Influence of metamizole on 1) minimal alveolar concentration of sevoflurane in dogs and 2) on thermal and mechanical nociception in conscious dogs

Objective To determine the acute anti-nociceptive and the minimal alveolar concentration (MAC) sparing effects of metamizole sodiummonohydrate (dipyrone) in dogs for possible perioperative analgesia. Study design Two groups of seven adult dogs were used in two separate randomised, blinded, controlled, cross-over studies. In each study, each dog received metamizole 50 mg kg(-1) intravenously (IV) and placebo (saline 0.9%) IV. Methods Sevoflurane MAC was determined using the bracketing technique and electrical stimulation (50 V, 50 Hz, 10 milliseconds) at a thoracic limb, before treatment and 1 and 4 hours post treatment. In conscious dogs, thermal thresholds were determined by ramped contact heat at the thoracic wall. Mechanical thresholds (MTs) were measured by constantly rising force pressing against the radial bone. Thresholds were determined pre and 45, 75, 105, 135, 165, 195, 225, 255, 285, 315, 345, 375, 435, 495, 555, 615, 675, 735 minutes and 24 hours post treatment. Parametric data were analyzed by analysis of variance for repeated measurements and paired t-tests. Friedman test was used for nonparametric data. Level of significance was set to <5%. Results Metamizole did not change MAC of sevoflurane significantly compared to baseline values [mean +/- SD Vol%; 2.7 +/- 0.5 (BL); 2.8 +/- 0.6 (1 hour); 2.8 +/- 0.4 (4 hours)] and placebo [2.8 +/- 0.5 (BL); 2.9 +/- 0.5 (1 hour); 2.9 +/- 0.4 (4 hour)]. Metamizole caused a significant rise in % TE up to 105 minutes (66.5 +/- 12.1%) and in MT up to 75 minutes (12.7 +/- 5.0 N) compared to baseline (55 +/- 10%; 7.9 +/- 1.8 N). There were no significant differences between treatments. Conclusion and clinical relevance Metamizole did not induce an anaesthetic sparing effect. In awake dogs metamizole induced only mild and short cutaneous anti-nociception. Metamizole as the sole analgesic drug in the perioperative periode is not recommended.