Analgesic Efficacy of Pentazocine Versus a Pentazocine-Naloxone Combination Following Oral Administration

Abstract

The effect of the addition of 0.5 mg naloxone on the analgesic em- cacy of pentazocine 50 mg was studied. A single oral dose of either pentazo- cine, the combination of pentazocine plus naloxone, or placebo was given in a randomized double-blind parallel group study. The study sample consisted of 48 patients with moderate pain and 76 patients with severe pain resulting from episiotomy, cesarean section, or gynecological surgery. An analysis of the entire sample showed both pentazocine and the combination to be significantly more effective than placebo for all measures, including global assessments. In addition, the combination was significantly less efficacious than pentazocine for the sum of the pain intensity difference (SPID), percentage of the sum of the pain intensity difference (%SPID), and for relief and pain intensity difference (PID) at the fourth hour. Because there was a significant interaction between drug and baseline pain intensity for the variable SPID, comparisons were made between pentazocine and the combination within each baseline pain intensity group. For patients with moderate baseline pain, the combina- tion produced significantly less pain relief than pentazocine for SPID and for relief and PID at hours 3 and 4. In patients with severe baseline pain, there was no significant difference between pentazocine and the combination of pentazo- cine plus naloxone. Further studies are needed to confirm the suggestion that naloxone taken orally may decrease the analgesia achieved with pentazocine; clinicians should be aware of this possibility.