Anaes · Local anaesthetic pharmacology
Local anaesthetic additives and adjuvants
Also known as Local anaesthetic adjuvants · Adrenaline as a vasoconstrictor additive · Clonidine and dexmedetomidine adjuvants · Perineural dexamethasone
Additives are combined with local anaesthetics to speed onset, prolong duration, improve block quality and spare opioid. Adrenaline (1:200,000) is the commonest additive, prolonging the block and lowering toxicity through vasoconstriction, but must never be used in end-arterial territories. Sodium bicarbonate alkalinises the solution for faster onset but precipitates bupivacaine. Alpha-2 agonists (clonidine, dexmedetomidine) prolong and improve blocks but cause hypotension, bradycardia and sedation. Dexamethasone (perineural or intravenous) prolongs the block and reduces rebound pain. Neuraxial opioids give synergistic analgesia but risk delayed respiratory depression. Hyaluronidase enhances spread in ophthalmic blocks, and preservatives (metabisulfite, methylparaben) cause many local-anaesthetic allergy reactions (Grelowska 2026, de Souza 2026, Hong 2026).
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A patient leaves theatre with a perfect single-shot erector spinae plane block, pain-free and smiling — and at 2am the block wears off into a wall of unremitting pain that the opioid PCA cannot catch. That surge is rebound pain, and the additive you put in the solution is exactly the lever that defers it and softens the landing.[3]
Four goals drive every additive decision: a faster onset, a longer duration, a denser block, and a lower dose of local anaesthetic and opioid — which trims both systemic toxicity and opioid side effects. No single agent is ideal, so the additive tunes the trade-off to the block, the patient and the surgery.[5]
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- [1]Grelowska E, et al. Dexamethasone vs. Dexmedetomidine as Adjuvants to Erector Spinae Plane Block in Total Knee Arthroplasty: A Randomized Double-Blind Controlled Trial J Clin Med, 2026.PMID 42355681
- [2]de Souza PMF, et al. Opioid-sparing analgesia with clonidine versus fentanyl in inguinal hernia repair: a randomized clinical trial Hernia, 2026.PMID 42364024
- [3]Hong B, et al. Consistent analgesic effect of intravenous dexamethasone on rebound pain after brachial plexus block: a causal machine learning approach Korean J Pain, 2026.PMID 42357812
- [4]Ramesh S, et al. Integrated Advanced Monitoring and Target-Controlled Infusion Anesthesia in a Child With Arthrogryposis Multiplex Congenita Cureus, 2026.PMID 42359210
- [5]Chooklin S, et al. In Search of Ideal Analgesia: Classical and Deep Rectus Sheath Block in Laparoscopic Cholecystectomy Local Reg Anesth, 2026.PMID 42358227
- [6]El-Tallawy SN, et al. Postoperative Pain Outcomes and Satisfaction in Preschool Versus School-Age Children: A Prospective Multicenter Observational Study Cureus, 2026.PMID 42338860