Background: Topical capsaicin and eutectic mixture of local anesthetics (EMLA) have been found to be equally effective in minimizing the pain of venipuncture. After the injection of capsaicin, both tertiary amine local anesthetics and their quaternary ammonium derivatives can elicit a prolonged and predominantly sensory/nociceptor selective block. We hypothesized that the combined application of capsaicin and ELMA will be more effective than their individual effect, and lower concentrations of individual drugs in this mixture may also be associated with reduced side effects.
Methods: One hundred twenty patients were randomized into 4 equal groups. The control group received plain lubricant cream; the EMLA group received EMLA cream; the capsaicin group received Myolaxin ointment (containing oleoresin capsaicin equivalent to capsaicin 0.075% w/w, methylsalicylate IP 20% w/w, menthol IP 10% w/w, camphor USP 5% w/w, and eucalyptus oil IP 5% w/w); and the EMLA + capsaicin group received EMLA cream and Myolaxin ointment mixed in equal amounts. An anesthesiologist applied the cream to a 10-cm(2) area (site of venous cannulation) on the dorsum of the nondominant hand of the patient 1 hour before venipuncture and covered the area with an occlusive transparent dressing. Venipuncture was performed with an 18-gauge cannula after removing the dressing. Venipuncture pain was graded by the patient on a 0 to 10 visual analog scale, where 0 means no pain and 10 means worst imaginable pain. P values (after correction for multiple comparisons) of <0.05 were considered significant.
Results: The incidence of no pain on venous cannulation (primary end point) was 0% in the control group (0/30). The incidence of no pain were significantly higher in the EMLA group (32%, 9/28, 95% corrected confidence interval for the difference 12%-57%, P = 0.0025), capsaicin group (30%, 9/30, 10%-53%, P = 0.0031), and EMLA + capsaicin groups (47%, 14/30, 25%-69%, P < 0.0001). Severity of venipuncture pain as assessed by visual analog scale median (interquartile range) was lower in the EMLA + capsaicin group 1 (2) compared with other groups 3 (1), 1.5 (3), and 1.5 (3) for control, EMLA, and capsaicin, respectively (P < 0.001, P = 0.04, and P = 0.04, respectively).
Conclusion: We observed that the combination of capsaicin and EMLA in a low concentration is as effective in managing venous cannulation as when applied as an individual drug alone. Larger studies with varying concentration of capsaicin and EMLA are recommended to more fully evaluate the potential advantages.