From Laughing Gas to Lidocaine
An inside look at the dynamics of anesthetics
DISCLAIMER: The material included in this article is intended for informational purposes only and does not constitute full prescribing information.
Evolution of Anesthesia
The concept of lowering the pain threshold has existed for centuries, but the first anesthetic agents — ether and nitrous oxide — weren’t introduced in dentistry until the 1840s. Anesthetics were used only during extractions until the first nerve block was introduced in the 1880s. Cocaine was the first local anesthetic used, and although effective for achieving profound anesthesia, was highly addictive. The first synthesized cocaine, procaine, was introduced at the turn of the 20th century. When mixed with a very small concentration of epinephrine, procaine was found to be highly effective, non-addictive and safe as a local anesthetic agent for most patients. Novocain procaine was widely used until it was replaced by lidocaine in the 1950s, which remains the gold standard to this day. The newest local anesthetic, articaine, has similar time of onset and profoundness of anesthesia as lidocaine, but is claimed to last two to three times longer.
A Closer Look at Local Anesthetics
Local anesthetics are the most widely used anesthetic agents in dentistry. The table at the bottom of this page shows the most common types of injectable local anesthetics in use today.
Determining Total Dose:
The total dose (mg) of a local anesthetic is a function of its concentration (%). For any given percent solution, the easiest way to calculate dose is to move the decimal one place to the right (reflecting mg/ ml) and then doubling it for the dose per cartridge (one cartridge = ~2 ml of solution). For example, one cartridge of 3% mepivacaine is equivalent to ~2 ml at 30 mg/ml, or ~60 mg total. Similarly, 2 1/2 cartridges of 2% lidocaine is equivalent to ~5 ml at 20 mg/ml, or 100 mg total.
Addition of Vasoconstrictors:
Solutions containing a vasoconstrictor like epinephrine increase the duration of the anesthetic by slowing down its rate of absorption. They vary in concentration, representing grams of solute dissolved in milliliters of solvent. The most common is epinephrine 1:100,000 (10 micrograms/ml). Higher concentrations may provide better hemostasis at the surgical site compared to lower concentrations. Remember, 1:200,000 (5 micrograms/ml) is half the concentration of 1:100,000. Similarly, 1:50,000 (20 micrograms/ml) is double the concentration of 1:100,000.
Adverse “Allergic” Reactions:
It is not unusual for patients to claim they are allergic to local anesthetics, when most likely they are sensitive to epinephrine. Since epinephrine is a hormone produced in the body, it is impossible to be allergic to it. However, some patients occasionally experience symptoms resembling an allergic reaction, which can be attributed to preservatives (methylparaben) or antioxidants (bisulfites) contained in the solution. Solutions without a vasoconstrictor should be used in these types of cases, or when a patient has severe heart disease or recent myocardial infarction
1 Perno Goldie, M. (2009). The evolution of analgesia and anesthesia in oral health care. RDH (29) 9
2 Becker, D. & Reed, K. (2006). Essentials of local anesthetic pharmacology. Anesthesia Progress, 53 (3), 98-109