Ch. 7

Question 1

What information is needed to calculate and determine the dose of local anesthetic drug to be administered?

Answer 1

Calculating recommended doses and/or determining the dose of local anesthetic drugs administered requires an understanding of the following:

1. Concentration for the selected anesthetic drug
2. Dilution percentages for vasoconstrictors
3. Standard cartridge volumes
4. Defined maximum recommended dose for each drug
5. Relevant patient factors such as general health status and weight

Question 2

How do clinicians commonly express and document doses of local anesthetic drugs?

Answer 2

Clinicians commonly express and document doses of local anesthetic drugs as the number of cartridges, milliliters of solution, and/or milligrams of drug administered. Regardless of the manner in which they are expressed, these doses are all calculated based upon milligrams.

Question 3

How many mg/mL are in a 1% local anesthetic solution?

Answer 3

A 1% local anesthetic solution contains one-hundredth the milligrams per milliliter or 10 mg/mL.

Question 4

How many mg of a 1% local anesthetic drug are in a standard cartridge?

Answer 4

A cartridge contains 1.8 mL of solution; at a concentration of 1%, one cartridge contains 18 mg of drug (10 mg x 1.8 mL = 18 mg/mL).

Question 5

How many mg/mL are in a 2% local anesthetic solution?

Answer 5

A cartridge contains 1.8 mL of solution; at a concentration of 2%, one cartridge contains 18 mg of drug (20 mg x 1.8 mL = 36 mg/mL).

Question 6

How many mg/mL are in a 0.5% local anesthetic solution?

Answer 6

A cartridge contains 1.8 mL of solution; at a concentration of 0.5%, one cartridge contains 18 mg of drug (0.5 mg x 1.8 mL = 9 mg/mL).

Question 7

What is the maximum recommended dose (MRD) per appointment for 2% lidocaine plain?

Answer 7

The maximum recommended dose (MRD) per appointment for 2% lidocaine plain is 500 mg.

Question 8

How many mg of 2% lidocaine plain are in two cartridges?

Answer 8

To calculate the mg of drug in two cartridges, multiply the number of cartridges by the total mg of drug in each cartridge for a 2% drug.
2 (cartridges) x 36 mg = 72 mg

Question 9

What factors are needed to calculate the local anesthetic drug dose delivered for a given patient?

Answer 9

The following factors are needed:

1. The number of mg of drug delivered.
2. The number of cartridges delivered.
3. The MRD for the drug delivered. (i.e., 500 mg for 2% lidocaine)
4. The weight of the patient.

Question 10

Determine the maximum dose for 2% lidocaine plain for a 100-pound patient.

Answer 10

To determine the maximum dose for a 100-pound patient, multiply the maximum dose for 2% lidocaine plain (3.2 mg/lb) by the patient weight (100).
3.2 mg/lb x 100 lbs = 320 mg
The maximum dose for 2% lidocaine plain for this patient is 320 mg.

Question 11

Determine the maximum dose for 4% prilocaine plain for a 120-pound patient.

Answer 11

To determine the maximum dose for a 120-pound patient, multiply the maximum dose for 4% prilocaine plain (4.0 mg/lb) by the patient weight (120).
4.0 mg/lb x 120 lbs = 480 mg
The maximum dose for 4% prilocaine plain for this patient is 480 mg.

Question 12

Determine the maximum dose for 3% mepivacaine for a 195-pound patient.

Answer 12

To determine the maximum dose for a 195-pound patient, multiply the maximum dose for 3% mepivacaine (3.0 mg/lb) by the patient weight (195).
3.0 mg/lb x 195 lbs = 585 mg
Given that the maximum dose for 3% mepivacaine is 400 mg, 585 mg exceeds the mg per appointment; therefore, this patient’s maximum dose for 3% mepivacaine is 400 mg.

Question 13

A 150-pound patient has received 128 mg of 2% lidocaine plain. How much additional 2% lidocaine plain can this patient safely receive at the same appointment?

Answer 13

This patient has received 128 mg of 2% lidocaine plain. The maximum of 2% lidocaine plain is 500 mg per appointment. Subtract the total initial dose delivered from the maximum dose per appointment to determine the maximum additional dose that can be delivered.
500 mg – 128 mg = 372 mg
The maximum additional dose for 2% lidocaine plain for this patient is 372 mg.

Question 14

A 150-pound patient has received 128 mg of 2% lidocaine plain. How many cartridges have been delivered?

Answer 14

To convert this number (128 mg) into clinically useful terms, determine the number of cartridges this would represent. To do this, divide the mg delivered by the mg per cartridge.
128 mg ÷ 36 mg/cartridge = 3.5 cartridges
A total of 3.5 cartridges have been delivered.

Question 15

3.5 cartridges of 2% lidocaine plain have been delivered to a 150-pound patient and an additional 372 mg of the same drug may be delivered. Compute the number of additional cartridges that may be administered.

Answer 15

To convert this number (372 mg) into number of cartridges, divide the 372 mg by the mg per cartridge.
372 mg ÷ 36 mg/cartridge = 10.3 cartridges
An additional 10 cartridges may be delivered.

Question 16

What factors are needed to calculate the local anesthetic drug doses when two different drugs are used?

Answer 16

The following factors are needed to compute the MRD for two drugs:

1. mg of the first drug delivered or to be delivered.
2. MRD of the first drug.
3. mg of the second drug delivered or to be delivered.
4. MRD of the second drug delivered.

Question 17

When two drugs are delivered with different MRDs, which MRD is applied when calculating total drug doses?

Answer 17

When two (or more) drugs are administered with different MRDs, the lowest MRD is applied when calculating total drug doses. For example, the MRD of 2% lidocaine is 500 mg and the MRD of 4% prilocaine is 600 mg. The total maximum recommended dose of both drugs is 500 mg.

Question 18

A 150-pound patient has received 128 mg of 2% lidocaine. How many mg of 4% prilocaine may be delivered as the second drug?

Answer 18

The MRD for 4% prilocaine is 600 mg. The MRD for 2% lidocaine (500 mg) is lower than the MRD for 4% prilocaine (600 mg) and therefore 500 mg will be used for calculating the dose limits.
This patient has received 128 mg of 2% lidocaine. Since the MRD for lidocaine will limit the total dose in this example, the patient can safely receive a maximum of 500 mg of drug. Subtract the total dose delivered initially from the MRD for this patient to determine the allowed additional dose.
500 mg – 128 mg = 372 mg
An additional 372 mg of 4% prilocaine may be delivered.

Question 19

A 150-pound patient can receive 372 mg of 4% prilocaine in addition to the 128 mg of 2% lidocaine. How many cartridges of 4% prilocaine can be delivered?

Answer 19

For this patient, 372 mg of 4% prilocaine can be delivered. To convert this number (372 mg) into clinically useful terms, determine the number of cartridges this would represent. Divide the additional mg allowed by the mg per cartridge.
372 mg ÷ 72 mg/cartridge = 5.1 cartridges
This patient may receive 5 cartridges of 4% prilocaine in addition to the 3.5 cartridges of 2% lidocaine delivered.

Question 20

What factors are needed to determine the dose for vasoconstrictor drugs in a given volume of solution?

Answer 20

Determining the dose for vasoconstrictor in a given volume of solution requires an understanding of dilution ratios or percentages, standard cartridge volumes, the defined maximum recommended doses for epinephrine and levonordefrin, and relevant patient factors such as general health status.

Question 21

What is the difference in calculating doses for vasoconstrictors compared to local anesthetic drug doses?

Answer 21

Calculations of vasoconstrictor doses are different compared to those used to determine local anesthetic drug doses. The main differences are that vasoconstrictors are expressed as dilution ratios rather than concentration percentages, and the maximum doses for vasoconstrictors are not weight dependent.

Question 22

How many mg/mL are in a 1:1000 ratio of vasoconstrictor?

Answer 22

1:1000 = 1 g or 1000 mg of vasoconstrictor per 1000 mL solution = 1 mg/mL

Question 23

How much epinephrine is contained in a 1:100,000 cartridge of solution?

Answer 23

One cartridge of 1:100,000 epinephrine contains 0.018 mg of epinephrine per cartridge.

Question 24

How much levonordefrin is contained in a 1:20,000 cartridge of solution?

Answer 24

One cartridge of 1:20,000 levonordefrin contains 0.09 mg/cartridge.
1:20,000 = 0.05 mg/mL or 0.05 x 1.8 mL = 0.09 mg/cart

Question 25

What factors are needed to calculate the dose of vasoconstrictor delivered?

Answer 25

The following factors are needed to calculate the dose of vasoconstrictor delivered.

1. The mg of vasoconstrictor in the solution.
2. The number of cartridges delivered.

Question 26

Calculate the mg of vasoconstrictor delivered in a 1:100,000 solution.

Answer 26

To calculate the milligrams of a 1:100,000 vasoconstrictor delivered, first multiply the total number of cartridges by the total mg of drug in each cartridge.
1 x 0.018 mg = 0.018 mg per cartridge

Question 27

Is the local anesthetic drug or the vasoconstrictor drug the limiting drug using the current adult MRD for 2% lidocaine with 1:100,000 epinephrine?

Answer 27

Using the current adult MRD for 2% lidocaine with 1:100,000 epinephrine, the limiting drug is the vasoconstrictor.

Question 28

The maximum safe dose for epinephrine is 0.2 mg for a healthy patient. Using this figure, determine the maximum dose of 1:100,000 epinephrine that can be delivered in the same appointment.

Answer 28

Divide the maximum safe dose (0.2 mg) by the mg of 1:100,000 epinephrine in the cartridge (0.018).
0.2 mg ÷ 0.018 = 11 cartridges
Considering only the dose of 1:100,000 epinephrine, 11 cartridges is the maximum safe dose per appointment.

Question 29

What is the maximum dose for epinephrine and levonordefrin per appointment for patients with ischemic heart disease?

Answer 29

Vasoconstrictor doses for patients with ischemic heart disease are restricted to 0.04 mg per appointment for epinephrine and 0.2 mg levonordefrin.

Question 30

How many mg of epinephrine are in one cartridge of a 1:100,000 solution?

Answer 30

One cartridge of a 1:100,000 solution contains 0.018 mg of epinephrine.
0.01 mg/mL x1.8 mL = 0.018 mg

Question 31

The maximum safe dose of epinephrine is 0.04 mg for a patient with ischemic heart disease. Using this figure determine the maximum dose for a 1:100,000 epinephrine solution per appointment.

Answer 31

Divide the maximum safe dose (0.04 mg) by the mg of 1:100,000 epinephrine in the cartridge (0.018).
0.04 mg ÷ 0.018 = 2.2 cartridges (rounded down = 2 cartridges)
A patient with ischemic heart disease can receive a maximum of 2 cartridges of 1:100,000 epinephrine per appointment.

Question 32

Using Clark’s Rule, what is the maximum dose for 2% lidocaine for a 75-pound child?

Answer 32

Clark’s Rule is based upon a child’s weight and states that the child’s weight (in pounds) is divided by 150 to get the approximate fraction of the adult dose to give to the child. To determine the maximum dose for a ten-year-old, 75-lb child using 2% lidocaine:
1. 75 ÷ 150 = 0.50 (1/2)
2. *300 mg x 0.50 = 150 mg (child’s dose)
The maximum dose for a 75-pound child would be approximately 1/2 of the adult MRD of 300 mg (8 cartridges). The child’s dose would be 150 mg or about 4 cartridges (150 mg/36 mg per cartridge = 4.16, which rounds down to 4.0).
*Based on the American Academy of Pediatric Dentistry (AAPD) recommended use of the lower MRDs compared with the current FDA-approved MRD values.

Question 33

Using Clark’s Rule, what is the maximum dose for 4% articaine for a six-year-old, 50-pound child?

Answer 33

Clark’s Rule is based upon a child’s weight and states that the child’s weight (in pounds) is divided by 150 to get the approximate fraction of the adult dose to give to the child. To determine the dose for a six-year-old, 50-lb child using 4% articaine:
1. 50 ÷ 150 = 0.33 (1/3)
2. *500 mg x 0.33 = 165 mg (child’s dose)
The dose for a 50-pound child would be approximately 1/3 of the adult MRD of 500 mg (6.9 cartridges). The child’s dose would be 165 mg or about 2.3 cartridges (165 mg/72 mg per cartridge = 2.29, which rounds down to 2.0).
*Based on the American Academy of Pediatric Dentistry (AAPD) recommended use of the lower MRDs compared with the current FDA-approved MRD values.