Researchers led by UCSF scientists are reporting that an experimental pain drug known as a kappa-opioid brings pain relief to female rats but not males, a finding that adds weight to a recent UCSF clinical finding, and highlights, they say, the need to evaluate drugs by gender.
Traditionally, kappa-opioids have been dismissed as ineffective analgesics in humans, though the drugs have shown mixed results in animal studies, depending on how they have been administered.
The finding, published in the March issue of Pain, may help to resolve the controversy about the drug's effectiveness, the researchers say, and underscores a weakness in traditional drug screening: Until the early 1990s, most drugs, including kappa-opioids, were primarily evaluated in men.
"The problem of gender differences, particularly in response to opioid drugs, is extremely important and widely under-appreciated," says the senior author of the study, Howard Fields, MD, PhD, a leading expert on the brain mechanisms of pain and a pain-treatment specialist. Fields is UCSF professor of neurology, a member of the Keck Center for Integrative Neuroscience and director of the UCSF Wheeler Center for the Neurobiology of Addiction.
"But regardless of the explanation", he says, "People need to understand that male and female brains are different, period. And this fact has to be taken into consideration when thinking about drug treatments, particularly drugs that act on the central nervous system."
The other co-authors of the Fields study were Sheralee A. Tershner PhD, formerly a post-doctoral fellow in the Fields lab and currently of the Department of Psychology, Western New England College, and Jennifer Mitchell, PhD, formerly a graduate student in the Fields lab.
The study was funded by the National Institute on Drug Abuse.
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