Standing sedation and pain management for ophthalmic patients.

Several ocular procedures, including examination, removal of corneal foreign bodies, nictitans surgery, eyelid repair, and tumor excision,can be successfully performed in the appropriately restrained and sedated standing horse. Sedation is best achieved with xylazine,with or without the addition of acepromazine. Additional analgesia can be provided with appropriate local anesthetic blocks.Surgical conditions are greatly improved by using an auriculopalpebral and supraorbital block and topical anesthetics. More elaborate standing sedation involving continuous rate infusions of lidocaine or detomidine combined with butorphanol may facilitate more involved surgery with appropriate support staff and equipment in animals that are at high risk for general anesthesia or when the latter is not an option. Short-term or long-term analgesia is most commonly provided with nonsteroidal anti-inflammatory drugs, but several newer techniques, including lidocaine and butorphanol infusions, may be effective. Topical treatment with opioids to provide analgesia and opioid antagonists to enhance corneal healing is an exciting new development that may revolutionize our approach to corneal ulcer therapy in the future if current research findings are supportive.     

Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses

Objective To assess the effectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty‐one adult horses aged 9.5 ± 6.9 years (range 1–23 years) and weighing 575 ± 290.3 kg. Methods Records of horses presented to our clinic over a 3‐year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean ± SD) of 7.5 ± 1.87 µg kg^?1. The initial infusion rate was 0.6 µg kg^?1 minute^?1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses. Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An effective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide sufficient analgesia for surgery and a significant proportion of animals required supplemental sedatives and analgesics.     

The sedative and analgesic effects of detomidine-butorphanol and detomidine alone in donkeys

Butorphanol and detomidine constitute an effective combination for sedation and analgesia in horses. This trial was undertaken to assess the effectiveness of this combination in donkeys. The detomidine and butorphanol were given intravenously one after the other. A dose of 10 microg/kg of detomidine and 25 microg/kg of butorphanol was used. Sedation is easily extended by additional doses of butorphanol. The average dose of detomidine was 11.24 microg/kg and that of butorphanol was 28.0 microg/kg. Four donkeys in the detomidine group required additional sedation and analgesia. Detomidine alone did not totally eliminate coronary band pain. Heart rates dropped significantly in the first minute after the injection of the combination. One donkey developed an atrioventricular block, while another developed a sino-atrial block. Four donkeys developed a Cheyne-Stokes respiratory pattern. The combination of detomidine and butorphanol is an effective combination for sedation and analgesia of donkeys for standing procedures.     

Evaluation of the sedative,analgesic, clinicophysiological and haematological effects of intravenous detomidine,detomidine‐butorphanol,romifidine and romifidine‐butorphanol in standing donkeys

The aim of this investigation was to determine and evaluate the sedative, analgesic, clinicophysiological and haematological effects of intravenous (i.v.) injection of detomidine, detomidine‐butorphanol, romifidine and romifidine‐butorphanol. Six standing donkeys were used. Each donkey received 4 i.v. treatments and the order of treatment was randomised with a one‐week interval between each treatment. We found that i.v. injection of a combination of detomidine‐butorphanol or romifidine‐butorphanol produced potent neuroleptanalgesic effects thus providing better, safe and effective sedation with complete analgesia in standing donkeys compared with injection of detomidine or romifidine alone. The changes and reduction in pulse rate were within acceptable limits. The changes in clinicophysiological, haematological and biochemical values were mild and transient in these clinically healthy donkeys.     

Electroencephalographic and electromyographic changes during the use of detomidine and detomidine-butorphanol combination in standing horses

Clinically, the use of detomidine and butorphanol is suitable for sedation and deepening of analgosedation. The aim of our study was to establish the influence of detomidine used alone and a butorphanol-detomidine combination on brain activity and to evaluate and compare brain responses (using electroencephalography, EEG) by recording SEF90 (spectral edge frequency 90%), individual brain wave fractions (beta, alpha, theta and delta) and electromyographic (EMG) changes in the left temporal muscle in standing horses. Ten clinically healthy cold-blooded horses were divided into two groups of five animals each. Group I received detomidine and Group II received detomidine followed by butorphanol 10 min later. SEF90, individual brain wave fractions and EMG were recorded with a pEEG (processed EEG) monitor using computerised processed electroencephalography and electromyography. The present study found that detomidine alone and the detomidine-butorphanol combination significantly reduced SEF90 and EMG, and they caused changes in individual brain wave fractions during sedation and particularly during analgosedation. The EMG results showed that the detomidine-butorphanol combination provided greater and longer muscle relaxation. Our EEG and EMG results confirmed that the detomidine-butorphanol combination is safer and more appropriate for painless and non-painless procedures on standing horses compared to detomidine alone.     

Intravenous anesthesia

Anticholinergics, tranquilizers, and sedative-hypnotics are the usual agents used for preanesthetic sedation of the horse. Of these drugs, the anticholinergics are of little importance in the horse. Acepromazine is the most useful and widely used tranquilizer, whereas xylazine is a safe and popular sedative. A newer sedative recently made available to the veterinarian for clinical use in horses is detomidine. Thiobarbiturates are seldom used alone any longer but are still useful when combined with guaifenesin for induction and maintenance of anesthesia. Other, more contemporary drug combinations that have largely replaced thiobarbiturates and chloral hydrate include xylazine with ketamine, xylazine with Telazol, detomidine with Telazol, and guaifenesin with ketamine and xylazine.     

Chemical restraint and analgesia in the horse

Chemical restraint in the standing horse is used for a variety of procedures in veterinary medicine. The choice of agent depends on the physical status, temperament, and size of the patient; the procedure to be performed; and safety for the patient, veterinarian, and owner. The combination of certain agents may provide more desirable restraint and analgesia than does the use of individual agents. The use of analgesics in the horse is not without side effects, some of which may be detrimental to the patient's condition. Analgesics should be chosen with these untoward effects in mind. Draft breeds possess differences that may provide a challenge to the practitioner. One such difference is their clinically apparent increased sensitivity to tranquilizers and sedative-hypnotics; consequently, reduced dose regimens for chemical restraint should be employed initially.     

Analgesic effect of butorphanol and levomethadone in detomidine sedated horses

The analgesic potency of butorphanol 25 microg/kg bodyweight (BW) and levomethadone 100 microg/kg BW, administered together with detomidine 10 microg/kg BW, was measured in twelve Warmblood horses in a randomized, blinded cross-over study. Detomidine with saline 10 ml 0.9% was used as placebo. The nociceptive threshold was determined using a constant current and a pneumatic pressure model for somatic pair Detomidine alone and in combination with butorphanol or levomethadone caused a significant temporary increase (P < 0.05) of the nociceptive threshold with a maximum effect within 15 min and a return to baseline levels within 90 min. Butorphanol and levomethadone increased the nociceptive threshold and prolonged the duration of anti-nociception significantly from 15 to 75 min (P < 0.05) after drug administration compared with detomidine alone to both test methods. No significant difference between butorphanol and levomethadone was registered. It is concluded that the addition of butorphanol or levomethadone to detomidine increases the nociceptive threshold to somatic pain and prolongs the analgesic effect of detomidine in the horse.     

Analgesic effect of butorphanol in ponies following castration

Reasons for performing study: In the UK butorphanol has a marketing authorisation for administration to horses for sedation in combination with detomidine, and at a higher dose (0.1 mg/kg bwt), for the alleviation of pain. There is only a limited number of clinical studies designed to examine the analgesic effects of butorphanol administration following surgery. Objective: To investigate the effect of premedication with butorphanol on post operative pain following castration under general anaesthesia in ponies. Hypothesis: Ponies receiving butorphanol would experience less pain after castration than ponies that did not receive butorphanol. Methods: A randomised, observer blinded clinical study in which 20 ponies received butorphanol and detomidine (Group B) or detomidine alone (Group C). Anaesthesia was induced with ketamine and diazepam and open castration performed. Pain was assessed by one individual using a dynamic interactive visual analogue scale (DIVAS) 100 mm in length (0 = no pain, 100 mm the maximum possible pain for that procedure). ‘Rescue’ analgesia was administered when DIVAS >50 mm and was butorphanol i.v. On the second occasion DIVAS was >50 mm, flunixin was administered i.v. Data from the DIVAS were analysed using a Mann Whitney Test. Results: Only one animal did not require rescue analgesia after surgery (Group C). DIVAS were not significantly different between groups (P = 0.063). Conclusions and potential relevance: Castration is sufficiently painful that administration of a single preoperative dose of butorphanol does not provide adequate post operative analgesia.     

Hormonal, metabolic and physiological effects of laparoscopic surgery using a detomidine-buprenorphine combination in standing horses

Objective To assess the hormonal, metabolic and physiological effects of laparascopic surgery performed under a sedative analgesic combination of detomidine and buprenorphine in standing horses. Study design Prospective study. Animals Eight healthy adult Dutch Warmblood horses and five healthy adult ponies undergoing laparoscopy were studied. Five healthy adult horses not undergoing laparoscopy were used as a control group. Methods The sedative effect of an initial detomidine and buprenorphine injection was maintained using a continuous infusion of detomidine alone. The heart and respiratory rate, arterial blood pH and arterial oxygen and carbon dioxide tensions were monitored, while blood samples were taken for the measurement of glucose, lactate, cortisol, insulin and nonesterified fatty acids (NEFA). The same variables were monitored in a control group of horses which were sedated, but which did not undergo surgery. At the end of the sedation period the effects of detomidine were antagonized using atipamezole. Results The protocol provided suitable conditions for standing laparoscopy in horses. Laparoscopy induced obvious metabolic and endocrine responses which, with the exception of NEFA values, were not significantly different from changes found in the control group. While atipamezole did not produce detectable adverse effects, it is possible that anatagonism may not be essential. Conclusions The technique described reliably produces adequate sedation and analgesia for laparoscopic procedures. The level of sedation/analgesia was controlled by decreasing or increasing the infusion rate. Antagonism of the effects of detomidine may not be necessary in all cases.     

Standing sedation in captive zebra (Equus grevyi and Equus burchellii)

Nine Grevy's zebras (Equus grevyi) and three Burchell's zebras (Equus burchellii) were immobilized in a standing position a total of 70 times for minor, nonpainful procedures over a 9-yr period. Standing sedation was successfully obtained with a combination of detomidine and butorphanol on 47 occasions (67.1%). Detomidine i.m. (median 0.10 mg/kg; range: 0.07-0.21) was administered by dart, followed 10 min later by butorphanol i.m. (median 0.13 mg/kg; range 0.04-0.24). The dosages were varied depending on the initial demeanor of the animal. On 23 occasions (32.9%), small amounts of etorphine (median 2.5 microg/kg; range 1.1-12.3 microg/kg) plus acepromazine (median 10 microg/kg; range 4.4-50 microg/kg) (as in Large Animal-Immobilon) had to be administered i.m. to gain sufficient sedation. In these latter cases, the animals were either excited or known for their aggressive character. The zebras were sufficiently immobilized for the length of most procedures (<45 min) without supplementation. At the end of the procedure, the animals were given atipamezole (2 mg per 1 mg detomidine used) and naltrexone (0.1 mg/kg) to reverse the sedative effects, irrespective of whether etorphine was used or not. Standing sedation, using the combination of the alpha-2 agonist detomidine and the partial agonist-antagonist opioid butorphanol (in some cases supplemented with etorphine + acepromazine), proved to be a very efficacious and safe method to be used in zebras under zoo conditions for short-lasting, nonpainful procedures.     

Comparison of Intraoperative Behavioral and Hormonal Responses to Noxious Stimuli between Mares Sedated with Caudal Epidural Detomidine Hydrochloride or a Continuous Intravenous Infusion of Detomidine Hydrochloride for Standing Laparoscopic Ovariectomy

Objective: To compare the presence or absence of pain, pain‐related behavioral responses, and hormonal responses to noxious stimuli during standing laparoscopic ovariectomy in mares sedated with continuous intravenous (IV) detomidine infusion and caudal epidural detomidine. Study Design: A double blind prospective study. Animals: Mares (n=12) Methods: Mares were divided into 2 treatment groups; 6 were sedated using continuous IV detomidine infusion and 6 were sedated with caudal epidural detomidine. All mares received IV xylazine (0.33 mg/kg) and butorphanol tartrate (5 mg) premedication before detomidine administration. Venous blood samples were taken to assess serum cortisol levels in each mare at 4 time points: a baseline cortisol measurement after the mares' arrival to the clinic, 10 minutes before surgery, at the removal of the 2nd ovary, and 10 minutes postsurgery. Two surgeons performed bilateral ovariectomy and at 8 time points involving surgical manipulations, noted the presence or absence of pain (yes/no) and scored the patient's response on a 10 cm visual analogue scale (VAS) for pain assessment with 0 indicating no pain responses and 10 cm indicating pain so severe that the mare required additional sedation or analgesia to complete the procedure. Each mare was also assigned a VAS score by each surgeon for the overall satisfaction of analgesia during the entire procedure. Results: Serum cortisol levels between the 2 detomidine administration groups differed significantly at the baseline (precortisol) measurement but not at the 3 remaining time points. Seven of the procedures within the surgeries did not differ significantly in VAS scores between the 2 groups. The initial grasp of the left ovary (the 1st ovary) in the continuous infusion group had a significantly higher (P=.05) median VAS score compared with the caudal epidural group. Conclusions: Mares sedated with a continuous IV infusion of detomidine have similar hormonal and behavioral responses to painful stimuli during standing laparoscopic ovariectomy as mares sedated with caudal epidural detomidine. Clinical Relevance: Sedation using a continuous IV infusion of detomidine can be used for laparoscopic ovariectomy in mares.     

Preliminary study of the effects of xylazine or detomidine with or without butorphanol for standing sedation in dairy cattle

The sedative effect induced by administering xylazine hydrochloride or detomidine hydrochloride with or without butorphanol tartrate to standing dairy cattle was compared in two groups of six adult, healthy Holstein cows. One group received xylazine (0.02 mg/kg i.v.) followed by xylazine (0.02 mg/kg) and butorphanol (0.05 mg/kg i.v.) 1 week later. Cows in Group B received detomidine (0.01 mg/kg i.v.) followed by detomidine (0.01 mg/kg i.v.) and butorphanol (0.05 mg/kg i.v.) 1 week later. Heart rate, respiratory rate, and arterial blood pressure were monitored and recorded before drugs were administered and every 10 minutes for 1 hour after drug administration. The degree of sedation was evaluated and graded. Cows in each treatment group had significant decreases in heart rate and respiratory rate after test drugs were given. Durations of sedation were 49.0 +/- 12.7 minutes (xylazine), 36.0 +/- 14.1 (xylazine with butorphanol), 47.0 +/- 8.1 minutes (detomidine), and 43.0 +/- 14.0 minutes (detomidine with butorphanol). Ptosis and salivation were observed in cows of all groups following drug administration. Slow horizontal nystagmus was observed from three cows following administration of detomidine and butorphanol. All cows remained standing while sedated. The degree of sedation seemed to be most profound in cows receiving detomidine and least profound in cows receiving xylazine.     

Propofol compared with propofoVguaiphenesin after detornidine premedication for equine surgery

Anaesthesia using propofol alone and in combination with guaiphenesin, after detomidine premedication, was evaluated for performance of minor surgical procedures (castration and tenotomy) in horses. Twelve male horses were premedicated with 0.015 mg/kg of detomidine intravenously (iv) and divided into two groups of six. One group of horses received 2 mg/kg of propofol iv and the other group received 0.5 mg/kg of propofol mixed with 100 mg/kg of a 7.5% solution of guaiphenesin in saline iv. Induction of anaesthesia was fast and smooth in both groups. All horses were easily intubated immediately afterwards but intubation was easier in the horses which received propofol and guaiphenesin. Heart rate fell by 20% in both groups after detomidine injection, stabilising between 45 and 53 beats/minute during anaesthesia with no difference between the groups. Respiratory depression developed after detomidine injection and was slightly intensified after induction of anaesthesia. Respiratory rate was significantly lower in the propofol group (14 ± 3 breaths/minute) than with propofol/guaiphenesin (19 ± 4 breaths/minute) at five minutes after induction. Anaesthesia induced respiratory acidosis in both groups and hypoxaemia also occurred, but once the horses stood up the arterial blood oxygen partial pressure returned to basal values. Surgical time ranged between 8 and 16 minutes and with the exception of one horse in the propofol/guaiphenesin group the horses did not show signs of pain or discomfort during surgery. Recovery to standing was fast and took 26 ± 2 minutes in the propofol and 29 ± 5 minutes in the propofol/ guaiphenesin group. Most horses stood up at the first attempt with minimal ataxia. These two anaesthetic techniques appear to be useful for minor surgical procedures performed within 16 minutes of induction of anaesthesia.     

Detomidine-butorphanol sedation in equine clinical practice

Combinations of detomidine (mean dose rate 13 micrograms/kg) and butorphanol (mean dose rate 26 micrograms/kg) were used to sedate 61 horses for a variety of surgical or diagnostic procedures in general equine practice. Three horses were sedated on more than one occasion. The degree of sedation was graded from 3 to 0 (deep sedation to no effect) and any side effects were recorded. Forty-three per cent of the horses were graded 3, 46 per cent were graded 2, 8 per cent were graded 1 and 3 per cent were graded 0. Bradycardia and ataxia were the major side effects. The combination was judged to be effective and safe for use in general practice. In 56 horses (92 per cent) the necessary procedure was carried out under excellent conditions and in only one horse was the degree of sedation considered to be totally unsatisfactory.     

Effect of sedation with detomidine and butorphanol on pulmonary gas exchange in the horse

Background

Sedation with α₂-agonists in the horse is reported to be accompanied by impairment of arterial oxygenation. The present study was undertaken to investigate pulmonary gas exchange using the Multiple Inert Gas Elimination Technique (MIGET), during sedation with the α₂-agonist detomidine alone and in combination with the opioid butorphanol.

Methods

Seven Standardbred trotter horses aged 3–7 years and weighing 380–520 kg, were studied. The protocol consisted of three consecutive measurements; in the unsedated horse, after intravenous administration of detomidine (0.02 mg/kg) and after subsequent butorphanol administration (0.025 mg/kg). Pulmonary function and haemodynamic effects were investigated. The distribution of ventilation-perfusion ratios (V_A/Q) was estimated with MIGET.

Results

During detomidine sedation, arterial oxygen tension (PaO₂) decreased (12.8 ± 0.7 to 10.8 ± 1.2 kPa) and arterial carbon dioxide tension (PaCO₂) increased (5.9 ± 0.3 to 6.1 ± 0.2 kPa) compared to measurements in the unsedated horse. Mismatch between ventilation and perfusion in the lungs was evident, but no increase in intrapulmonary shunt could be detected. Respiratory rate and minute ventilation did not change. Heart rate and cardiac output decreased, while pulmonary and systemic blood pressure and vascular resistance increased. Addition of butorphanol resulted in a significant decrease in ventilation and increase in PaCO₂. Alveolar-arterial oxygen content difference P(A-a)O₂ remained impaired after butorphanol administration, the V_A/Q distribution improved as the decreased ventilation and persistent low blood flow was well matched. Also after subsequent butorphanol no increase in intrapulmonary shunt was evident.

Conclusion

The results of the present study suggest that both pulmonary and cardiovascular factors contribute to the impaired pulmonary gas exchange during detomidine and butorphanol sedation in the horse.     

The effects of xylazine,detomidine, acepromazine and butorphanol on equine solid phase gastric emptying rate

The aim of this study was to measure the effects of specific commonly used sedative protocols on equine solid phase gastric emptying rate, using the 13C-octanoic acid breath test (13C-OABT). The gastric emptying of a standard 13C-labelled test meal was measured once weekly in 8 mature horses over two 4 week treatment periods. Each horse acted as its own control. In treatment Period 1, saline (2 ml i.v.), xylazine (0.5 mg/kg i.v.), detomidine (0.01 mg/kg i.v.) or detomidine/butorphanol combination (0.01/0.02 mg/kg i.v.) was administered in randomised order after ingestion of the test meal. During treatment Period 2, test meal consumption was followed by saline, xylazine (1.0 mg/kg i.v.), or detomidine (0.03 mg/kg i.v.) administration, or preceded by acepromazine (0.05 mg/kg i.m.) in randomised order. The 13C:12C ratio of sequential expiratory breath samples was determined by isotope ratio mass spectrometry, and used to measure the gastric half-emptying time, t 1/2, and duration of the lag phase, t lag, for each of the 64 tests. In treatment Period 1, detomidine/butorphanol prolonged both t 1/2 and t lag with respect to xylazine 0.5 mg/kg and the saline control (P < 0.05). In Period 2, detomidine 0.03 mg/kg delayed each parameter with respect to saline, acepromazine and xylazine 1.0 mg/kg (P < 0.001). Xylazine 1.0 mg/kg also lengthened t lag relative to the saline control (P = 0.0004), but did not cause a significant change in t 1/2. Comparison of treatment periods showed that the inhibitory effect of detomidine on gastric emptying rate was dose related (P<0.05). These findings may have clinical significance for case selection when these agents are used for purposes of sedation and/or analgesia.     

Standing surgery and procedures of the head

Although most surgical procedures of the head are technically easier to perform with the horse under general anesthesia, other factors will influence whether a surgical procedure is performed with the horse standing or recumbent under the influence of general anesthesia. The accessibility of the head lends itself to many standing surgical procedures if the proper combination of analgesia and physical and chemical restraint is used. Traumatic injuries of the head (lacerations, facial bone fractures, and oral fractures) may involve vital structures, and a thorough examination is indicated. Failure to treat a traumatic injury may result in facial deformity, bony sequestra, paranasal sinusitis, salivary-cutaneous fistula, cutaneous fistulas into a nasal passage or paranasal sinus, nasal septal deformities, and ocular dysfunction. Proper management of these injuries typically results in a cosmetic outcome because of the head's abundant blood supply. Other surgical procedures that can be performed in the standing horse include centesis and trephination of the paranasal sinuses, certain dental procedures, alar fold stabilization, and extirpation of epidermal inclusion cysts of the nasal diverticulum.     

Combined use of detomidine with opiates in the horse

The effects of administration of one of four opiates (pethidine 1 mg/kg bodyweight (bwt), morphine 0.1 mg/kg bwt, methadone 0.1 mg/kg bwt, and butorphanol 0.05 mg/kg bwt) given intravenously to horses and ponies already sedated with detomidine (10 micrograms/kg bwt) were investigated. Behavioural, cardiovascular and respiratory effects of the combinations were compared with those occurring with detomidine alone. Addition of the opiate increased the apparent sedation and decreased the response of the animal to external stimuli. At doses used, butorphanol produced the most reliable response. Side effects seen were increased ataxia (greatest following methadone and butorphanol) and excitement (usually muzzle tremors and muscle twitching). Following pethidine, generalised excitement was sometimes seen. Marked cardiovascular changes occurred in the first few minutes after morphine or pethidine injection, but within 5 mins cardiovascular changes were minimal. Following morphine or pethidine there was a significant increase in arterial carbon dioxide tension. Fourteen clinical cases were successfully sedated using detomidine/butorphanol combinations.     

The intravenous pharmacokinetics of butorphanol and detomidine dosed in combination compared with individual dose administrations to exercised horses

In equine and racing practice, detomidine and butorphanol are commonly used in combination for their sedative properties. The aim of the study was to produce detection times to better inform European veterinary surgeons, so that both drugs can be used appropriately under regulatory rules. Three independent groups of 7, 8 and 6 horses, respectively, were given either a single intravenous administration of butorphanol (100 µg/kg), a single intravenous administration of detomidine (10 µg/kg) or a combination of both at 25 (butorphanol) and 10 (detomidine) µg/kg. Plasma and urine concentrations of butorphanol, detomidine and 3-hydroxydetomidine at predetermined time points were measured by liquid chromatography–tandem mass spectrometry (LC-MS/MS). The intravenous pharmacokinetics of butorphanol dosed individually compared with co-administration with detomidine had approximately a twofold larger clearance (646 ± 137 vs. 380 ± 86 ml hr⁻¹ kg⁻¹) but similar terminal half-life (5.21 ± 1.56 vs. 5.43 ± 0.44 hr). Pseudo-steady-state urine to plasma butorphanol concentration ratios were 730 and 560, respectively. The intravenous pharmacokinetics of detomidine dosed as a single administration compared with co-administration with butorphanol had similar clearance (3,278 ± 1,412 vs. 2,519 ± 630 ml hr⁻¹ kg⁻¹) but a slightly shorter terminal half-life (0.57 ± 0.06 vs. 0.70 ± 0.11 hr). Pseudo-steady-state urine to plasma detomidine concentration ratios are 4 and 8, respectively. The 3-hydroxy metabolite of detomidine was detected for at least 35 hr in urine from both the single and co-administrations. Detection times of 72 and 48 hr are recommended for the control of butorphanol and detomidine, respectively, in horseracing and equestrian competitions.