A DOUBLE-BLEND CONTROLLED STUDY OF THE EFFECTS ON RESPIRATION OF PENTAZOCINE, PHENOPERIDINE AND MORPHINE IN NORMAL MAN

Abstract

Three drugs and saline were given intravenously, on separate occasions, to eight normal subjects. The doses used were pentazocine 20 mg, phenoperidine 1.5 mg and morphine sulphate 10 mg, each per 70 kg body weight End-tidal Pco₂ and ventilatory pattern were followed continuously; expired volume and oxygen consumption were measured before and at intervals after injection; a rebreathing carbon-dioxide response test was also applied. The three drugs produced similar, and significant increases, of the order of 5 torr in Pco₂ and dissimilar, significant, reductions in ventilation which could be related to dissimilar effects on oxygen consumption: injection of morphine or of phenoperidine was followed within 10 minutes by an average reduction in oxygen consumption by 20–30 per cent whereas after pentazocine the reduction was only about 10 per cent. The rises in Pco₂ provided a guide to respiratory depression which was as consistent and as statistically significant as most quoted changes in parameters of carbon-dioxide response tests. The results of the carbon dioxide-response test used in this trial were very variable.