Sex Differences in Response to Cutaneous Anesthesia: a Double Blind Randomized Study

The existing literature on experimentally induced pain indicates that there are sex differences, with females displaying greater sensitivity. In epidemiological studies, sex differences are also noted in the prevalence of a number of pain syndromes, with females reporting more severe pain, more frequent pain, and pain of longer duration. Complicating the interpretation of pain differences between men and women in clinical samples are reports of sex differences in response to pain-reducing medications. Studies in human subjects suggest that women respond better to certain opioid analgesics than men following third molar extraction, but few studies have assessed sex effects in effectiveness of topical anesthetics. The purpose of this study was to test for sex differences in response to a topical anesthetic, Lidocaine, using double blind, placebo controlled experimental methodology, in combination with a magnitude matching psychophysical protocol using a pressure algometer. The subjects were 21 female and 23 male adult volunteers. Twenty-four subjects (12 males and 12 females) were randomly assigned to the Lidocaine condition and 20 subjects were randomly assigned to the placebo control condition (9 males and 11 females). The effect size across sex for subjects in the Lidocaine treatment condition on the response bias variable was large indicating the males rated the stimuli as less painful than the females. Sex differences were not observed for discriminability in the Lidocaine treatment condition. This study did not show sex differences in the placebo condition. These results are particularly interesting in light of previous work that has shown similar pain stimuli (pressure pain) to be the stimulation most sensitive to sex differences. Results of this study suggest that the protocol employed (pressure pain stimulus with magnitude matching task) is sensitive to both anesthetic treatment and sex differences and represents an improvement in pain assessment methodology for use in experimental studies and in the clinic.