Pharmacological Tests in 100 Patients with Intractable Pain

Purpose. In order to determine the pain mechanisms involved in the intractable pain syndrome and to find an appropriate pain treatment for each patient, and to make a pharmacological differential diagnosis of the mechanisms of pain involved, we performed the so called the drug challenge test (DCT) using Ketamine, Phentolamine, Thiamylal, Morphine and Lidocaine in 100 patient suffering from intractable pain. Methods. DCI was performed with one study drug per day. After securing a vein for transfusion, bolus physiological saline was injected intravenously in order to evaluate placebo effect 2 times with a 5 minute interval determining pain grade by the numerical rating scale (NRS). Physiological saline was followed by the test drug after 5 minutes from administration of the second bolus of physiological saline and NRS was observed every 1 and 5 minutes after the administration of the study drug. If NRS did not become zero, supplemental administration was performed every 5 minutes up to 3 times. The dose of each study drug per injection was as follows; Phentolamine： 5 mg, Thiamylal 50 mg and Morphine 3 mg. The Lidocaine test consisted of two administrations of physiological saline followed by a single bolus injection of 1 mg/kg of Lidocaine which was followed by continuous infusion of 1 mg/ kg Lidocaine for 30 minutes. NRS was determined intermittently at 5 minutes intervals. Patients whose NRS decreased from 10 (pre-treatment) to 6 were considered to be responders. Results. Test-positive percentages were as follows; 81% with Morphine, 62% with Ketamine, 45% with Thiamylal, 44% with Lidocaine and 35% with Phentolamine. There was a significant difference in the pain relief effect by sympathetic nerve block between responders and non-responders with the Phentolamine test. Conclusions. It was suggested that the results of DCI may reflect the variety of mechanisms involved in the intractable pain syndrome. It was concluded that the drug challenge test using these 5 different drugs whose actions are known may useful tool to detect the pain generating mechanism and appropriate pain treatment for each patient with intractable pain.