Opioid-induced hyperalgesia: What to do when it occurs?

While treating cancer pain with opioids, we can sometimes
observe a decline in analgesic efficacy of a given opioid dose, in
particular with disease progression. If this phenomenon occurs
whilst there is no obvious disease progression, this has been
traditionally attributed to development of pharmacological
tolerance. However, there is now increasing evidence for
the phenomenon of opioid-induced hyperalgesia as another
mechanism to explain the loss of effectiveness of opioids.
Opioid-induced hyperalgesia has been defined as increasing pain
sensitivity in patients chronically exposed to opioids without any
evidence for new causes of pain. Opioid-induced hyperalgesia
has been described in a large number of animal studies, since a
first publication of this phenomenon in 1971, which reported
that repeated injection of morphine produced hyperalgesia in
rats (1).