Dosing local anaesthetics for acute pain management

Use the lowest dose of local anaesthetic that provides adequate analgesia or anaesthesia. The dose required is usually much lower than the maximum dose because multiple factors influence local anaesthetic effect; see Factors influencing doses of local anaesthetics. Product information may provide a guide to the usual dose for specific procedures.

See Maximum single doses of local anaesthetics for maximum single doses of local anaesthetics and Examples of calculating the maximum volume of a local anaesthetic for an example of calculating the maximum volume of a local anaesthetic.

Table 1. Factors influencing doses of local anaesthetics
Factor	Comment
site of injection	influences the volume and concentration of local anaesthetic that can be administered: volume of local anaesthetic depends on the space it is injected into (eg small volumes are required for digital nerve blocks to reduce the risk of compression on surrounding tissues) concentration of local anaesthetic can overcome volume restrictions (ie a higher concentration results in a smaller volume of solution), but high concentrations can be toxic to some tissues
vascularity of the tissues	highly vascular tissues rapidly absorb local anaesthetics into the systemic circulation; this causes reduced duration of action, higher dose requirement and higher risk of systemic toxicity the following sites are listed in descending order of vascularity: interpleural, intercostal, caudal, epidural, brachial plexus, sciatic and femoral nerves, subcutaneous tissue
block density	lower doses may provide analgesia by preferentially blocking sensory nerves (eg nociceptors) higher doses provide anaesthesia by blocking sensory, motor and autonomic nerves
patient age	overdose can occur relatively easily in children, particularly young children elderly patients may require lower doses because of age-related physiological changes (eg decreased clearance and metabolism)
patient comorbidities	kidney or liver impairment increases the risk of toxicity due to decreased clearance and metabolism local anaesthetics enhance cardiac conduction defects; use with caution in patients with cardiac conditions consult product information for advice

Some proprietary preparations combine a vasoconstrictor (adrenaline [epinephrine]) with a short-acting local anaesthetic (eg lidocaine) to reduce local anaesthetic systemic absorption, prolong its local effect and reduce the risk of systemic toxicity. Larger doses of short-acting local anaesthetics can be used when combined with adrenaline.

The combination of long-acting local anaesthetics with adrenaline (epinephrine) is beyond the scope of this topic.

Use of adrenaline-containing preparations in end-artery regions (eg fingers, toes, nose, ears) can increase the risk of ischaemic necrosis—seek specialist advice.

Table 2. Maximum single doses of local anaesthetics
lidocaine without adrenaline (epinephrine) lidocaine with adrenaline (epinephrine) prilocaine bupivacaine with or without adrenaline (epinephrine) levobupivacaine ropivacaine
Local anaesthetic	Dosing [NB1]	Comments
Short acting
lidocaine without adrenaline (epinephrine)	available concentrations [NB2]: 0.5% (5 mg/mL) 1% (10 mg/mL) 2% (20 mg/mL)	do not repeat the maximum dose within 1.5 hours topical application and infiltration techniques are useful for short procedures lidocaine 5% patches are used as adjuvants (eg to manage neuropathic pain)
	maximum single dose [NB3]: 3 mg/kg
lidocaine with adrenaline (epinephrine)	available concentrations (expressed as lidocaine+adrenaline) [NB2]: 0.5% (5 mg/mL)+1:200 000 (5 micrograms/mL) 1% (10 mg/mL)+1:200 000 (5 micrograms/mL) 1% (10 mg/mL)+1:100 000 (10 micrograms/mL) 2% (20 mg/mL)+1:200 000 (5 micrograms/mL) 2% (20 mg/mL)+1:80 000 (12.5 micrograms/mL)	do not repeat the maximum dose within 1.5 hours topical application and infiltration techniques are useful for short procedures
	maximum single dose (lidocaine) [NB3]: 7 mg/kg
prilocaine	available concentration [NB2]: 0.5% (5 mg/mL)	preferred for intravenous regional blocks due to lower toxicity and rapid metabolism less painful for infiltration anaesthesia compared to lidocaine with adrenaline preparations methaemoglobinaemia may occur due to metabolite toxicity, particularly with higher doses or repeat administration
	maximum single dose [NB3]: 6 mg/kg
Long acting [NB4]
bupivacaine	available concentration [NB2]: 0.25% (2.5 mg/mL) 0.5% (5 mg/mL)	most cardiotoxic local anaesthetic; see Local anaesthetic poisoning cardiotoxicity may manifest before neurotoxicity
	maximum single dose [NB3]: 2 mg/kg
levobupivacaine	available concentration [NB2]: 0.25% (2.5 mg/mL)	structurally related to bupivacaine but has a reduced risk of neurotoxicity and cardiotoxicity may provide a longer sensory block compared to bupivacaine may be preferred to bupivacaine if high doses are required for anaesthetic blocks because of its more favourable toxicity profile
	maximum single dose [NB3]: 2 mg/kg
ropivacaine	available concentration [NB2]: 0.2% (2 mg/mL) 0.75% (7.5 mg/mL) 1% (10 mg/mL)	structurally related to bupivacaine but has a reduced risk of neurotoxicity and cardiotoxicity motor block may be slower in onset, shorter in duration and less intense compared to bupivacaine may be preferred when motor block is not desired (eg obstetric epidural analgesia)
	maximum single dose [NB3]: 3 mg/kg
Note: NB1: These doses are a guide only and vary with different sites of injection, vascularity, age and health of the patient. The lowest dose necessary should be used; consult product information. NB2: To convert a percentage concentration to a mg/mL concentration, multiply by 10 (eg 2% = 20 mg/mL). NB3: Use ideal body weight in overweight patients. NB4: If prolonged analgesia is required, long-acting local anaesthetics are preferred to reduce the risk of cumulative systemic toxicity that can occur with repeat doses of short-acting local anaesthetics. NB5: The combination of long-acting local anaesthetics with adrenaline (epinephrine) is beyond the scope of this topic.

Figure 1. Examples of calculating the maximum volume of a local anaesthetic.

[NB1]

EXAMPLE 1

A 70 kg patient requires a local anaesthetic via infiltration to suture a leg wound. Lidocaine 2% (20 mg/mL) with adrenaline (epinephrine) 1:80 000 (12.5 micrograms/mL) will be used.

Calculate the maximum dose in milligrams based on the patient’s weight

maximum safe single dose of lidocaine with adrenaline (epinephrine) 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 (to convert a percentage concentration to mg/mL, multiply by 10 [eg 2% = 20 mg/mL]).

490 mg ÷ 20 mg/mL = 24.5 mL

Therefore, the total volume administered must not exceed 24.5 mL

EXAMPLE 2

A 20 kg child requires a local anaesthetic for a femoral nerve block for a fractured femur. Ropivacaine 0.75% will be used.

Calculate the maximum dose in milligrams based on the patient’s weight

maximum safe single dose of ropivacaine is 3 mg/kg

3 mg/kg × 20 kg = 60 mg

Use the concentration of solution (mg/mL) to convert the calculated dose to volume (to convert a percentage concentration to mg/mL, multiply by 10 [eg 0.75% = 7.5 mg/mL]).

60 mg ÷ 7.5 mg/mL = 8 mL

Therefore, the total volume administered must not exceed 8 mL

Note: NB1: Caution is required when calculating local anaesthetic doses because miscalculations are common and cause significant harm.

Combining a short-acting local anaesthetic with a long-acting local anaesthetic (to provide both a fast onset and longer block duration) adds additional complexity to drug regimens and increases the risk of dose calculation errors. The Pain and Analgesia Expert Group recommends using a single local anaesthetic to reduce the risk of patient harm.

Note: To reduce the risk of patient harm, only use a single local anaesthetic.