Chloroprocaine

Chloroprocaine is an ester local anaesthetic with very rapid onset and the shortest duration of the clinically used agents, because plasma pseudocholinesterase hydrolyses it in seconds. It is used for short surgical epidural anaesthesia, rapid extension of labour epidural blocks for emergency caesarean section, short spinal anaesthesia and peripheral nerve block for brief procedures.

Class. Ester local anaesthetic (ultra-short duration).

Mechanism. Reversible blockade of voltage-gated sodium channels.

Pharmacokinetics. Onset 6 to 12 minutes epidural, 3 to 5 minutes spinal. Duration 30 to 60 minutes epidural, 40 to 60 minutes spinal. Plasma half-life about 20 seconds in adults and about 40 seconds in neonates, by pseudocholinesterase hydrolysis to 4-amino-2-chlorobenzoic acid and beta-diethylaminoethanol. Very low systemic accumulation and negligible placental transfer.

Indications are short surgical anaesthesia (epidural, spinal, blocks), rapid extension of labour epidural block for urgent delivery, and ambulatory surgery.

Maximum doses (adults)

• Plain: 11 mg/kg, not above 800 mg.
• With adrenaline: 14 mg/kg, not above 1000 mg.
• Concentrations: 1% is 10 mg/mL, 2% is 20 mg/mL and 3% is 30 mg/mL.

Techniques

• Spinal (preservative-free 1% hyperbaric or isobaric): 40 to 50 mg (4 to 5 mL) for short procedures of up to about 40 to 60 minutes; reduce in older adults and pregnancy.
• Epidural, surgical: 2 to 3% in 15 to 25 mL (300 to 750 mg), in incremental doses.
• Emergency extension of an existing labour epidural for caesarean section: 3% in 10 to 20 mL, in two or three divided boluses.
• Peripheral nerve block: 2 to 3% in 10 to 25 mL, depending on the block.
• Infiltration: 1 to 2%.
• No loading dose or titration beyond incremental dosing.

Children. Preservative-free formulation only for neuraxial use; weight-based limits as adults (11 mg/kg plain); use the lowest effective volume.

Contraindications. Hypersensitivity to ester anaesthetics or para-aminobenzoic acid; sulphite allergy (some preparations contain bisulfite); pseudocholinesterase deficiency; use of preserved formulations for neuraxial injection; infection at the site; coagulopathy or anticoagulation for neuraxial blocks; adrenaline-containing preparations in end-arterial sites.

Boxed-warning-level risks. Neurotoxicity with preserved formulations given neuraxially (preservative-free only); systemic toxicity with intravascular injection (rare because of rapid hydrolysis).

Adverse effects. Common: hypotension, nausea, back pain, transient pain on injection. Serious: high or total spinal block, neurological deficit after preserved formulation, allergic reactions, methaemoglobinaemia (rare), local anaesthetic systemic toxicity.

Interactions. Chloroprocaine epidurally can reduce the analgesic effect of later epidural bupivacaine and of epidural morphine or fentanyl. Suxamethonium and cholinesterase inhibitors prolong effect. Para-aminobenzoic acid antagonises sulphonamides. Adrenaline interacts with tricyclic antidepressants, monoamine oxidase inhibitors and non-selective beta blockers.

Common prescribing errors. Using a preserved solution for spinal or epidural use; expecting a long block; failing to plan analgesia after the short block; using it after epidural fentanyl or morphine without expecting reduced opioid effect; overdosing by adding to other local anaesthetic infiltration.

Special groups

• Pregnancy: widely used for emergency caesarean section extension because of rapid onset and negligible foetal exposure.
• Breastfeeding: compatible.
• Older adults: reduce spinal and epidural doses by 20 to 30%.
• Kidney impairment: no dose change.
• Liver impairment: no dose change for single doses; reduced pseudocholinesterase can prolong effect.
• Regional: confirm that the vial is preservative-free before neuraxial use; organophosphate exposure (pesticides) reduces cholinesterase and prolongs ester effect.

Formulations. Preservative-free solutions 1% (spinal), 2% and 3% (epidural, blocks); preserved solutions 1, 2 and 3% (infiltration, blocks only).

Administration. Aspirate and inject in 3 to 5 mL increments, with pauses. For emergency caesarean section, give 10 to 20 mL of 3% in divided doses while moving to theatre.

Baseline. Allergy history, coagulation status, pseudocholinesterase deficiency history, sulphite allergy, cardiac status, and anticoagulant timing for neuraxial techniques.

Monitoring. Continuous electrocardiogram, blood pressure and oxygen saturation during blocks. Sensory and motor recovery checks. Plan analgesia before the block wears off (about 45 to 60 minutes).

Therapeutic drug monitoring. Not used.

Dose reduction and stopping thresholds. Stop injection at any sign of toxicity or allergy. Reduce doses in older adults and in states of low cholinesterase.

Referral and escalation. Seizures or collapse: stop injection, give oxygen and airway support, benzodiazepine, and 20% lipid emulsion 1.5 mL/kg over 1 minute then 15 mL/kg/hour (maximum cumulative 12 mL/kg). Prolonged motor block beyond expected needs neurological review and imaging for haematoma.