Equianalgesia, opioid switch and opioid association in different clinical settings: a narrative review

Emergency or postoperative pain often represents an authentic challenge in patients who were already on opioid treatment for chronic pain. Thus, their management requires not only the physician's ability to treat acute pain, but also competence in switching the opioid that lost efficacy. Different aspects should be considered, such as opioids titration, switching, association and equianalgesia. The objective of this paper is to provide a narrative review, which has been elaborated and discussed among clinicians through an iterative process involving development and review of the draft during two web-based meetings and via email. This expert opinion aims to facilitate the correct opioid use through appropriate practices with a focus on pain treatment in emergency and postoperative pain. Equianalgesia tables were reviewed and integrated by clinicians and researchers with expertise in anesthesia, postoperative medicine, intensive care, emergency medicine pharmacology and addiction medicine. Special populations (liver/kidney failure, elder, pediatric, pregnancy/lactation) are discussed in detail along with other critical scenarios, such as: (i) rapid pain worsening in chronic pain (aggravating pain due to disease progression or tolerance development to analgesic therapy); (ii) acute pain on maintenance treatment; and (iii) pain management of complicated patients in emergency care. Extended and updated equianalgesia tables and conversion rates for 17 different opioid formulations (of 9 different molecules) are presented as follows. Opioids remain the class that best suits clinical needs of emergency and post-operative medicine. However, it should be stressed that equianalgesia can be affected by drug-to-drug interactions and pharmacological imprecision, in a complex field where clinical experience may be the main guiding principle.