Anaes · Local anaesthetic pharmacology

Local anaesthetic pharmacokinetics, dosing and maximum doses

Also known as Local anaesthetic maximum doses · Local anaesthetic systemic toxicity (LAST) · Lipid emulsion rescue · Mg per kg dose calculation

Local anaesthetic pharmacokinetics and safe dosing rest on a small set of exam-critical ideas. Onset is governed by pKa (a pKa closer to 7.4 means more un-ionised drug at physiological pH and faster onset), the total dose (mass of drug) and tissue perfusion, while duration is governed by protein binding (more bound means longer), lipid solubility, intrinsic vasoactivity and the addition of a vasoconstrictor (adrenaline) (Little, 2026; Christensen, 2026; Copur, 2026). The maximum recommended adult doses are: lidocaine 3 mg per kg plain and 7 mg per kg with adrenaline; bupivacaine 2 mg per kg plain and 2 mg per kg with adrenaline; levobupivacaine 2 mg per kg; ropivacaine about 3 to 3.5 mg per kg; prilocaine 6 mg per kg plain and 8 mg per kg with adrenaline; and mepivacaine 5 mg per kg plain and 7 mg per kg with adrenaline (Christensen, 2026; Little, 2026). Toxicity depends on the peak plasma concentration, which is determined by the total dose and the rate of absorption from the site, highest at intercostal sites and lowest subcutaneously, so the same mg per kg dose is more dangerous intercostally (Christensen, 2026; Merchant, 2026). Always calculate the dose in mg per kg, aspirate before injecting and inject slowly (Christensen, 2026; Little, 2026). Local-anaesthetic systemic toxicity (LAST) presents with CNS signs (perioral tingling, tinnitus, agitation progressing to tonic-clonic seizures and coma) and then cardiovascular collapse, worst with bupivacaine; the specific antidote is intravenous lipid emulsion 1.5 mL per kg bolus then infusion, with small adrenaline boluses and prolonged resuscitation (Meral, 2026).