4: Local Anesthetics Commonly Used in Dentistry: Assessment, Analysis, and Associated Dental Management Guidelines

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Local Anesthetics Commonly Used in Dentistry: Assessment, Analysis, and Associated Dental Management Guidelines

LOCAL ANESTHETIC CLASSIFICATION AND PHARMACOTHERAPEUTICS

There are two distinct types of local anesthetics: amides and esters. Amides are subdivided into amides with epinephrine and amides without epinephrine (Table 4.1).

Table 4.1 Summary: Local Anesthetics (LAs)

LAs: Generic/Trade Name LAs: Facts, Advice, or Alerts
AMIDE LA WITH EPINEPHRINE
Amide LA Alerts: Use only 2 carpules of any LA in compromised patients.
Avoid LAs with epinephrine and epinephrine cords with Hyperthyroidism; severe coronary artery disease; MAO and Tricyclic antidepressants; Prophylthiouracil (PTU); Lanoxin (Digoxin); Theophylline; bisulfite allergy; G6PD anemia and with serum creatinine >2mg/dL or CrCl <50/minute. Use 5–10% Aluminum chloride (Hemodent) cords when needed.
2% Lidocaine (Xylocaine) with 1:l00,000 epinephrine:
Pregnancy Category B
Concentration/carpule: 36mg
Lasts: 60 minutes
Recommended Dose: 3mg/lb
Healthy adult: Max. 11.5 carpules
4% Prilocaine HCL (Citanest Forte) with 1:200,000 Epinephrine:
Pregnancy Category B
Concentration/carpule: 72mg
Lasts: 2 hours
Recommended Dose: 2.7mg/lb
Healthy adult: Max. 5 carpules
Avoid with: Congenital methemoglobinemia; ASA III/IV status hypoxic states; moderate-to-severe anemia/kidney disease and multiple sclerosis
0.5% Bupivacaine (Marcaine) with 1:200,000 epinephrine:
Pregnancy Category C
Concentration/carpule: 9mg
Lasts: 90 minutes or longer
Recommended dose: 0.6mg/lb. Healthy adult: Max. 9 carpules
4% Septocaine (Articaine) with 1:100,000/1:200,000 Epinephrine:
Pregnancy Category C
Concentration/carpule: 68mg in 1.7mL single use carpule
Lasts: 45–75 minutes
Recommended dose: 3.2mg/lb
Healthy adult: Max. 6 carpules
Has 1.5 times Lidocaine potency. Action occurs within 1–3 minutes.
Avoid use in all conditions listed under Citanest Forte.
NEWER AMIDE LA WITH EPINEPHRINE:
0.5% Ropivacaine (Naropin) with 1:200,000 epinephrine:
Pregnancy Category B
Concentration: Available in single dose carpules in 2 (0.2%), 5 (0.5%), 7.5 (0.75%) and 10mg/mL (1%) concentrations.
Lasts: 120-360 minutes
Healthy Adult Dose: Surgical anesthesia is 5mg; Minor nerve block dose not to exceed 200mg.
AMIDE WITH LEVONORDEFRIN:
2% Mepivacaine (Carbocaine) with 1:20,000 Levonordefrin (NeoCobefrin):
Pregnancy Category C
Infiltration/block anesthesia
Dose: 36mg/carpule
Healthy adult: Max. 5 carpules
Avoid with: Hyperthyroidism, severe coronary disease, MAOIs, bisulfite allergy, G6PD anemia
AMIDES WITHOUT EPINEPHRINE:
3% Mepivacaine HCL (Carbocaine):
Pregnancy Category C
Concentration/carpule: 54mg
Lasts: 20 minutes
Recommended dose: 3mg/lb
Healthy adult: Max. 7.5 carpules
Safe with G6PD anemia
4% Prilocaine HCL (Citanest Plain):
Pregnancy Category B
Safe to use in the hypertensive pregnant patient
Concentration/carpule: 72mg
Lasts: 30 minutes
Recommended dose: 2.7mg/lb Healthy adult: Max. 5 cartridges
Avoid in all conditions listed under Citanest Forte.
ESTER ANESTHETICS:
Propoxycaine and Procaine (Ravocaine):
Pregnancy Category C
Concentration/carpule: 43.2mg
Lasts: 30-40 minutes
Healthy adult: Max. 9 cartridges
Not available; highly allergenic
Topical Benzocaine: Pregnancy Category C Avoid in all states listed under Citanest Forte.

Classification of Amides with Epinephrine

  • 2% lidocaine with 1:100,000 epinephrine (Xylocaine)
  • 4% prilocaine HCL with 1:200,000 epinephrine (Citanest Forte)
  • 0.5% bupivacaine with 1:200,000 epinephrine (Marcaine)
  • 4% septocaine with 1:100,000 and 1:200,000 epinephrine (Articaine)
  • 0.5% Ropivacaine with 1:200,000 epinephrine (Naropin)

Amide with Levonordefrin (NeoCobefrin)

  • 2% mepivacaine HCL (Carbocaine) with 1:20,000 levonordefrin (NeoCobefrin), a sympathomimetic amine

Classification of Amides Without Epinephrine

  • 3% mepivacaine HCL (Carbocaine)
  • 4% prilocaine HCL (Citanest Plain)

Classification of Ester Local Anesthetics

  • Injectable propoxycaine and procaine (Ravocaine)
  • Topical benzocaine

Metabolism of Local Anesthetics

Metabolism of all amide local anesthetics other than septocaine does not begin until those local anesthetics reach the liver where they are metabolized and then, for the most part, excreted through the renal system.

Septocaine (Articaine) is unique among amide-type local anesthetics in the way that it is metabolized. Septocaine is actually a hybrid of both an amide and an ester class anesthetic because of the presence of both an amide and an ester intermediate chain in its chemical composition. Biotransformation of 90–95% of septocaine begins immediately upon the drug entering the blood stream where the plasma carboxyesterase enzymes initiate the metabolic breakdown process via hydrolysis of the ester chain to its primary metabolite, articainic acid, which is inactive. The remainder of septocaine (5–10%) is metabolized in the liver by the hepatic microsomal enzymes. Amides have a high rate of first pass metabolism as the local anesthetic (LA) passes through the liver. Slow absorption from tissue is less likely to result in toxicity. If toxicity occurs, it often results from accidental parenteral injection or due to LA overdose.

Ester local anesthetics are metabolized in the plasma, by plasma cholinesterase, and plasma cholinesterase is synthesized in the liver. There is no real advantage to using ester local anesthetics over the amides in a cirrhotic patient. Benzocaine as a topical anesthetic is the only ester used today in dentistry and, as further discussed in this chapter, benzocaine products should not be used in children less than 2 years of age.

Age is one factor that alters the pharmacokinetics of local anesthetics (LAs). The half-life of LAs can be altered in the elderly because of decreased hepatic blood flow from disease processes such as liver disease or congestive heart failure (CHF). These disease processes can also impair the ability of the liver to produce enzymes. All these factors contribute to elevated levels of amide local anesthetics in these patients compared to patients with normal liver function.

Hormonal changes during pregnancy are primarily responsible for the enhanced potency of local anesthetics. Thus, pregnancy can also alter the metabolism of LAs, and the dose of LAs should be reduced by 30%, regardless of the trimester of pregnancy.

Factors Affecting Onset and Duration of Local Anesthetics

The onset and duration of action depends on multiple factors:

1. Tissue pH: With infection, the pH of the tissue decreases, becoming more acidic. An acidic pH is responsible for the delayed effectiveness or ineffectiveness of the local anesthetic.
2. Lipid solubility: The intrinsic potency, onset of action, and duration for a local anesthetic are dependent on the lipophilic-hydrophobic balance and the hydrogen ion concentration. Lipophilic LA molecules have a tendency to bind to membrane lipids. The lipid membrane is a hydrophobic environment. LA duration of action is associated with lipid solubility. Highly lipid soluble LAs have a longer duration of action because of decreased clearance and increased protein binding.
3. Local anesthetic concentration formulation: The high-concentration local anesthetics prilocaine (Citanest) and septocaine (Articaine) require fewer injections compared to the low-concentration local anesthetics, such as lidocaine. Low-concentration preparations are preferred for use in the pediatric population and 0.5% bupivacaine (Marcaine) should be avoided in children.
4. Presence of a vasoconstrictor: By themselves, local anesthetics cause vasodilation, diffuse very rapidly, and last for a shorter duration of time. Presence of a vasoconstrictor improves the duration and depth of anesthesia, thus decreasing the need for more anesthetic use per visit. There are two types of vasoconstrictors used in dentistry: epinephrine and levonordefrin.

a. Epinephrine: Epinephrine is the most common vasoconstrictor added in 1:50,000, 1:100,000, or 1:200,000 concentrations in various local anesthetics. Epinephrine causes vasoconstriction by stimulating the α1 receptors in the mucus membranes. Epinephrine also affects the β1 receptors in the heart and the β2 receptors in the skeletal muscles. Stimulation of the β1 receptors causes tachycardia and an increased systolic blood pressure (SBP). Stimulation of the β2 receptors causes vasodilation and a decreased diastolic blood pressure (DBP). The reflex tachycardia triggered by epinephrine becomes an issue in patients with significant cardiovascular disease and should thus be avoided or significantly limited, in such cases.
b. Levonordefrin (NeoCobefrin): Levonordefrin (NeoCobefrin) is a sympatho-mimetic amine that acts as a vasoconstrictor, producing less cardiac and CNS stimulation than epinephrine. It has a fast onset of action, providing effective anesthesia and has very few side effects. Levonordefrin increases the systolic and diastolic BP but it causes a reflex bradycardia (decreased heart rate). Reflex bradycardia is a beneficial side effect in patients with mild-to-moderate cardiovascular heart disease. The potency of 1:20,000 levonordefrin is equivalent to the potency of 1:100,000 epinephrine.
5. Infiltration versus block anesthesia: Infiltration anesthesia is more rapid in onset compared to block anesthesia, but it is shorter lasting than block anesthesia.

Local Anesthetics and Cross-Reactivity

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Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 4: Local Anesthetics Commonly Used in Dentistry: Assessment, Analysis, and Associated Dental Management Guidelines
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