Efficacy and Kinetics of Carprofen, Administered Preoperatively or Postoperatively, for the Prevention of Pain in Dogs Undergoing Ovariohysterectomy

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Abstract
Objective—To determine what effect the timing of carprofen administration has on the severity of postoperative pain in dogs undergoing ovariohysterectomy and to investigate the pharmacokinetics of carprofen under these conditions. Study Design—A prospective, randomized, double-blind, clinical trial. Animals—Sixty-two adult bitches weighing between 10 and 25 kgs, undergoing elective ovariohysterectomy. Methods—Examinations were performed for 20 hours postoperatively using subjective visual assessment scoring systems (DIVAS) and objective mechanical nociceptive threshold measurements. Forty dogs were assigned to one of three groups: (1) preoperative carprofen; (2) postoperative carprofen; and (3) no analgesics (saline injections). The dose of carprofen was 4.0 mg/kg subcutaneously. In another 22 bitches, the pharmacokinetics of carprofen given preoperatively or postoperatively at the same dose were examined. Results—The dogs given carprofen preoperatively had lower pain scores than the other groups, significantly so at 2 hours postextubation (P < .01 and P < .05, Kruskal-Wallis and post hoc Dunn's). Mechanical pain thresholds measured at the distal tibia showed the development of hyperalgesia at 12 and 20 hours postextubation; this was prevented by both the preoperative (P < .05 at 12 and 20 hours, Kruskal-Wallis) and postoperative (P <.05 at 20 hours, Kruskal-Wallis) administration of carprofen. Mechanical pain threshold testing at the wound showed a significant analgesic effect of carprofen. Plasma concentrations of carprofen were not directly related to analgesia; maximum plasma concentration, the area under the curve to the last data point, and area under the first moment curve up to the last data point were all significantly higher in the dogs given carprofen postoperatively (P < .05, Mann-Whitney). Conclusion—Preoperative administration of carprofen has a greater analgesic effect than postoperative administration in the early postoperative period in dogs undergoing ovariohysterectomy. Plasma levels of carprofen are not related to the degree of analgesia achieved. Clinical Relevance—Carprofen provides effective analgesia after canine ovariohysterectomy. The timing of analgesic administration is important to optimize the control of postoperative pain.