A qualitative systematic review of peri-operative dextromethorphan in post-operative pain

BACKGROUND

The N-methyl-D-aspartate (NMDA) receptor antagonist, dextromethorphan (DM), has received interest as an adjunctive agent in post-operative pain management. Clinical trials have been contradictory. This systematic review aims to evaluate the available literature examining the analgesic efficacy of DM in post-operative patients.

METHODS

Twenty-eight randomized, double-blind, clinical studies, with 40 comparisons, including a variety of dosing regimens comparing DM treatment with placebo, were included. Meta-analysis was intended but deemed to be inappropriate because of the substantial difference in methodology and reporting between trials. The outcome measures (pain scores at rest, time to first analgesic request and supplemental analgesic consumption) were evaluated qualitatively by significant difference (P<0.05) as reported in the original investigations.

RESULTS

DM did not reduce the post-operative pain score with a clinically significant magnitude. The time to first analgesic request was significantly prolonged in most comparisons with DM. Significant decreases in supplemental opioid consumption were observed in the majority of parenteral DM studies and in about one-half of the oral studies. The decreases were of questionable clinical importance in most comparisons, although a relationship between a decrease in opioid consumption and opioid-related side-effects was established in some studies.

CONCLUSION

Based on the studies available, DM has the potential to be a safe adjunctive agent to opioid analgesia in post-operative pain management, but the consistency of the potential opioid-sparing and pain-reducing effect must be questioned. Consequently, it is not possible to recommend dose regimens or routine clinical use of DM in post-operative pain. The route of administration may be important for the beneficial effect.

Intra-operative remifentanil might influence pain levels in the immediate post-operative period after major abdominal surgery

BACKGROUND

Remifentanil, a widely used analgesic agent in anaesthesia, has a rapid onset and short duration of action. In clinical settings, this requires an appropriate pain strategy to prevent unacceptable pain in the post-operative period. The aim of this study was to investigate whether remifentanil had any impact on post-operative pain and opioid consumption after major abdominal surgery.

METHODS

Fifty patients undergoing major abdominal surgery were randomized to receive either remifentanil 0.4 microg/kg/min or placebo intra-operatively, in addition to basic combined general and epidural anaesthesia, in this double-blind study. Patients received patient-controlled analgesia with morphine for 24 h post-operatively. Morphine consumption, assessment of pain at rest and during coughing, side-effects and levels of sensory block were recorded during the first 24 h post-operatively.

RESULTS

Twenty-one patients receiving remifentanil and 18 patients receiving placebo completed the study. The median visual analogue scale (VAS) score at rest from 0 to 2 h was significantly increased in the remifentanil group [40 mm (27-61 mm)] vs. placebo [13 mm (3-35 mm)] (P < 0.05). No significant differences in morphine consumption, VAS score during coughing or adverse effects were observed between the groups.

CONCLUSION

The results are weak and difficult to interpret. They could indicate that a high dose of remifentanil added to otherwise sufficient combined general and epidural anaesthesia may induce opioid-induced hyperalgesia and/or clinically acute opioid tolerance after major abdominal surgery; however, as no significant differences could be observed between the groups after 2 h post-operatively, the clinical relevance of these observations is questionable.

Effects of gabapentin on postoperative morphine consumption and pain after abdominal hysterectomy: a randomized, double-blind trial

BACKGROUND

Preliminary clinical studies have suggested that gabapentin may produce analgesia and reduce the need for opioids in postoperative patients. The aim of the present study was to investigate the opioid-sparing and analgesic effects of gabapentin administered during the first 24 h after abdominal hysterectomy.

METHODS

In a randomized, double-blind study, 80 patients received oral gabapentin 1200 mg or placebo 1 h before surgery, followed by oral gabapentin 600 mg or placebo 8, 16 and 24 h after the initial dose. Patients received patient-controlled analgesia with morphine at doses of 2.5 mg with a lock-out time of 10 min for 24 h postoperatively. Pain was assessed on a visual analogue scale (VAS) at rest and during mobilization, nausea, somnolence and dizziness on a four-point verbal scale, and vomiting as present/not present at 2, 4, 22 and 24 h postoperatively.

RESULTS

Thirty-nine patients in the gabapentin group, and 32 patients in the placebo group completed the study. Gabapentin reduced total morphine consumption from median 63 (interquartile range 53-88) mg to 43 (28-60) mg (P < 0.001). We observed a significant inverse association between plasma levels of gabapentin at 2 h postoperatively, and morphine usage from 0 to 2 h, and from 0 to 4 h postoperatively (R2 = 0.30, P = 0.003 and R2 = 0.24 P = 0.008, respectively). No significant differences in pain at rest or during mobilization, or in side-effects, were observed between groups.

CONCLUSION

Gabapentin in a total dose of 3000 mg, administered before and during the first 24 h after abdominal hysterectomy, reduced morphine consumption with 32%, without significant effects on pain scores. No significant differences in side-effects were observed between study-groups.