Pharmacokinetics of furosemide in thoroughbred horses subjected to supramaximal treadmill exercise with and without controlled access to water.

BACKGROUND: The primary objective of this study was to assess the disposition of furosemide in Thoroughbred horses treated intravenously with 1 mg/kg of furosemide 4 and 24 h before supramaximal treadmill exercise without and with controlled access to water, respectively. Another objective was to determine whether furosemide was detectable in the plasma of horses after exposure to supramaximal treadmill exercise. Thoroughbred horses (n = 4-6) were administered single intravenous doses of 1 mg/kg of furosemide at 4 and 24 h before supramaximal exercise on a high-speed treadmill, with controlled and free access to water, respectively. Plasma furosemide concentrations were determined using liquid chromatography. RESULTS: Furosemide was detected in all the horses, regardless of whether they were treated 24 h or 4 h before excersice. In both treatment sequence groups of 2 horses, the concentration time profiles of furosemide during the first 4 h after its administration were relatively similar. The average maximum observed concentrations, AUC0-1.5h, and AUC0-3h, of both groups of horses were not different (p > 0.05). There were no significant differences in systemic clearance based on the geometric mean (95% confidence interval) (409 (347-482) mL/h/kg) for 4 h and 320 (177-580) mL/h/kg) for 24 h) between horses that were exercised 4- and 24-h post-furosemide administration. The plasma concentration of furosemide in all the horses fell below the limit of quantification (25 ng/mL) within 12 h after drug administration. In the group treated 24 h before exercise, none of the horses had detectable furosemide at the time of supramaximal treadmill exercise. In the group treated 4 h before exercise, furosemide was detected 1 h before and 2 h after supramaximal treadmill exercise in 4/4 and 3/4 horses, respectively. The mean AUC3-last h of both groups of horses were not different (p > 0.05). CONCLUSIONS: Water restriction did not exert any apparent effect on the disposition of furosemide. It remains to be determined, however, whether the attained plasma concentration of furosemide in combination with other controlled water access protocols have any direct or indirect pharmacological effect that may affect the athletic performance of the horse.

The lipidome of Thoroughbred racehorses before and after supramaximal exercise.

BACKGROUND: A comprehensive study of the effect of supramaximal exercise in lipid homeostasis of Thoroughbreds provides the basis for future research on the role of lipids on energy metabolism in racehorses. OBJECTIVE: To compare the plasma lipidome of Thoroughbreds before and after supramaximal exercise using an untargeted lipidomics approach. STUDY DESIGN: Pilot experimental study. METHODS: Four Thoroughbred horses were used. The maximal oxygen consumption (VO2 max ) was calculated for each horse. Horses then underwent treadmill exercise at the speed for which the oxygen requirements had been calculated to be 115% VO2 max . Plasma samples were obtained before (T0) and immediately (T1), 15 (T2) and 30 (T3) minutes post-exercise, and evaluated using liquid chromatography/mass spectrometry. Data analysis consisted of principal component analysis and one-way repeated measures analysis of variance. RESULTS: A total of 933 plasma lipids were detected. Supramaximal exercise-induced significant changes in the signal intensity of 13 lipids; all ubiquitous in the organism as major components of biological membranes or energy substrates. MAIN LIMITATIONS: A treadmill was used to replicate track conditions. Also, sample size involved only four horses and the statistical analyses failed to achieve the desired power of 80%. CONCLUSIONS: The findings in this pilot study suggest that supramaximal exercise induces changes in specific plasma lipids in Thoroughbred racehorses. While the biological significance of these findings remains to be determined, these results provide baseline information for future studies in lipidomics applied to equine exercise physiology. Further research is warranted to better understand the role of lipids on energy metabolism in Thoroughbred racehorses.

Ex vivo binding of the immunosuppressant mycophenolic acid to dog and cat plasma proteins and the effect of co-incubated dexamethasone and prednisolone.

Mycophenolic acid (MPA) has been shown to be promising for the treatment of autoimmune diseases in dogs and cats. In humans, MPA is highly bound to plasma proteins (~97%). It has been recommended to monitor free drug plasma concentrations because the free MPA correlates with its immunosuppressive effect. However, it is unknown if MPA is highly bound to plasma proteins in dogs and cats. The objectives of this study were to determine the extent of plasma protein binding of MPA and evaluate the effect of prednisolone and dexamethasone on the extent of protein binding of MPA in dogs and cats. The extent of plasma protein binding of MPA was determined in plasma collected from clinically healthy adult cats (n = 13) and dogs (n = 14) by combining high-throughput dialysis and ultra-high-liquid chromatography. This study reveals that MPA is highly bound to plasma proteins (>90%) in dogs and cats, mean extent of binding of MPA at 15 µg/ml to plasma proteins being 96% (range, 95%-97%) and 92% (range, 90%-93%) for dogs and cats, respectively. In dog plasma, MPA is primarily bound to albumin. In vitro, prednisolone increased the unbound MPA in dogs (p < .01) but not in cats (p = .07) while dexamethasone had no effect on MPA plasma binding in either species (p > .05). Results of this study provide valuable information for designing future pharmacokinetic and pharmacodynamic studies and also therapeutic monitoring programs for dogs and cats.

Pharmacokinetics of Mycophenolic Acid after Intravenous Administration of Mycophenolate Mofetil to Healthy Cats.

BACKGROUND: Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is becoming increasingly popular as an alternative immunosuppressant in feline medicine. Pharmacokinetic information is not available for cats. OBJECTIVE: The purpose of this study was to determine whether MMF is biotransformed into the active metabolite MPA and to evaluate the disposition of MPA after a 2-hour constant rate intravenous (IV) infusion of MMF in healthy cats. ANIMALS: Healthy cats (n = 6). METHODS: This was a prospective pilot study. All cats were administered MMF at 20 mg/kg every 12 hours over a 2-hour constant rate infusion for 1 day. The concentrations of MPA and its derivatives in blood were determined using a validated UHPLC-UV method. RESULTS: All cats biotransformed MMF into MPA. The mean AUC0-14 h ranged from 6 to 50 h*mg/L after IV dosing of MMF. Transient large bowel diarrhea was recorded in 2 of 6 cats after medication administration. CONCLUSION AND CLINICAL IMPORTANCE: The disposition of MPA in plasma was highly variable, which could result in high interindividual variability in the safety and efficacy of treatment with MMF in cats.

Enhanced cytotoxicity of bleomycin, cisplatin, and carboplatin on equine sarcoid cells following electroporation-mediated delivery in vitro.

Electroporation is a method used to deliver poorly permeant chemotherapeutic drugs to tumor cells, potentiating the cytotoxic effects of drugs and overall clinical response. Despite existing evidence of the potential benefits of electroporation to enhance the antitumoral effects of drugs, there is a lack of understanding about the effects of electroporation on equine tumor cells. This study investigated the combined effects of electroporation and bleomycin, cisplatin, and carboplatin on an equine sarcoid cell line (EqS04b). The use of electroporation increases the cytotoxic effects of bleomycin, cisplatin, and carboplatin on the equine sarcoid cell line by 5-fold, 4-fold, and 3-fold, respectively. These very promising findings demonstrate proof of principle for future preclinical studies on different tumor cells to investigate the in vivo effects of electroporation in sarcoid tumors.

Clinical and pharmacokinetic effects of regional or general anaesthesia on intravenous regional limb perfusion with amikacin in horses.

REASONS FOR PERFORMING STUDY: Antimicrobial i.v. regional limb perfusion (IV-RLP) is clinically performed on anaesthetised or sedated horses with or without regional anaesthesia. To date, no scientific data are available on the clinical and pharmacokinetic effects of these anaesthetic protocols on antimicrobial IV-RLP, which is believed to result in better tourniquet efficiency due to decreased movement. OBJECTIVE: To determine the effects of regional or general anaesthesia on the clinical and synovial pharmacokinetic parameters of amikacin administered by IV-RLP to horses. STUDY DESIGN: Experimental crossover study. METHODS: Eight healthy horses received 4 treatments of amikacin IV-RLP in a randomised, blinded, crossover design: standing sedation without regional anaesthesia (CNT); standing sedation with i.v. regional anaesthesia; standing sedation with perineural regional anaesthesia (PNA); or general anaesthesia. Synovial fluid amikacin concentrations were measured over 24 h and regional pharmacokinetic parameters calculated. Heart and respiratory rates, visual analogue scale of discomfort, number of times the limb was lifted and number of additional sedations administered were recorded. Analysis of variance crossover analysis was applied with significance level at P < 0.05. RESULTS: Amikacin concentrations and regional pharmacokinetic parameters did not differ significantly among treatments. Visual analogue scores (mean ± s.d.) were significantly lower with PNA (19 ± 15) vs. i.v. regional anaesthesia (69 ± 36) or CNT (81 ± 13; P < 0.001). Significantly less lifting of the limb (mean ± s.d.) occurred with PNA (20 ± 20) vs. CNT (54 ± 22; P < 0.04). CONCLUSIONS: Perineural regional anaesthesia before IV-RLP was most effective in providing comfort to standing, sedated horses without significantly affecting the regional pharmacokinetic parameters of amikacin. High variability of synovial amikacin concentrations was present. The use of general anaesthesia for IV-RLP is not justified based on this study.

Effects of repeated intra-articular administration of amikacin on serum amyloid A, total protein and nucleated cell count in synovial fluid from healthy horses.

REASONS FOR PERFORMING STUDY: Serum amyloid A (SAA) in synovial fluid has recently been used as a marker for septic arthritis in horses but the effects of repeated intra-articular (IA) administration of amikacin on synovial SAA concentrations are unknown. OBJECTIVES: To report the effect of repeated IA administration of amikacin on SAA, total protein (TP), nucleated cell count (NCC) and differential NCC in synovial fluid of healthy equine joints. METHODS: A controlled, 2 period crossover study was performed on 5 clinically healthy horses. Each intercarpal joint received one of 2 treatments every 48 h for 5 consecutive times: arthrocentesis alone (control group) or arthrocentesis combined with IA administration of 500 mg of amikacin (treatment group). Clinical and lameness examinations were performed daily. Serum SAA and synovial SAA, TP, NCC and differential NCC were measured and statistically compared. Significance level was set at P < 0.05. RESULTS: Horses remained healthy and nonlame throughout the study. Baseline values for all variables were not significantly different between groups. Values for TP in the treatment group were significantly higher than in the control group after the first sample (P < 0.05). In both groups NCC increased significantly (P < 0.05) after the first sample. No significant changes were identified in differential NCC. In both groups, all synovial and most serum SAA concentrations remained below the lower limit of quantification. CONCLUSIONS: Repeated IA administration of amikacin caused increased values of TP and NCC in synovial fluid, with some TP concentrations falling within the range reported for septic arthritis. In contrast, synovial SAA concentrations did not increase in either group. POTENTIAL RELEVANCE: Synovial SAA could serve as a more reliable marker than TP and NCC when evaluating a joint previously sampled or treated with amikacin.