Severe uncontrolled pain in buttock in a patient on naltrexone: a diagnostic challenge.

A 26-year-old woman with a history of intravenous drug use was admitted to hospital with worsening pain in the right buttock radiating to the lateral part of the thigh and to the calf with no suspicion of cauda equina compression. Eventually, a diagnosis of sacroiliitis was made and appropriate antibiotics were administered. Provision of analgesia for this patient was difficult. On admission her medications included naltrexone, venlafaxine and tramadol. Initially naltrexone was continued and analgesia provided by epidural local anaesthetic and clonidine, intravenous ketamine and oral agents. After several days, naltrexone was ceased and opioids were used in addition to the other analgesics. The epidural analgesia was only partially effective, perhaps because of inadequate blockade of the L4-S1 nerve roots, which carry sensation from the sacroiliac joint. Naltrexone is a long-acting opioid antagonist. If opioid analgesia is planned, it is necessary to cease naltrexone for 24 to 72 hours. In an emergency, if non-opioid techniques prove ineffective, short-acting opioids can be titrated to effect in a monitored environment.