Pain management in horses and farm animals

Pharmacokinetics, pharmacodynamics and antinociceptive effects of buprenorphine following transdermal administration to horses

OBJECTIVE

This study describes the pharmacokinetics and pharmacodynamics, including antinociceptive effects, of a transdermal buprenorphine solution in horses. It was hypothesized that transdermal application would lead to sustained blood concentrations and antinociceptive effects with fewer adverse effects compared with intravenous (IV) injection.

STUDY DESIGN

Prospective nonrandomized four-part parallel experimental study.

ANIMALS

A group of eight horses (three mares and five geldings) aged 6-12 years.

METHODS

Horses were administered incremental doses of 15, 30 and 45 μg kg-1 of buprenorphine transdermal solution and a single IV dose of 5 μg kg-1 of buprenorphine with a 2 week washout period between treatments. Concentrations of buprenorphine were determined in plasma using liquid chromatography-tandem mass spectrometry and modeled using a nonlinear mixed effects population pharmacokinetic model to determine pharmacokinetic parameters. Pharmacodynamic effects, including changes in locomotor activity, heart rate, body temperature, gastrointestinal borborygmi, thermal and mechanical nociceptive thresholds were recorded. Mixed effects analysis of variance and post hoc comparisons were performed using a Bonferroni multiple comparison adjustment to assess differences in pharmacodynamic parameters between baseline and each time point within each dose group and between dose groups at the same time point.

RESULTS

Transdermal application of buprenorphine resulted in low systemic concentrations relative to IV injection. Bioavailability after transdermal application was 11%. Thermal nociceptive thresholds were significantly (p < 0.05) increased (4.3-10.7% relative to baseline) for up to 72 hours in the IV dose group, but only sporadically in the transdermal dose groups (2.5-9.9% relative to baseline). Changes in locomotor activity, heart rate and borborygmi varied over time and with dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Limited thermal antinociceptive effects were observed at the transdermal doses studied likely owing to limited absorption relative to IV dosing. Future studies may be directed toward investigating antinociceptive effects of higher transdermal doses and different application sites.

Basic Postoperative Care of the Equine Colic Patient

The 3 time periods around colic surgery (preoperative, operative, and postoperative) are all critical to successful outcomes. Although much focus is often paid to the first 2 time periods, the importance of sound clinical judgment and rational decision-making in the postoperative period cannot be overstated. This article will outline the basic principles of monitoring, fluid therapy, antimicrobial therapy, analgesia, nutrition, and other therapeutics routinely used in patients following colic surgery. Discussions of the economics of colic surgery and expectations for normal return to function will also be included.

Synopsis of the pharmacokinetics, pharmacodynamics, applications, and safety of firocoxib in horses

According to in vitro and in vivo investigations, firocoxib (FX), a second-generation coxib, is a highly selective COX-2 inhibitor in horses. With a COX-1/COX-2 IC₅₀ ratio of 643 in horses, FX spares the COX-1 inhibitory effects. It is approved for the treatment of musculoskeletal problems and lameness in horses and dogs with osteoarthritis (OA). For the treatment of OA in horses, both an injectable formulation for IV administration at a dose of 0.09 mg/kg for five days and an oral paste formulation at a dose of 0.1 mg/kg for 14 days are licensed. Numerous analytical methods were reported in the literature to quantify FX in biological fluids, using HPLC and LC-MS. FX presents remarkable pharmacokinetics and pharmacodynamics compared to other coxibs. It has an oral bioavailability of 80% or higher and is effectively absorbed by horses. Its volume of distribution is around 2 L/kg, and it is slowly eliminated. Due to the long elimination half-life (around 2 days), which allows a once daily dosing, a single 0.3 mg/kg loading dose has been recommended. This enables the establishment of steady-state drug concentrations within 24 h, making it appropriate for acute treatment as well. Its IC₈₀ is equal to 103 ng/mL in whole blood and, with an EC₅₀ of 27 ng/mL, it has the highest affinity for its receptor compared to the other commonly administered NSAIDs in horses.

A multiparametric approach to assessing residual pain experienced by dairy cows undergoing digestive tract surgery under multimodal analgesia

This study assessed residual pain responses of dairy cows undergoing fistulation surgery under multimodal analgesia using a multiparametric method combining behavioural and physiological indicators. A longitudinal study was conducted on five dairy cows, each acting as her own control. The surgery consisted of implanting a ruminal and a duodenal cannula in each cow. The multimodal drug protocol consisted of a combination of N-Methyl-D aspartic Acid antagonists, α2-agonists, and local anaesthetic during surgery, and non-steroidal anti-inflammatory drugs (NSAIDs) and opioid treatment postsurgery. Cow responses to surgery were monitored by direct behavioural observation, physiological assay indicators, and milk production from day (D) -6 days before surgery (D-6) to D13 postsurgery. From the data recorded, the variables that contributed most to the discrimination of days pre- and postsurgery were identified using factorial discriminant analysis. Components 1 and 2 of the factorial discriminant analysis explained 68.2% and 17.9%, respectively, of the total variance. Component 1 was mainly explained by haptoglobin (contribution to axis: 0.885), oxidative stress (ratio of oxidized gluthatione to reduced glutathione (GSH/GSSG), -0.746; vitamin E, -0.683; vitamin A, -0.597; malondialdehyde (MDA), 0.416), and behavioural indicators (general attitude, 0.594). On this axis, the higher the score, the higher were the apathy and haptoglobin and MDA concentrations, and the lower were the GSH/GSSG ratio and concentrations of vitamins A and E. This axis opposed cows on D-6 to cows on D3 and D5; cows on D1 and D13 were intermediate. Component 2 was mainly explained by the Hypothalamic-pituitary-adrenal axis (non-esterified fatty acid (NEFA), 0.686; cortisol, 0.669), milk yield (-0.725), oxidative stress (MDA, -0.584; nitric oxide (NO), 0.454), and behavioural indicators of pain (ear position, 0.467; leg postures, 0.431). On this axis, the higher the score, the higher the NEFA, cortisol, and nitric oxide concentrations; the more the ear and leg pain postures; and the lower the milk production and MDA concentrations. This axis opposed cows on D13 to cows on D1. These results suggest that cows may experience some pain only on D1, whereas on subsequent days, the inflammatory response and oxidative stress did not seem to be associated with pain. Our results should be considered for different surgeries to improve analgesia immediately after surgery, and to provide antioxidants along with NSAIDs to promote recovery.

Assessment of a multimodal analgesia protocol in goats undergoing claw amputation

Objective: To evaluate the anti-nociceptive, sedative and behavioral effect of multimodal analgesic drugs in goat's undergoing unilateral claw amputation. Design: A randomized experimental design. Animals: Sixteen goats were randomly assigned into 4 groups (4 bucks per group). Procedure: Animals used in this study were randomly assigned into 4 groups, four animals for each group. All goats were anaesthetized by intravenous regional anesthesia (IVRA) of the right forelimb cephalic vein with 2% lidocaine in a dose of 3mg/kg body weight (BW) before surgery. Administration of carprofen (50 mg/ml) at a dose 0.1 mg/kg BW took place before surgery on day 0 and was then repeated once daily for another 3 consecutive days postoperatively in groups Lidocaine (L), carprofen_lidocaine (CL), carprofen – romifidine - lidocaine (CRL), and carprofen – romifidine - butorphenol - lidocaine (CRBL). Heart rate (HR), respiratory rate (RR), rectal temperature (RT), serum IL-6 level, sedation score, and lameness score were determined at preset time intervals and the animals’ behavior was recorded. Results: The mean average of HR, RR and RT in IVRA treated animals was significantly increased until the end of surgery followed by gradual decrease up to 90 min post-surgery. In CRL and CRBL it showed a significant decrease compared to controls. There was a significant decrease in lameness score in CRL and CRBL treated animals from 30 min until 2 hours and for 3 days post-surgery. After injection of romifidine it showed a significant decrease of IL-6 levels compared to lidocaine and CL treated animals. Conclusion and clinical relevance: It was concluded that, the use of romifidine and buterphanol in the analgesic protocol during claw amputation in goats, alleviate pain response and potentiate the analgesic effects of IVRA. Addition of carprofen to the analgesic protocol can be used for long- term treatment of orthopedic pain in goats without complications.

Pain therapy - Are there new options on the horizon?

This article reviews the role of analgesic drugs with a particular emphasis on opioids. Opioids are the oldest and most potent drugs for the treatment of severe pain, but they are burdened by detrimental side effects such as respiratory depression, addiction, sedation, nausea, and constipation. Their clinical application is undisputed in acute (e.g., perioperative) and cancer pain, but their long-term use in chronic pain has met increasing scrutiny and has contributed to the current opioid crisis. We discuss epidemiological data, pharmacological principles, clinical applications, and research strategies aiming at novel opioids with reduced side effects.

[Pain inhibition by opioids-new concepts]

BACKGROUND

Opioids are the oldest and most potent drugs for the treatment of severe pain but they are burdened by detrimental side effects, such as respiratory depression, addiction potential, sedation, nausea and constipation. Their clinical application is undisputed in the treatment of acute (e.g. perioperative) and cancer pain but their long-term use in chronic pain has met increasing criticism and has contributed to the current "opioid crisis".

OBJECTIVES

This article reviews the pharmacological principles and new research strategies aiming at novel opioids with reduced side effects. The basic mechanisms underlying pain and opioid analgesia and other effects of opioids are outlined. To illustrate the clinical situation and medical problems, the plasticity of opioid receptors, intracellular signaling pathways, endogenous and exogenous opioid receptor ligands, central and peripheral sites of analgesic and side effects are discussed.

CONCLUSION

The epidemic of opioid misuse has shown that there is a lack of fundamental knowledge about the characteristics and management of chronic pain, that conflicts of interest and validity of models must be more intensively considered in the context of drug development and that novel analgesics with less addictive potential are urgently needed. Currently, the most promising perspectives appear to be augmenting endogenous opioid actions and the selective activation of peripheral opioid receptors.

[Pain inhibition by opioids-new concepts]

BACKGROUND

Opioids are the oldest and most potent drugs for the treatment of severe pain but they are burdened by detrimental side effects, such as respiratory depression, addiction potential, sedation, nausea and constipation. Their clinical application is undisputed in the treatment of acute (e.g. perioperative) and cancer pain but their long-term use in chronic pain has met increasing criticism and has contributed to the current "opioid crisis".

OBJECTIVES

This article reviews the pharmacological principles and new research strategies aiming at novel opioids with reduced side effects. The basic mechanisms underlying pain and opioid analgesia and other effects of opioids are outlined. To illustrate the clinical situation and medical problems, the plasticity of opioid receptors, intracellular signaling pathways, endogenous and exogenous opioid receptor ligands, central and peripheral sites of analgesic and side effects are discussed.

CONCLUSION

The epidemic of opioid misuse has shown that there is a lack of fundamental knowledge about the characteristics and management of chronic pain, that conflicts of interest and validity of models must be more intensively considered in the context of drug development and that novel analgesics with less addictive potential are urgently needed. Currently, the most promising perspectives appear to be augmenting endogenous opioid actions and the selective activation of peripheral opioid receptors.

New concepts in opioid analgesia

INTRODUCTION

Opioids are the oldest and most potent drugs for the treatment of severe pain, but they are burdened by detrimental side effects such as respiratory depression, addiction, sedation, nausea, and constipation. Their clinical application is undisputed in acute (e.g. perioperative) and cancer pain, but their long-term use in chronic pain has met increasing scrutiny and has contributed to the current 'opioid crisis.'

AREAS COVERED

This article reviews pharmacological principles and research strategies aiming at novel opioids with reduced side effects. Basic mechanisms underlying pain, opioid analgesia, and other opioid actions are outlined. To illustrate the clinical situation and medical needs, plasticity of opioid receptors, intracellular signaling pathways, endogenous and exogenous opioid receptor ligands, central and peripheral sites of analgesic, and side effects are discussed.

EXPERT OPINION

The epidemic of opioid misuse has taught us that there is a lack of fundamental knowledge about the characteristics and management of chronic pain, that conflicts of interest and validity of models must be considered in the context of drug development, and that novel analgesics with less abuse liability are badly needed. Currently, the most promising perspectives appear to be augmenting endogenous opioid actions and selectively targeting pathological conformations of peripheral opioid receptors.

Salivary alpha-amylase activity and cortisol in horses with acute abdominal disease: a pilot study

BACKGROUND

The aim of this study was to evaluate salivary alpha-amylase (sAA), considered a non-invasive biomarker for sympathetic nervous system (SNS) activity, and salivary cortisol as possible pain-induced stress biomarker, in horses with acute abdominal disease. Therefore, a prospective observational study was performed in which both biomarkers were analyzed in a group of horses with acute abdomen syndrome, and compared with a group of healthy control horses by an unpaired Student's t-test. In addition, the possible relationship between both biomarkers, the score in Equine Acute Abdominal Pain scales version 1 (EAAPS-1 scale), Heart Rate (HR) and Respiratory Rate (RR), plasma lactate, the systemic inflammatory response syndrome (SIRS) score and serum amyloid A (SAA) concentration was assessed by a Spearman correlation test.

RESULTS

A total of 30 horses were included in the study, 19 with acute abdominal disease diagnosed as large colon displacements, simple impactions of the pelvic flexure, spasmodic colics and enteritis and 11 healthy ones. sAA activity (24.5 median-fold, P <  0.0001) and salivary cortisol (1.7 median-fold, P <  0.01) were significantly higher in horses with acute abdomen than in healthy horses. sAA activity was significantly correlated with EAAPS-1 scale (r = 0.78, 95% confidence interval [CI] 0.38-0.89, P < 0.001) and SIRS score (r = 0.49, 95% CI 0.03-0.78, P < 0.05). Neither sAA nor salivary cortisol correlated with HR, RR, plasma lactate and SAA.

CONCLUSIONS

Although this study should be considered as preliminary one, alpha-amylase measurements in saliva could be a biomarker of pain-induced stress in horses with acute abdominal disease.

Total intravenous anaesthesia in a goat undergoing craniectomy

BACKGROUND

Cerebral coenurosis is a disease of the central nervous system in sheep and goats, and is usually fatal unless surgical relief is provided. Information regarding neuroanaesthesia in veterinary medicine in goats is scant.

CASE PRESENTATION

We describe anaesthetic management of an intact female goat (2 years; 16 kg) presented for craniectomy. The goat was sedated with xylazine (0.05 mg kg-1, i.m.) and morphine (0.05 mg kg-1, i.m.). General anaesthesia was induced 20 min later with propofol and maintained with a constant rate infusion of propofol (0.2 mg kg-1 min-1). A cuffed endotracheal tube was placed and connected to a rebreathing (circle) system and mechanical ventilation with 100% oxygen was initiated. A bolus of lidocaine (1 mg kg-1), midazolam (0.25 mg kg-1) and fentanyl 2.5 μg kg-1 was delivered via the intravenous route followed immediately by a constant rate infusion of lidocaine (50 μg kg-1 min-1), midazolam (0.15 mg kg-1 h-1) and fentanyl (6 μg kg-1 h-1) administered via the intravenous route throughout surgery. Craniectomy was undertaken and the goat recovered uneventfully.

CONCLUSION

Total intravenous anaesthesia with propofol, lidocaine, fentanyl and midazolam could be an acceptable option for anaesthesia during intracranial surgery in goats.

Effects of Firocoxib, Flunixin Meglumine, and Phenylbutazone on Platelet Function and Thromboxane Synthesis in Healthy Horses

OBJECTIVE

Determine the effects of nonsteroidal anti-inflammatory drugs (NSAID) on platelet function and thromboxane synthesis immediately after drug administration and following 5 days of NSAID administration in healthy horses.

STUDY DESIGN

Randomized cross-over study.

ANIMALS

Healthy adult horses (n=9; 6 geldings and 3 mares).

METHODS

Horses received either flunixin meglumine (1.1 mg/kg IV every 12 hours), phenylbutazone (2.2 mg/kg IV every 12 hours), or firocoxib (loading dose of 0.27 mg/kg IV on day 1, then 0.09 mg/kg IV every 24 hours for 4 days) for a total of 5 days. Blood samples were collected prior to drug administration (day 0), 1 hour after initial NSAID administration (day 1), and then 1 hour post-NSAID administration on day 5. Platelet function was assessed using turbidimetric aggregometry and a platelet function analyzer. Serum thromboxane B₂ concentrations were determined by commercial ELISA kit. A minimum 14 day washout period occurred between trials.

RESULTS

At 1 hour and 5 days postadministration of firocoxib, flunixin meglumine, or phenylbutazone, there was no significant effect on platelet aggregation or function using turbidimetric aggregometry or a platelet function analyzer. There was, however, a significant decrease in thromboxane synthesis at 1 hour and 5 days postadministration of flunixin meglumine and phenylbutazone that was not seen with firocoxib.

CONCLUSION

Preoperative administration of flunixin meglumine, phenylbutazone, or firocoxib should not inhibit platelet function based on our model. The clinical implications of decreased thromboxane B₂ synthesis following flunixin meglumine and phenylbutazone administration are undetermined.

Effects of preoperative carprofen on cardio-respiratory, hormonal and metabolic stress response in calves during umbilical surgery under isoflurane inhalation anaesthesia

The aim of this study was to examine the effects of preoperative carprofen on the cardiorespiratory, hormonal and metabolic stress response during umbilical surgery under isoflurane anaesthesia combined with local anaesthesia, in calves. A randomised, blinded experimental study was conducted in 24 calves. Carprofen (n = 12; 1.4 mg/kg) or physiological saline solution (controls; n = 12) was administered 1 h prior to surgery. Anaesthesia was induced with xylazine (0.1 mg/kg, IM) and, after the onset of sedation (i.e. after 5-8 min), ketamine was administered (2 mg/kg, IV). Anaesthesia was then maintained with isoflurane (ISO) in oxygen to effect and completed by infiltration of the incision line with 20 mL of 2% procaine. Cardiorespiratory, endocrine and metabolic parameters were examined before, during and after surgery at short intervals. In both groups, anaesthesia appeared adequate for the surgical intervention. Heart rate, stroke index and arterial blood pressure were significantly elevated after the onset of surgery. Oxygen partial pressure and oxygen delivery increased, while the oxygen extraction ratio decreased intraoperatively, ensuring sufficient oxygen supply. In the control group, the mean surge in serum cortisol concentrations tended to be higher (P = 0.089) and systemic vascular resistance (SVR) was significantly greater (P <0.05) than in the carprofen group during surgery. In conclusion, the anaesthetic protocol used in this study induced reliable analgesia in both groups. The lower serum cortisol levels and SVR may indicate a reduced surgical stress response in calves undergoing umbilical surgery under ISO anaesthesia after administering carprofen preoperatively.

Determination of the minimum infusion rate of alfaxalone during its co-administration with fentanyl at three different doses by constant rate infusion intravenously in goats

OBJECTIVE

To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to standardized noxious stimulation during its co-administration with fentanyl at three different doses by constant rate infusion (CRI) intravenously (IV) in goats.

STUDY DESIGN

Prospective, blinded, randomized crossover, experimental.

ANIMALS

Eight healthy goats; four does and four wethers.

METHODS

For induction of anaesthesia, a bolus of fentanyl was administered at 0.005 mg kg(-1) (LFent), 0.015 mg kg(-1) (MFent) or 0.03 mg kg(-1) (HFent) followed by alfaxalone at 2.0 mg kg(-1) . For maintenance, the goats received alfaxalone at an initial infusion rate of 9.6 mg kg(-1)  hour(-1) and one of three fentanyl treatments: 0.005 mg kg(-1)  hour(-1) (LFent), 0.015 mg kg(-1)  hour(-1) (MFent) or 0.03 mg kg(-1) hour(-1) (HFent). The MIR of alfaxalone was determined during fentanyl CRI by testing for responses to stimulation (clamping on a digit with Vulsellum forceps) every 30 minutes. Some cardiopulmonary parameters were measured.

RESULTS

The alfaxalone MIR median (range) was 6.7 (6.7-8.6), 2.9 (1.0-6.7) and 1.0 (1.0-4.8) mg kg(-1)  hour(-1) during LFent, MFent and HFent, respectively. Alfaxalone MIR was significantly lower during MFENT and HFENT compared to LFENT. Significantly low oxygen haemoglobin saturation (SaO2 ) and arterial oxygen partial pressure (PaO2 ), observed 2 minutes into anaesthesia after all fentanyl treatments, were the most remarkable adverse cardiopulmonary effects observed. Recovery from anaesthesia was severely affected by high doses of fentanyl with excitatory behavioural signs predominant for up to 2 hours post-administration after MFent and HFent.

CONCLUSIONS AND CLINICAL RELEVANCE

Fentanyl reduces alfaxalone MIR in goats in a dose-dependent manner. Immediate oxygen supplementation after induction of general anaesthesia is recommended to prevent hypoxaemia. Doses of fentanyl equal to or greater than 0.015 mg kg(-1)  hour(-1) tend to be associated with severe excitatory behaviour and should be avoided when fentanyl is administered to goats.

Opioid Receptors

Opioids are the oldest and most potent drugs for the treatment of severe pain. Their clinical application is undisputed in acute (e.g., postoperative) and cancer pain, but their long-term use in chronic pain has met increasing scrutiny. This article reviews mechanisms underlying opioid analgesia and other opioid actions. It discusses the structure, function, and plasticity of opioid receptors; the central and peripheral sites of analgesic actions and side effects; endogenous and exogenous opioid receptor ligands; and conventional and novel opioid compounds. Challenging clinical situations, such as the tension between chronic pain and addiction, are also illustrated.

ORIGEM E DISTRIBUIÇÃO ANTIMÉRICA DOS NERVOS FEMORAIS EM CAPRINOS RECÉM-NATOS DA RAÇA SAANEN

O nervo femoral foi estudado em 33 caprinos recém-natos da raça Saanen (22 machos e 11 fêmeas), que, após morte natural, foram fixados com solução de formaldeído a 10%. Nos machos, o nervo femoral teve sua origem nos ramos espinhais ventrais de L4 e L5 em oito animais (36%); em seis animais (27%) teve sua origem nos ramos espinhais ventrais de L5 e L6; em cinco animais (23%) teve sua origem no ramo espinhal ventral de L5; em dois animais (9%) teve sua origem nos ramos espinhais ventrais de L4, L5 e L6; em um animal (5%) teve sua origem dos ramos espinhais ventrais de L5 e L6 e no ramo espinhal ventral de S1. Nas fêmeas, teve sua origem nos ramos espinhais ventrais de L4 e L5 em sete animais (64%); em três animais (27%) teve sua origem nos ramos espinhais ventrais de L5 e L6 e em um animal (9%) teve sua origem nos ramos espinhais ventrais de L4, L5 e L6. Os nervos femorais emitiram, em todos os animais, número variável de ramos para os músculos psoas maior, psoas menor, quadríceps femoral, sartório e pectíneo.

Physiological and analgesic effects of continuous-rate infusion of morphine, butorphanol, tramadol or methadone in horses with lipopolysaccharide (LPS)-induced carpal synovitis

BACKGROUND

Continuous-rate infusion (CRI) of drugs results in more stable plasma drug concentrations than administration of intermittent boluses, thus providing greater stability of physiological parameters. The aim of this study was to evaluate the physiologic and analgesic effects of the administration of morphine, butorphanol, tramadol or methadone by CRI in horses with induced synovitis of the radiocarpal joint.

RESULTS

Increased values of cardiorespiratory parameters and body temperature were observed in all groups after initiation of opioid administration, and these increases were sustained throughout the CRI period. Morphine, butorphanol and methadone each caused a reduction in gut sounds, and this effect was greatest in animals that received morphine. Administration of morphine or methadone reduced the degree of lameness after the end of intravenous infusion. Administration of tramadol did not alter the degree of lameness in the animals.

CONCLUSIONS

CRI of morphine or methadone, but not butorphanol or tramadol, provided analgesia in horses with carpal synovitis. All of these opioids increased cardiovascular and respiratory parameters and reduced gut sounds during CRI.

The effects of midazolam and butorphanol, administered alone or combined, on the dose and quality of anaesthetic induction with alfaxalone in goats

Goats are rarely anaesthetised; consequently, scant information is available on the efficacy of anaesthetic drugs in this species. Alfaxalone is a relatively new anaesthetic agent, of which the efficacy in goats has not yet been studied. In this study, the sedative and alfaxalonesparing effects of midazolam and butorphanol, administered alone or concomitantly, in goats were assessed. Eight clinically healthy goats, four does and four wethers, were enlisted in a randomised crossover manner to receive intramuscular sedative treatments consisting of saline 0.05 mL/kg, or midazolam 0.30 mg/kg, or butorphanol 0.10 mg/kg, or a combination ofmidazolam 0.30 mg/kg with butorphanol 0.10 mg/kg before intravenous induction of general anaesthesia with alfaxalone. Following induction, the goats were immediately intubated and the quality of anaesthesia and basic physiological cardiorespiratory and blood-gas parameters were assessed until the goats had recovered from anaesthesia. The degree of sedation, quality of induction and recovery were scored. When compared with saline (3.00 mg/kg), midazolam,administered alone or with butorphanol, caused a statistically significant increased level of sedation and a reduction in the amount of alfaxalone required for induction (2.00 mg/kg and 1.70 mg/kg, respectively). Butorphanol alone (2.30 mg/kg) did not cause significant changes in level of sedation or alfaxalone-induction dose. During induction and recovery, the goats were calm following all treatments, including the control group. Cardiorespiratory and blood gasparameters were maintained within clinically acceptable limits. The present study showed that midazolam, administered alone or combined with butorphanol, produces a degree of sedation that significantly reduces the dose of alfaxalone required for induction of general anaesthesia in goats, without causing any major adverse cardiorespiratory effects.

A comparison of two morphine doses on the quality of recovery from general anaesthesia in horses

Previous studies indicated that perioperative morphine improves recovery quality after general anaesthesia in horses. This clinical trial investigated whether this effect was dose-dependant. Twenty-six horses anaesthetised for surgery were block-randomised to receive one of two intraoperative morphine treatments: Treatment M1 consisted of a constant rate infusion (CRI) of morphine at 0.1mg/kg/h, begun after a loading dose (LD) of 0.15 mg/kg. Treatment M2 was a CRI of 0.2mg/kg/h preceded by an LD of 0.3mg/kg. During recovery, times at the first attempt and at achieving sternal recumbency and standing, and the total recovery duration were not different between groups. Total recovery quality score was not significantly different between groups. Scores for the "sternal phase" were higher (of poorer quality) for M2 but scores in both groups were low. Morphine doses of M2, which are greater than those described previously, do not appear to alter or improve the quality or duration of recovery in horses after surgical anaesthesia.

Targeting inflammation and wound healing by opioids

Opioid receptors are expressed on peripheral sensory nerve endings, cutaneous cells, and immune cells; and local application of opioids is used for the treatment of inflammatory pain in arthritis, burns, skin grafts, and chronic wounds. However, peripherally active opioids can also directly modulate the inflammatory process and wound healing. Here, we discuss the underlying mechanisms of opioid action and the conceivable therapeutic approaches for opioid treatment, as investigated in experimental and clinical studies. A large number of in vitro experiments and animal model investigations have produced evidence that peripherally active opioids can reduce plasma extravasation, vasodilation, proinflammatory neuropeptides, immune mediators, and tissue destruction. In contrast to currently available anti-inflammatory agents, opioids have not demonstrated organ toxicity, thus making them interesting candidates for drug development. Few clinical studies have tapped into this potential to date.

Opioids, sensory systems and chronic pain

Opioids are the oldest and most potent drugs for the treatment of severe pain. Their clinical application is undisputed in acute pain (e.g. associated with trauma or surgery) but their long-term use in chronic pain has met increasing scrutiny. Therefore, this article will review sensory mechanisms related to opioid analgesia and side effects with a special emphasis on chronic pain. Central and peripheral sites of analgesic actions and side effects, as well as conventional and novel opioid compounds will be discussed. Since pain is a complex bio-psycho-social phenomenon, non-pharmacological considerations important for the understanding of opioid analgesic efficacy are also included. Finally, examples of challenging clinical situations such as the perioperative management of patients receiving long-term opioid treatment are illustrated.

Pharmacokinetics of intra-articular morphine in horses with lipopolysaccharide-induced synovitis

OBJECTIVE

To describe the pharmacokinetics of intra-articularly (IA) administered morphine.

STUDY DESIGN

Experimental randomized, cross-over study.

ANIMALS

Eight adult healthy mixed breed horses aged 6.5 +/- 2.3 (mean +/- SD) years and weighing 535 +/- 86 kg.

METHODS

Unilateral radiocarpal synovitis was induced by IA injection of 3 microg lipopolysaccharide (LPS) on two occasions (right and left radiocarpal joint, respectively) separated by a 3-week wash-out period. Treatments were administered 4 hours post-LPS-injection: Treatment IA; preservative free morphine IA (0.05 mg kg(-1)) plus saline intravenous (IV) and treatment IV; saline IA plus preservative free morphine IV (0.05 mg kg(-1)). Concentrations of morphine, morphine-3-glucuronide and morphine-6-glucuronide (M6G) were determined repeatedly in serum and synovial fluid (SF) by high-performance liquid chromatography mass spectrometry, at 2 and 4 hours and then at 4 hours intervals until 28 hours post-treatment.

RESULTS

Injection of LPS elicited a marked and comparable synovitis in all LPS-injected radiocarpal joints. IA administered morphine was detectable in SF of all eight joints 24 hours post-treatment and in 6/8 joints 28 hours post-treatment. The terminal half-life of morphine in SF was estimated to be 2.6 hours. IA administration of morphine resulted in mean serum concentrations of morphine below 5 ng mL(-1) from 2 to 28 hours after treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Intra-articularly administered morphine remained within the joint for at least 24 hours. At the same time only very low serum concentrations of morphine and M6G were detected. The present results suggest that IA morphine at 0.05 mg kg(-1) may be used for IA analgesia lasting at least 24 hours and give strong support to the theory that previously observed analgesic and anti-inflammatory effects of IA morphine in horses are most likely to be mediated peripherally.

Neuropathic pain management in chronic laminitis

Managing pain in horses afflicted by chronic laminitis is one of the greatest challenges in equine clinical practice because it is the dreadful suffering of the animals that most often forces the veterinarian to end the battle with this disease. The purpose of this review is to summarize our current understanding of the complex mechanisms involved in generating and amplifying pain in animals with laminitis and, based on this information, to propose a modified approach to pain therapy. Furthermore, a recently developed pain scoring technique is presented that may help better quantify pain and the monitoring of responses to analgesic treatment in horses with laminitis.