Low dose flunixin meglumine: effects on eicosanoid production and clinical signs induced by experimental endotoxaemia in horses

Effect of Procaine Penicillin G and Flunixin Meglumine on Serum Amyloid A Response in Healthy Adult Horses

This study was designed to determine the effect of PPG and/or flunixin meglumine on SAA response when used at clinical dosing regimens in healthy adult horses. Six healthy adult horses were enrolled in a crossover study design including one control and three treatment groups: no treatment (control); PPG alone (intramuscularly q12h for 72h); flunixin meglumine alone (intravenously q24h for 72h); and PPG (intramuscularly q12h for 72h) and flunixin meglumine (intravenously q24h for 72h). Whole blood was collected at 0, 24, 48, 72, 96 and 120 hours post-initial drug administration to measure SAA using a commercial lateral-flow immunoassay. The washout period was 30 days. Individual SAA values were within the reference range (≤ 20 µg/mL) for almost all horses in the control group. One control horse displayed a SAA value of 28 µg/mL at 72 hours. All horses from the PPG group showed normal SAA values throughout the study. Apart from one horse (SAA of 24 µg/mL at 96 hours) from the flunixin meglumine group, all horses showed normal SAA values. For the PPG and flunixin meglumine group, 5 horses had SAA values within reference range. One horse displayed increased SAA values (32-45 µg/mL) between 48 to 96 hours post-drug administration. There was no difference in area under the SAA time curve amongst control and treatment groups (P > 0.05). The administration of intramuscular PPG and/or intravenous flunixin meglumine does not trigger an inflammatory response that induces a SAA value above reference range in most adult healthy horses.

The Clinical Pharmacology and Therapeutic Evaluation of Non-Steroidal Anti-Inflammatory Drugs in Adult Horses

This review firstly examines the underlying pathophysiology of pain and inflammation associated with orthopedic disease and endotoxemia. Then, it reviews the clinical pharmacology (pharmacokinetics and pharmacodynamics) of both conventional and non-conventional NSAIDs in the adult horse, and finally provides an overview of different modalities to evaluate the therapeutic efficacy of NSAIDs in research.

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.

Non-Steroidal Anti-Inflammatory Drugs and Associated Toxicities in Horses

Effective pain management in horses can be a challenge despite the understanding that appropriate analgesia improves animal welfare and increases treatment success. The administration of NSAID drugs, particularly phenylbutazone and flunixin, are common practice in equine veterinary patients. Known for their analgesic and anti-inflammatory properties, NSAIDs are used for the treatment of a variety of conditions in horses, from gastrointestinal to orthopedic pain. Despite extensive usage, NSAIDs have a narrow margin of safety and the body of literature documenting the efficacy and side effects of different NSAIDs is broad. The three main side effects associated with excessive or prolonged NSAID usage in horses include gastroduodenal ulceration, right dorsal colitis (RDC) and renal papillary necrosis. The use of cyclooxygenase-2 selective NSAIDS, such as firocoxib, are theoretically safer. The aim of this paper is to review the current literature on the use and efficacy of different NSAIDs, summarise the associated side effects of NSAID usage and evaluate the current state of knowledge for the diagnosis and treatment of such toxicities.

BEVA primary care clinical guidelines: Analgesia

Primary care guidelines provide a reference point to guide clinicians based on a systematic review of the literature, contextualised by expert clinical opinion. These guidelines develop a modification of the GRADE framework for assessment of research evidence (vetGRADE) and applied this to a range of clinical scenarios regarding use of analgesic agents. Key guidelines produced by the panel included recommendations that horses undergoing routine castration should receive intratesticular local anaesthesia irrespective of methods adopted and that horses should receive NSAIDs prior to surgery (overall certainty levels high). Butorphanol and buprenorphine should not be considered appropriate as sole analgesic for such procedures (high certainty). The panel recommend the continuation of analgesia for 3 days following castration (moderate certainty) and conclude that phenylbutazone provided superior analgesia to meloxicam and firocoxib for hoof pain/laminitis (moderate certainty), but that enhanced efficacy has not been demonstrated for joint pain. In horses with colic, flunixin and firocoxib are considered to provide more effective analgesia than meloxicam or phenylbutazone (moderate certainty). Given the risk of adverse events of all classes of analgesic, these agents should be used only under the control of a veterinary surgeon who has fully evaluated a horse and developed a therapeutic, analgesic plan that includes ongoing monitoring for such adverse events such as the development of right dorsal colitis with all classes of NSAID and spontaneous locomotor activity and potentially ileus with opiates. Finally, the panel call for the development of a single properly validated composite pain score for horses to allow accurate comparisons between medications in a robust manner.

Sparing the gut: COX-2 inhibitors herald a new era for treatment of horses with surgical colic

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to manage a wide variety of conditions in horses, including management of colic. Flunixin meglumine is by far the most commonly used drug in the control of colic pain and inflammation and has become a go-to for not only veterinarians but also horse-owners and nonmedical equine professionals. NSAID use, however, has always been controversial in critical cases due to a high risk of adverse effects associated with their potent cyclo-oxygenase (COX) inhibition. There are two important COX isoenzymes: COX-1 is generally beneficial for normal renal and gastrointestinal functions and COX-2 is associated with the pain and inflammation of disease. Newer selective NSAIDs can target COX-2-driven pathology while sparing important COX-1-driven physiology, which is of critical importance in horses with severe gastrointestinal disease. Emerging research suggests that firocoxib, a COX-2-selective NSAID labelled for use in horses, may be preferable for use in colic cases in spite of the decades-long dogma that flunixin saves lives.

Diagnosis and Treatment of Undifferentiated and Infectious Acute Diarrhea in the Adult Horse

Acute, infectious, diarrhea in adult horses is a major cause of morbidity and is associated with numerous complications. Common causes include salmonellosis, clostridiosis, Coronavirus, and infection with Neorickettsia risticii (Potomac horse fever). Treatment is empirical and supportive until results of specific diagnostic tests are available. Supportive care is aimed at restoring hydration, correcting electrolyte imbalances, and limiting the systemic inflammatory response. The mainstays of therapy are intravenous fluid therapy, electrolyte supplementation where necessary, nonsteroidal anti-inflammatory agents, and nutritional support. Specific therapies include colloid oncotic support, antibiotics, hyperimmune plasma, polymyxin B, pentoxifylline, probiotics, binding agents, gastroprotectants, laminitis prevention, and coagulation prophylaxis.

Nonsteroidal Anti-inflammatory Drug Use in Horses

Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective anti-inflammatory and analgesic agents and are arguably the most commonly used class of drugs in equine medicine. This article provides a brief review of the mechanism of action, therapeutic uses, pharmacokinetics, and adverse effects associated with their use in horses. The use of COX-2 selective NSAIDs in veterinary medicine has increased over the past several years and special emphasis is given to the use of these drugs in horses. A brief discussion of the use of NSAIDs in performance horses is also included.

Treatment of endotoxaemia and septicaemia in the equine patient

Endotoxins, constituents of the cell wall of gram-positive and gram-negative bacteria, regularly result in severe illness and death in horses. In endotoxaemia, these constituents are present in the systemic circulation; in septicaemia, whole microbes invade normally sterile parts of the body. Interaction of these endotoxins with pathogen recognition receptors leads to an inflammatory response that cannot always be sufficiently contained and hence needs direct treatment. Over the last decennia, our understanding of the pathophysiology of endotoxaemia and septicaemia has significantly increased. Based on improved understanding of the interaction between receptors and endotoxins as well as the subsequent downstream signalling pathways, new therapeutic targets have been identified in laboratory animal species and humans. Important species differences in the recognition of endotoxins and pathogens by their receptors as well as the inflammatory response to receptor activation hamper extrapolation of this information to the horse (and other species). Historically, horses with endotoxaemia and septicaemia have been treated mainly symptomatically and supportively. Based on the identified therapeutic targets, this review describes the current knowledge of the treatment for endotoxaemia and septicaemia in the horse with reference to the findings in other animal species and humans.

A review of equine sepsis

Sepsis is defined as an exaggerated, systemic inflammatory response to infection and is a common condition in horses. Systemic inflammatory response syndrome (SIRS) associated with bacterial infection is a hallmark of sepsis. Sepsis in neonatal foals is a common sequela of failure of passive transfer and, in addition to development of SIRS, may be characterised by bacteraemia, pneumonia, enterocolitis, omphalophlebitis, meningoencephalitis or arthritis. Sepsis in mature horses is most commonly observed secondary to gastrointestinal lesions that result in disrupted mucosa and bacterial translocation into circulation (endotoxaemia). Pleuropneumonia and metritis may also cause sepsis in mature horses. Diagnosis of sepsis is based on SIRS criteria as well as suspected or confirmed infection. Due to the relatively low sensitivity of microbial culture and the subjectivity of sepsis scoring, many sepsis biomarkers are being studied for their usefulness in diagnosis and prognostication of sepsis in horses. Treatment of sepsis requires an intensive care approach that includes antimicrobial drug administration, fluid resuscitation and pressure support, and treatment for inflammation, endotoxaemia and coagulopathy. Early recognition of sepsis and prompt antimicrobial drug treatment are critical for a successful outcome. Multiple organ dysfunction syndrome may occur in severe cases of sepsis, with common manifestations including laminitis and coagulopathies. Although prognosis for septic mature horses depends highly on the primary disease process, the overall survival rate in septic neonatal foals ranges from 26 to 86%, with most studies indicating a survival rate of 45-60%.

The use of nonsteroidal anti-inflammatory drugs in critically ill horses

OBJECTIVE

To review the physiology of the cyclooxygenase (COX) enzymes with reference to the beneficial effects of nonsteroidal anti-inflammatory drugs (NSAIDs) related to their analgesic and antiendotoxic properties as well as the mechanisms responsible for adverse gastrointestinal, renal, and coagulation effects.

DATA SOURCES

Human and veterinary peer reviewed literature

VETERINARY DATA SYNTHESIS

NSAIDs are frequently administered to critically ill horses for their analgesic and anti-inflammatory effects. However, NSAIDs have significant side effects principally on the gastrointestinal mucosa and kidneys. These side effects may be exacerbated in critically ill horses if they have gastrointestinal damage or are volume depleted

CONCLUSIONS

This review provides important information for equine veterinarians and criticalists on the advantages and disadvantages of using traditional NSAIDs and newer equine COX-2 selective NSAIDs for the management of different conditions in critically ill horses.

Update on the management of neonatal sepsis in horses

Despite advances in neonatal intensive care sepsis, severe sepsis and septic shock remain the biggest killers of neonatal foals. Management of this severe syndrome remains difficult, requiring intensive intervention. Key aspects of management include infection control, hemodynamic support, immunomodulatory interventions, and metabolic/endocrine support. Infection control largely consists of early antimicrobial therapy, plasma transfusions, and local therapy for the infected focus. In cases with severe sepsis or septic shock, hemodynamic support with fluids, vasoactive agents, and respiratory support insuring oxygen delivery to vital organs is important. Nutritional support is important, but close monitoring is needed to avoid hyperglycemia and hypoglycemia.

Effects of the addition of endotoxin during perfusion of isolated forelimbs of equine cadavers

OBJECTIVE

To examine the effect of endotoxins on metabolism and histopathologic changes of isolated perfused equine forelimbs.

SAMPLE

Forelimbs (comprising the metacarpus and digit) were collected from cadavers of 12 healthy adult horses after slaughter at an abattoir (14 limbs; 1 forelimb of 10 horses and both forelimbs of 2 horses).

PROCEDURES

Forelimbs were perfused for 10 hours with autologous blood, with and without the addition of endotoxin (80 ng of lipopolysaccharide [LPS]/L). Two limbs of the endotoxin exposure group and 2 nonperfused limbs were loaded to failure of the suspensory apparatus of the pedal bone to evaluate the effect of body weight. Metabolic and histologic variables were evaluated.

RESULTS

Blood pressure increased during the first hour and did not differ between groups. Lactate dehydrogenase activity was similar in both groups and increased significantly during the 10-hour period; glucose consumption at 5 hours and lactate concentration at 8 hours were significantly higher in limbs exposed to endotoxin. The width of secondary epidermal lamellae was greater in LPS limbs. In the primary dermal lamellae of LPS limbs, there were significantly more vessels with an open lumen and aggregates of intravascular neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

In the blood-perfused isolated forelimbs of equine cadavers, exposure to LPS led to significant changes in the laminar tissue as well as to metabolic changes. Therefore, endotoxin should be considered as a causative factor for laminitis and not merely as a risk factor.

Effects of flunixin meglumine and ketoprofen on mediator production in ex vivo and in vitro models of inflammation in healthy dairy cows

In this study, ex vivo assays were carried out in dairy cows to evaluate the anti-inflammatory effects of two nonsteroidal anti-inflammatory drugs: ketoprofen (KETO) and flunixin meglumine (FM). Twelve healthy Holstein dairy cattle were randomly allocated to two groups (n=6): group 1 received FM and group 2 received KETO at recommended therapeutic dosages. The anti-inflammatory effects of both drugs were determined by measuring the production of coagulation-induced thromboxane B2 (TXB2 ), lipopolysaccharides (LPS) (10 μg/mL)-induced prostaglandin E2 (PGE2 ), and calcium ionophore (60 μm)-induced leukotrien B4 (LTB4 ). Cytokine production was assessed by measuring tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ) and interleukin-8 (CXCL8) concentrations after incubation in the presence of 10 μg/mL LPS. The IC50 of FM and KETO was determined in vitro by determining the concentration of TXB2 and PGE2 in the presence of scalar drug concentrations (10(-9) -10(-3) m). Both FM and KETO inhibited the two COX isoforms in vitro, but showed a preference for COX-1. FM and KETO showed similar anti-inflammatory effects in the cow.

Carbohydrate alimentary overload laminitis

In acute laminitis, the suspensory apparatus of the distal phalanx fails at the lamellar dermal/epidermal interface. A grading system for the histopathology of laminitis is based on the consistent pattern of histologic changes to the secondary epidermal lamellae, basal cells, and basement membrane that occur as carbohydrate-induced laminitis develops. The actual trigger factors of carbohydrate-induced laminitis remain unidentified.

The pharmacologic basis for the treatment of developmental and acute laminitis

The treatment of laminitis has been fraught with confusion and controversy for several decades, mainly because of a lack of understanding of the pathophysiology of the disease process. However, recent advances in laminitis research have greatly improved our understanding of the disease process. This article discusses the various treatment options for laminitis in the context of the findings of recent scientific investigations of laminitis pathophysiology.

Polymyxin B protects horses against induced endotoxaemia in vivo

REASONS FOR PERFORMING STUDY

A safe, affordable and effective treatment for endotoxaemia in horses is needed in order to reduce the incidence of this potentially fatal condition.

OBJECTIVE

To evaluate the effect of polymyxin B (PMB) on signs of experimentally-induced endotoxaemia.

HYPOTHESIS

PMB ameliorates the adverse effects of endotoxaemia without causing nephrotoxicity.

METHODS

Four groups of 6 healthy mature horses each received 20 ng endotoxin/kg bwt i.v. over 30 mins. Additionally, each group received one of the following i.v.; 5000 u PMB/kg bwt 30 mins before endotoxin infusion; 5000 u PMB/kg bwt 30 mins after endotoxin infusion; 1000 u PMB/kg bwt 30 mins prior to endotoxin infusion; or saline. Clinical response data and samples were collected to determine neutrophil count, serum tumour necrosis factor (TNF) activity, plasma thromboxane B2 concentration and urine gamma glutamyltranspeptidase (GGT) to creatinine ratio.

RESULTS

Treatment with PMB before or after administration of endotoxin significantly reduced fever, tachycardia and serum TNF, compared to horses receiving saline. The differences in response to endotoxin were greatest between horses that received saline vs. those that received 5000 u PMB/kg bwt prior to endotoxin. Urine GGT:creatinine did not change significantly.

CONCLUSIONS AND POTENTIAL RELEVANCE

This study indicates that PMB may be a safe and effective treatment of endotoxaemia, even when administered after onset. Although nephrotoxicity was not demonstrated with this model, caution should be exercised when using PMB in azotaemic patients.

Prevention of ischaemia-induced small intestinal adhesions in foals

REASONS FOR PERFORMING STUDY

Treatments addressing variously theorised pathophysiological mechanisms of small intestinal adhesions have been reported. This study applied those classes of treatments to the most clinically relevant aetiology of post operative adhesions.

HYPOTHESIS

Treatments addressing the pathophysiology of ischaemia-reperfusion induced adhesions would accordingly reduce the incidence of adhesions from this model.

METHODS

Four classes of treatments were administered for 72 h to 16 foals subjected to complete ischaemia followed by reperfusion to create peritoneal adhesions. These groups were: 1) FPG group--flunixin meglumine (1.1 mg/kg bwt i.v., divided q.i.d.), potassium penicillin G (22,000 iu/kg bwt i.v., q.i.d.) and gentamicin (2.2 mg/kg bwt i.v., t.i.d.); 2) HEP group--heparin (80 iu/kg bwt subcut., b.i.d.); 3) DMSO group--dimethylsulphoxide (DMSO) (20 mg/kg bwt [diluted in 500 ml normal saline] i.v., b.i.d.); and 4) SCMC group--sodium carboxymethylcellulose (500 ml 3% sterile solution intraperitoneally, administered only at the beginning of surgery).

RESULTS

Post operative intestinal obstruction did not occur in any foal. After 10 days, necropsy revealed bowel-to-bowel adhesions in none of the FPG or DMSO groups, in 2/4 of the SCMC group, in 3/4 of the HEP group and 5/6 foals subjected to the procedure without treatment (UIR group).

CONCLUSIONS

Inhibition of the inflammation associated with ischaemia and reperfusion in foals treated with FPG or DMSO decreased small intestinal adhesions in foals.

POTENTIAL RELEVANCE

Although anti-inflammatory therapy was shown to eliminate bowel-bowel adhesions in this controlled study, it must be remembered that clinical cases are without control. These therapies are advised to improve the result but are unlikely to eliminate the problem.

Update on treatments for endotoxemia

Endotoxemia is a major cause of morbidity and mortality in horses affected by colic. This article briefly reviews the pathogenesis of endotoxemia in horses with colic, reviews current established treatments, and describes new advances in the treatment of endotoxemia.

Equine endotoxaemia--a state-of-the-art review of therapy

The pathophysiology of endotoxaemia, a leading cause of death in the horse, is beginning to be understood in greater detail. Endotoxin may be absorbed into the systemic circulation in a number of different ways: most commonly the body's normal defense mechanisms are disrupted or bypassed, or the normal clearance mechanisms overwhelmed. Following this wide-spread effects are observed, although the most significant are seen in the cardiovascular system. Fever, arterial hypoxaemia and signs of abdominal pain are also common. With increased understanding of the disease new therapeutic agents have become available, however, while the newer agents offer some advantages it is important to recognise that supportive care is the mainstay of treatment for endotoxaemia. Supportive care consists of aggressive fluid therapy (crystalloid, colloid and hypertonic), the administration of non-steroidal antiinflammatory drugs and, where appropriate, antimicrobials. The principles of supportive care are discussed in detail. Other therapies such as hyperimmune plasma, polymyxin B, pentoxifylline, dimethyl sulfoxide and heparin are commonly used in the treatment of equine endotoxaemia and their use is reviewed here. Furthermore, newer agents such as anti-tumour necrosis factor antibodies, detergent, activated protein C and insulin, which have yet to gain widespread acceptance but may have an important role in the treatment of endotoxaemia in the future, are examined.

Expression of the cyclooxygenase isoforms in the prodromal stage of black walnut-induced laminitis in horses

OBJECTIVE

To compare the levels of mRNA expression of cycooxygenase (COX)-1 and COX-2 in the digital laminae of normal horses and horses in the developmental stages of laminitis experimentally induced by administration of black walnut extract (BWE).

SAMPLE POPULATION

Samples of mRNA extracted from the digital laminae of 5 control horses and 5 horses at the onset of leukopenia after administration of BWE.

PROCEDURE

Specimens of laminae were collected from anesthetized horses prior to euthanasia. Expression of COX-1 and COX-2 mRNA in laminae of control and affected horses was evaluated via real-time quantitative polymerase chain reaction techniques.

RESULTS

Expression of COX-2 mRNA was significantly increased in the BWE-treated group, compared with that in control horses. In contrast to COX-2 regulation, COX-1 mRNA expression was not significantly different between groups. Interestingly, despite consistent clinical signs such as leukopenia in all BWE-treated horses, distinct differences in COX-2 mRNA expression were detected among those 5 horses (compared with values for control horses, the increase in COX-2 mRNA expression ranged from no increase to a 30-fold increase).

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that there was a significant upregulation of COX-2 mRNA expression during the developmental stages of laminitis, with no significant change in expression of the COX-1 isoform. These data appear to provide support for aggressive use of nonsteroidal anti-inflammatory drugs in horses at risk for laminitis; further investigation into the clinical value of selective COX-2 inhibitors for treatment of laminitis in horses appears to be warranted.

Sepsis in adults and foals

Sepsis develops in horses when the host response to the invading pathogens is not properly balanced according to the severity of the insult. Several clinical conditions frequently encountered in equine practice may be associated with the development of sepsis and have the potential to progress to more severe forms, such as severe sepsis, MODS, and septic shock. Consequently, it is important for equine practitioners to be aware of the manifestations,pathophysiology, and treatment of sepsis. Although enormous progress has been made in recent years in our understanding of the pathophysiology of sepsis. more work remains to be done in improving basic critical care guidelines and basic monitoring in equine intensive care units and in critically evaluating potential equine sepsis therapy. Fortunately, we can learn from the important advances made recently in the treatment of human sepsis patients;hence, rapid progress may be expected in a near future, especially as more and more veterinarians show interest in the discipline of equine critical care. With the completion of several genome projects and the availability of high-throughput genetic techniques, one hopes that we will further refine our understanding of the events underlying the development of severe sepsis and septic shock, which could lead to more appropriate therapeutic intervention targeted to each individual according to the state of the immune response in that horse.

Postoperative management of the large colon volvulus patient

Horses with large colon volvulus (LCV) often require intensive postoperative medical management. Although early referral and surgical intervention are critical for minimal postoperative complications and a successful outcome, this is often not possible for many reasons. Endotoxemia, extensive mucosal damage with subsequent severe hypoproteinemia, and focal ischemic necrosis are the major causes of postoperative morbidity and mortality. Although fluid therapy, flunixin meglumine, and antimicrobials are still the mainstay of perioperative management, synthetic colloids are being used to maintain plasma oncotic pressure, hyperimmune antiendotoxic plasma and polymixin B are being used for management of endotoxemia, and lidocaine and constant rate infusion of butorphanol can be used for postoperative analgesia. The use of heparin, dimethyl sulfoxide, and corticosteroids for management of LCV are still controversial. Future studies are required to investigate nutritional improvement and methods to manage cases after surgery to prevent recurrence.

Treatment of acute and chronic gastrointestinal inflammation

Treating inflammation in the equine gastrointestinal tract remains a challenge. Our most potent anti-inflammatory drugs, COX inhibitors and glucocorticoids, have unwanted effects on the gastrointestinal tract and host defense that often limit their use. Newer strategies targeting specific cells and molecules that regulate a subset of the events occurring during inflammation are rapidly becoming available and should allow clinicians to reduce the detrimental effects of inflammation without inhibiting the beneficial aspects.

Treatment of endotoxemia

Although recognition of clinical signs of endotoxemia is not difficult, determining the underlying cause for the development of endotoxemia may be a challenging task. For this reason, importance must be placed on performance of a thorough physical examination, attention to detail, and determination of whether or not surgical intervention is required. In most instances, a definitive diagnosis may require repeated examinations and laboratory work. In the meantime, affected animals require treatment for endotoxemia, with the aim being to reduce the duration of endotoxemia, prevent the interaction of additional endotoxins with cell surface receptors, and reduce the synthesis and release of inflammatory mediators.

Effects on plasma endotoxin and eicosanoid concentrations and serum cytokine activities in horses competing in a 48-, 83-, or 159-km endurance ride under similar terrain and weather conditions

OBJECTIVE

To determine plasma endotoxin concentration in horses competing in a 48-, 83-, or 159-km endurance race and its importance with regard to physical, hematologic, or serum and plasma biochemical variables.

ANIMAL

3 horses.

PROCEDURE

Weight and rectal temperature measurements and blood samples were obtained before, during, and after exercise. Blood samples were analyzed for plasma endotoxin concentration; serum antiendotoxin antibody titers; thromboxane B2 (TxB2) and 6-keto-prostaglandin F1alpha (PGF1alpha) concentrations; tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) activities; WBC, plasma protein, lactate, serum electrolyte, and calcium concentrations; PCV; and creatine kinase activity.

RESULTS

Detection of plasma endotoxin increased during exercise for horses competing at all distances but occurred more frequently in the 48- and 83-km groups. Plasma lactate concentration was significantly greater when endotoxin was concurrently detected. Endotoxin in plasma was not significantly associated with success of race completion. Plasma TxB2 and PGF1alpha concentrations and serum IL-6 activity significantly increased with exercise. Horses that had an excellent fitness level (as perceived by their owners) had greater decreases in serum antiendotoxin antibody titers during exercise than did horses perceived as less fit. In horses with better finish times, TxB2 and PGF1alpha concentrations were significantly greater and TNFalpha activity was significantly less than that of slower horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF1alpha concentrations and serum TNFalpha activity may be associated with performance success.

Management of gastrointestinal pain

Choice of an analgesic for gastrointestinal pain requires consideration of the cause of the pain, desired duration of pain relief, need for sedation, and potential side effects and toxicity, particularly in light of other drugs being used and effects on the gastrointestinal tract. It is imperative that close monitoring be continued to ensure that surgical lesions or worsening conditions are detected. Recent research in the field may lead to new drugs, drug combinations, and avenues of treatment that minimize the side effects of these drugs while maximizing their efficacy.

Nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are substances other than steroids that inhibit a component of the inflammatory cascade. This article is dedicated to those substances which specifically inhibit cyclooxygenase. NSAIDs are used extensively in the veterinary field. This article discusses their pharmacologic mechanism of action, indications, and toxicity. The two isoforms of cyclooxygenase (COX-1 and COX-2) are reviewed along with the newer NSAID which are more effective and less toxic due to more specific COX-2 inhibition. Specific effects on soft tissue, bone, cartilage, and synovium are summarized. Pain modulation is extensively reviewed as well as the antiendotoxic and antithrombotic uses.

The Future of Antiinflammatory Therapy

The cells and mediators that make up the inflammatory response have the potential to injure tissues and contribute to the pathophysiology of many inflammatory diseases. Strategies to reduce neutrophil migration into sites of inflammation and subsequent activation by inhibiting integrin-mediated adhesion hold promise for successful treatment of a variety of inflammatory diseases. New pharmacologic agents that specifically target prostanoid mediators of inflammation by specifically inhibiting the activity of cyclooxygenase 2 are potent antiinflammatory agents with fewer gastrointestinal side effects than nonspecific cyclooxygenase inhibitors. These areas of antiinflammatory research are rapidly yielding drugs with diverse future applications in equine medicine.

Evaluation of polymyxin B in an ex vivo model of endotoxemia in horses

OBJECTIVE

To evaluate effects of polymyxin B sulfate (PMB) on response of horses to endotoxin, using an ex vivo model.

ANIMALS

8 healthy horses.

PROCEDURE

In a crossover design, 3 doses of PMB (100, 1,000, and 10,000 U/kg of body weight) and physiologic saline solution (control) were evaluated. Prior to and for 24 hours after administration of PMB, blood samples were collected into heparinized tubes for use in 2 assays. For the endotoxin-induced tumor necrosis factor (TNF) assay, blood samples were incubated (37 C for 4 h) with 1 ng of Escherichia coli or Salmonella Typhimurium endotoxin/ml of blood. Plasma was harvested and assayed. For the residual endotoxin activity assay, plasma was collected into sterile endotoxin-free borosilicate tubes, diluted 1:10 with pyrogen-free water, and incubated for 10 minutes at 70 C. Escherichia coli endotoxin (0.1 or 1 ng/ml of plasma) was added to the thawed samples prior to performing the limulus ameobocyte lysate assay. Serum creatinine concentrations were monitored for 1 week.

RESULTS

Compared with baseline values, PMB caused a significant dose- and time-dependent decrease in endotoxin-induced TNF activity. Compared with baseline values, residual endotoxin activity was significantly reduced after administration of 10,000 U of PMB/kg. Compared with baseline values, 1,000 and 5,000 U of PMB/kg should inhibit 75% of endotoxin-induced TNF activity for 3 and 12 hours, respectively. Serum creatinine concentrations remained within the reference range.

CONCLUSION AND CLINICAL RELEVANCE

Results of the study suggest that PMB is a safe, effective inhibitor of endotoxin-induced inflammation in healthy horses.

Effect of eltenac in horses with induced endotoxaemia

Ten horses were used in a crossover study to evaluate the effectiveness of eltenac against endotoxaemia. Eltenac (0.5 mg/kg bwt) or saline control was given i.v. then 15 min later, intravenous infusion of endotoxin was begun and continued for 120 min (total dose 100 ng/kg bwt). Horses were monitored for heart and respiratory rates, pulmonary and carotid arterial pressure and core body temperature. Blood was sampled at intervals for measurement of haematological variables and plasma concentrations of lactate, prostanoid metabolites, tumour necrosis factor (TNF) and stress hormones. In comparison with saline-treatment, use of eltenac significantly protected against endotoxin-induced changes in respiratory rate, core temperature, systemic arterial blood pressure (SAP), pulmonary arterial pressure, PCV, and plasma protein, 6-keto prostaglandin F1 alpha, thromboxane B2, epinephrine, and cortisol concentrations. Despite statistical effect of eltenac on SAP, values in both treatment groups remained well above baseline throughout the evaluation period. Significant protective effect of eltenac was not found for heart rate, white blood cell count, plasma lactate concentration or TNF activity. On the basis of these results, it is expected that use of eltenac will provide clinical benefit in horses with naturally occurring endotoxaemia.

Pharmacologic considerations in the treatment of neonatal septicemia and its complications

This article focuses on the pharmacologic properties of drugs commonly used in the treatment of neonatal septicemia and its complications. Rational therapy demands an awareness of not only the pharmacology of individual drugs but also the interactions and anticipated fate of such drugs in the rapidly changing physiologic environment of the neonate. Further research in the area of equine neonatal pharmacology should greatly assist our understanding of the impact of the disease state on the unique physiology of the newborn and should allow us to better predict the ultimate fate of drugs commonly used for such purposes. Careful dosing and close monitoring of pharmacologic effects are critical for a successful outcome. In the future, newer therapeutic strategies that are safe and efficacious may provide a means to circumvent many of the problems currently encountered with treating the septicemic newborn foal.