Lidocaine hydrochloride (lidocaine HCl) is one of the most widely used amide local anesthetics, particularly in dentistry and minor surgical procedures. Introduced in 1948, lidocaine quickly replaced procaine due to its superior pharmacological properties, such as a faster onset of action, greater potency, and longer duration of anesthesia. Classified as an amide anesthetic, lidocaine is known for its potency, rated at 2 (with procaine at 1), making it highly effective for a wide range of clinical applications.
Lidocaine is metabolized in the liver by microsomal mixed-function oxidases, converting it into metabolites like monoethyl glycine and xylidide, the latter of which is a potentially toxic local anesthetic. These metabolites are excreted primarily via the kidneys, with less than 10% of the drug being excreted unchanged. Lidocaine has a rapid onset of action (3 to 5 minutes), making it useful for procedures that require quick and effective anesthesia. Its potency and toxicity ratings are both 2 when compared with procaine, emphasizing its strength and safety when used appropriately.
Lidocaine's vasodilatory properties are moderate, which can result in faster systemic absorption unless combined with a vasoconstrictor like epinephrine. Two common formulations of lidocaine include 2% with epinephrine 1:50,000 and 2% with epinephrine 1:100,000. The addition of epinephrine not only reduces the absorption rate but also extends the duration of anesthesia. For instance, with epinephrine 1:100,000, lidocaine provides about 60 minutes of pulpal anesthesia and 3 to 5 hours of soft tissue anesthesia. This makes it an ideal choice for procedures requiring prolonged anesthesia with minimal systemic absorption.
The FDA-approved maximum recommended dose (MRD) for lidocaine is 7.0 mg/kg, or 3.2 mg/lb of body weight, not to exceed an absolute maximum of 500 mg. For healthy adults, this dose is generally well tolerated, but adjustments should be made for pediatric, elderly, or compromised patients to minimize the risk of toxicity. Lidocaine’s pregnancy classification is B, and it is considered safe for use during lactation.
