Comparison of hydromorphone and butorphanol for management of pain in equine patients undergoing elective arthroscopy: a randomized clinical trial



      To compare the effects of hydromorphone and butorphanol in horses undergoing arthroscopy and describe the pharmacokinetics of hydromorphone in anesthetized horses.

      Study design

      Randomized controlled clinical trial.


      A total of 40 adult horses admitted for elective arthroscopy.


      Horses were randomly assigned to be administered intravenous hydromorphone (0.04 mg kg–1; group TxH; n = 19) or butorphanol (0.02 mg kg–1; group TxB; n = 21) prior to surgery as part of a standardized anesthetic protocol. Pain was scored by two observers unaware of group assignment using the Equine Utrecht University Scale for Facial Assessment of Pain (EQUUS-FAP) and a composite pain scale (CPS) prior to surgery (baseline), 2 hours (P2) and 4 hours (P4) following recovery from anesthesia. Blood samples were collected at various time points for determination of plasma hydromorphone concentration using liquid chromatography–tandem mass spectrometry. Data were analyzed with a mixed-effect model.


      Median (range) baseline EQUUS-FAP was 1.2 (0.0–4.0) with no effect of group, time points or interaction. Baseline CPS was similar between groups. Group TxH baseline CPS was 2.5 (0.0–10.0), increased at P2 [4.5 (0–10.0); p = 0.046] and returned to baseline values at P4 [3.0 (0.0–11.0)]. Group TxB baseline CPS was 2.0 (0.0–8.0), increased at P2 [3.5 (0.0–11.0); p = 0.009] and P4 [5.0 (0.0–11.0); p < 0.001]. Pharmacokinetic terminal half-life was 774 ± 82.3 minutes, area under the curve was 1362 ± 314 ng minutes mL–1, clearance was 30.7 ± 7.23 mL minute–1 kg–1 and volume of distribution at steady state was 884 ± 740 mL kg–1.


      Hydromorphone, but not butorphanol, decreased CPS back to baseline at P4 after recovery.

      Clinical relevance

      Hydromorphone may provide superior postoperative analgesia compared with butorphanol in horses undergoing arthroscopy.


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