Comparison of Fentanyl and Hydromorphone Constant Rate Infusions for Pain Management in Dogs in an Intensive Care Unit

Objective: To compare the efficacy and quality of analgesia provided by constant rate infusions (CRIs) of hydromorphone and fentanyl in dogs in the intensive care unit (ICU).

Study Design: Prospective, randomized, blinded, clinical trial.

Animals: A total of 29 client-owned dogs.

Methods: Dogs prescribed a μ-opioid agonist infusion for postsurgical or medical pain were randomized to be administered either hydromorphone (0.025 or 0.05 mg kg bolus, followed by a 0.03 mg kg hour infusion) or fentanyl (2.5 or 5 μg kg bolus, followed by a 3 μg kg hour infusion). The technical staff and clinicians were blinded as to which drug was administered. Pain scores, using the Colorado State University Canine Acute Pain Scale, sedation scores and nausea scores were assigned at regular intervals and compared between groups. Dose escalation and de-escalation of the study drug were performed according to set protocols. Adverse clinical signs and all other medications administered were recorded and compared between groups. The study drug was discontinued if the animal remained painful despite dose escalations, or if adverse effects were noted.

Results: The pain scores were of low magnitude and were not significantly different between groups. The use of concurrent analgesia, sedation/anxiolytic medications and antacid/antiemetic medications was not different between groups. Sedation and nausea scores were not statistically different between groups.

Conclusions And Clinical Relevance: Hydromorphone and fentanyl CRIs appear to be equally effective for adequate pain relief in dogs, with no significant differences in adverse effects. Therefore, either drug may be chosen for control of postsurgical or medical pain in an ICU setting.