Opioid hyperalgesia.

PURPOSE OF REVIEW

Opioids are invaluable in the treatment of moderate-to-severe pain. Unfortunately, their prolonged use may be associated with the onset of opioid-induced hyperalgesia (OIH). This review focuses on recent clinical studies that support or refute the existence of OIH in patients.

RECENT FINDINGS

Whether or not OIH is a clinical reality is an ongoing debate. In recent years, the majority of clinical trials investigating whether chronic-opioid treatment causes paradoxical pain sensations have been conducted in opioid addicts, patients maintained on methadone and human volunteers receiving acute-morphine infusions. That opioid-maintained patients have different nociceptive profiles compared with opioid naïve patients has been both raised and rejected. Independent studies have reinforced the opinion that the development of OIH is based on confounders including pain modality tested, route of drug administration and specific opioid in question.

SUMMARY

Improvements in paradoxical pain intensity upon discontinuation of opioid therapy suggests that a multidisciplinary method of pain relief is favoured for chronic-pain patients. Quantitative-sensory testing of pain is offered as the most appropriate way of diagnosing hyperalgesia. We can, thus far only reliably validate the existence of OIH development in normal human volunteers receiving acute-morphine infusions.