Respiratory depression after intrathecal opioids

Morphine 20 mg and pethidine 50 mg were accidentally injected intrathecally in a patient who had received large doses of opioids epidurally for cancer pain and who had shown tolerance to their effects. The well established tolerance to spinal opioids did not protect the patient against a moderate degree of respiratory depression. Morphine concentrations 6.5 hours after the morphine injection were 103,500 ng/ml and 52 ng/ml in cerebrospinal fluid and serum, respectively.