Naloxone and pentazocine given after morphine

Morphine 0.3 mg kg-1 was i.m. given to 25 patients after upper abdominal operations, for analgesia purpose. One hour later, naloxone 0.01 mg was injected i.v. for every 1 mg morphine given. Ten minutes later, pentazocine 0.5 mg kg-1 was also injected i.v. in order to appreciate how it could counteract the reduction in analgesia level caused by naloxone. Complete analgesia could be found in all patients after the mentioned dose of morphine. The minute-ventilation and respiratory frequency were reduced from 7.74 +/- 0.66 to 6.88 +/- 0.77 l (decrease not significant J and from 22.76 +/- 0.98 to 17.44 +/- 0.88 (p less than 0.001). Naloxone partially restored their values, to 7.70 +/- 0.55 l and 18.96 +/- 0.88, but 17 patients out of 25 immediately complained of wound pain. Pentazocine improved analgesia again, in all patients, but also depressed the minute-ventilation to 6.43 +/- 0.48 l, without evident changes in respiratory frequency. If the respiratory changes after morphine and naloxone-pentazocine are compared, it is to emphasize that the distribution of the values was much less after the drug combination, 0.56 in comparison with 1.44, P (Fischer Snédécor test) less than 0.001, showing a more homogeneous improving of the minute-ventilation. In conclusion, if pentazocine is added to naloxone, while a respiratory depression caused by morphine has to be reversed, the analgesia level is maintained and the respiration is insignificantly reduced.