Heparin: a review of its pharmacology and therapeutic use in horses

Periovulatory anticoagulant therapy enhances embryo recovery rates in superovulated mares

Although protocols for superovulation have been described in horses, this technique has been discouraged due to the low embryo recovery rates in superovulated mares. The reason for these poor results is poorly understood, but the formation of a blood clot in the ovulation fossa following ovulations has been hypothesized. Therefore, this study aimed to assess the safety and effect of periovulatory anticoagulant therapy on embryo recovery of superovulated mares. In experiment 1, five mares were assigned to receive five anticoagulant treatments in a crossover design: intravenous injections of 150 (H1), 300 (H2), 400 (H3), 450 (H4), 600 (H5) IU/kg of unfractionated heparin (UFH, heparin sodium); and had blood samples sequentially collected for up to 48 h post-treatment to test Prothrombin (PT) and activated partial thromboplastin time (aPTT). In experiment 2, four mares were treated in a crossover design with intravenous injection of 450 IU/kg of UFH and 1 mg/kg of low molecular weight heparin (LMWH, enoxaparin) and had blood collected as previously for analysis of plasma anti-Xa activity. In experiment 3, eleven mares had four cycles randomly assigned to four groups. In the control group, mares did not receive any treatment. In contrast, in groups G1, G2, and G3, mares were superovulated with equine pituitary extract and treated 34 h after the induction of ovulation with a placebo (NaCl 0.9 %, G1), 450 IU/kg of UFH (G2), or 1 mg/kg of LMWH. Mares in all groups had ovulation induced with hCG plus histrelin acetate and were bred with fresh semen from one stallion. Embryo flushing was performed nine days post-ovulation. In experiment 1, only mares in groups H4 and H5 had increased aPTT and PT for up to 12 h, and in all groups, aPTT and PT values returned to baselines at 24 h post-treatment. In experiment 2, plasma anti-Xa activity was increased by both therapies for up to 12 h after treatment and was at baseline levels 24 h post-treatment. In experiment 3, periovulatory therapy with anticoagulants increased embryo recovery rates per cycle (G2, 250 %; G3, 260 %) compared to control-assigned cycles (60 %; P < 0.05), whereas G1-assigned cycles (160 %) had intermediate embryo recovery. In conclusion, periovulatory anticoagulant therapies may be an alternative to improve embryo recovery in superovulated mares.

Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment

BACKGROUND

Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking.

HYPOTHESIS/OBJECTIVES

To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks.

ANIMALS

Eleven healthy adult horses.

METHODS

Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Weekly, iASD closure was monitored using transthoracic and intracardiac echocardiography. Relationship between activated clotting time and anti-factor Xa activity during postoperative enoxaparin treatment was assessed in vitro and in vivo.

RESULTS

Transseptal puncture was successfully achieved in all horses within a median duration of 22 (range, 10-104) minutes. Balloon dilatation of the puncture site for sheath advancement was needed in 4 horses. Atrial arrhythmias occurred in 9/11 horses, including atrial premature depolarizations (N = 1), atrial tachycardia (N = 5), and fibrillation (N = 3). Serum cardiac troponin I concentrations increased after TSP, but remained under the reference value in 10/11 horses. Median time to iASD closure was 14 (1-35) days. Activated clotting time correlated with anti-factor Xa activity in vitro but not in vivo.

CONCLUSIONS AND CLINICAL IMPORTANCE

Transseptal puncture was successfully performed in all horses. The technique was safe and spontaneous iASD closure occurred in all horses. Clinical application of TSP will allow characterization and treatment of left-sided arrhythmias in horses.

Metabolic and Endocrine Insights in Donkeys

Donkey medicine is gaining attention due to their increased use as companion animals, in shows, asinotherapy, etc. The increasing demand and unique aspects call for specialized care, requiring new information (physiology, infectious disorders, pharmacology, etc.). Since obesity is common in this species, hyperlipemia, metabolic syndrome and insulin dysregulation (ID) are common disorders in donkeys, in some cases with high mortality, either directly (multiorgan dysfunction) or indirectly due to poor quality of life (chronic laminitis). Donkeys have long-life expectancy and are often afflicted with pituitary pars intermedia dysfunction (PPID), a neurodegenerative and endocrine disease. Hyperlipemia is diagnosed based on high plasma triglyceride concentration in association with clinical findings and laboratory abnormalities from affected tissues (liver, kidney and pancreas). The measurement of resting serum insulin and plasma ACTH concentrations is the first step in ID and PPID diagnosis. In donkeys with clinical signs of ID (obesity or recurrent laminitis) or PPID (hypertrichosis, regional adiposity, laminitis and weight loss), where these hormones are in the normal or non-diagnostic range (donkey-specific cut-off values and reference ranges need to be established), dynamic tests are recommended (oral sugar test or thyrotropin-releasing hormone, respectively). Equine treatment protocols apply to donkeys, although pharmacological studies for most drugs, except pergolide, are lacking.

Assessment of thrombin generation in horses using a calibrated automated thrombogram

BACKGROUND

The amount of thrombin generated reflects the endogenous thrombin potential (ETP), which depends on the balance of pro- and anticoagulant factors. The calibrated automated thrombogram (CAT) allows for the direct measurement of thrombin generation during the clotting process.

OBJECTIVES

(1) To describe the results of the CAT assay in horses, (2) to establish intra-assay and intra- and interindividual variation of thrombin generation in healthy horses, and (3) to compare in vitro low-molecular-weight heparin (LMWH) sensitivity between healthy and sick horses. The hypothesis for the last objective is that inhibition of thrombin generation in sick horses requires higher heparin concentrations.

METHODS

The plasma of 10 healthy mixed breed horses was used for the determination of normal thrombin generation parameters (lag time, time to peak, peak thrombin concentration, and ETP). Five of the healthy horses were compared with five horses with systemic inflammatory response syndrome (SIRS). In vitro heparin sensitivity was determined using LMWH.

RESULTS

The intra-assay variation was small (<5%) for all parameters. Relatively large intra- and interindividual variation were observed in healthy horses. Four of the five sick horses with SIRS had a thrombogram compatible with a hypercoagulable state. The in vitro heparin sensitivity test suggested decreased sensitivity to LMWH in hypercoagulable states.

CONCLUSIONS

The CAT assay could detect coagulopathy in horses. In vivo experiments are needed to confirm that it can be used to monitor responses to LMWH therapy.

A pilot study evaluating the Calibrated Automated Thrombogram assay and application of plasma-thromboelastography for detection of hemostatic aberrations in horses with gastrointestinal disease

Background

Critically ill horses, such as horses with gastrointestinal (GI) disease, often suffer from hemostatic aberrations. Global hemostatic tests examining the initiation of coagulation, clot strength and fibrinolysis, such as the Calibrated Automated Thrombogram (CAT) and plasma-thromboelastography (TEG) have not been evaluated in horses. This study aimed to evaluate CAT and apply plasma-TEG in horses.

Test performance of CAT was evaluated on equine platelet poor plasma with intra- and inter-assay variability (CV) and a heparin dilution curve. To examine clinical performance of both tests, group comparisons were assessed comparing healthy horses, horses with mild and severe GI disease with both CAT and plasma-TEG.

Results

For CAT, intra- and inter-assay CVs were established for lag-time (1.7, 4.7%), endogenous thrombin potential (1.6, 4.6%), peak (2.6, 3.9%) and time to peak (ttPeak) (1.9, 3.4%). Increasing heparin concentrations led to the expected decrease in thrombin generation. In the group comparison analysis, CAT showed significant higher peak (p = 0.04) and ttPeak (p = 0.008) in the severe GI disease group compared to horses with mild GI disease and healthy horses, respectively. Plasma-TEG showed an increased angle (p = 0.032), maximum amplitude (p = 0.017) and shear elastic force (G) (p = 0.017) in the severe GI disease group compared to healthy horses.

Conclusions

CAT performed well in horses. Both CAT and plasma-TEG identified hemostatic aberrations in horses with severe GI disease compared to healthy horses. Further studies including more horses, are needed to fully appreciate the use of CAT and plasma-TEG in this species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03058-7.

A Pilot Randomised Clinical Trial Comparing a Short-Term Perioperative Prophylaxis Regimen to a Long-Term Standard Protocol in Equine Colic Surgery

Background: For surgical interventions classified as clean or clean-contaminated, including laparotomy, guidelines in human and veterinary medicine recommend a short-term perioperative antibiotic prophylaxis (PAP). In equine colic surgery, however, PAP commonly exceeds 24 h. Objectives: The aim of this study was to compare a single-shot to a 5-day lasting PAP considering surgical site infections (SSI) and other adverse effects probably associated with the particular antimicrobial regimen. Study design: The study was designed as a randomised non-inferiority pilot study including horses subjected to colic surgery while receiving one of two distinct PAP regimens. Methods: All horses (n = 67) included in the study received the standard physical examination before and after surgery. Colic surgery was performed according to the current standard of the clinic. Horses were randomly assigned to two groups, receiving either the “single-shot” or the “5-day lasting” antibiotic prophylaxis. The “single-shot” group (n = 30) received penicillin and gentamicin only once before and, if needed, during surgery, whereas the “5-day lasting” group (n = 37) received antibiotics for five days. In addition to the standard laboratory examinations, serum amyloid A and fibrinogen were determined preoperatively and during five days after surgery. SSI, postoperative colitis and haemolytic anaemia were classified as postoperative complications potentially related to antibiotic use. Results: The outcome of this preliminary non-inferiority clinical trial showed that the occurrence of postoperative adverse events (i.e., SSI, postoperative colitis and haemolytic anaemia) lacked significant differences between the study groups. Main limitations: The main limitations of this study are the limited group sizes and our inability to blind the study. Conclusions: Single-shot PAP seems to be an alternative approach considering the 5-day lasting protocol commonly used in equine abdominal surgery. However, a proper hygiene management together with a close clinical and laboratory monitoring of the equine patient is indispensable.

Inflammatory Response of Healthy Horses Subjected to Small Colon Enterotomy and Treated or Not With Heparin

The acute phase response is a response to injury and depends on the severity of the trauma. Heparin is routinely used for postsurgical treatment of horses to prevent abdominal adhesions; however, its effect on inflammation is unknown. This study aimed to assess systemic inflammatory response of horses subjected to small colon enterotomy and to evaluate heparin effects on postsurgical inflammation. Ten adult horses were subjected to small colon enterotomy and were assigned to a control or a treatment group. Both groups received prophylactic antibiotics and flunixin, and the treatment group received 150 IU/kg heparin subcutaneously after surgery and every 12 hours for five days. WBC counts, peritoneal fluid evaluation, determination of serum and peritoneal haptoglobin (Hp), and serum amyloid A (SAA) were performed before, 12 hours, and 1, 2, 4, 6, 10, and 14 days after enterotomy. Forty-eight hours after surgery, a significant increase in serum Hp was observed in the control group, and SAA concentrations increased significantly in the both groups between 24 hours, 48 hours, and 4 days after surgery. The SAA and serum Hp concentrations produced no significant differences between the groups. Peritoneal Hp increased significantly in the control group 4 days after surgery and was significantly higher in the control group than in the treated group 14 days after surgery. Serum Hp and SAA identified the acute phase response changes faster, however, were not able to identify differences between groups. Peritoneal Hp concentrations identified inflammatory differences between the groups 14 days after surgery; the difference suggests that heparin may act decreasing inflammation.

Accidental overdose of intravenously injected unfractionated heparin followed by prolonged clotting times in an anaesthetised Shetland pony

A six-year-old Shetland pony stallion was presented for elective castration. During surgical preparations, undiluted heparin (120 iu/kg) was unintentionally used for intravenous catheter flushing instead of heparinised saline solution. Surgery was cancelled for that day. Thromboelastography was used to monitor blood coagulation immediately after the accidental heparin overdose and on the following days. Three days after the heparin overdose, the coagulation parameters had returned to normal values and the pony was castrated. Anaesthesia and surgery were uneventful without any signs of coagulopathy. One day after surgery, the pony started to show signs of colic and was further diagnosed with colitis, most likely unrelated to heparin but due to repeated administration of penicillin and anaesthesia. Despite intensive treatment, the pony deteriorated progressively and was euthanased due to poor prognosis. Drug overdose is an example of medication error and is one of the most common errors in medicine.

Engineering a simple lateral flow device for animal blood coagulation monitoring

Increasing numbers of animals are diagnosed with thromboembolism, requiring anticoagulation treatment to prevent thrombotic events. Frequent and periodic coagulation monitoring is critical to ensure treatment effectiveness and patient safety by limiting blood coagulation ability within the desired therapeutic range. Point-of-care diagnostics is an ideal candidate for frequent coagulation monitoring due to rapid test results and no need for laboratory setting. This article reports the first utilization of no-reaction lateral flow assay (nrLFA) device for simple and low-cost animal blood coagulation monitoring in resource-limited setting. The nrLFA device consists of sample pad, analytical membrane and wicking pad, without conjugate pad, reagent printing or membrane drying. Citrated and heparinized animal blood were utilized to mimic different blood coagulation abilities in vitro by adding reversal agents CaCl2 and protamine sulfate. The travel distance of red blood cells (RBCs) on the nrLFA after a pre-determined test time serves as endpoint marker. Upon adding 500 mM CaCl2 solution to citrated bovine, canine, rabbit and equine blood, the average travel distance decreases from 10.9 to 9.4 mm, 8.8 to 5.7 mm, 12.6 to 9 mm, and 15.3 to 11.3 mm, respectively. For heparinized bovine and rabbit blood, the average distance decreases from 14.5 to 11.4 mm and from 9.8 to 7.2 mm, respectively, when adding 300 mg/l protamine sulfate solution. The effect of hematocrit on RBC travel distance in the nrLFA was also investigated. The nrLFA device will potentially improve treatment efficiency, patient safety, quality of life, and satisfaction for both animal patients and their owners.

The role of heparin in sepsis: much more than just an anticoagulant

Despite progress in antibiotic treatment, mechanical ventilation, fluid resuscitation and blood glucose maintenance, sepsis remains a cause of high mortality in the intensive care unit to date, there are no proven treatment strategies for the routine management of septic patients. The extensive interaction between inflammation and coagulation contributes to the basic pathophysiology of sepsis. Thus, the agents that attenuate the activation of both inflammation and coagulation may improve the outcome in sepsis. Apart from the well-known anticoagulant effects of heparin, it also possesses various immunomodulatory properties and protects glycocalyx from shedding. Hence, heparin seems to be such an agent. Immunothrombosis plays an important role in early host defence against bacterial dissemination, thus the proper timing for anticoagulant therapy should be determined. We review the available experimental and clinical data supporting the use of heparin in sepsis. At this time the use of heparin in the treatment of sepsis is conflicting. Future trials of heparin therapy for sepsis should concentrate on the very severely ill patients, in whom benefit is most likely to be demonstrated.

Musculoskeletal Disease in Aged Horses and Its Management

Musculoskeletal disorders are the most prevalent health problem in aging horses. They are not life threatening, but are painful and an important welfare issue. Chronic joint disease (osteoarthritis) and chronic laminitis are the most prevalent. Treating osteoarthritis in the elderly horse is similar to treating performance horses, but aims at providing a stable situation with optimal comfort. Immediate medical treatment of flare-ups, long-term pain management, and adaptation of exercise and living conditions are the mainstays of treatment. Laminitis in the geriatric horse is related often to pituitary pars intermedia dysfunction, which may be treated with additional pergolide.

Peritoneal reactivity evaluation in horses subjected to experimental small colon enterotomy and treated with subcutaneous heparin

Heparin is routinely administered in postoperative abdominal surgery aiming to prevent adhesions formation; however, there is no consensus indicating its effectiveness. This study evaluated the effect of heparin on peritoneal reactivity after abdominal surgery, through the association between peritoneal fluid features and ultrasonographic and laparoscopic examination. Ten adult horses were used: control group (CG) and treated group (TG). Both groups underwent laparotomy and small colon enterotomy. TG received subcutaneous heparin at 150 IU/kg every 12 hours for 5 days. The animals underwent ultrasonography and peritoneal fluid examination prior to enterotomy (M0) 12 hours (M1), 1 day (M2), 2 days (M3), 4 days (M4), 6 days (M5), 10 days (M6), and 14 days after enterotomy (M7) with laparoscopic examination being performed on the fifth postoperative day. Peritoneal inflammatory response was observed in both groups. The peritoneal fluid of TG animals showed higher echogenicity during heparin therapy. No inflammatory difference was observed between groups through peritoneal fluid features, except for the higher D-dimer concentration in CG. On laparoscopy, slightly diffuse peritoneal reactivity for both groups was observed, being higher for TG. Laparoscopy and ultrasonography association allowed detailed access to the abdominal cavity. Ultrasonography assessed the diffuse peritoneal inflammation, and laparoscopy allowed the detailed analysis of the segments. No gross beneficial reactions resulting from the use of heparin on peritoneal reactivity were observed; however, it was observed by D-dimer evaluation that the TG had less fibrin deposition, which is directly related to a lower rate of abdominal adhesions formation.

Peritoneal response to abdominal surgery: the role of equine abdominal adhesions and current prophylactic strategies

Intra-abdominal adhesions constitute a significant clinical and surgical problem that can lead to complications such as pain and bowel occlusion or subocclusion. These adhesions are frustrating and potentially fatal, representing a major postoperative complication in abdominal surgery. It is estimated that 32% of horses undergoing laparotomy will present clinical symptoms due to adhesions, but the true prevalence is not known because a large proportion of animals with postoperative recurrent colics are medically treated or submitted to euthanasia without necropsy. Adhesions are highly cellular, vascularized, dynamic structures that are influenced by complex signaling mechanisms. Understanding their pathogenesis could assist in applying better therapeutic strategies and in developing more effective antiadhesion products. Currently, there are no definitive strategies that prevent adhesion formation, and it is difficult to interpret the results of existing studies due to nonstandardization of an induction model and evaluation of their severity. The best clinical results have been obtained from using minimally traumatic surgical techniques, anti-inflammatory agents, antimicrobials, anticoagulants, and mechanical separation of serosal surfaces by viscous intraperitoneal solutions or physical barriers. This paper aims to review adhesion formation pathogenesis, guide the understanding of major products and drugs used to inhibit adhesion formation, and address their effectiveness in the equine species.

Pharmacokinetics and thrombolytic effects of the recombinant tissue-type plasminogen activator in horses

Background

To test the efficacy of the recombinant tissue-type plasminogen activator (rt-PA) alteplase in horses, the thrombolytic effect was tested in in vitro generated equine thrombi. The extent of lysis was determined by measuring the decrease in thrombi weight over a period of 4 hours. In vivo pharmacokinetics of alteplase were determined in 6 healthy horses. A single dose (1 mg/kg) was applied via intravenous infusion over a period of 30 minutes Coagulation-related variables, blood count and clinical parameters were taken before the treatment and until 48 h after treatment. In addition, plasma rt-PA concentration was measured until 300 min after commencing the infusion.

Results

In vitro, a dose dependent decrease of thrombus weight ranging from a 56 (± 6.5) % decrease for 0.5 μg/ml to 92 (± 2.1) % decrease for 5 μg/ml rt-PA was noted. The D-dimer concentration in the lysis medium correspondingly increased from 0.10 up to 10.8 mg/l.

In vivo, none of the horses showed an adverse reaction to the alteplase infusion. In some horses blood parameters were slightly altered. The 1 mg/kg dose yielded the following pharmacokinetic parameters: Cmax = 1.25 ± 0.27 μg/ml; CL = 21.46 ± 5.67 ml/min/kg; dominant half life (t1/2α) = 6.81 ± 1.48 minutes; median elimination half life (t1/2β) = 171 min (range: 85–1061); AUC = 50.33 ± 17.62 μg · min /ml.

Conclusion

These findings indicate that a single dose of 1 mg/kg alteplase results in rt-PA plasma concentrations comparable to those in humans and might be sufficient for a thrombolytic therapy in horses. Further studies must be performed to determine the alteplase effectiveness in horses with jugular vein thrombosis.

Pharmacodynamics of multi-dose low molecular weight heparin in healthy horses

OBJECTIVES

To compare the pharmacodynamics of once daily and twice daily administration of low molecular weight heparin (LMWH) administration in horses.

STUDY DESIGN

Randomized cross over study.

ANIMALS

Adult mixed breed healthy mares (n = 6).

METHODS

LMWH (dalteparin) was administered (50 U/kg subcutaneously) either every 12 or 24 hours for 3 consecutive days. Anti-factor Xa activity was measured before and at select time points after LMWH administration. Packed cell volume (PCV), platelet count, partial thromboplastin time (PTT), and anti-thrombin (AT) activity were monitored throughout the study.

RESULTS

No changes in PCV, platelet count, or AT activity were detected with either frequency of daily LMWH administration. Values for PTT increased throughout the study but never exceeded the normal reference interval. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range (0.1-0.2 U/mL) when LMWH was administered twice daily, but fell below this range ≈ 16 hours after administration when given once daily. For both once and twice daily LMWH administration, the area under the curve was significantly greater after the last dose of LMWH when compared to the first dose.

CONCLUSIONS

Administration of LMWH once or twice daily for 3 consecutive days appears to be safe in healthy adult horses. Anti-factor Xa activity was maintained within or above the suggested thromboprophylactic range for 24 hours with twice daily LMWH administration but not with once daily administration.

Trombectomia com cateter de Fogarty no tratamento da tromboflebite jugular experimental em eqüinos

Trombose da veia jugular é problema freqüente na medicina eqüina, implicando muitas vezes em conseqüências fatais. O objetivo deste trabalho foi avaliar em eqüinos a aplicabilidade da trombectomia com cateter de Fogarty, técnica rotineiramente empregada pela medicina humana, no restabelecimento da perviedade vascular. Foram utilizados 10 eqüinos divididos em dois grupos de cinco animais, em que se induziu a trombose da veia jugular direita, através do acesso cirúrgico à veia e aplicação de sutura estenosante e injeção de glicose a 50%. No grupo controle avaliou-se a evolução da tromboflebite sem qualquer tipo de intervenção terapêutica. Os animais do grupo tratado foram submetidos à trombectomia com cateter de Fogarty. Foram avaliados os parâmetros clínicos gerais, regionais, ultra-sonográficos e angiográficos, nos momentos pré-indução (M-PRÉ), indução da trombose (MTI) e 10 dias de evolução da trombose (M10). A técnica empregada induziu a tromboflebite, que obstruiu completamente um segmento da veia jugular de todos os animais. Os animais do grupo controle mantiveram os trombos obstruindo totalmente o lume vascular até o final do período de avaliação, sendo que avaliações regionais mostraram principalmente o edema parotídeo e o ingurgitamento vascular, cranial à tromboflebite da veia jugular. O grupo tratado apresentou as veias jugulares pérvias ao final do experimento, confirmadas pelos exames ultra-sonográficos e angiográficos, com remissão total dos sinais clínicos. Concluiu-se que a técnica da trombectomia com cateter de Fogarty foi eficiente na desobstrução da veia jugular submetida à trombose experimental.

Structure, biological activity, and enzymatic transformation of fucoidans from the brown seaweeds

Recent advances in the study of fucoidans, biologically active sulfated alpha-L-fucans of diverse structures and synthesized exclusively by marine organisms, are overviewed. Their structure, biological activity, the products of their enzymatic degradation and the different enzymes of degradation and modification are considered.

Field fracture management

Emergency management of distal limb and skull fractures in horses is vital to the successful outcome of these cases. Distal limb fractures, in particular, require careful assessment and counseling of the owner as well as adequate stabilization or coaptation of the fracture. Horses with limb or skull fractures may also have concurrent pain, blood loss, and other fluid losses that can result in shock requiring fluid therapy before definitive treatment of the fracture. Proper emergency fracture stabilization, initial treatment in the field, and patient transport are discussed.

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.

Enxertos vasculares homólogos e heterólogos conservados em glicerina na fleboplastia da jugular em eqüinos

Doze eqüinos foram divididos aleatoriamente em dois grupos de seis animais (grupos I e II), com a finalidade de estudar a compatibilidade tecidual e a propriedade de indução de trombos de dois tecidos biológicos conservados em glicerina a 98%. Esses tecidos foram usados na restauração da jugular externa e se constituíram de artéria carótida comum homóloga (ACCHo), no grupo I, e veia jugular externa heteróloga (VJEHe), no grupo II. Para a restauração, utilizaram-se duas técnicas de anastomose da jugular, sendo, no grupo I, a técnica de bypass e, no grupo II, a substituição de um segmento da jugular esquerda por meio de anastomose vascular término-terminal. Para avaliar a trombogênese local e a histocompatibilidade, foram realizados exames clínicos, hematológicos, ecoDopplercardiográficos e histológicos dos segmentos vasculares enxertados. Os segmentos foram colhidos após 45 dias da avaliação pós-operatória, tendo a jugular direita como testemunha para os exames histológicos. Ambos os tecidos foram compatíveis quando implantados nos eqüinos, sem processo inflamatório acentuado, indicativo de rejeição. A técnica de bypass não foi eficiente na restauração da jugular, ocorrendo trombose obliterante dos enxertos de ACCHo. A substituição completa do segmento da jugular por VJEHe pode ser viável para o restabelecimento do fluxo sangüíneo da jugular de eqüinos, desde que se mantenha a igualdade dos diâmetros entre o enxerto e o vaso receptor.

Pharmacokinetics of recombinant hirudin in healthy horses

REASONS FOR PERFORMING STUDY

Recombinant (r)-hirudin is a specific inhibitor of thrombin that is independent of the activity of antithrombin.

OBJECTIVES

To evaluate pharmacokinetic properties and coagulatory changes of r-hirudin in healthy horses.

METHODS

Two clinically healthy horses received a single i.v. bolus of 0.4 mg/kg bwt r-hirudin and 6 clinically healthy horses received the same dose subcutaneously (subcut.) q. 12 h for 3 days. Coagulation times and r-hirudin plasma concentration were determined over 720 mins and 3 days after i.v. and subcut. administration, respectively.

RESULTS

In all horses, treatment with r-hirudin was not associated with systemic or local side effects. After i.v. injection, the 2 horses showed an elimination half-life of 58 and 80 mins, respectively. After subcut. administration, maximum plasma concentration of r-hirudin occurred at 128 +/- 55 mins and declined with a terminal half-life of 561 +/- 364 mins. Maximum response of activated partial thromboplastin time (aPTT) occurred 1.5 h after administration of r-hirudin. A prolongation of 1.9 +/- 0.2 times the pretreatment value was noted.

CONCLUSIONS

Pharmacokinetics of r-hirudin in healthy horses were similar to those in man and other animal species.

POTENTIAL RELEVANCE

The results of this study indicate that r-hirudin can be used in horses, but further studies should be performed in order to prove its effectiveness in diseased horses.

Comparison of unfractioned and low molecular weight heparin for prophylaxis of coagulopathies in 52 horses with colic: a randomised double-blind clinical trial

REASONS FOR PERFORMING STUDY

Unfractioned heparin (UFH) is widely used for prophylaxis of coagulation disorders, especially in colic-affected horses. However, it is accompanied by certain side effects.

OBJECTIVES

To compare the efficacy and side effects of unfractioned and low molecular weight heparin (LMWH) in horses with colic.

METHODS

The study was carried out as a randomised, double-blind, controlled clinical trial. Fifty-two horses with colic were treated subcutaneously with either UFH (heparin calcium, 150 iu/kg bwt initially, followed by 125 iu/kg bwt q. 12 h for 3 days and then 100 iu/kg bwt q. 12 h) or LMWH (dalteparin, 50 iu/kg bwt q. 24 h). All horses underwent daily physical examination including assessment of jugular veins, local reaction to heparin injections, haematological evaluation and coagulation profiles over up to 9 days.

RESULTS

The type of heparin used did not affect the general behaviour and condition. There were significantly more jugular vein changes in horses treated with UFH. Packed cell volume decreased significantly within the first few days of UFH treatment, but did not change significantly in horses treated with LMWH. Activated partial thromboplastin time (aPTT) and thrombin time (TT) were prolonged in horses treated with UFH but not in those treated with LMWH.

CONCLUSIONS

It was concluded that, in comparison to UFH, LMWH has markedly fewer side effects in horses.

POTENTIAL RELEVANCE

Therefore, LMWH is recommended for prophylaxis of coagulation disorders in colic patients.

A rapid and simple method for the separation of pure lymphocytes from horse blood

A method for the separation of pure and viable lymphocytes and granulocytes from the same blood sample in horses was reported. By centrifuging equine heparinized blood at 100 xg for 10 min at room temperature (r.t.), the resulting supernatant plasma was an almost pure (97.71 +/- 0.30%; n = 15) suspension of highly viable (98.72 +/- 0.28%) lymphocytes. When sodium citrate was used as an anticoagulant, lymphocyte suspensions collected in the same manner showed lower purity (87.89 +/- 1.59%; n = 9) and higher yields (56.56 +/- 3.89%, n = 9 versus 36.11 +/- 2.23%, n = 15). Where needed, a further centrifugation at 250 xg for 3 min (r.t.) of heparinized lymphocyte preparations removed an average of 87.39% (n = 15) contaminating platelets. A suspension of 85.96 +/- 2.20% pure granulocytes (93.23 +/- 1.74% neutrophils; n = 14) with minimal contamination by erythrocytes and high viability (93.11 +/- 1.26%) was obtained by performing a flash red blood cell lysis on the white-greyish layer resulting from the centrifugation of the heparinized blood samples. Among the several methods available, the procedure described herein is easy, rapid, cheap and reproducible.

Effect of administration of a phospholipid emulsion on the initial response of horses administered endotoxin

OBJECTIVE

To evaluate the effect of a phospholipid emulsion (PLE) on the initial response of horses to administration of endotoxin.

ANIMALS

12 healthy adult horses.

PROCEDURES

Horses were assigned to 2 treatment groups (6 horses/group). The control group was administered 1 L of saline (0.9% NaCl) solution, and the treated group was administered PLE (200 mg/kg, IV); treatments were administered during a period of 120 minutes. An infusion of endotoxin was initiated in both groups starting 1 hour after initiation of the saline or PLE solutions. Physical examination and hemodynamic variables were recorded, and blood samples were analyzed for concentrations of tumor necrosis factor (TNF)-alpha, interleukin-6, thromboxane B2 (TxB2), 6 keto-prostaglandin F (PGF)1alpha, total leukocyte count, and PLE concentrations. An ANOVA was used to detect significant differences.

RESULTS

Administration of PLE resulted in significantly lower rectal temperature, heart rate, cardiac output, right atrial pressure, and pulmonary artery pressure and higher total leukocyte counts in treated horses, compared with values for control horses. The TNF-alpha concentration was significantly less in treated horses than in control horses. The TxB2 and 6 keto-PGFF1alpha concentrations were significantly different between treated and control horses at 30 minutes (TxB2) and at 30 and 60 minutes (6 keto-PGF1alpha).

CONCLUSIONS AND CLINICAL RELEVANCE

Prior infusion of PLE in horses administered a low dose of endotoxin decreased rectal temperature, heart rate, pulmonary artery pressure, and TNF-alpha concentrations. Results of this study support further evaluation of PLE for use in the treatment of horses with endotoxemia.

Comparison of pharmacokinetic variables for two low-molecular-weight heparins after subcutaneous administration of a single dose to horses

OBJECTIVE

To determine pharmacokinetic variables and to evaluate the influence on clotting times after SC administration of single doses of dalteparin and enoxaparin to horses.

ANIMALS

5 healthy adult horses.

PROCEDURES

The study was designed as a 4-period crossover study. Each horse received a single SC injection of dalteparin (50 and 100 anti-Xa U/kg) and enoxaparin (40 and 80 anti-Xa U/kg). Plasma anti-Xa activities and clotting times were measured, and pharmacokinetic variables were determined. Absolute and relative maximal prolongation of clotting times was calculated, and correlation between plasma anti-Xa activities and clotting times was determined.

RESULTS

The SC administration of each of the doses of the 2 preparations was well tolerated. Time course of the anti-Xa activities could be described in a 1-compartment model. Comparison of low- and high-dose treatments revealed a disproportionate increase of the area under the plasma activity-time curve and prolongation of the terminal half-life, but the increase in maximum plasma activity was proportionate, and peak plasma concentrations corresponded with concentrations recommended in human medicine. There were only mild changes in activated partial thromboplastin time (aPTT), whereas the influence on thrombin time (TT) was greater, dose-dependent, and more variable. A weak-to-moderate correlation between aPTT and plasma anti-Xa activities and a moderate-to-strong correlation between TT and plasma anti-Xa activities were found.

CONCLUSIONS AND CLINICAL RELEVANCE

Pharmacokinetic and anticoagulatory properties of low-molecular-weight heparins in horses are similar to those found in humans. Once-daily SC administration of dalteparin or enoxaparin may be useful as an anticoagulatory treatment in horses.

Equine cardiac disease. Clinical pharmacology and therapeutics

Cardiac disease is often life-threatening and challenging to treat. Prolonged therapy is indicated in many cases, which can lead to problems with treatment costs, owner compliance, and potential drug toxicity. Many therapies are empirical or based on data from other species because of a lack of well-designed prospective clinical trials in horses. This article reviews the clinical pharmacology and therapeutics of heart failure, cardiac arrhythmias, myocardial disease, endocarditis, and pericardial disease.

The pharmacologic basis for the treatment of developmental and acute laminitis

Each horse with laminitis is presented to the veterinarian at a different stage in progression of the condition and with varying severity. The pathogenic timing is often unknown and is difficult to determine. Because timing and severity are related to both the lesion's severity and responsiveness to treatment, these factors are critical to treatment selection and success. It is erroneous to assume that each horse with laminitis should receive each treatment. It is therefore important to ascertain as logically and objectively as possible the pathophysiological stage of development of each horse when it is examined. Therapeutic failure may result from inappropriate interpretation of the clinical signs and pathophysiologic condition of the patient in order to coordinate a treatment regimen.

The sepsis-coagulant axis: a review

Activation of coagulation is a normal component of the acute inflammatory response. Inflammatory cytokines initiate coagulation events locally at sites of inflammation by converting endothelium from an antithrombotic surface to a prothrombotic surface; by stimulating tissue factor production, which activates both the extrinsic and intrinsic coagulation systems; and by stimulating production of platelet-activating factors. The fibrinolytic system is initially activated but is subsequently inhibited. This results in a marked imbalance in coagulation and fibrinolysis resulting in a net procoagulant state. When thrombin generation and platelet activation exceed the body's capacity to inactivate or remove these factors, disseminated intravascular coagulation (DIC) results. DIC directly contributes to multiple organ failure and death associated with sepsis. Presently available treatments (i.e., heparin and aspirin) are relatively ineffective in treating DIC; however, newer, more potent drugs may soon be available for clinical use.

Adjunctive methods in equine gastrointestinal surgery

The medical management of postoperative abdominal disorders remains a diagnostic and therapeutic challenge for the equine clinician. Recent advances in the development of techniques and medications to offset or attenuate ischemia-reperfusion injury, endotoxemia, and ileus are encouraging and potentially will decrease the incidence of additional complications.

Necrotizing enterocolitis in horses: a retrospective study

The clinical and clinicopathologic characteristics of fatal necrotizing enterocolitis were examined in 16 horses (age 4 months to 12 years). At initial presentation, 8 of 16 horses were pyrexic (median temperature, 38.4 degrees C; range, 33.8 to 40.6 degrees C); all 16 were tachycardic (median heart rate, 93 bpm, range, 66 to 138 bpm); 13 of 16 were tachypneic (median heart rate, 36 bpm, range, 16 to 80 bpm), dehydrated, and had discolored mucous membranes. All horses that were pyrexic were also tachycardic and tachypneic. PCV was high (> 45%) in 14 horses. Six horses were leukopenic (< 5,000 cells/microL); 12 were neutropenic (< 2,300 cells/microL), and 14 had > 100 band neutrophils/microL. Twelve horses were acidemic (pH < 7.37; range, 6.88 to 7.33) and the venous bicarbonate concentration was low (< 23 mEq/L) in 14 horses. Median anion gap in 16 horses was 31.5 mEq/L (> 15 mEq/L in 15 horses). Eleven of 16 horses were hyponatremic (< 137 mEq/L), 1 horse was hypernatremic (> 143 mEq/L), 3 were hypokalemic (< 3.2 mEq/L), 6 were hyperkalemic (> 4.5 mEq/L), and 14 were hypochloremic (< 98 mEq/L). Serum creatinine concentrations were high (> 1.4 mg/dL) in 15 horses. Abdominal fluid was examined in 12 horses 4 had total protein concentrations > 2.5 g/dL and 6 had nucleated cell counts > 5,000/ microL and < 10,000/microL; none had > 10,000/microL. Eight of 12 samples revealed a nondegenerate neutrophilia (> 50%). Abdominal fluid collected from 4 horses immediately before death was normal in 2 horses and indicative of suppurative inflammation in 2. All 8 horses tested had low or nonexistent serum immunofluorescent antibody titers to Ehrlichia risticii. Four of 16 horses had Salmonella spp isolated from feces or tissues. All 16 horses either died (5 of 16; 31%) or were euthanized because of a grave prognosis. Median time to death was 45.5 hours (range, 7 to 113 hours) from the time of admission. Death was preceded by severe abdominal pain in 14 horses. Fatal necrotizing enterocolitis of horses is characterized by a brief course, profound dehydration, electrolyte derangements, acid-base abnormalities, and terminally, severe abdominal pain. Abdominal fluid analysis was frequently not indicative of the severity of disease.