Total intravenous anesthesia with propofol-ketamine-xylazine with or without remifentanil in thoroughbred horses undergoing castration.

We evaluated the clinical efficacy of total intravenous anesthesia (TIVA) with propofol-ketamine-xylazine (PKX) with or without remifentanil for castration in horses. Twenty-four Thoroughbred horses were premedicated with intravenous (IV) xylazine (1.0 mg/kg) and midazolam (0.02 mg/kg) and anesthetized with IV ketamine (1.5 mg/kg) and propofol (1.0 mg/kg). Surgical anesthesia was maintained with constant infusion of propofol (3.0 mg/kg/hr)-ketamine (3.0 mg/kg/hr)-xylazine (1.0 mg/kg/hr) (group PKX: n=8), PKX combined with remifentanil (3.0 µg/kg/hr) (group PKXR3: n=8), or PKX combined with remifentanil (6.0 µg/kg/hr) (group PKXR6: n=8). During anesthesia, none of the horses showed any limb movements, but five, two, and two horses in the PKX, PKXR3, and PKXR6 groups, respectively, showed cremaster muscle contractions. One horse in the PKX group required doubling the PKX infusion rate to continue surgery. Adverse effects of remifentanil (trembling of the nose tip or tongue) were observed in one and three horses in the PKXR3 and PKXR6 groups, respectively. Heart rate and arterial blood pressure were well maintained in all groups. Ventilation was assisted in four, five, and six horses in the PKX, PKXR3, and PKXR6 groups, respectively. Recovery scores in the PKX group were fair in one horse, good in three horses, and excellent in four horses, whereas recovery in all horses in the PKXR3 and PKXR6 groups was judged to be excellent. TIVA with PKX combined with remifentanil 3.0 µg/kg/hr could provide more sufficient anesthetic depth than PKX with fewer clinically significant adverse effects than that with remifentanil 6.0 µg/kg/hr.

Rational determination of cefazolin dosage regimen in horses based on pharmacokinetics/pharmacodynamics principles and Monte Carlo simulations.

A pharmacokinetics/pharmacodynamics (PK/PD) approach was used to determine the best empirical dosage regimen of cefazolin (CEZ) after intramuscular (IM) administration of CEZ in horses. Seven horses received a single IM or intravenous (IV) administration of CEZ of 5 mg/kg bodyweight (BW) according to a crossover design. CEZ plasma concentrations were measured using LC-MS/MS. The plasma concentrations in these seven horses and those of six other horses obtained in a previous study with an IV CEZ dose of 10 mg/kg were modelled simultaneously using NonLinear Mixed-Effect modelling followed by Monte Carlo simulations to establish a rational dosage regimen. A 90% Probability of Target Attainment (PTA) for a PK/PD target of a free plasma concentration exceeding MIC90 (fT > MIC ) for 40% of the dosing interval was set for selecting an effective dosing regimen. The typical half-life of absorption and bioavailability after IM administration were 1.25 h and 96.8%, respectively. A CEZ dosage regimen of 5 mg/kg BW q12h IM administration achieved therapeutic concentrations to control both Streptococcus zooepidemicus and Staphylococcus aureus. For the same dose, the fT > MIC after IM administration was significantly longer than after IV administration, and the IM route should be favoured by clinicians for its efficiency and convenience.

Incidence of surgical site infection after internal fixation of the first phalangeal bone and the third metacarpal/metatarsal bone fractures in Thoroughbred racehorses.

Surgical site infection (SSI) is one of the major complications of equine fracture surgery. The purpose of this study was to investigate the incidence of and risk factors for SSI after internal fixation of the first phalangeal bone (P1) and the third metacarpal/metatarsal bone (MC3/MT3) fractures in Thoroughbred racehorses. Between 2011 and 2020, 451 cases underwent surgery with screws or a locking compression plate (LCP) for sagittal fractures of P1 or condylar fractures of MC3/MT3. Overall, 2.9% (13/451) of the cases developed an SSI. The incidence was significantly higher in plate fixation (21.4%) than in screw fixation (2.3%). There was no significant association with other variables, such as sex, age, number of screws, experience of surgeon, or prophylactic antimicrobials. The median duration of hospitalization for screw fixation was 14 days without an SSI and 20 days with an SSI, and those for plate fixation were 26 and 25-88 days, respectively, indicating that the development of SSI prolongs the duration of hospitalization. On the other hand, there were no significant differences in discharge and race resumption rates between cases with and without an SSI. These data indicate that the incidence of SSI in this study was low and that it was higher following plate fixation than screw fixation.

Pharmacokinetic/pharmacodynamic analysis of cephalothin after intramuscular administration in Thoroughbred horses.

A pharmacokinetic/pharmacodynamic (PK/PD) approach was used to determine a dosage regimen of cephalothin (CET) after intramuscular (IM) administration in horses. CET plasma concentrations were measured in eight horses after a single IM administration of 11 mg/kg bwt of CET. The data were modeled using a nonlinear mixed-effect model, and the probability of target attainment (PTA) of the PK/PD target was calculated for 5,000 horses generated by Monte Carlo simulations. IM administrations of CET at 11 mg/kg bwt q 8 hr and q 6 hr achieved a PTA of 90% against the MIC90 of S. zooepidemicus and S. aureus, respectively, and were considered to be effective dosage regimens. The total dose for the IM administration recommended in this study was lower than that for intravenous (IV) administration in previous studies.

Study on ultrasonic wave propagation in equine leg bone for screening bucked shin.

For simple, safe, portable, and inexpensive evaluation suitable for leg bone diseases of racehorses in the field, an ultrasonic measurement technique was applied to evaluate wave velocities. A digital model of the third metacarpal bone with the bucked shin was fabricated using high-resolution peripheral quantitative computerized tomography data of a racehorse. This model was anisotropic and heterogeneous, and was constructed using the measured ultrasonic wave velocities in the bone. With this model, ultrasonic wave propagation along the bone axis was simulated using the elastic finite-difference time-domain method. We found two main waves with different propagation velocities. The fast-waves showed a wave velocity close to the longitudinal wave in the axial direction. However, the apparent velocities changed dramatically owing to bone surface irregularities (changes of the shape) in the area of bucked shin. The slow-waves showed a wave velocity close to the shear wave, which was unaffected by the bone surface irregularities. The simple comparison of different wave behaviors may be a suitable parameter for the initial in vivo screening of bucked shin in the legs of racehorses, which can be performed in the field.

Concentration of cephalothin in body fluids and tissue samples of Thoroughbred horses.

Cephalothin (CET) concentrations in body fluids (plasma, synovial fluid, pleural fluid, peritoneal fluid, and aqueous humor) and tissue samples (bone, lung, jejunum, hoof, and subcutaneous tissue) were investigated to consider the treatment of infectious diseases in horses. CET 22 mg/kg body weight was intravenously administered to 12 horses. Samples were collected from four different horses at 1, 3, and 5 hr after administration. The CET concentration in body fluids other than aqueous humor was maintained above the MIC90 values of Streptococcus zooepidemicus and Staphylococcus aureus until 5 hr, but it was not maintained above that of S. aureus in bone. CET (22 mg/kg twice a day) is effective for septic arthritis, pleuritis, and peritonitis caused by gram-positive bacteria but ineffective for osteomyelitis.

Utility of systemic voriconazole in equine keratomycosis based on pharmacokinetic-pharmacodynamic analysis of tear fluid following oral administration.

OBJECTIVE: To clarify the detailed pharmacokinetics (PK) of orally administered voriconazole in tear fluid (TF) of horses for evaluating the efficacy of voriconazole secreted into TF against equine keratomycosis. ANIMALS STUDIED: Five healthy Thoroughbred horses. PROCEDURES: Voriconazole was administrated through a nasogastric tube to each horse at a single dose of 4.0 mg/kg. TF and blood samples were collected before and periodically throughout the 24 hours after administration. Voriconazole concentrations in plasma and TF samples were analyzed using liquid chromatography-electrospray tandem-mass spectrometry. The predicted voriconazole concentration in both samples following multiple dosing every 24 hours was simulated by the superposition principle. RESULTS: The mean maximum voriconazole concentrations in plasma and TF were 3.3 µg/mL at 1.5 h and 1.9 µg/mL at 1.6 h, respectively. Mean half-life in both samples were 16.4 and 25.2 h, respectively. The ratio of predicted AUC0-24 at steady state in TF (51.3 µg∙h/mL) to previously published minimum inhibitory concentration (MIC) of Aspergillus and Fusarium species was >100 and 25.7, respectively. CONCLUSIONS: This study demonstrated the detailed single-dose PK of voriconazole in TF after oral administration and simulated the predicted concentration curves in a multiple oral dosing. Based on the analyses of PK-PD, the simulation results indicated that repeated oral administration of voriconazole at 4.0 mg/kg/d achieves the ratio of AUC to MIC associated with treatment efficacy against Aspergillus species. The detailed PK-PD analyses against pathogenic fungi in TF can be used to provide evidence-based medicine for equine keratomycosis.

Optimal double-spin method for maximizing the concentration of platelets in equine platelet-rich plasma.

This study optimized the double-spin conditions for preparing equine platelet-rich plasma (PRP): leukocyte-rich PRP (L-PRP) and leukocyte-poor PRP (P-PRP). Whole blood samples were centrifuged at various double-spin conditions. Both L-PRP and P-PRP were prepared at each stage, and complete blood counts and growth factor concentrations were compared. Samples centrifuged at 160 × 900 g, 160 × 2,000 g, and 400 × 2,000 g exhibited the highest platelet counts. P-PRP had significantly lower leukocyte and erythrocyte contents than L-PRP, especially at 400 × 2,000 g. No significant differences were observed in growth factor concentrations. Our data suggest that optimum L-PRP preparation should include centrifugation under the aforementioned conditions, whereas centrifugation at 400 × 2,000 g is optimal for P-PRP.

Concentration of Marbofloxacin in equine subcutaneous tissue fluid after subcutaneous administration in encapsulated microparticles.

Surgical-site infections (SSIs) at implant sites in horses are sometimes difficult to control with systemic antimicrobials. Because one of the likely reasons is insufficient antimicrobial concentrations, there is a need to increase these concentrations in and around the infected tissue. Marbofloxacin (MAR)-encapsulated microparticles (MAR-MPs) made of biodegradable poly (lactic-co-glycolic) acid are capable of sustained release in vitro. We examined the concentration of MAR in the subcutaneous tissue fluid at sites where MAR-MPs had been administered. On day 0, six 3- × 4-cm subcutaneous pockets were created in the neck of each of six Thoroughbred horses under sedation and local anesthesia. MAR-MPs containing 50 mg of MAR were added to each pocket, which was then sutured. On days 1, 2, 3, 4, and 7, subcutaneous tissue fluid from one pocket per horse was collected and analyzed by LC-MS/MS. From days 1 to 7, the median MAR concentration in the subcutaneous tissue fluid ranged from 17.7 (4.89-125.6) to 33.05 (15.1-71.6) µg/mL. The median concentrations in the subcutaneous tissue fluid exceeded the MIC90 (the minimum inhibitory concentration that would inhibit the growth of 90 % of the tested bacterial isolates) of MAR for clinical isolates reported previously. The area of swelling at the site of administration was significantly larger on days 1 to 4 than just after administration (P < 0.05). MAR-MPs could be useful for controlling SSIs that require high antimicrobial concentrations for extended periods when they are used with strategies that reduce side effects.

Platelet lysate does not have an anti-inflammatory effect on monoiodoacetic acid-induced equine persistent synovitis.

OBJECTIVE: To clarify the anti-inflammatory effect of platelet lysate (PL) on equine persistent synovitis by using a model of synovitis induced by monoiodoacetic acid (MIA). METHODS: Nonseptic synovitis was induced by administering MIA into both antebrachiocarpal joints of 6 clinically healthy horses on day 0. On days 23, 30, and 37, carpal circumference measurement and synovial fluid collection for assays (leucocytes, LDH, tumor necrosis factor-α, and TGF-ß1) were performed, after which PL was injected into 1 antebrachiocarpal joint and saline into the contralateral joint. Synovium and synovial fluid were obtained on day 44 for histological analysis and quantification of inflammation-related genes (matrix metalloproteinase-13, a disintegrin and metalloproteinase with thrombospondin motifs 4, receptor activator of nuclear factor κ-Β ligand, and collagen type I α2 chain) and the abovementioned proteins. RESULTS: The LDH level on day 44 was significantly lower in the PL-injected joint than in the saline-treated one. However, no significant differences were found in the other indices quantified, including osteoclast counts on the synovium. CONCLUSIONS: Multiple IA administration of PL does not exert anti-inflammatory effects on the equine persistent synovitis induced by MIA. CLINICAL RELEVANCE: Intra-articular PL administration did not alter many inflammatory biomarkers, suggesting that PL does not have a direct anti-inflammatory effect. However, the reduction in synovial LDH levels suggests that PL promoted joint tissue repair and may consequently alleviate inflammation at the site of administration.

Pharmacokinetics/pharmacodynamics cut-off determination for fosfomycin using Monte Carlo simulation in healthy horses.

Fosfomycin (FOM) is an approved veterinary medicinal product for large animals in Japan, but Clinical breakpoint (CBP) for antimicrobial susceptibility test (AST) is not defined for animals. This study aimed at conducting a pharmacokinetics/pharmacodynamics (PK/PD) analysis to determine the PK/PD cutoff for the CBP in horses. Drug concentrations following single intravenous administration (IV) of 20 mg/kg body weight (BW) FOM in nine horses were measured using liquid chromatography/mass spectrometry. The data were modelled using a nonlinear mixed-effects model, followed by Monte Carlo simulations. A 90% probability of target attainment for a PK/PD target of the ratio of Area Under the free plasma concentration-time curve divided by the minimal inhibitory concentration (MIC) >24 hr was set as PK/PD cut-off. The PK/PD cutoff for FOM 20 mg/kg BW q12 hr IV was estimated with the MIC value of ≤16.0 mg/L, and this regimen was considered effective against E. coli (MIC90; 16.0 mg/L) in healthy horses based on the MIC90 values of the wild population. Owing to the relevance of FOM to human health, veterinarians should use q 12 hr FOM 20 mg /kg against E. coli infections with an MIC <16 µg/mL, as suggested by our PK/PD cutoff after AST.

Rational quinidine dosage regimen for atrial fibrillation in Thoroughbred racehorses based on population pharmacokinetics.

Introduction: Quinidine (QND) sulfate is an effective treatment for atrial fibrillation (AF) in horses, and several dosage regimens have been proposed to address its wide variability in response and potential adverse effects. The purpose of this study was to analyze the variability in plasma quinidine concentrations using population pharmacokinetics to determine an effective and safe dosage regimen for Thoroughbred horses. Methods: Six healthy Thoroughbred horses were treated with 20 mg/kg quinidine sulfate dihydrate (16.58 mg/kg QND base) administered PO or 5 mg/kg quinidine hydrochloride monohydrate (4.28 mg/kg QND base) administered IV (single administration), and blood samples were taken regularly. Four healthy horses were treated with 20 mg/kg quinidine sulfate dihydrate administered twice (every 6 h) via PO route. For the other 19 Thoroughbred racehorses that developed AF, blood samples were taken during quinidine therapy. Quinidine concentrations were measured in all plasma samples using liquid chromatography with tandem mass spectrometry, and the data from 29 horses were modeled using a nonlinear mixed-effects model, followed by Monte Carlo simulations (MCS). Results: The median quinidine concentration for successful sinus rhythm conversion was 2.0 µg/mL (range: 0.5-2.7 µg/mL) in AF horses, while a median concentration of 3.8 µg/mL (range: 1.6-5.1 µg/mL) showed adverse effects. MCS predicted that plasma quinidine concentrations for quinidine sulfate dihydrate PO administration (loading dose: 30 mg/kg, maintenance dose: 6.5 mg/kg q 2 h) reached 1.4, 2.0 and 2.7 µg/mL in 90, 50 and 10% of the horse populations, respectively. Increasing the loading dose to 45 mg/kg and the maintenance dose to 9 mg/kg q 2 h, the plasma concentrations achieved were 1.9, 2.8, and 3.8 µg/mL in 90, 50, and 10% of horse populations, respectively. Discussion: Using simulations, different empirical dosing regimens were proposed to achieve plasma quinidine concentrations immediately or progressively, representing a tradeoff between optimizing therapeutic effects and minimizing adverse effects. A combination of these dosing regimens is recommended to gradually increase the therapeutic concentration levels of quinidine for safe and effective treatment of AF in racehorses.

Oral Administration of Meloxicam and Flunixin Meglumine Have Similar Analgesic Effects After Lipopolysaccharide-Induced Inflammatory Response in Thoroughbred Horses.

Flunixin meglumine (FM), a nonselective cyclooxygenase (COX) inhibitor, is most frequently selected for the treatment of equine systemic inflammatory response syndrome (SIRS)/endotoxemia. However, FM has considerable adverse effects on gastrointestinal function. The aims of this study were to compare the effect of meloxicam (MX), a COX-2 selective inhibitor commonly used in equine clinical practice, with FM, and to investigate the potential for clinical application in horses with SIRS/endotoxemia. Fifteen horses were divided into three groups of five and orally administered MX (0.6 mg/kg), FM (1.1 mg/kg), or saline as placebo at 30 minutes after LPS challenge. Clinical parameters, including behavioral pain scores, were recorded and blood for clinical pathological data was collected at various times from 60 minutes before to 420 minutes after LPS infusion. The pain score were significantly lower in both the MX and FM groups than in the placebo group, with no significant difference between them. Body temperature was significantly lower in the MX and FM groups than in the placebo group. Heart rates and respiratory rates, hoof wall surface temperature, and leukocyte counts changed similarly between the MX and FM groups. TNF-α and cortisol were lower in the FM group than in the MX group. The results suggest that MX suppresses the inflammatory response after LPS infusion and has an analgesic effect similar to that of FM. Given the adverse effects of nonselective COX inhibitors, clinical application of MX may be beneficial in horses with SIRS/endotoxemia.

Clostridioides difficile infection in thoroughbred horses in Japan from 2010 to 2021.

We encountered 34 Clostridioides difficile (C. difficile) infection (CDI) cases among Thoroughbred horses in Japan from 2010 to 2021. Among them, 79.4% (27/34) either died or were euthanised. The risk factors associated with CDI and mortality among Japanese Thoroughbred horses remain unclear. We used genetic methods to examine C. difficile strains and their relationships with prognosis. Twenty-two (64.7%) cases were hospitalised at the onset of colitis. Outcomes were balanced for hospitalisation rates at the onset of colitis. The mortality rates of cases treated with metronidazole (65.0%) were significantly lower than untreated cases (100%). The predominant genotype of C. difficile isolate was polymerase chain reaction ribotype (RT) 078, isolated from 12 cases (35.3%), followed by RT014 (six cases, 17.6%). Binary toxin (C. difficile transferase [CDT])-positive strains, including all RT078 strains, were isolated from 16 horses. Mortality rates in RT078 strain (75.0%) or CDT-positive strain (83.3%) cases were comparable to that in cases of other types. Sufficient infection control is needed to prevent CDI in Thoroughbred horses. A timely and prompt CDI diagnosis leading to metronidazole treatment would improve CDI outcomes.

Characteristic Inflammatory Biomarkers in an Equine Model of Persistent Synovitis Induced By the Intra-Articular Administration of Monoiodoacetic Acid.

Persistent synovitis damages the articular cartilage in horses. To evaluate the effectiveness of treatment for synovitis using a model induced by intra-articular administration of monoiodoacetic acid (MIA), it is necessary to identify inflammatory biomarkers characteristic of the MIA model. Synovitis was induced by administering MIA into the unilateral antebrachiocarpal joints of five horses, and saline was injected into the contralateral joints as a control on day 0. Clinical and ultrasonographic examinations and synovial fluid collection were performed on days 0, 1, 2, 7, 14, 21, 28, and 35. Leukocyte, lactate dehydrogenase (LDH), tumor necrosis factor-α (TNF-α), interleukin-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), and transforming growth factor-ß1 (TGF-ß1) concentrations in the synovial fluid were measured. Synovium was obtained after euthanasia on day 42 and histologically examined before quantification of the gene expression of inflammatory biomarkers by real-time PCR. Acute inflammatory symptoms persisted for approximately 2 weeks before returning to control levels. However, some indicators of chronic inflammation remained elevated until day 35. On day 42, synovitis continued histologically, with osteoclasts. The expressions of matrix metalloproteinase 13 (MMP13), a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4), receptor activator of nuclear factor kappa-Β ligand (RANKL), and collagen type I α2 chain (Col1a2) were significantly higher in the MIA model than in the control. In the MIA model, representative inflammatory biomarkers in the chronic inflammatory stage were persistently expressed in both synovial fluid and tissue, suggesting that they may be useful for the assessment of the anti-inflammatory effect of drugs.

Platelet Lysate Enhances Equine Skeletal Muscle Regeneration in A Bupivacaine-Induced Muscle Injury Model☆.

This study aimed to verify the effects of platelet lysate (PL) administration on the repair of injured horse tissue. Skeletal muscle injuries were induced in 26 Thoroughbreds by bupivacaine administration. PL or saline was administered 1 day (1D) after injury. Muscle samples from 22 horses injected with PL or saline were obtained by needle biopsy at 2, 3, 4, or 7 days (2D, 3D, 4D, or 7D, respectively) after injury, and growth-factor concentrations and muscle regeneration-associated gene expression levels were determined. Intact samples were similarly collected before injury, and samples of injured muscle not treated with PL or saline (sham samples) were also obtained at 1D, 2D, 3D, 4D, and 7D as references for comparison. Samples from the remaining 4 horses were obtained by surgical incision following euthanasia at 5 days (5D) and 7D after injury, followed by histological analysis. Although increased growth factor levels caused by PL administration were observed for up to 1-day post-administration (2D), gene expressions were enhanced for up to 6 days post-administration (7D). Moreover, the number of embryonic myosin heavy chain (MHC-e)-positive myofibrils at 5D was higher in the PL-treated group than in the saline-treated group, whereas no significant between-group difference in the number of myofibrils was recorded at 7D. Thus, PL administration in muscle injury upregulated the expression of various genes associated with muscle regeneration and promoted morphological regeneration within 6 days of treatment, although growth factor levels from PL decreased at the injected site by approximately 2 days post-administration.

Incidence of carpal fractures and risk factors for recurrent fractures after arthroscopic removal of carpal chip fracture fragments in Thoroughbred racehorses.

BACKGROUND: We aimed to investigate the recent incidence of carpal fractures and the risk factors for recurrent ipsilateral fractures after arthroscopic removal of clinically active unilateral carpal chip fracture fragments in Thoroughbred racehorses. METHODS: The findings for horses managed under the Japan Racing Association that developed carpal bone fractures between 2014 and 2018 were retrospectively reviewed. The proportion of cases that developed a recurrent carpal fracture in the originally affected joint was calculated, and the risk factors for recurrent fractures were analysed. RESULTS: In total, 2858 carpal fractures were recorded in the study period (incidence, 0.8%). Of the 554 horses that resumed racing after the treatment of the unilateral major carpal chip fracture, 144 had a recurrent fracture (26.0%). Chip fractures of the third carpal bone (odds ratio [OR]: 3.7) or a combination of the distal end of the radius and intermediate carpal bone (OR: 3.0) were associated with a significantly higher risk of recurrent fractures than the distal aspect of the radial carpal bone. CONCLUSIONS: The incidence of carpal fractures remained similar to that reported in Japan in the 1990s. The rate of recurrent ipsilateral fractures differed among lesion sites.

Protective efficacy of a reverse genetics-derived inactivated vaccine against equine influenza virus in horses.

Updating vaccine strains is essential to control equine influenza. We evaluated the protective efficacy of an inactivated equine influenza vaccine derived from viruses generated by reverse genetics (RG) in horses in an experimental viral challenge study. Wild-type (WT) virus (A/equine/Tipperary/1/2019) and virus generated by RG (consisting of hemagglutinin and neuraminidase genes from A/equine/Tipperary/1/2019 and six other genes from high-growth A/Puerto Rico/8/34) were inactivated by formalin for vaccine use. Twelve 1-year-old naïve horses with no antibodies against equine influenza virus were assigned to three groups (each n = 4): control, WT, and RG. They were vaccinated twice, 4 weeks apart, and were challenged with A/equine/Tipperary/1/2019 2 weeks after the second vaccination. All four horses in the control group and one horse in the WT group had pyrexia for multiple days and respiratory illness, and one horse in the RG group had pyrexia for 2 days without respiratory illness. The mean rectal temperatures and the mean concentrations of serum amyloid A in the WT and RG groups were significantly lower than those in the control group, with no significant differences between them. The WT and RG vaccines significantly reduced viral shedding relative to the control. The protective efficacy of the RG-derived inactivated vaccine against equine influenza virus is comparable to that of the vaccine derived from WT viruses in horses. The RG technique can make it easy to update equine influenza vaccine strains.

Medication control of flunixin in racing horses: Possible detection times using Monte Carlo simulations.

BACKGROUND: For medication control in several jurisdictions, withdrawal time is the period of refrain from racing after drug administration. It is set by adding a safety period to an experimental detection time. However, there are no reports of statistical analyses of detection time for the determination of withdrawal time in flunixin meglumine-treated horses. OBJECTIVE: To analyse the population pharmacokinetics of flunixin in horses through the generation of a dataset for detection time statistical analysis and predictions via Monte Carlo simulation. STUDY DESIGN: Experimental study. METHODS: Drug plasma and urine concentrations following single intravenous administration of flunixin 1.1 mg/kg bodyweight (BW) in 10 horses and multiple administration of q 24 hours for 5 days in 10 horses were measured using liquid chromatography with tandem mass spectrometry (LC-MS/MS). Data were modelled using a nonlinear mixed effect model followed by Monte Carlo simulation. Irrelevant plasma concentration (IPC) and irrelevant urine concentration (IUC) were calculated using the Toutain approach. Detection times were obtained considering the time after the last administration for selected quantiles of 5000 hypothetical horses under the international screening limit (ISL) proposed by the International Federation of Horseracing Authorities (plasma: 1 ng/mL, urine; 100 ng/mL). RESULTS: For a regimen of 1.1 mg/kg BW q 24 hours, the IPC and IUC values were 2.0 and 73.0 ng/mL respectively. Detection times in plasma above the ISL for 90% of simulated horses were estimated as 74 hours after a single 1.1 mg/kg dose administration, 149 and 199 hours after multiple doses over 5 days at either 24- or 12-hour intervals respectively. Corresponding detection times in urine were 46, 68 and 104 hours respectively. MAIN LIMITATION: Only female horses were investigated. CONCLUSIONS: Statistical detection times for different flunixin meglumine regimens indicated a delay of detection time in plasma after multiple administrations under ISL.

Rational dosage regimens for cephalothin and cefazolin using pharmacokinetics and pharmacodynamics analysis in healthy horses.

BACKGROUND: First-generation cephalosporins have good activity against gram-positive bacteria and are extensively used in horses. There are few reports of pharmacokinetics and pharmacodynamics (PK/PD) analysis of cephalosporins in horses. OBJECTIVE: To optimise the dosages of the two first-generation cephalosporins cephalothin (CET) and cefazolin (CEZ) in horses using PK/PD concepts. STUDY DESIGN: Experimental study with single administration. METHODS: Drug plasma concentrations following a single intravenous (i.v.) administration of 22 mg/kg bodyweight (bwt) CET in 12 horses and of 10 mg/kg bwt CEZ in six horses were measured using LC-MS/MS. Data were modelled using a nonlinear mixed effect modelling followed by Monte Carlo simulations. Minimum inhibitory concentrations (MICs) against Streptococcus zooepidemicus and Staphylococcus aureus isolated from horses were determined by the microbroth dilution method. RESULTS: The percentages of CET and CEZ binding to serum proteins were 19.9% ± 8.4% and 15.2% ± 8.5% respectively. For both CET and CEZ, the MIC90 against S. zooepidemicus was 0.12 mg/L and against S. aureus was 0.5 mg/L. For CET, to achieve a probability of target attainment (PTA) of 90% for a PK/PD target of a free serum plasma concentration exceeding the MIC90 for 40% of the dosing interval, an empirical CET dosage regimen of 22 mg/kg bwt q8h and 22 mg/kg bwt q4h i.v. administration were required for S. zooepidemicus and S. aureus respectively. For CEZ, the corresponding dosage regimens were 10 mg/kg bwt q12h and 10 mg/kg bwt q8h. MAIN LIMITATIONS: Small sample size only in healthy horses. CONCLUSIONS: For CET, more frequent administration than that currently recommended (22 mg/kg bwt q6-12h) is required to empirically control S. aureus infection in horses. For CEZ, less frequent administration compared to the dosage regimen currently proposed (10-22 mg/kg bwt q6h) could control S. zooepidemicus and S. aureus infections in horses.