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Q What is an amide local anesthetic agent?

A. As opposed to ester local anesthetic agents, which are metabolized by hydrolysis, amides are metabolized through a biotransformation in the liver by microsomal enzymes. There are five amide local anesthetic agents in use today: lidocaine, mepivacaine, prilocaine, bupivacaine, and articaine.

THE 5 DRUGS AND WHAT THEY DO

Q. What sets each drug apart?

A. Lidocaine, the first of the amide local anesthetics, was introduced in 1948. It quickly became the most popular local anesthetic used in both medicine and dentistry because it was far superior to the older drugs available in rate of onset, duration of anesthesia, and depth of anesthesia. Lidocaine was followed in 1955 by mepivacaine and in 1965 by prilocaine. In the late 1970s, bupivacaine, a longer acting local anesthetic, was introduced. In 2000 in the United States , the newest amide was introduced—articaine. These five local anesthetics serve dentistry worldwide.

The average patient is actually in the dental chair receiving dental treatment for approximately 44 minutes in a general dentistry office. Therefore, local anesthetics that provide pulpal anesthesia for approximately 1 hour are the preferred drugs. The local anesthetics available today can be divided into three categories based on the expected duration of clinical anesthesia. Short acting local anesthetics provide pulpal anesthesia lasting for up to 30 minutes. Intermediate acting local anesthetics provide pulpal anesthesia lasting for approximately 1 hour. The long-acting local anesthetics provide pulpal anesthesia in excess of an hour and a half. Their primary use is for postsurgical pain control.

In the short acting group, only one drug is clinically relevant—3% mepivacaine—which has an onset of approximately 3 to 5 minutes and duration of pulpal anesthesia lasting between 20 and 40 minutes. Soft tissue duration is approximately 2 to 3 hours.

One long acting local anesthetic is bupivacaine. It is a very potent local anesthetic used in a very low concentration—0.5%—in combination with epinephrine in a 1:200,000 concentration. Bupivacaine with epinephrine has a relatively slow onset of anesthesia, about 6 to 10 minutes, and the longest duration of anesthesia. Its duration of pulpal anesthesia following nerve block is approximately an hour and a half to 3 hours. More significantly, its duration of soft tissue anesthesia is up to 12 hours, which is why bupivacaine is most often used at the conclusion of a surgical dental procedure to aid the dentist in postsurgical pain control for the patient.

The largest category of anesthetics is the intermediate active drugs. These drugs provide pulpal anesthesia lasting for approximately 1 hour. This category includes: articaine with epinephrine, lidocaine with epinephrine, mepivacaine with levonordefrin (neocobefrin), and prilocaine with epinephrine. Lidocaine is available as a 2% concentration with epinephrine in a 1:50,000 and 1:100,000 concentration. Both of these concentrations provide the same onset, depth, and duration of anesthesia.—approximately 1 hour pulpal and 3 to 5 hours soft tissue.

Given there is no difference in the depth, duration, or onset of anesthesia whether it be 1:50,000 or 1:100,000, there is no reason to use epinephrine in a 1:50,000 concentration for pain control. By using epinephrine 1:50,000 for pain control, you are simply giving the patient twice as much epinephrine without any benefit relative to the depth of anesthesia. So for pain control purposes, a 1:100,000 is much preferred. The only reason to consider using epinephrine in a 1:50,000 concentration would be for hemostasis.

Dental hygienists, of course, are working with soft tissues all the time and deal with bleeding when the tissues aren’t healthy. To help minimize bleeding during procedures, the local infiltration into the tratment site of small amounts of local anesthetics that contain epinephrine will produce vasoconstriction and, therefore, decrease bleeding. Even though 1:100,000 concentration works well, there is some scientific evidence that a 1:50,000 concentration is, in some small degree, better.

Q. Should the injection be directed at the level of the depth of the pocket?

A. Yes. This is the only compelling use for the epinephrine in the 1:50,000 concentration. If you are working on the lower right side (mandibular right quadrant), you would give an inferior alveolar mandibular nerve block with a local anesthetic, for example, lidocaine with epinephrine 1:100,000. Then if any hemostasis was required, you can either keep the 1:100,000 or switch the epinephrine to 1:50,000 and then locally infiltrate just enough local anesthetic into the papilla (into the soft tissue) to produce the degree of necessary ischemia. With lidocaine, when the tissue turns white, you stop. Now mepivacaine is available as a 2% concentration with levonordefrin, which is available as a 1:20,000 concentration. Levonordefrin is a synthetic vasoconstrictor. It is not epinephrine but it has epinephrine-like properties. However, it is only one-fifth as potent as epinephrine, therefore, it is available in a 1:20,000 concentration, which is equivalent to an epinephrine 1:100,000 concentration or five times more concentrated. At 1:20,000, levonordefrin is as effective as epinephrine in a 1:100,000 concentration, so the indications and contraindications are the same as those for epinephrine.

Q. Why would you select mepivacaine instead of lidocaine?
A. For the same reason that some people prefer Pepsi instead of Coca-Cola. They are basically all the same drug. I like Pepsi because it tastes better to me. Which drug is preferred is a decision made by dental professionals themselves. The onset of anesthesia and the depth and duration of lidocaine, mepivacaine, and prilocaine are all the same.

Mepivacaine 2% with levonordefrin has the same onset, depth, and duration of anesthesia both in pulpal and soft tissue as lidocaine with epinephrine. The only difference is that the levonordefrin is not as effective as a vasoconstrictor. Prilocaine in a 4% concentration comes with epinephrine in a 1:200,000 concentration and provides an onset of 3 to 5 minutes, 60 to 90 minutes of duration of pulpal anesthesia, and between 3 and 8 hours of soft tissue anesthesia. Prilocaine is not typically used with epinephrine for hemostasis because it doesn’t work as well as the higher concentrations of epinephrine. But for pain control, prilocaine is an excellent medication. It’s also available as a 4% plain, which is an interesting drug because if used by infiltration, 4% prilocaine provides no more than 10 or 15 minutes of pulpal anesthesia. However 4% prilocaine by nerve block can get pulpal anesthesia lasting from from 40 minutes to an hour. If you need a longer than 20 minute duration of action, a drug like prilocaine administered by nerve block as in inferior alveolar provides pulpal anesthesia lasting anywhere from 40 minutes to an hour. So these are the original three amide local anesthetics.

The most recent addition to the armamentarium in the United States, which was made available in June of 2000, is articaine. Articaine is available as a 4% concentration with epinephrine 1:100,000. It is available in 133 countries worldwide, and except in America,>is also available with epinephrine in a 1:200,000 concentration. In the United States, we only have the 4% concentration of articaine with 1:100,000 epinephrine. Articaine’s onset of anesthesia is approximately 2 to 3 minutes, slightly faster than the other medications. It’s duration of pulpal anesthesia is 1 hour and its soft tissue duration is approximately 3 to 5 hours, which fits into the same exact category as the previous three drugs. It’s been available for almost 5 years now and in this period it has become the second most popular local anesthetic in theUnited States.

NEW AMIDE PRODUCT

Q. A new amide product on the market is a topically applied local anesthetic agent for use in periodontal pockets*. Can we use this product in combination with local anesthetic agents?

A. Yes, the new periodontal gel can be used in combination with injectable local anesthetics. There are no contraindications. It is not absorbed to any significant degree so blood levels of its components (lidocaine and prilocaine) are not significant. Indeed the area of tissue exposure to the gel is quite limited. Overdose specifically from combining the periodontal gel plus an injectable local should not be a significant consideration or problem, assuming the injectable drug is used appropriately.

Q. How is this new product used?

A. The periodontal pocket is filled with the anesthetic gel with a blunt tip applicator where it thickens at body temperature so the anesthetic remains in the pocket. The onset of anesthesia is between 30 seconds and 2 minutes with lasting effects for 15-20 minutes in soft tissue.

Q. Is there a maximum dosage with this agent? How many sites can we place the agent in during a 1 hour appointment?

A. The anesthetic effect, as assessed by probing of pocket depths, has a duration of approximately 20 minutes (individual overall range 14 to 31 minutes). It may be re-applied if needed. The maximum recommended dose at one treatment session is five cartridges or 8.5 g gel. Typically, 1 cartridge (1.7 g) or less is sufficient for one quadrant of the dentition. It is important to note that the pocket nees to be filled with the gel, not just a couple of drops.

* Oraqix®, DENTSPLY Oral Pharmaceuticals,York, Pa

From Dimensions of Dental Hygiene. June 2005;3(6):22, 24, 26.