A randomized, double-blind, placebo-controlled trial comparing pethidine to metamizol for treatment of post-anaesthetic shivering

1 Shivering is frequent during the post-anaesthetic recovery period, and there is no clear consensus about the best strategy for its treatment. We tested the efficacy of two commonly used analgesic drugs, pethidine and metamizol. 2 A randomized, double-blind, placebo-controlled clinical trial was performed, including 104 adult patients who presented with post-anaesthetic shivering during the recovery from general anaesthesia. They were randomized to receive placebo (n = 32), metamizol 25 mg kg(-1) (n = 37), or pethidine 0.4 mg kg(-1) (n = 35). The response to treatment was assessed 5, 15 and 45 min after drug administration, and the main outcome variable was complete suppression of shivering. 3 The efficacy at 5, 15 and 45 min was as follows: placebo 6%, 16% and 37%; metamizol 13.5%, 32% and 76%, and pethidine 89%, 91% and 89%. With both active drugs the efficacy at all three time intervals was significantly higher than that with placebo (P < 0.05). The differences (at 5 and 15, but not at 45 min) between pethidine and metamizol were statistically significant (P < 0.05). Both drugs were well tolerated. 4 The persistence of shivering at 45 min in two thirds of placebo-treated patients indicates that drug treatment is worthwhile; metamizol produces a better postanaesthetic shivering response than placebo, especially 15 and 45 min after drug administration; the efficacy of pethidine was the highest and the response to it appeared more quickly; however, at 45 min it was similar to that observed with metamizol. 5 Both metamizol and pethidine suppress postanaesthetic shivering, but the latter induces a quicker and more reliable response.