Transcript Therapeutics Week 1

Chapter 9:
Local Anesthetics
Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved.
Chapter 9 Outline
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History
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Ideal local anesthetic
Chemistry
Mechanism of action
Pharmacokinetics
Pharmacologic effects
Adverse reactions
Compositions of local anesthetic solutions
Local anesthetic agents
Vasoconstrictors
Choice of local anesthetic
Topical anesthetics
Doses of local anesthetic and vasoconstrictor
Copyright © 2011, 2007 Mosby, Inc., an affiliate of Elsevier. All rights reserved.
2
Local Anesthetics
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
Haveles (p. 112)
No drugs are used more often in the dental
office than local anesthetic agents

Use can become routine, but these agents have a
potential for systemic effects in addition to desired
local effects
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3
History


Haveles (p. 112) (Figs. 9-1, 9-2)
“Painless” dentistry through use of a local
anesthetic is a relatively recent development


Indigenous South American people chewed leaves
that made them feel better
Tasting it produced not only a loss of taste, but
also of the sensation of pain
cont’d…
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4
History
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Koller noticed that cocaine in the eye
produced complete anesthesia
Sigmund Freud was also experimenting with
cocaine and its effects on the central nervous
system (CNS)

CNS stimulation, toxicity, and the potential for
abuse were quickly recognized as major problems
with the widespread use of cocaine as a local
anesthetic
cont’d…
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5
History
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Einhorn synthesized procaine in 1905; many
years later, its use became common in
dentistry
The amide lidocaine (Xylocaine) was
released in 1952
mepivacaine (Carbocaine) was released in
1960
More recently, bupivacaine (Marcaine) has
been made available for dental use
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6
Ideal Local Anesthetic
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
Haveles (pp. 112-113)
Many local anesthetic agents are not clinically
acceptable


The ideal local anesthetic should possess certain
properties
No local anesthetic in use today meets all of those
requirements, although many acceptable agents
are available
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7
Properties of the Ideal Local
Anesthetic
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Haveles (p. 113) (Box 9-1)
Potent local anesthesia
Reversible local anesthesia
Absence of local reactions
Absence of allergic reactions
Rapid onset
Satisfactory duration
Adequate tissue penetration
Low cost
Stability in solution
Sterilization by autoclave
Ease of metabolism and excretion
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8
Chemistry

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Local anesthetic agents are divided
chemically into two major groups—amides
and esters


Haveles (pp. 113-114) (Table 9-1)
A few agents fall outside these two groups
The importance of this division is associated
with potential allergic reactions

Cross-hypersensitivity between amides and esters
is unlikely
cont’d…
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9
Chemistry

The structure of local anesthetic is composed
of the following three parts
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Aromatic nucleus (R)
Linkage (either an ester or amide, followed by an
aliphatic chain, R)
Amino group
The aromatic nucleus (R) is lipophilic and the
amino group is hydrophilic
Esters are largely metabolized in the plasma
and amides in the liver
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10
Mechanism of Action
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Action on nerve fibers
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Haveles (pp. 113-115) (Fig. 9-3; Box 9-2)
A resting nerve fiber has a large number of positive
ions on the outside and a large number of negative
ions on the inside
The nerve action potential results in the opening
of sodium channels and in inward flux of sodium


This results in a change from the –90-mV potential to
a +40-mV potential
The outward flow of potassium ions repolarizes the
membrane and closes the sodium channels
cont’d…
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11
Mechanism of Action
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
Haveles (p. 114)
Action on nerve fibers
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Local anesthetics attach themselves to specific
receptors in the nerve membrane
After combining with the receptor, local
anesthetics block conduction of nerve impulses by
decreasing the permeability of the nerve cell
membrane to sodium ions
cont’d…
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12
Mechanism of Action
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Decreasing permeability to sodium ions
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Decreases the rate of depolarization of the nerve
membrane
Increases the threshold for excitability
Prevents propagation of the action potential
Local anesthetics may reduce permeability by
competing with calcium for the membrane
binding sites and by preventing the onset of
nerve conduction
cont’d…
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13
Mechanism of Action
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
Haveles (pp. 114-115) (Fig. 9-4)
Ionization factors
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Local anesthetic agents are weak bases occurring
equilibrated between
• Fat-soluble (lipophilic) free base
• Water-soluble (hydrophilic) hydrochloride salt
The proportion in each form is determined by
• The acid dissociation constant (pKa) of the local
anesthetic
• The pH of the environment
cont’d…
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14
Mechanism of Action
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In the acidic pH of the dental cartridge (4.5),
the proportion of the drug in the ionized form
increases, increasing solubility

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Once injected into tissues (pH 7.4), the amount of
local anesthetic in the free-base form increases
This provides for greater tissue (lipid) penetration
cont’d…
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15
Mechanism of Action
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In an acidic environment such as infection or
inflammation (pH lower), the amount of free
base is reduced (more in ionized form)
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This is one reason dental anesthesia with a local
anesthetic is more difficult when infection is present
Other reasons include dilution by fluid,
inflammation, and vasodilation in the area
The free base form is needed to penetrate the
nerve membrane

The cationic form exerts blocking action by binding
to the specific receptor site
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16
Pharmacokinetics
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
Haveles (p. 112)
Absorption depends on its route

When injected into tissues the rate depends on
the vascularity of the tissues
• This is a function of the degree of inflammation present,
the vasodilating properties of the local anesthetic agent,
the presence of heat, or use of massage
cont’d…
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17
Pharmacokinetics
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Haveles (p. 112)
Absorption
 Reducing the systemic absorption of a
local anesthetic is important when it is
used in dentistry
• With reduced absorption, the chance of
systemic toxicity is reduced
cont’d…
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18
Pharmacokinetics
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A vasoconstrictor is added to the local
anesthetic to reduce absorption
The vasoconstrictor
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Reduces the blood supply to the area
Limits systemic absorption
Reduces systemic toxicity
cont’d…
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19
Pharmacokinetics
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
Haveles (p. 112)
Absorption
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With topical application, especially on mucous
membranes or if the surface is denuded,
absorption can approximate that produced by
intravenous injection
It is also determined by the proportion of the agent
present in the free-base form (nonionized)
cont’d…
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20
Pharmacokinetics
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
Haveles (p. 115)
Distribution
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After absorption, local anesthetics are distributed
throughout the body
• Highly vascular organs have higher concentrations of
anesthetics

Local anesthetics cross the placenta and bloodbrain barrier
• Lipid solubility affects the potency of the agent
• Bupivacaine 0.5% is about 10 times more lipid soluble
than lidocaine used as a 2% solution
cont’d…
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21
Pharmacokinetics
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
Haveles (p. 115)
Metabolism
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Local anesthetic agents are metabolized
differently, depending on whether they are amides
or esters
• Esters are hydrolyzed by plasma pseudocholinesterases
and liver esterases
• Procaine is hydrolyzed to para-aminobenzoic acid
(PABA), a metabolite that may be responsible for its
allergic reaction
cont’d…
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22
Pharmacokinetics
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
Haveles (p. 115)
Metabolism
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Amide local anesthetics are metabolized primarily
by the liver
• In severe liver disease or with alcoholism, amides may
accumulate and produce systemic toxicity


A small amount of prilocaine is metabolized to
orthotoluidine, which can produce
methemoglobinemia if given in very large doses
Cimetidine can interfere with metabolism of
amides by reducing hepatic blood flow
cont’d…
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23
Pharmacokinetics
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
Haveles (p. 115)
Excretion
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Metabolites and some unchanged drug of both
esters and amides are excreted by the kidneys
Both parent drug and metabolites can accumulate
with end-stage renal disease
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24
Pharmacologic Effects


Haveles (pp. 115-116)
Peripheral nerve conduction (blocker)

The main clinical effect of local anesthetic is
reversible blockage of peripheral nerve conduction
• These agents inhibit movement of the nerve impulse along
the fibers, at sensory endings, at myoneural junctions, and
at synapses


They do not penetrate the myelin sheath, but they
affect myelinated fibers only at the nodes of Ranvier
Local anesthetics affect small, unmyelinated fibers
first and large; heavily myelinated fibers last
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25
Common Order of Nerve
Function Loss
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Haveles (p. 116) (Box 9-3)
Autonomic
Cold
Warmth
Pain
Touch
Pressure
Vibration
Proprioception
Motor
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26
Pharmacologic Effects
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
Haveles (pp. 115-116)
Antiarrhythmic
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Local anesthetics have a direct effect on cardiac
muscle by blocking cardiac sodium channels and
depressing abnormal cardiac pacemaker activity,
excitability, and conduction
• They also depress strength of cardiac contraction and
produce arteriolar dilation, leading to hypotension

These properties make than useful in treatment of
arrhythmias
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27
Adverse Reactions
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
Haveles (p. 116) (Table 9-2)
Toxicity
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Adverse reactions and toxicity are directly related
to the plasma level of the drug
• Their potential for danger must be minimal
• Deaths from local anesthetics are difficult to document,
dental-related mortality is even rarer
cont’d…
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28
Adverse Reactions
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Factors influencing toxicity include

Drug: inherent toxicity and amount of vasodilation
 Concentration
 Route of administration
 Rate of injection
 Vascularity
 Patient’s weight
 Rate of metabolism and excretion
cont’d…
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29
Adverse Reactions
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Haveles (p. 116)
Toxicity
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CNS effects
CNS stimulation may occur before CNS
depression
• CNS stimulation caused by depression of inhibitory fibers
results in restlessness, tremors, and convulsions
• CNS depression caused by depression of both inhibitory
and facilitative fibers results in respiratory and
cardiovascular depression, and coma follows
cont’d…
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30
Adverse Reactions
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
Haveles (pp. 116-117)
Toxicity
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Cardiovascular effects
• Local anesthetic agents can produce myocardial
depression and cardiac arrest with peripheral vasodilation
• Usual concentrations that are achieved with administration
of dental anesthesia would not be expected to result in
any of these adverse reactions
• It is postulated that the effect of these agents on heart
conduction may produce a fatal arrhythmia
cont’d…
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31
Adverse Reactions
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
Haveles (pp. 116-117)
Local effects
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
Most commonly the result of physical injury
caused by injection technique or administration of
an excessive volume too quickly to be accepted
by the tissues
Occasionally a hematoma may be produced
cont’d…
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32
Adverse Reactions


Haveles (p. 117)
Malignant hyperthermia
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An inherited disease that is transmitted as an
autosomal-dominant gene with reduced penetration
and variable expression
Symptoms include an acute rise in calcium, which
produces muscular rigidity, metabolic acidosis, and
extremely high fever
• Mortality is above 50%
Treatment includes supportive measures and the
administration of dantrolene
cont’d…
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33
Adverse Reactions
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In the past, it was thought that amide local
anesthetics might precipitate malignant
hyperthermia, but they are currently no longer
implicated

Patients with a family history of malignant
hyperthermia can be given amide local anesthetic
agents
cont’d…
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34
Adverse Reactions
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
Haveles (p. 117)
Pregnancy and nursing considerations
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Elective dental treatment should be rendered
before a patient becomes pregnant
Most sources suggest that lidocaine may be
administered to a pregnant woman if dental
treatment is needed
cont’d…
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35
Adverse Reactions
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Pregnancy and nursing considerations

Fetal bradycardia has been reported when larger
doses are administered to the mother near term
• Lidocaine and prilocaine are U.S. Food and Drug
Administration (FDA) pregnancy category B
• Mepivacaine, articaine, and bupivacaine are FDA
pregnancy category C
cont’d…
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36
Adverse Reactions
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
Haveles (p. 117)
Allergy
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Allergic reactions that result from local anesthetics
have been reported
• They range from rash to anaphylactic shock
An allergy history should be elicited from each
patient before a local anesthetic agent is chosen
Esters have a much greater allergic potential;
some question has surfaced about whether
amides can produce allergic reactions at all
cont’d…
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37
Adverse Reactions
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
Haveles (p. 117)
Allergy
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Patients giving a history of allergies to all local
anesthetic agents may be “tested” by giving them
an amide by injection
Use of skin testing is unreliable; it can give both
false-positive and false-negative results
cont’d…
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38
Adverse Reactions
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
Haveles (p. 117)
Allergy

Another approach is to use the antihistamine
diphenhydramine (Benadryl) as a local anesthetic
 Antihistamines, because of their similarity in
structure to local anesthetics, have some local
anesthetic action
 diphenhydramine (Benadryl) in a concentration of
1% plus 1:100,000 epinephrine is recommended
to be given by injection to produce a block
• No prepared product is available; this combination must
be prepared from its constituents
cont’d…
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39
Adverse Reactions

Allergy

Local anesthetics with vasoconstrictors also
contain a sulfite that serves as an antioxidant
• In sulfite-sensitive patients, the sulfites may produce a
hypersensitivity reaction that exhibits itself as an acute
asthmatic attack
• The reaction is the same as the “salad bar” syndrome, a
hypersensitivity reaction to sulfites
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40
Composition of Local Anesthetic
Solutions
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
Haveles (pp. 117-118)
Local anesthetic usually contains several other
ingredients such as the following

Vasoconstrictor: to retard absorption, reduce
systemic toxicity, and prolong duration of action
 Antioxidant: to retard oxidation of epinephrine
 Sodium hydroxide: to adjust the pH between 6 and 7
 Methylparaben and propylparaben: preservatives
added to multidose parenteral solutions
• No dental cartridge contains methylparaben
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41
Local Anesthetic Agents
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
Haveles (p. 118)
Amides

Many local anesthetic agents are available with
similar pharmacologic and clinical effects and
systemic toxicity
• Dental issues associated with local anesthetics are listed
in Box 9-4
• Table 9-3 lists the local anesthetics available in dental
cartridges
cont’d…
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42
Local Anesthetic Agents
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
Haveles (p. 118)
Amides

The only class of anesthetics used parenterally
• Esters are occasionally used topically
• The relative lack of allergenicity of the amides is probably
responsible for this
cont’d…
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43
Local Anesthetic Agents
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
Haveles (pp. 118-120)
Amides: lidocaine



Introduced in 1948, it became an anesthetic
standard to which other local anesthetics were
compared
Rapid onset related to its tendency to spread well
through the tissues
Lidocaine 2% with vasoconstrictor provides
profound anesthesia of medium duration
• The local anesthetic solution most commonly used in
dental offices
cont’d…
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44
Local Anesthetic Agents
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
Haveles (p. 118) (Fig. 9-5)
Amides: lidocaine
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No cross-allergenicity among the amide lidocaine,
other available amides, or esters has been
documented
In toxic reactions, one is likely to observe CNS
depression initially rather than the CNS stimulation
characteristic of other local anesthetics
Adverse reactions include hypotension, positional
headache, and shivering
cont’d…
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45
Local Anesthetic Agents
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
Haveles (p. 119)
Amides: lidocaine

In dentistry, lidocaine 2% with 1:100,000
epinephrine is used for infiltration and block
anesthesia
• Lidocaine is used for topical anesthesia as a 5%
ointment, a 10% spray, and a 2% viscous solution

Lidocaine with epinephrine 1:100,000 provides a
1.0- to 1.5-hour duration of pulpal anesthesia
• Soft-tissue anesthesia is maintained for 3 to 4 hours
cont’d…
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46
Local Anesthetic Agents
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
Haveles (p. 119)
Amides: lidocaine


A new dose form of lidocaine is a patch applied to
mucosal membranes for local anesthesia
Its maximal effect occurs after about 10 minutes,
which is probably too long to wait
cont’d…
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47
Local Anesthetic Agents
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
Haveles (p. 119)
Amides: mepivacaine
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
Introduced in 1960, its rate of onset, duration,
potency, and toxicity are similar to those of
lidocaine
Mepivacaine is not effective topically; however, it is
used for infiltration, block, spinal, epidural, and
caudal anesthesia
The usual dose form in dentistry is a 2% solution
with addition of 1:20,000 levonordephrin (NeoCobefrin) as a vasoconstrictor
cont’d…
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48
Local Anesthetic Agents
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
Haveles (p. 119)
Amides: mepivacaine


Because mepivacaine produces less vasodilation
than lidocaine, it can be used as a 3% solution
without a vasoconstrictor
Can be used for short procedures when a
vasoconstrictor is contraindicated
cont’d…
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49
Local Anesthetic Agents
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
Haveles (p. 119)
Amides: prilocaine



Prilocaine is related chemically and
pharmacologically to both lidocaine and mepivacaine
Chemically, lidocaine and mepivacaine are xylidine
derivatives, whereas prilocaine is a toluidine
derivative
Prilocaine appears to be less potent and less toxic
than lidocaine and has a slightly longer duration of
action
cont’d…
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50
Local Anesthetic Agents


Haveles (p. 119)
Amides: prilocaine



Although toxicity of prilocaine is 60% that
occurring with lidocaine, several cases of
methemoglobinemia have been reported after its
use
Prilocaine is metabolized to orthotoluidine and in
large doses can induce some methemoglobinemia
Prilocaine should not be administered to patients
with any condition in which problems of
oxygenation may be especially critical
cont’d…
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51
Local Anesthetic Agents


Haveles (p. 119)
Amides: prilocaine



Drugs that affect the hemoglobin, such as
acetaminophen, may exacerbate the adverse
reaction
Prilocaine is used for infiltration, block, epidural,
and caudal anesthesia
It is available in dental cartridges as a 4%
concentration both with and without 1:200,000
epinephrine
cont’d…
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52
Local Anesthetic Agents


Haveles (p. 119)
Amides: prilocaine



Prilocaine’s niche in dentistry involves situations in which
the desired duration of action is somewhat longer than
that obtained with mepivacaine both without and with
vasoconstrictor
Prilocaine plain has a duration of action slightly longer
than mepivacaine plain, and prilocaine with epinephrine
has a duration of action slightly longer than lidocaine
with epinephrine
The other potential advantage of prilocaine is that the
concentration of epinephrine (1:200,000) is lower than in
other local anesthetic amide combinations
cont’d…
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53
Local Anesthetic Agents


Haveles (p. 119)
Amides: bupivacaine

Bupivacaine is related to lidocaine and mepivacaine
 More potent but less toxic than the other amides
 The major advantage is its greatly prolonged
duration of action
 Indicated in lengthy dental procedures when pulpal
anesthesia of greater than 1.5 hours is needed or
when postoperative pain is expected
cont’d…
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54
Local Anesthetic Agents


Haveles (p. 119)
Amides: bupivacaine



Available in dental cartridges as a 0.5% solution
with 1:200,000 epinephrine
Should not be used in patients prone to selfmutilation
Bupivacaine has been used for infiltration, block,
and peridural anesthesia
cont’d…
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55
Local Anesthetic Agents


Haveles (p. 119)
Amides: articaine

Articaine was approved for use in the United
States in 2000
• Its delay in the United States was a result of the addition
of methylparaben to both multidose vials and single-dose
cartridges

Articaine is derived from thiophene
• This allows for greater lipid solubility and ability to cross
lipid barriers such as nerve membranes
• This mechanism may account for its enhanced action
compared with other local anesthetics
cont’d…
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56
Local Anesthetic Agents


Haveles (p. 119)
Amides: articaine

Articaine also differs from other amide local
anesthetics because it has an extra ester linkage
• This extra linkage causes articaine to be hydrolyzed by
plasma esterase
• Only 5% to 10% of articaine is metabolized by the liver;
the other 90% to 95% is metabolized in the blood
cont’d…
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57
Local Anesthetic Agents


Haveles (p. 120)
Amides: articaine




Articaine is excreted by the kidneys
The average patient can tolerate twice as much
lidocaine as compared with articaine before the
maximal dose is reached
Articaine, similar to prilocaine, may cause
methemoglobinemia in very high doses
Articaine rarely causes paresthesia after a
mandibular block when the 4% solution is used
cont’d…
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58
Local Anesthetic Agents


Haveles (p. 120)
Amides: articaine


Articaine is used for local, infiltrative, and
conductive anesthesia
Available as a 4% concentration with 1:100,000
epinephrine in a 1.7 ml cartridge unlike the more
common 1.8 ml dental cartridge
cont’d…
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59
Local Anesthetic Agents


Haveles (p. 120)
Esters


No esters are currently available in a dental
cartridge
Esters, such as benzocaine, are commonly used
topically
cont’d…
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60
Local Anesthetic Agents


Haveles (p. 120)
Esters: procaine




Procaine is a PABA ester
Procaine is used as an antiarrhythmic agent and is
combined with penicillin to form procaine penicillin G
Procaine is not used in dentistry today because of
the high rate of allergic reaction
The allergic reaction is usually a result of PABA and
not procaine
cont’d…
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61
Local Anesthetic Agents


Haveles (p. 120)
Esters: propoxycaine

Propoxycaine, another ester of PABA, is not
available in a dental cartridge
cont’d…
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62
Local Anesthetic Agents


Haveles (p. 120)
Esters: tetracaine



Tetracaine, an ester of PABA, has a slow onset
and long duration, and is generally estimated to
have at least 10 times the potency and toxicity of
procaine
Great care must be exercised if used for topical
anesthesia
Tetracaine is available in various sprays, solutions,
and ointments for topical application
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63
Other Local Anesthetics


Haveles (p. 120)
Dyclonine



Dyclonine is a topical local anesthetic that is
neither an ester nor an amide
Its side effects involving the cardiovascular system
and CNS are similar to those of the other local
anesthetics
The onset of local anesthesia is 2 to 10 minutes,
and its duration is 30 to 60 minutes
cont’d…
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64
Other Local Anesthetics


Haveles (p. 120)
Benzonatate


Benzonatate is a tetracaine congener indicated in
the management of nonproductive cough
A topical anesthetic that acts on the respiratory
stretch receptors, which produces its antitussive
properties
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65
Vasoconstrictors


Haveles (p. 120) (Box 9-5)
Overview

Vasoconstricting agents are included in local
anesthetic solutions for many reasons
• Vasoconstrictors are members of the autonomic nervous
system drugs call the adrenergic agonists or
sympathomimetics
• When a local anesthetic solution does not contain a
vasoconstrictor, the anesthetic drug is more quickly removed
from the injection site and distributed into systemic circulation
than if the solution contained a vasoconstrictor
• Any anesthetic given without a vasoconstrictor is more likely
to be toxic than those given without a vasoconstrictor
cont’d…
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66
Vasoconstrictors


Haveles (p. 121) (Figs. 9-6, 9-7)
Overview

The decision about whether epinephrine should be
used in a patient is made by weighing the risks and
benefits
 A sufficient concentration must be used to keep the
local anesthetic localized at its site of action and
provide adequate depth, duration, and low systemic
toxicity of the anesthetic
 1:100,000 and 1:200,000 produce about the same
amount of vasoconstriction and the same distribution
of the local anesthetics
cont’d…
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67
Vasoconstrictors


Haveles (p. 121) (Fig. 9-7)
Overview


Research shows that a patient can produce endogenous
epinephrine far in excess of that administered in dentistry
in the presence of inadequate anesthesia, which
sometimes occurs when vasoconstrictors are avoided
Patients with uncontrolled high blood pressure,
hyperthyroidism, angina pectoris, and cardiac arrhythmias
and those who have had a myocardial infarction or
cerebrovascular accident in the past 6 months should
make an appointment for elective dental treatment after
their medical condition is under control
cont’d…
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68
Vasoconstrictors


Haveles (p. 122) (Table 9-4)
Overview

Patients with cardiovascular disease who are able to
withstand elective dental treatment can receive
epinephrine-containing local anesthetic agents
 Anesthetic should be administered in the lowest
possible dose by means of the best technique,
including aspiration and a very slow injection rate to
minimize systemic absorption
 The maximal safe dose of epinephrine for the healthy
patient is 0.2 mg and for the cardiac patient is 0.04 mg
cont’d…
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69
Vasoconstrictors


Haveles (p. 122)
Drug interactions


The two epinephrine drug interactions that are
most likely to be clinically significant
Tricyclic antidepressants
• Administration of epinephrine may produce an
exaggerated increase in pressor response

Nonselective β-blockers
• Hypertension and reflex bradycardia may be exhibited
cont’d…
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70
Vasoconstrictors


Drug interactions


The two drug interactions commonly mentioned but not
usually clinically significant are
Monoamine oxidase inhibitors (MAOIs)



Haveles (p. 122)
Epinephrine can be given to patients taking MAOIs,
because epinephrine is eliminated primarily by reuptake
and secondarily by catechol-O-methyltransferase
(COMT) rather than by monoamine oxidase (MAO)
Indirect acting sympathomimetic agents should be
avoided in patients taking MAOIs
Phenothiazines

Phenothiazines are α-blockers, and when an α- and βagonist is given, the beta effects predominate
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71
Choice of Local Anesthetic


Haveles (pp. 122-124) (Figs. 9-8, 9-9; Box 9-6; Table
9-6)
Local anesthetic should be chosen depending
on the duration of local anesthesia desired and
the side effects that must be avoided

pKa is related to duration of action
• With lower pKa, the local anesthetic is distributed more in the
base form and so is better absorbed


Duration of action is primarily related to its proteinbinding capacity
• Duration is unrelated to the local anesthetic’s half-life
Lipid solubility determines the potency of a local
anesthetic agent
cont’d…
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72
Choice of Local Anesthetic


Haveles (pp. 123, 125) (Table 9-7)
The vasodilating property can affect both the
potency and duration of action


The dental practitioner should become familiar
with a short-, an intermediate-, and a long-acting
agent
The duration of the procedure and any patientspecific information will determine the anesthetic
of choice
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73
Topical Anesthetics


Haveles (p. 123) (Table 9-8)
Benzocaine, an ester, is the most commonly
used topical anesthetic



Lidocaine, an amide, is the second most
commonly used
Comparison should take into account their onset,
duration of action, and allergenic potential
The patient should be instructed to avoid eating
for 1 hour after application to oral mucosa so that
the gag reflex can become fully functional
cont’d…
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74
Topical Anesthetics


Haveles (pp. 123-124)
Amides: lidocaine

Lidocaine is available as the base or hydrochloride
salt
• The base is preferred when large areas of the mucosal
surface are ulcerated, abraded, denuded, or erythematous

Base is available as a jelly and an oral topical solution
• The hydrochloride salt is water soluble and penetrates the
tissue better

Hydrochloride is available as an ointment, an oral topical, and
an oral aerosol
cont’d…
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75
Topical Anesthetics


Haveles (p. 124)
Amides: lidocaine and prilocaine (injection-free
local anesthesia)



The combination of lidocaine and prilocaine gel
(Oraqix) applied into the periodontal pocket offers pain
relief during scaling and root planing procedures
Lidocaine provides rapid anesthesia, and prilocaine
has a slower onset of action
The more common side effects include pain,
soreness, irritation, edema or redness at the area of
application, and taste changes
cont’d…
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76
Topical Anesthetics


Haveles (p. 124)
Esters: benzocaine



Benzocaine, an ester of PABA, cannot be
converted to a water-soluble form for injection
Poorly absorbed and lacks significant systemic
toxicity
Benzocaine is used in many dental offices,
although a hypersensitivity reaction is possible
cont’d…
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77
Topical Anesthetics


Haveles (pp. 124-125)
Esters: cocaine


Cocaine is a naturally occurring ester of benzoic
acid that is potent and extremely toxic
Although cocaine has ideal pharmacokinetics, the
systemic absorption and subsequent CNS
stimulation and its great potential for abuse make
the use of cocaine as a local anesthetic untenable
cont’d…
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78
Topical Anesthetics


Haveles (p. 125) (Box 9-7)
Precautions in topical anesthetics


Some local anesthetics are absorbed rapidly when
applied topically to mucous membranes
To avoid toxic reactions from surface anesthesia,
the dental health care provider should consider
many factors
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79
Doses of Local Anesthetic and
Vasoconstrictor


Haveles (pp. 125-126)
The amounts of local anesthetic and
vasoconstrictor contained in a certain volume
of solution can be calculated from the
concentration of that solution


The dental health care provider should be able to
determine the number of milligrams of both local
anesthetic and vasoconstrictor given in any clinical
situation
The maximal safe dose for each component
should not be exceeded
cont’d…
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80
Doses of Local Anesthetic and
Vasoconstrictor


Haveles (p. 126)
Each dose should be recorded in the patient’s
chart as soon as possible after the injection

Information recorded should include the strength
of both ingredients and the volume of solution
used or the number of milligrams of each given
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81