From the Guidelines
The likelihood of experiencing Local Anesthetic Systemic Toxicity (LAST) or lidocaine toxicity 24 hours after the last injection is extremely low to virtually nonexistent. Lidocaine has a relatively short half-life of approximately 1.5-2 hours in most adults with normal hepatic function, as noted in studies such as 1. After 24 hours, the drug would have undergone approximately 12 half-lives, meaning that less than 0.01% of the original dose would remain in the bloodstream. This makes systemic toxicity highly improbable at this point.
The metabolism of lidocaine occurs primarily in the liver through the cytochrome P450 system, and its metabolites are excreted through the kidneys. Patients with severe liver disease or significant renal impairment may experience slightly prolonged elimination, but even in these cases, 24 hours is generally sufficient for drug clearance to levels well below the toxic threshold, as discussed in 1. Symptoms of LAST typically manifest within minutes to hours after administration, not days later.
Key factors that could influence lidocaine toxicity include:
- Duration of infusion, with prolonged infusions potentially leading to non-linear pharmacokinetics 1
- Acid-base status, with acidaemia increasing the dissociation of lidocaine from plasma proteins
- Hypoxaemia
- Hypoalbuminaemia and other conditions where plasma proteins are depleted
- Drug interactions, such as with beta-blockers or amiodarone, which can reduce lidocaine metabolism or clearance
- Body weight, with both low and high body mass index potentially associated with increased risk of adverse reactions
If a patient is experiencing concerning symptoms 24 hours after lidocaine administration, clinicians should strongly consider alternative diagnoses rather than attributing these to lidocaine toxicity, based on the information provided in 1 and 1.
From the Research
Local Anesthetic Systemic Toxicity (LAST) Lidocaine Toxicity
- The likelihood of experiencing Local Anesthetic Systemic Toxicity (LAST) lidocaine toxicity 24 hours after the last injection is not explicitly stated in the provided studies 2, 3, 4, 5, 6.
- However, the studies suggest that lidocaine toxicity can occur at any time after administration, and the risk factors for toxicity include high doses, intravenous administration, and individual patient susceptibility 2, 3, 5, 6.
- The studies also highlight the importance of prompt recognition and treatment of lidocaine toxicity, including the use of intravenous lipid emulsion as an antidote 2, 5, 6.
- The mechanisms of lidocaine toxicity are complex and involve the central nervous system, including the unmasking of L-type Ca²⁺ current-mediated action potentials in thalamocortical neurons 4.
- The provided studies do not provide a specific percentage likelihood of experiencing LAST lidocaine toxicity 24 hours after the last injection, and more research would be needed to determine this likelihood.
Risk Factors and Prevention
- The studies emphasize the importance of dose adjustment and careful monitoring of patients receiving lidocaine, particularly those with advanced heart failure or other susceptible factors 3, 5.
- The use of intravenous lipid emulsion as an antidote for lidocaine toxicity is highlighted in several studies 2, 5, 6.
- Education and awareness of the risks and symptoms of lidocaine toxicity are crucial for prompt recognition and treatment 5, 6.