title: Opioid-induced hyperalgesia (OIH).
abstract: OBJECTIVE
  Opioids are commonly used for pain control; however, they can cause hyperalgesia. The reason why this can happen is not known. The objective of this review was to describe the mechanisms, factors implicated, and drug modulation.
  
  
  BACKGROUND
  The factors implicated in the development of opioid-induced hyperalgesia (OIH), such as duration of use, dose, and type of opioids are described. Mechanisms involved include the glutamatergic system and N-methyl-D-aspartate receptors (NMDA), spinal cyclooxygenase (COX) activation, excitatory amino acids, dynorphin, cytokines and chemokines; prostaglandins, and descending facilitation. Modulation of hyperalgesia could be done through: NMDA receptor antagonists, alpha2-adrenergic agonists, and COX inhibitors.
  
  
  CONCLUSIONS
  This is a very complex subject, which involves a series of pathophysiological mechanisms that could contribute for OIH and patient discomfort, bringing disastrous consequences.
authors.affiliation: Department of Anesthesiology, Pain, and Intensive Care Medicine of the Escola Paulista de Medicina of Universidade Federal de São Paulo (EPM/UNIFESP), SP.
authors.forename: Plínio da Cunha
authors.initials: Pda C
authors.lastname: Leal
authors.forename: Jefferson
authors.initials: J
authors.lastname: Clivatti
authors.forename: João Batista Santos
authors.initials: JB
authors.lastname: Garcia
authors.forename: Rioko Kimiko
authors.initials: RK
authors.lastname: Sakata
mesh_terms: D000701:Analgesics, Opioid / Q000009:adverse effects*; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced*
chemical_list: D000701:Analgesics, Opioid