Lidocaine is not typically administered by the intramuscular route. Lidocaine is an amide local anesthetic that can be administered as a topical, infiltration, block, spinal, epidural, and caudal anesthesia. It also can be used intravenously to treat cardiac arrhythmias during surgery.
Patients with severe liver disease or alcoholism may be unable to break down the local anesthetic, so the amount of amide local anesthetic and other drugs should be decreased to prevent systemic toxicity.
Local anesthetic should not be administered
Local anesthetics must be in a weak base form that is equilibrated in a fat-soluble free base and a water-soluble hydrochloric salt. The dental cartridge is acidic (4.5), increasing solubility in the liquid medium. Once injected into the tissue, which is slightly basic (7.4), the amount of the free-base form increases, providing greater tissue penetration, meaning that the local anesthetic must be primarily nonionized for tissue absorption. If the tissue in inflamed, the pH drops, increasing the ionized portion and making the local anesthetic less effective.
Weak acid form
Weak base form
The faster the rate of injection is, the less the local area can accept the volume injected. This decreases the amount of local anesthetic that enters systemic circulation.
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Both statements are true.
The addition of a vasoconstrictor to local anesthetic prolongs the duration of action, increases the depth of anesthesia, and reduces systemic toxicity by keeping the local anesthetic distribution to systemic circulation to a minimum.
Reduce systemic toxicity
Prolong duration of action
Increase depth of anesthesia
Shorten duration of action
Amide local anesthetics rarely cause an allergic reaction. Esters are metabolized into paraaminobenzoic acid (PABA), causing esters to have a much greater allergic potential.
Two cartridges of lidocaine 1:100,000 would have 0.04 mg of epinephrine or the cardiac dose of a vasoconstrictor, which is considered the safe dosage; 5, 8, or 11 cartridges would deliver too high of a dose of epinephrine for safety.
Cocaine is an adrenergic agent, which stimulates heart rate and blood pressure. Vasoconstrictors are also adrenergic agonists or sympathomimetics, which would have an additive effect when combined with cocaine. The use of a local anesthetic with a vasoconstrictor in a cocaine abuser could cause a dangerous rise in blood pressure and heart rate that could cause a myocardial infection.
Possible myocardial infarction
Cholinergic stimulation by the vasoconstrictor
Adrenergic stimulation by the vasoconstrictor
The most common local adverse reaction to local anesthesia is physical injury by the injection technique or the administration of an excessive volume too quickly to be accepted by the tissues, resulting in a hematoma. This can often be avoided by slow, careful injection into the tissue. Lidocaine toxicity is rare in dentistry, due to the small amount of local anesthetics typically used in dental procedures.
Psychogenic shock or fainting
Physical injury at injection site such as a hematoma
Central nervous system excitation
Lidocaine 2% with 1:100,000 epinephrine in the lowest effective dose possible would be indicated for the pregnant patient if local anesthetic is required. Both lidocaine and prilocaine are in the Food and Drug Administration's pregnancy category B, whereas mepivacaine, articaine, and bupivacaine are category C drugs.
Bupivacaine 0.5% with 1:200,000 epinephrine
Prilocaine 4% with 1:200,000 epinephrine
Articaine 4% with 1:100,000 epinephrine
Mepivicaine 3%, plain
Lidocaine 2% with 1:100,000 epinephrine
The mechanism of action of local anesthetic is to decrease the permeability of nerve membrane, preventing depolarization. Nerve impulses are transmitted when the nerve action potential opens the sodium and potassium ion channels in the nerve membrane. The inward flow of sodium ions and the outward flow of potassium ions repolarizes the membrane and closes sodium channels. Local anesthetics attach themselves to the cell membrane and decrease the permeability of the nerve membrane to the flow of sodium ions, blocking nerve conduction. Because the message of pain is not transmitted, local anesthetics do not affect the perception or the reaction to pain.
Decreases reaction to pain
Increases permeability of nerve membrane, facilitating depolarization
Decreases permeability of nerve membrane, preventing depolarization
Decreases perception of pain
Bupivacaine has the longest duration of action and is indicated in lengthy dental procedures, producing pulpal anesthesia of 90 to 180 minutes. Mepivicaine 3% (plain) is has the shortest duration of action, with only 20 to 40 minutes of pulpal anesthesia. Prilocaine 4% with 1:200,000 epinephrine and Articaine 4% with 1:100,000 epinephrine have similar durations of action, achieving pulpal anesthesia for approximately 60 to 90 minutes. Lidocaine 2% with 1:100,000 epinephrine has an intermediate duration of action, achieving pulpal anesthesia for approximately 60 minutes.
Cimetidine decreases hepatic blood flow, slowing the metabolism of the amides. Although the small doses used in dentistry would probably not cause toxicity, large doses could become toxic. Cimetidine does not affect renal excretion.
Decrease renal excretion
Increase renal excretion
Increase lidocaine metabolism
No effect on lidocaine metabolism
Decrease lidocaine metabolism
Benzocaine, an ester, is the most commonly used topical anesthetic in dental products and is found in many over-the-counter products for teething, sunburn, and other skin irritations. Lidocaine, an amide, is the second most commonly used agent. When choosing a topical anesthetic, consideration of onset, duration, and allergic potential should be made. Patients should be instructed to avoid eating for an hour after application to oral mucosa to allow the gag reflex to return completely.
Lidocaine 2% with 1:100,000 epinephrine is used for infiltration and block anesthesia in dentistry and is the most commonly used formulation of local anesthetic used in dentistry today. Lidocaine 2% 1:200,000 is actually twice as safe as lidocaine 2% 1:100,000, due to having half the dose of epinephrine, but it is not widely used. Mepivicaine 3% plain is widely used by clinicians who does not wish to use a vasoconstrictor. Mepivicaine 2% 1:20,000 levonordefrin (Neo-Cobefrin) is an alternative amide local anesthetic with a vasoconstrictor.
Lidocaine 2% 1:100,000
Mepivicaine 3% plain
Lidocaine 2% 1:200,000
Mepivicaine 2% 1:20,000 levonordefrin (Neo-Cobefrin)
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