Modification of local anesthetic toxicity by vasoconstrictors

Area of Science:

• Pharmacology
• Toxicology
• Anesthesiology

Background:

• Local anesthetics are widely used for pain management.
• Vasoconstrictors like epinephrine and levonordefrin are often added to local anesthetics to prolong their duration of action and reduce systemic absorption.
• The interaction between local anesthetics and vasoconstrictors can influence their toxicity and systemic effects.

Purpose of the Study:

• To investigate the impact of epinephrine and levonordefrin on the toxicity and lethality of four common local anesthetics (procaine, lidocaine, tetracaine, bupivacaine) in a mouse model.
• To determine if physical restraint modifies the observed effects of vasoconstrictors on local anesthetic toxicity.

Main Methods:

• Male mice were intravenously injected with varying doses of procaine, lidocaine, tetracaine, or bupivacaine, alone or combined with epinephrine or levonordefrin (15 mcg/kg).
• Dose-response curves were generated, and median toxic dose (CD50) and median lethal dose (LD50) values were calculated using probit analysis.
• Experiments were also conducted under conditions of tight physical restraint.

Main Results:

• Both epinephrine and levonordefrin reduced the toxicity and lethality of procaine.
• Epinephrine, but not levonordefrin, increased the toxicity and lethality of bupivacaine and the lethality of tetracaine.
• Neither vasoconstrictor significantly altered lidocaine toxicity in mice, although epinephrine increased lidocaine lethality in rats.
• Physical restraint decreased the LD50 values for all tested local anesthetics and abolished the modifying effects of the vasoconstrictors.

Conclusions:

• The effects of epinephrine and levonordefrin on local anesthetic toxicity are anesthetic-specific and can be influenced by the animal model.
• Physical restraint significantly impacts local anesthetic toxicity and can mask the effects of vasoconstrictors.
• These findings highlight the complex interplay between local anesthetics, vasoconstrictors, and physiological conditions in determining systemic toxicity.