Dosing

LAs’ nonselective voltage-gated sodium channel blockade is responsible for most of their adverse drug effects. High plasma levels, other than overdose, may be caused by (1) repeated doses, (2) rapid absorption, (3) intravascular injection, (4) low plasma protein binding, and (5) slow clearance.14,21-25,27-29 Determine the dosage for healthy adults based on body weight; however, if a patient weighs ≥ 150 lbs. no more than the maximum recommended dose (MRD) should be administered (Table 4).19-25,27-29

Table 4. Maximum Recommended Dosages.21-25
LA formulations mg/mL mg/cartridge MRD – mg/lb. MRD in mg
Lidocaine, 2% plain 20 36 2 300
Lidocaine, 2% w/epinephrine 20 36 3.2 500
Mepivacaine, 2% plain 30 54 3 400
Mepivacaine, 2% w/levonordefrin 20 36 3 400
Prilocaine, 4% plain 40 72 4 600
Prilocaine, 4% w/epinephrine 40 72 4 600
Articaine, 4% w/epinephrine 40 72 3.2 500
Bupivacaine, 0.5% w/epinephrine 5 9 0.6 90

Since the MRD of LAs vary and there is wide variation in weight among pediatric patients, the maximum dose for each child should be carefully calculated.21-25,27,30-32 Although there are many rules and formulae to calculate dosages, manufacturers’ recommendations provide a reasonable approach.21-25,27,30-32 Using the information in Table 4, the MRD of lidocaine 2% w/epinephrine 1:100,000 that can be safely administered to a child of 25 lbs. is as follows:

Step 1 – Determine MRD in mg
MRD in mg/lb. x weight of patient in lbs. = Total MRD in mg
i.e., 3.2 mg/lb. x 25 lbs. = 80 mg

Step 2 – Determine MRD in mL
Total MRD in mg ÷ mg per mL = Total MRD in mL
i.e., 80 mg ÷ 20 mg = 4.0 mL

Step 3 – Determine MRD in cartridges
Total MRD in mg ÷ mg per cartridge = Total MRD in cartridges
i.e., 80 mg ÷ 36 = 2.22 cartridges

Similarly, using the information in Table 4 to calculate the MRD of mepivacaine 3% plain that can be safely administered to a child of 25 lbs. is as follows:

Step 1 – Determine MRD in mg
MRD in mg/lb. x weight of patient in lbs. = Total MRD in mg
i.e., 3 mg/lb. x 25 lbs. = 75 mg

Step 2 – Determine MRD in mL
Total MRD in mg ÷ mg per mL = Total MRD in mL
i.e., 75 mg ÷ 30 mg = 2.5 mL

Step 3 – Determine MRD in cartridges
Total MRD in mg ÷ mg per cartridge = Total MRD in cartridges
i.e., 75 mg ÷ 54 = 1.38 cartridges