Therapeutic agents commonly used to treat PHN include the lidocaine patch, oral tricyclic antidepressants (TCAs), and antiepileptic drugs. While TCAs are the most widely studied drug class, they fail to provide at least moderate pain relief in nearly half of PHN patients, and with considerable side effects. The role of opioids in treating chronic non-cancer pains such as PHN has been considered controversial because of questionable effictiveness, side effects of the drugs, and their potential for addiction and cognitive impairment.
In a study published in the October 8 issue of Neurology, the American Academy of Neurology's scientific journal, researchers from The Johns Hopkins University and the National Institutes of Health have demonstrated that opioids are not only highly effective in reducing pain in PHN patients, they caused no appreciable effect on any cognitive measure. The double-blind study compared treatment outcomes using opioids, TCAs and placebo, with 44 of 76 randomized patients completing all three cycles (approximately eight weeks per treatment). The treatment periods were separated by a one-week drug-free, washout period.
The primary opioid studied was controlled release morphine, with methadone as the alternate; the primary TCA was nortriptyline, with desipramine as the alternate. (Patients who could not tolerate the primary treatment drugs were offered the alternate drug of the same class within the treatment period.)
Pain intensity ratings, pain relief, and cognitive function were the primary outcome measures. Greater mean decreases in pain ratings followed therapy with both TCAs and opioids than with placebo, which had no effect on pain. The reduction in pain ratings tended to be greatest with opioids. The mean percent pain relief ratings were similar with the two active drug treatments, and greater than with the placebo.
Regarding cognitive function, treatment with opioids did not influence performance on any measure, whereas TCAs slightly worsened performance on several tests. "Among patients who completed all three treatment periods, more subjects preferred the opioids," notes study author Srinivasa Raja, MD, of The Johns Hopkins University School of Medicine. "Even when considering the more common side effects with opioids - nausea, constipation, loss of appetite and drowsiness -- the patients who were exposed to both active drugs still preferred the opioids."
In addition, while effectively treating the pain, the opioids did not cause significant cognitive decline, as measured after two months of drug treatment. "This study provides further convincing evidence that opioids are effective in treating the pain in PHN patients, and that opioids can provide a useful alternative treatment for neuropathic pain," said Raja. Yet despite the favorable trends towards superior effectiveness and minimal cognitive effects of opioids in this study, "We consider it premature to argue that opioids should be the treatment of first choice in PHN, or neuropathic pain in general," cautions Raja. The study authors recommend more long-term studies of the risks and benefits of opioids relative to other treatments for PHN.
The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. For more information about the American Academy of Neurology, visit its website at www.aan.com.
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