Double-blind testing fails to confirm analgesic response to extradural morphine

We report two patients with chronic non-malignant pain in whom morphine given intravenously via a patient-controlled analgesia system produced partial pain relief but was accompanied by severe side effects. Open administration of epidural morphine resulted in complete pain relief with minimal side effects and the patients were considered as candidates for implanted opioid delivery systems. However, when the epidural morphine was given in a double-blind and placebo-controlled manner, morphine did not produce greater analgesia than placebo and no dose-response relationship was seen. These cases show that careful investigation is necessary before proceeding to implanted systems and that changing the route did not improve the analgesia:side effect balance for morphine in these patients.