Continuous infusion of meptazinol and pethidine in the relief of post-operative pain.

Thirty patients who had undergone major abdominal surgery were randomly assigned to a continuous infusion of either 0.45 mg meptazinol/kg/hr or 0.3 mg pethidine/kg/hr. Analgesia was assessed by rating scale, ranging from 0 (no pain) to 10 (unbearable pain), and by questionnaire. Respiration rate was closely monitored and end-tidal PCO2 measured. Both drugs provided effective analgesia. The median rating of pain over the 24 hr post operation was 2.6 with meptazinol and 2.9 with pethidine, a difference that was not statistically significant. No patient in either group reported a distressing degree of discomfort. Although no patients exhibited clinically significant respiratory depression or sleep apnoea, high (greater than 6 Kpa) end-tidal PCO2 values were significantly more frequent in the pethidine than in the meptazinol group (P less than 0.01). This suggests a greater margin of safety with the use of meptazinol. The smaller effect of meptazinol on respiratory activity might make it especially appropriate for administration by continuous infusion--a technique which has practical advantages over intermittent intramuscular injection and which has been shown to be more effective in the control of post-operative pain. Patients' responses in the present study demonstrate the efficacy of continuous infusion as a means of relieving post-operative pain and confirm previous findings that 0.5 mg/kg/hr meptazinol provides a good degree of analgesia.