| Individual local anaesthetic drugs |
Lignocaine
Lignocaine is an aminoamide local anaesthetic and is also an antiarrhythmic drug. In specialised pain management units, intravenous or continuous subcutaneous infusions of lignocaine are used for neuropathic pain. Alkalinisation with sodium bicarbonate increases the rate of onset of block (see Wounds and lacerations for information). Allergy rarely occurs. See Table 1.7 for duration of action and maximum doses.
Topical lignocaine has a role in managing localised neuropathic pain such as postherpetic neuralgia. A eutectic mixture of lignocaine 2.5% and prilocaine 2.5% is used topically to produce dermal anaesthesia before cannula insertion and minor surgical procedures, and is commonly used in children. This mixture is usually applied topically under an occlusive dressing for 30 to 60 minutes.
For adverse effects of local anaesthetics, see Adverse effects.
Prilocaine
Prilocaine is equipotent to lignocaine, but is less toxic and has a slightly longer duration of action. Prilocaine is the preferred agent for regional intravenous local anaesthesia (Bier block). See Table 1.7 for duration of action and maximum doses.
Prilocaine is also used topically in combination with lignocaine.
The main disadvantage is methaemoglobinaemia at high doses in susceptible patients. Doses greater than 600 mg, or 8 mg/kg, can lead to reduced blood oxygen-carrying capacity and cyanosis, often with delayed onset. Prilocaine should be used cautiously in infants under three months of age due to their lower levels of methaemoglobin reductase compared to adults. For further adverse effects, see Adverse effects.
Bupivacaine
Bupivacaine is a long-acting local anaesthetic. It is used for infiltration, peripheral nerve and plexus blocks, and epidural and spinal anaesthesia or analgesia. Onset time is about five minutes after infiltration, up to 20 minutes after epidural and major plexus blocks, and rapid after intrathecal use, although peak effect is further delayed (eg 15 minutes after intrathecal and 30 to 45 minutes after epidural use). See Table 1.7 for duration of action and maximum doses. For adverse effects, see Adverse effects.
Levobupivacaine
Levobupivacaine is the S-isomer of bupivacaine and may confer some safety advantages over bupivacaine. For continuous epidural analgesia, levobupivacaine can be co-administered with fentanyl, morphine or clonidine. The 0.75% solution (75 mg/10 mL) can be used to achieve a dense local anaesthetic block, but is not approved for obstetric or paediatric use. See Table 1.7 for duration of action and maximum doses. For adverse effects, see Adverse effects.
Ropivacaine
Ropivacaine is a long-acting analogue of bupivacaine produced as the pure S-enantiomer. It has lower arrhythmogenic and cardiac depressant effect than racemic bupivacaine. An advantage of ropivacaine is the greater differential in the response of sensory and motor nerves to local anaesthetic block. Profound sensory and motor block can be obtained when administered at high concentration via the epidural route, whereas lower concentrations allow analgesic block without significant motor impairment. The addition of adrenaline confers no advantage in the clinical use of ropivacaine. See Table 1.7 for duration of action and maximum doses. For adverse effects, see Adverse effects.
Procaine
Procaine is a benzoic acid ester local anaesthetic with low toxicity and some vasodilator activity. See Table 1.7 for duration of action and maximum doses. For adverse effects, see Adverse effects.
Amethocaine
Amethocaine (tetracaine) is a benzoic acid ester local anaesthetic, primarily used in topical anaesthesia (eg ophthalmic procedures). As a 4% gel or cream formulation, amethocaine has been shown to be effective topically to produce dermal anaesthesia before cannula insertion and minor surgical procedures. It may have a faster onset than lignocaine+prilocaine. Localised erythema has been noted. It is only available for hospital use [Note 1]. Amethocaine use in other local anaesthetic techniques is limited due to its systemic toxicity. For adverse effects, see Adverse effects.
Cocaine
Cocaine is a benzoic acid ester local anaesthetic that also causes local vasoconstriction. Toxicity and potential for abuse have limited its clinical use. Cocaine is used primarily for topical anaesthesia of the upper respiratory tract. Topical solutions, with a concentration of 1% to 10%, can be applied using cotton applicators or packs, or be instilled, or used as a spray on the mucous membranes of the oral, laryngeal, and nasal cavities. For adverse effects, see Adverse effects.
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