Chapter 9 Flashcards
Most often used drug in dentistry
Local anesthetics
What was the first local anesthetic
Cocaine
Properties of the ideal local anesthetic
- Potent local anesthesia
- Reversible local anesthesia
- Abscence of local reactions
- Abscence of allergic reactions
- Rapid onset
- Satisfactory onset
- Adequate tissue penetration
- Low cost
- stability in solution
- sterilizatioln in autoclave
- ease of metabolism and excretion
2 major groups of local anesthetics
Esters
Amides
Other —> minor group
Where are esters metabolized
in the plasma
Where are amides metabolized
in the liver
Components of local anesthetic
- Aromatic nucleus - lipophilic ( lipid soluble )
- Linkage ( ester or amide, followed by aliphatic chain )
- Amino group - hydrophilic ( water soluble )
Why is it important to know if a local anesthetic is an ester or amide?
Potential allergic reactions
What if a person is allergic to one agent in a group of anesthetics?
They are likely to be alergic to another agent in that group
Cross hypersensitivity between the amides and esters
is unlikely
Cation
Ion with a positve charge
Anion
Ion with a negative charge
Resting nerve
Has a large number of positive ions ( cations ) on the outside and a large number of negative ions ( anions ) on the inside
Membrane potentions of -90 mV to -60 mV charge
What happens when an action potention goes from -90 mV to 40 mV
It triggers the efflux of potassium until a resting action potential of -90 mV is reestablished
What happens when local anesthetics bind to receptors in the nerve membrane and blocks conduction of the nerve impulse by decreasing the permeability of the cell membrane to sodium ions
Increases the threshold of excitability and prevents the propagation of the action potential
pH of local anesthetics without vasoconstrictors
range in pH from 5 to greater than 6
pH of local anesthetics with vasocontrictors
range in pH from 3 yo 5 because of the addition of sodium bisulfate
Local anesthetics occur in equilibrium between 2 forms
A free base and a salt
Free base
Viscid liquids or amorphous solids Fat soluble Unstable Alkaline Uncharged, nonionized Penetrates nerve tissue Form present in tissue ( pH 7.4 )
Salt
Crystaline solids Water soluble Stable Acidic Charged, cation ( ionized ) Active form at side of actions Form present in dental cartridge ( pH 4.5 - 6.0 )
Proportion of drug in each form is determined by
pK
pH of the environment
pK
The pH at which half is in each form ( base and acid equally)
If there is a dental infection or abscess in the area to be injected will anesthesia be more difficult to achieve?
Yes
The area prior to injection is more acidic than normal with a lower pH with what?
Dental infection or abscess
The nonionized form is needed for?
to penetrate the nerve membrane
The ionized form is needed to?
Exert the blocking action by binding to the specific receptor site
Local anesthetics: Pharmacokinetics
Absorptions depends on its route
Rate of absorption depends on vascularity of the tissues
Degree of inflammation present
Vasodilating properties of the local anesthetic agent
Presence of heat
Use of massage
The vasoconstrictor
The vasoconstrictor
Reduces the blood supply to the area
Limits systemic absorption
Reduces systemic toxicity
Local anesthetics: Absorptions
Mucous membranes or denuded surface = increased absorption
Absorption also determine by the proportion of the agent present in the free-base form (nonionized)
Local anesthetics: Distribution
Highly vascular organs have higher concentrations of anesthetics
Local anesthetics cross the placenta and blood-brain barrier
Lipid solubility affects the potency of the agent
Esters are hydrolyzed by
plasma pseudocholinesterases and liver esterases
Amides are metabolized by the
liver
Cimetidine (Tagamet)
reduces hepatic blood flow and may increase the systemic level of an amide
What is the function or pharmacologic effect of a local anesthetic?
Blocks the conduction of peripheral nerves
Produces an antiarrhythmic effect on the heart
Order of nerve function loss when losing local anesthetics
Autonomic (first)
Pain (middle)
Motor (last)
Pharmacologic effects
Direct effect on cardiac muscles Block cardiac sodium channels Depress abnormal cardiac pacemaker activity, excitability, and conduction Depress strength of cardiac contraction Produce arteriolar dilation Treatment of arrhythmias
Adverse reactions of local anesthetics
Directly related to the plasma level of the drug
These peopl are more prone to adverse or toxic effects of local anesthetics
Children, elderly, and debilitated
Adverse reaction toxicity affecting the CNS system
CNS stimulation
CNS depression
Adverse reaction toxicity affecting cardiovascular system
Myocardial depression
Cardiac arrest with peripheral vasodilation
Usual concentrations not expected to result in any of these adverse reactions
Adverse reaction local effects
Result of injection technique
Result of administration of an excessive volume too quickly
Hematoma
An inherited disease that is transmitted as an autosomal-dominant gene
Malignant hyperthermia
Malignant hyperthermia
Acute rise in calcium leading to muscular rigidity, metabolic acidosis, and extremely high fever; mortality rate 50%
dantrolene (Dantrium)
Used to treat malignant hyperthermia
Lidocaine and Prilocaine FDA pregnancy category
B
Mepivacaine, Articaine, Bupivacaine FDA pregnancy category
C
Have a much higher allergic potential
Esters
Sulfite
a component of local anesthetics with a vasoconstrictor.
it serves as an antioxidant but may be associated with allergic reactions
Vasoconstrictor - Epinephrine
Retards absorption, reduce systemic toxicity, and prolong duration of action
Most commonly used dental anesthetic
Lidocaine
2% lidocaine with 1:100,000 epinephrine
provides 1-1.5 hours of pulpal anesthesia and 3-4 hours of soft tissue anesthesia
Not effective topically
Mepivacaine (Carbocaine, Polocaine, Isocaine)
Prilocaine
Toludine derivitave
Less potent and less toxic then lidocaine
Bupivacaine
More potent and toxic the lidocaine and mepivacaine
Prolonged duration of action, useful for dental surgery
Should not be used in children or mentally challenged patients
Articaine
Derived from thiophene
Greater lipid solubility
Hydrolyzed by plasma esterase
Metabolized mainly in blood
in a 1.7 ml cartidge unlike the more common 1.8 ml dental cartridge
Articaine (Septocaine)
Commonly used ester topically
Benzocaine
Procaine (Novocain)
Not used in dentristy
Vasoconstrictors
Prolong the duration of action
Increase the depth of anesthesia
Delay systemic absorption
Reduce the toxic effect in the systemic circulation
Members of the autonomic nervous system drugs called the sympathomimetics or adrenergic agonists
vasoconstrictors
Tricyclic antidepressants
Administration of epinephrine may produce an exaggerated increase in pressor response
Nonselective B-blockers
Administration of epinephrine may produce hypertension and reflex bradycardia
Epinephrine cardiac dose
0.04 mg
Epinephrine healthy patient
0.2 mg
Second most commonly used topical anesthetic
Lidocaine
