In 2018, the European Medicines Agency (EMA) reported 16 cases of hyperalgesia (severe pain) in patients taking transmucosal fentanyl.

Hyperalgesia is a known adverse effect of opioids. The key symptom is an increase in the intensity of pain felt, an increase associated with the effects of the opioid. It is difficult to distinguish it from an increase in pain intensity caused by the painful condition itself. In the latter case, the pain intensity usually diminishes with an increase in the opioid dose, whereas with hyperalgesia, the opposite applies.

Another symptom of hyperalgesia is hypersensitivity to painful stimuli. This aspect has been studied with fentanyl in people without pain (healthy volunteers). Hyperalgesia was more intense with the highest doses of fentanyl.

The French patient information leaflet concerning fentanyl products dating from August 2018 mentions hyperalgesia among its adverse effects.

In practice, when the analgesic effect of an opioid appears to be diminishing and the worsening of the painful disease does not appear to be the cause, other causes of pain should be considered, including addiction to the opioid or hyperalgesia.

When hyperalgesia is likely, a reduction of the opioid dose or even discontinuation of the drug should be considered.

©Prescrire 1 July 2019

"Fentanyl and other opioids: hyperalgesia" Prescrire Int 2019; 28 (206): 182. (Pdf, subscribers only).

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