USAGES

This is the third of seven pages which constitute a course in local anesthetics. Each page stands on its own, however for a thorough understanding of dental local anesthetics the reader is advised to read the pages in order.

<==Local anesthetic toxicity

How anesthetics make you numb==>


Toxicity; How much is too much?

The maximum dose for local anesthetic solutions is somewhere between 70 mg to 500 mg for an average 70 kg (154 lb) patient. Of course, the maximum dose is dependent upon the age, weight and health of the patient, the type of solution used, and whether vasoconstrictor is present or not. These anesthetic agents are distributed in concentrations that are appropriate to their toxicity and their anesthesia producing qualities. The carpules (cartridges) that these drugs are distributed in contain 1.8 ml of solution (Articaine carpules contain 1.7 ml).

Since people vary in age, weight and health, the maximum dose of any given drug that any individual can tolerate varies widely and can be computed arithmetically. The maximum dose (for a normal adult weighing 154 pounds) for Articaine is 500 mg. The maximum dose for lidocaine and mepivicaine is 300 mg. The maximum dose of prilocaine is 400 mg, and the maximum dose of bupivicaine is 90 mgm. A 2% solution contains 20 mg of anesthetic agent per milliliter which means that each 1.8 ml cartridge contains 36 mg of agent. In the case of lidocaine, this works out to about 13 carpules delivered at one time. For children, it works out to about 1/3 to 1/2 that number depending on their weight. These doses are not considered lethal. They are simply the doses at which some people begin to feel toxic systemic effects from the drugs which may include CNS (Central Nervous System) effects of sedation, light headedness, slurred speech, shivering or twitching or, in rare cases, seizures; or cardiovascular effects such as hypotension (low blood pressure). The incidence of toxicity to local anesthetics in the dental setting is extremely rare and generally revolve around very unusual patient centered physiologic abnormalities rather than poor anesthetic technique on the part of the dentist. The most frequent dose related toxic effect in the dental setting is nervousness and high heart rate, due not to the effect of the anesthetic itself, but rather to the systemic effect of the vasoconstrictor.



Table of maximum doses

The following table is based on The Handbook of Local Anesthesia (Malamed, S.F.). All carpules of anesthesia except articaine contain 1.8 ml of anesthesia. A carpule of articaine contains 1.7 mg. A 2% solution of any anesthetic solution translates to 20 mg /ml, a 3% solution translates to 30 mg/ml etc. Thus a carpule of 2% lidocaine contains:

20 mg/ml X 1.8 ml/carpule = 36 mg/carpule.

The maximum doses in parentheses take into account factors beyond raw toxicity such as the rate of absorption, patient health status, tissue conditions, age considerations and other forms of human variability. They are probably the better guidelines. The third column indicates maximum doses for the average 154 lb (70 kg) patient.

These guidelines do NOT take into consideration the physiologic effects of increasing doses of vasoconstrictor if present.



mg/Kg
mg/lb
Max dose
/70 kg pt.
Max number of carpules /70 kg pt

Articaine (4%) 7.0 3.17 500 7.35
Mepivicaine (3%) 6.6 (4.5) 3 (2) 400 (300) 7.4 (5.5)
Lidocaine (2%) 7.0 (4.4) 3.17 (2) 500 (300) 13.8 (8.3)
Prilocaine (4%) 8.0 (6.0) 3.6 (2.72) 600 (400) 8.3 (5.5)
Bupivicaine (.5%) 1.3 .59 90 10



<==Local anesthetic toxicity How anesthetics make you numb==>