
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Miscellaneous Antidepressants
buprion (Wellbutrin)
maprotiline (Ludiomil)
mirtazapine (Remeron)
nefazodone (Serzone)
trazodone (Desyrel)
venlafaxine (Effexor)
|
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Monoamine Oxidase Inhibitors
phenelzine (Nardil)
tranylcypromine (Parnate)
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Alpha/Beta Adrenergic Blocking
carvedilol (Coreg)
labetolol (Normodyne, Trandate) |
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Selective Serotonin Reuptake
Inhibitors
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fluoxetine (Prozac)
fluvoxamine (Luvox)
paroxetine (Paxil)
sertraline (Zoloft) |
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<==Anesthetic
agents and their history
Toxicity and
dosage==>
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