Onset and duration of intradermal mixtures of bupivacaine and lidocaine with epinephrine

Background/objective: Bupivacaine and lidocaine are often used concurrently, in theory, to combine the more rapid onset of lidocaine and the longer duration of bupivacaine. The purpose of this study was to evaluate this concept. Methods: Twenty-five subjects were enrolled in a double-blinded, randomized block design study to evaluate the onset and duration of four different mixtures of lidocaine and bupivacaine with epinephrine. The study was designed to achieve 80% power to detect an effect size of 0.37 at 5% overall significance. The four mixtures tested were: 0.25% bupivacaine with epinephrine (1:200,000); 1% lidocaine with epinephrine (1:100,000); 0.125% bupivacaine and 0.5% lidocaine with epinephrine (1:150,000); and 0.25% bupivacaine and 1% lidocaine with epinephrine (1:150,000). Four intradermal injections were made in the volar forearms of each participant. Time to effect and duration were measured by sensation of a sharp skin prick. Results: Mean time to onset ranged from 12 s to 29 s without statistical significance across all tested solutions (P=0.891). Mean duration of effect ranged from 6 h 38 min to 7 h 25 min with a statistically significant difference across the tested solutions (P=0.036). Conclusions: No statistical benefit was measured when comparing lidocaine with epinephrine, bupivacaine with epinephrine, and mixtures of these local anesthetics with regard to onset of action. While a statistical difference was observed in duration of effect, the clinical benefit measured was narrow.