Analgesic effects of butorphanol tartrate and phenylbutazone administered alone and in combination in young horses undergoing routine castration

Abstract

Objective-To compare the analgesic efficacy of administration of butorphanol tartrate, phenylbutazone, or both drugs in combination in colts undergoing routine castration. Design-Randomized controlled clinical trial. Animals-36 client-owned colts. Procedures-Horses received treatment with butorphanol alone (0.05 mg/kg [0.023 mg/ lb], IM, prior to surgery and then q 4 h for 24 hours), phenylbutazone alone (4.4 mg/kg [2.0 mg/lb], IV, prior to surgery and then 2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 3 days), or butorphanol and phenylbutazone at the aforementioned dosages (12 horses/group). For single-drug-treated horses, appropriate placebos were administered to balance treatment protocols among groups. All horses were anesthetized, and lidocaine hydrochloride was injected into each testis. Physical and physiological variables, plasma cortisol concentration, body weight, and water consumption were assessed before and at intervals after surgery, and induction of and recovery from anesthesia were subjectively characterized. Observers assessed signs of pain by use of a visual analogue scale and a numerical rating scale. Results-Significant changes in gastrointestinal sounds, fecal output, and plasma cortisol concentrations were evident in each treatment group over time, compared with preoperative values. At any time point, assessed variables and signs of pain did not differ significantly among groups, although the duration of recumbency after surgery was longest for the butorphanol-phenylbutazone-treated horses. Conclusions and Clinical Relevance-With intratesticular injections of lidocaine, administration of butorphanol to anesthetized young horses undergoing routine castration had the same apparent analgesic effect as phenylbutazone treatment. Combined butorphanolphenylbutazone treatment was not apparently superior to either drug used alone. (J Am Vet

Effects of a continuous rate infusion of butorphanol in isoflurane-anesthetized horses on cardiorespiratory parameters, recovery quality, gastrointestinal motility and serum cortisol concentrations

“…This result is consistent with results of previous studies indicating that butorphanol does not significantly alter cardiorespiratory function in horses after administration intramuscular, intravenuous or at continuous rate infusion 7,8,13,14 .…”

“…However, it is this increased cortisol could have been caused by the effect of butorphanol, as observed by Pascoe et al 15 , where the use of a synthetic kappa opioid agonist (U5088H) resulted in increased cortisol concentrations in primates, which was not observed with mu and delta opioid agonists. As in the study of Sanz et al 14 , where the horses receiving butorphanol as an analgesic in postoperative orchiectomy had higher values of plasma cortisol that horses receiving phenylbutazone.…”

Buprenorphine provides better anaesthetic conditions than butorphanol for field castration in ponies: results of a randomised clinical trial

“…However, each time rescue is required, surgery is interrupted until the effect of the rescue drug develops, and the apparently longer BUT surgery time may simply be further reflection of the better surgical conditions in the BUP group. A need for additional doses of anaesthetic agent has often been reported in studies of field castration in ponies, even when a higher dose of butorphanol (50 μg/kg) was given (Corletto and others 2005, Leece and others 2009, Sanz and others 2009, Kloppel and Leece 2011), and the current study is no exception. It is surprising, however, that Corletto and others (2005) reported poorer anaesthetic quality after morphine (100 μg/kg) than butorphanol, whereas in the present study more anaesthetic was required after butorphanol than after buprenorphine.…”

“…However, μ-opioid receptor agonists are considered the best analgesics, and butorphanol is usually regarded as less effective in treating moderate to severe pain (Muir 1981, Wagner 1999). Although butorphanol has been shown to be a suitable opioid for horses undergoing castration (Corletto and others 2005, Leece and others 2009, Sanz and others 2009, Kloppel and Leece 2011), a μ-opioid receptor agonist might be more appropriate as the opioid component of preanaesthetic medication before a surgical procedure. The quality of sedation and surgical conditions with morphine, the gold standard μ-opioid receptor agonist, was inferior, although acceptable, to butorphanol; unfortunately postoperative analgesia was not reported (Corletto and others 2005).…”

Nonsteroidal Anti‐Inflammatory Drugs and Corticosteroids

“…Care should be taken to avoid perivascular injection when administering phenylbutazone intravenously as it can result in tissue necrosis and sloughing (Dowling, 2010). Phenylbutazone is effective for the treatment of both soft tissue and bone pain in horses (Sanz et al, 2009;Foreman et al, 2008). Phenylbutazone has a prolonged half-life in horses and repeated dosing can extend the clinical efficacy well beyond the time when drug administration is discontinued, which could have implications for prepurchase examinations and competition (Dowling, 2010).…”