Which component of a local anesthetic is most likely to cause an allergic reaction?

Sodium bisulfite is the component of a local anesthetic most likely to cause an allergic reaction, primarily because it is used as a preservative in multidose vials of anesthetics. This compound is a sulfite, and certain individuals, especially those with asthma or sulfite sensitivities, may experience allergic reactions to sulfite preservatives. Reactions can range from mild to severe, including symptoms such as respiratory distress or anaphylaxis.

The other components listed generally have a lower incidence of causing allergic reactions. Lidocaine is a commonly used amide anesthetic, and while rare allergic reactions can occur with it, they are infrequent. Epinephrine is often added to local anesthetics to prolong their effect and decrease bleeding; although some patients may have a sensitivity to it, true allergies are rare. Sodium chloride, typically used to create isotonic solutions, does not elicit allergic reactions. Thus, sodium bisulfite stands out as the most significant concern regarding allergic responses in patients receiving local anesthesia.