8 Higher mu-opioid binding potential was seen in young women compared with men in some cortical and subcortical areas. However, binding in the thalamus and the amygdala declined in postmenopausal women to levels below those of men. The clinical significance of these gender-related differences awaits delineation, but the higher receptor content may play a role in the greater pain sensitivity of healthy younger women compared with men. Since the mu-receptor opioids produce more nausea, sedation, confusion, constipation, and respiratory depression than the kappa opioids, there may be clinical advantages to greater use of the kappa opioids in women. Because there was negligible and only short-lasting pain relief in men given the kappa opioids, there would be little role for these drugs for the management of pain in men.
Examples are pentazocine, nalbuphine, and butorphanol.
However, the large clinical trials of these drugs for the relief of chronic osteoarthritis pain and rheumatoid arthritis pain included significant numbers of women for whom the drugs were efficacious. The drugs have also been widely used and are efficacious for the treatment of mild to moderate pain from many etiologies in women as well as in men. It is, therefore, difficult to put in clinical perspective the results of the small, carefully controlled study by Walker and Carmody 9 on electrical pain in which selected doses of ibuprofen produced relief from electrically induced pain only in men. The premarketing efficacy trials for these newer agents, however, included large numbers of women, and there is little question that both celicoxib and rofecoxib effectively reduce pain of osteoarthritis and rheumatoid arthritis in women as well as men. Women are more likely than men to have been exposed to sulfa medications and to have developed drug allergies to sulfa-containing compounds.