Doses of local anaesthetics in dentistry
Use the lowest dose of local anaesthetic necessary to prevent the patient from experiencing dental pain.
#dtg3-c56-s8__tdtg3-c56-tbl4 gives the maximum safe single doses of local anaesthetics available in dental cartridges. For maximum safe single doses of local anaesthetics available in other presentations, see Table Maximum single doses of local anaesthetics. The dose required to prevent the patient from experiencing dental pain is usually much lower than the maximum dose, provided the method of administration is appropriate for the indication, and the local anaesthetic is injected into the correct site. The product information may provide a guide to the usual dose.
The dose required for an individual patient will depend on the area to be anaesthetised, the vascularity of the tissues, whether infiltration or regional block is used, and the age and physical condition of the patient. Overdose can occur relatively easily in children, particularly young children. Elderly patients may require a lower dose because of age-related physiological changes.
Before administering local anaesthetic, always calculate the maximum safe single dose. A worked example of calculating the maximum volume of a safe single dose of local anaesthetic shows a worked example of a dose calculation.
A 70 kg patient requires a local anaesthetic for a dental procedure. Lidocaine 2% (20 mg/mL) with adrenaline (epinephrine) 1:80 000 (12.5 micrograms/mL) will be used [NB1].
Calculate the maximum dose in milligrams based on the patient’s weight
maximum safe single dose of lidocaine with adrenaline is 7 mg/kg
7 mg/kg × 70 kg = 490 mg
Use the concentration of solution (mg/mL) to convert the calculated dose to volume
490 mg ÷ 20 mg/mL = 24.5 mL
Convert the calculated volume to number of 2.2 mL dental cartridges [NB2]
24.5 mL ÷ 2.2 mL/cartridge = 11 cartridges
Therefore, the total volume administered must not exceed 24.5 mL or 11 cartridges containing 2.2 mL each.
NB1: To convert a percentage concentration to mg/mL, multiply by 10 (eg 2% = 20 mg/mL).
NB2: Dental cartridges are available in a variety of volumes (eg 1.7 mL, 1.8 mL, 2.2 mL).
Multiple repeated doses within a short time period can result in accumulation of local anaesthetic, and potentially lead to systemic toxicity. In case of incomplete or failure of local anaesthetic injection, a repeat dose may be tried, provided the total dose administered to the patient does not exceed the maximum single dose (see #dtg3-c56-s8__tdtg3-c56-tbl4).
Some clinicians combine local anaesthetics to take advantage of the properties of each drug. If combining local anaesthetics, exercise caution because the effects and toxicities are additive, and there are few data to support this practice. There is a lack of consensus on the optimal method of determining the maximum doses of the individual drugs; the method described below provides a pragmatic way to determine the total maximum dose. However, be mindful that the dose required may be much lower than this calculated maximum; always use the lowest effective dose.
If combining local anaesthetics, calculate the maximum volume of each of the anaesthetics to be used—noting that maximum volumes are concentration dependent (see A worked example of calculating the maximum volume of a safe single dose of local anaesthetic for a worked example). From these calculated maximums, identify the lowest maximum volume, and ensure the combined volume of the anaesthetics to be used (ie the sum of the volumes of each anaesthetic) does not exceed this. For example, if combining lidocaine 2% with adrenaline (epinephrine) 1:80 000 and ropivacaine 3% for use in a 70 kg patient, calculate the maximum volume of each drug. For this patient, the maximum volumes of safe single doses are 24.5 mL of lidocaine 2% with adrenaline (epinephrine) 1:80 000 and 28 mL of ropivacaine 3%. The lowest of these two maximum volumes is 24.5 mL, so the combined volume of lidocaine and ropivacaine must not exceed 24.5 mL.