Table 5 exhibits the general differences in pharmacodynamic properties among the “plain” local anesthetics (without vasoconstrictors). Table 5: Pharmacodynamic Differences Among Commonly Used Local Anesthetics Medication Potency Duration of Action
Onset of Action
Articaine
Moderate
Moderate
Fast
Bupivacaine
High
High
Moderate
Etidocaine
High
High
Fast
Lidocaine
Moderate
Moderate
Fast
Mepivacaine
Moderate
Moderate
Fast
Prilocaine
Moderate
Moderate
Fast
Procaine
Low
Short
Moderate
Tetracaine Moderate Note . Adapted from “The ADA/PDR Guide to Dental Therapeutics” (5th ed.), by the American Dental Association and the Physicians’ Desk Reference, 2009, PDR Network, pp. 11-13; “Local Anesthetics: Review of Phar Anesthesia Progress, 59(2), pp. 90-102; “An Update on Local Anesthetics in Dentistry,” by D. A. Haas, 2002, Journal of the Canadian Dental Association, 68(9), pp. 546-551; “Local Anesthetics: Pharmacology and Toxic 54(4), pp. 587-599; and “Legal Considerations,” by D. J. Orr, II, 2021, in S. F. Malamed (Ed.), Handbook of Local Anesthesia (7th ed.), High High
Elsevier Mosby, p. 412. Pharmacokinetics
Pharmacokinetics focuses specifically on the absorption of drugs, the distribution to their site of action within the body, their metabolism, and finally their excretion. In the case of local anesthetics, absorption of the parenteral formulations – following routes of administration such as intravenous, intramuscular, and subcutaneous, in which absorption bypasses the gastrointestinal tract – represents few challenges because the medications are being injected directly into the target area. In contrast, when some local anesthetics are administered topically, their absorption depends on local characteristics such as mucosal keratinization, adipose, fascia, and layers of musculature, as well as blood flow to the area. Distribution also represents few challenges as the medication tends to be deposited directly at the targeted area whether injected or applied topically. Lidocaine Lidocaine is often considered the prototype of the amide class of local anesthetics. It was first produced and marketed by the Swedish drug manufacturer Astra in 1948 (Gordh, Gordh, & Lindqvist, 2010; Singh, 2012), and it continues to be one of the most widely used and versatile local anesthetics (Goodchild & Donaldson, 2018b). It is several times more potent than procaine and has a faster onset of action, a longer duration of Mepivacaine Mepivacaine was originally introduced in 1957 (Singh, 2012) as an intermediate-duration amide local anesthetic. It has pharmacologic properties similar to lidocaine such as a rapid onset of action (usually within 2 to 4 minutes), although its duration of action may be slightly longer (1 to 2.5 hours in the mandible and 2.5 to 5.5 hours in the maxilla). Available preparations are either a 3% mepivacaine plain solution or a 2% mepivacaine solution in combination with 1:20,000 levonordefrin as the vasoconstrictor. The drug has an elimination half-life of about 114 minutes. In dentistry, local anesthetic toxicity occurs more frequently in children and most often with the use of mepivacaine (Moore & Hersh, 2010; El- Boghdadly & Chin, 2016). Plain mepivacaine Prilocaine Prilocaine is also an intermediate-duration amide local anesthetic, with a pharmacologic profile similar to that
Metabolism and excretion, however, depend much more on the drug’s molecular structure as previously described, and these differences will be highlighted in the following subsections. The half-life (t1/2) of the various local anesthetics ranges from 90 minutes for common agents such as lidocaine to nearly 300 minutes for bupivacaine. Half-life is the time it takes the body to eliminate half the amount of local anesthetic injected. An understanding of half-life is essential in helping practitioners avoid exceeding the maximum recommended limits of local anesthetic administration during lengthy procedures, since accumulation of these medicines beyond their maximum recommended limits is possible with medication readministration at a rate that may be faster than the drug’s half-life.
TYPES OF LOCAL ANESTHETICS
action, and a reduced allergenicity profile. Two-percent lidocaine hydrochloride combined with 1:100,000 epinephrine may be considered the gold standard for routine dental use, although it is also available as a plain solution or with the more concentrated 1:50,000 epinephrine for vasoconstriction. The drug has an elimination half-life of about 96 minutes. is often preferred in pediatric dentistry for its shorter duration of activity, but it can lead to higher systemic blood levels, which have a slow clearance rate. Even with the addition of the vasoconstrictor levonordefrin, blood levels are not reduced as they are with lidocaine with epinephrine, and mepivacaine (especially 3% mepivacaine without a vasoconstrictor) has been associated with the most reported fatalities due to excessive dosing (Hersh, Helpin, & Evans, 1991; Moore, 1992; El-Boghdadly & Chin, 2016). Regardless, given its low pKa, mepivacaine may have some distinct advantages over other local anesthetics when used for infiltration in infected and inflamed tissues.
of lidocaine. The primary differences between prilocaine and lidocaine are that prilocaine has an increased volume
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