Pharmacodynamics in horses refers to the study of how drugs affect the equine body, encompassing the mechanisms of action, the relationship between drug concentration and effect, and the duration of these effects. This field examines how drugs interact with biological systems in horses to produce therapeutic or adverse effects. Key aspects include receptor binding, post-receptor effects, and chemical interactions. Understanding pharmacodynamics is essential for determining appropriate dosages, predicting drug interactions, and assessing therapeutic outcomes in equine medicine. This page compiles peer-reviewed research studies and scholarly articles that explore the pharmacodynamic properties of various drugs in horses, focusing on their effects, efficacy, and safety profiles.
Gordon E, Sandquist C, Cebra CK, Heidel J, Poulsen K, Schlipf JW.To evaluate whether topical ocular application of 1% morphine sulfate would change corneal sensitivity and to identify the duration of action. Methods: Eight healthy adult horses. Methods: Corneal touch threshold (CTT) was measured in the center of one randomly selected eye of each horse by Cochet-Bonnet esthesiometer (Luneau Cochet-Bonnet Esthesiometer; Western Ophthalmics, Lynnwood, WA, USA). Immediately following baseline CTT measurement, 0.3 ml of 1.0% preservative-free morphine sulfate (Morphine Sulfate 25 mg/ml Preservative-free; Hospira, Lake Forest, IL, USA) (3 mg) was applied to th...
McElligott EM, Sommardahl CS, Cox SK.OBJECTIVE To determine the pharmacokinetics of chloramphenicol base after PO administration at a dose of SO mg/kg (22.7 mg/lb) in adult horses from which food was not withheld. DESIGN Prospective crossover study. ANIMALS 5 adult mares. PROCEDURES Chloramphenicol base (SO mg/kg) was administered PO to each horse, and blood samples were collected prior to administration (0 minutes) and at 5, 10, 15, and 30 minutes and 1, 2, 4, 8, and 12 hours thereafter. Following a washout period, chloramphenicol sodium succinate (25 mg/kg [11.4 mg/lb]) was administered IV to each horse, and blood samples were ...
Mendoza FJ, Serrano-Rodriguez JM, Buzon-Cuevas A, Perez-Ecija A.Alternatives to surgical castration are necessary for controlling the sexual behaviour of stallions with breeding potential in training and competition. Flutamide is a potent selective non-steroidal androgen receptor competitive antagonist that has been used in human beings as an anti-androgenic drug. In this study, the pharmacokinetics and bioavailability of flutamide and its main active metabolite, 2-hydroflutamide, were determined in seven healthy mature stallions. Single doses of flutamide (1mg/kg intravenously, 1mg/kg orally in fasted horses, 5mg/kg orally in fasted horses and 5mg/kg oral...
Raidal SL, Andrews FM, Nielsen SG, Trope G.Limited data are available on the relative pharmacokinetics and pharmacodynamics of different omeprazole formulations. Objective: To compare pharmacokinetic and pharmacodynamic effects of a novel omeprazole formulation against a currently registered product. Methods: Masked 2 period, 2 treatment crossover. Methods: Twelve clinically healthy horses were studied over two 6-day treatment periods. Horses were randomly assigned to receive a novel omeprazole paste (Ulcershield: ULS) or a currently registered reference omeprazole product (OMO). Gastric pH was measured continuously for 10 h on the day...
Sykes BW, Kathawala K, Song Y, Garg S, Page SW, Underwood C, Mills PC.Pilot investigations have suggested that a novel, long-acting, injectable i.m. formulation of omeprazole (LA-OMEP) can induce acid suppression for up to 7 days following a single injection. Objective: To investigate the pharmacodynamics and assess the clinical efficacy of the LA-OMEP formulation. Methods: Part A comprised a pharmacodynamic study. Part B consisted of a pilot clinical trial. Methods: Part A enrolled six adult Thoroughbred horses with percutaneous gastrotomy tubes. Intragastric pH was measured for continuous 23-h periods (08.00-07.00 h) for eight consecutive days (days 0-7). A si...
Cesar FB, Stewart AJ, Boothe DM, Ravis WR, Duran SH, Wooldridge AA.Nine horses received 20 mg/kg of intravenous (LEV ); 30 mg/kg of intragastric, crushed immediate release (LEV ); and 30 mg/kg of intragastric, crushed extended release (LEV ) levetiracetam, in a three-way randomized crossover design. Crushed tablets were dissolved in water and administered by nasogastric tube. Serum samples were collected over 48 hr, and levetiracetam concentrations were determined by immunoassay. Mean ± SD peak concentrations for LEV and LEV were 50.72 ± 10.60 and 53.58 ± 15.94 μg/ml, respectively. The y-intercept for IV administration was 64.54 ± 24.99 μg...
Maldonado PA, Montoya TI, Acevedo JF, Keller PW, Word RA.Although the positive effects of vaginal estrogens and the selective estrogen receptor modulator, ospemifene (OS), on the vaginal epithelium are well recognized, less is known regarding the effects of these therapies on the lower urinary tract or vaginal muscularis. Clinical evidence suggests that vaginally administered estrogen may improve overactive bladder-related symptoms. The objective of this study was to compare the effects of OS, vaginal conjugated equine estrogens (CEE), or both on the vaginal wall and lower urinary tract in a rat model of menopause. Contractile force of the bladder n...
Calzetta L, Roncada P, di Cave D, Bonizzi L, Urbani A, Pistocchini E, Rogliani P, Matera MG.Equine asthma is a disease characterised by reversible airflow obstruction, bronchial hyper-responsiveness and airway inflammation following exposure of susceptible horses to specific airborne agents. Although clinical remission can be achieved in a low-airborne dust environment, repeated exacerbations may lead to irreversible airway remodelling. The available data on the pharmacotherapy of equine asthma result from several small studies, and no head-to-head clinical trials have been conducted among the available medications. Objective: To assess the impact of the pharmacological interventions...
Lefebvre RA, Callens C, Van Colen I, Delesalle CJG.Postoperative ileus (POI) remains an important cause of death in horses. The recently developed selective 5-HT receptor agonists such as prucalopride target 5-HT receptors on myenteric cholinergic neurons to enhance acetylcholine release and GI motility. No clearcut in vitro evaluation whether highly selective 5-HT receptor agonists enhance submaximal cholinergic neurotransmission towards the muscle layer has been performed in horses. Objective: To identify functional 5-HT receptors in equine jejunum. Methods: In vitro experimental study. Methods: Circular and longitudinal smooth muscle strips...
Leathwick DM, Sauermann CW, Geurden T, Nielsen MK.A previously described model for the dynamics of the parasitic stages of Parascaris spp. was modified to include eggs outside the host and the genetics of anthelmintic resistance before being used to address questions regarding the development of resistance. Three broad questions were addressed; i) How sustainable is the current common practice of treating foals monthly for their first year of life (i.e. 12 treatments/year)? ii) Does the timing of treatments have an effect on resistance development? (i.e. do certain treatments select for resistance more strongly than others?), and iii) How sus...
Serrano-Rodríguez JM, Gómez-Díez M, Esgueva M, Castejón-Riber C, Mena-Bravo A, Priego-Capote F, Ayala N, Caballero JMS, Muñoz A.Pharmacokinetic and pharmacodynamic (PK/PD) properties of the angiotensin-converting enzyme inhibitor (ACEI) benazeprilat have not been evaluated in horses. This study was designed to establish PK profiles for benazepril and benazeprilat after intravenous (IV) and oral (PO) administration of benazepril using a PK/PD model. This study also aims to determine the effects of benazeprilat on serum angiotensin converting enzyme (ACE), selecting the most appropriate dose that suppresses ACE activity. Six healthy horses in a crossover design received IV benazepril at 0.50mg/kg and PO at doses 0 (place...
Raidal SL, Burnheim K, Evans D, Hughes KJ.Sedation is often required to perform pulmonary function testing (PFT) in horses, but drug effects may influence respiratory function. The current study was designed to characterise the effects of sedation and bronchodilator administration on absolute and relative indices of pulmonary function during eupnoeic respiration and carbon dioxide-induced hyperpnoea (rebreathing) in healthy horses using a pneumotachographic spirometry system. Sedation with acetylpromazine (ACP), xylazine, or both drugs in combination was associated with significant reductions in respiratory frequency, minute ventilati...
Saps M, Miranda A.There is little evidence for most of the medications currently used to treat functional abdominal pain disorders (FAPDs) in children. Not only are there very few clinical trials, but also most have significant variability in the methods used and outcomes measured. Thus, the decision on the most appropriate pharmacological treatment is frequently based on adult studies or empirical data. In children, peppermint oil, trimebutine, and drotaverine have shown significant benefit compared with placebo, each of them in a single randomized clinical trial. A small study found that cyproheptadine was be...
Berlin S, Kirschbaum A, Spieckermann L, Oswald S, Keiser M, Grube M, Venner M, Siegmund W.The treatment of equine lung infections by Rhodococcus equi with rifampicin is empirically based because pharmacokinetic/pharmacodynamic (PK/PD) indices and pivotal clinical outcome data are not available. Objective: To evaluate the pharmacokinetics and pulmonary distribution of rifampicin into epithelial lining fluid (ELF) and bronchoalveolar lavage cells (BALC) to predict antimicrobial activity in the lung using PK/PD indices. Methods: Controlled, randomised, two-period, crossover, repeated-dose study with an initial arm to measure disposition after i.v. administration of rifampicin. Methods...
Cenani A, Brosnan RJ, Madigan S, Knych HK, Madigan JE.Propranolol has been suggested for anxiolysis in horses, but its sedation efficacy and side effects, both when administered alone and in combination with α-adrenoceptor agonists, remain undetermined. This study aimed to document the pharmacokinetics and pharmacodynamics of propranolol, romifidine and their combination. Methods: Randomized, crossover study. Methods: Six adult horses weighing 561 ± 48 kg. Methods: Propranolol (1 mg kg; treatment P), romifidine (0.1 mg kg; treatment R) or their combination (treatment PR) were administered intravenously with a minimum of 1 week between treatment...
Sykes BW, Underwood C, Mills PC.Esomeprazole warrants further investigation as a treatment for equine gastric ulcer syndrome. Objective: To investigate the duration of intraday acid suppression achieved with two doses of esomeprazole under two dietary conditions. Methods: A four way crossover design. Methods: Six adult Thoroughbreds instrumented with percutaneous gastrotomy tubes were used. Intragastric pH was measured for continuous 23 h periods (08.00-07.00 h) for 6 consecutive days (Days 0-5). Baseline data was recorded on Day 0 and esomeprazole was administered on Days 1-5. Two doses (0.5 and 2.0 mg/kg bwt/day per os onc...
The goal of the current study was to evaluate the comparative efficacy of ivermectin (IVM) against small strongyles (cyathostomins) following its oral and intramuscular (IM) administration, in naturally parasitized horses. The parasitological data were complemented with the assessment of the plasma disposition kinetics of IVM. The trial included two different experiments. In experiment I, 40 horses naturally infected with small strongyles were randomly allocated into four experimental groups (n=10) and treated with IVM (0.2mg/kg) as follows: IVM oral paste, animals were orally treated with Eqv...
Salas-Romero J, Gomez-Cabrera K, Molento MB, Lyons ET, Delgado A, González L, Arenal A, Nielsen MK.Equine cyathostomin parasites are ubiquitous in grazing horses and have been shown to cause severe inflammatory disease in the large intestine of horses. Decades of intensive anthelmintic therapy have led to widespread anthelmintic resistance in cyathostomins across the world. In Cuba, no anthelmintic products are formulated and sold for equine usage and little is known about anthelmintic efficacy of ruminant and swine formulations used. A strongyle fecal egg count reduction test was used to assess the efficacy of a liquid formulation of ivermectin labelled for use in swine, ruminants and carn...
Knych HK, Stanley SD, McKemie DS, Steinmetz SJ.Romifidine is an alpha-2 adrenergic agonist used for sedation and analgesia in horses. As it is a prohibited substance, its purported use at low doses in performance horses necessitates further study. The primary goal of the study reported here was to describe the serum concentrations and pharmacokinetics of romifidine following low-dose administration immediately prior to exercise, utilizing a highly sensitive liquid chromatography-tandem mass spectrometry assay that is currently employed in many drug testing laboratories. An additional objective was to describe changes in heart rate and rhyt...
Crosignani N, Luna SP, Dalla Costa T, Pimenta EL, Detoni CB, Guterres SS, Puoli Filho JN, Pantoja JC, Pigatto MC.We investigated the thermal, electrical and mechanical antinociceptive and physiological effects (heart rate, respiratory rate, arterial blood pressure, head height and abdominal auscultation score), and pharmacokinetics, of 0.5 mg/kg of the injectable formulation (ORAL) or nanoparticulated methadone (NANO) given orally, in six adult mares, using a crossover, blind and prospective design. Repeated-measure models were used to compare parametric data between and within treatments, followed by Tukey's test. Nonparametric data were analysed with Wilcoxon signed-rank, adjusted by Bonferroni tests....
Edwards SH, Khalfan SA, Jacobson GA, Pirie AD, Raidal SL.OBJECTIVE To determine plasma drug concentrations after IV administration of a bolus followed by continuous rate infusion (CRI) of sodium benzylpenicillin and ceftiofur sodium to healthy adult horses. ANIMALS 6 Thoroughbred mares (3 to 9 years old; mean ± SD body weight, 544 ± 55 kg) with no history of recent antimicrobial treatment. PROCEDURES Horses were used in 2 experiments conducted 14 days apart. For each experiment, horses were housed individually in stables, and catheters were placed bilaterally in both jugular veins for drug administration by CRI (left catheter) and for intermittent...
Ramsay EC, Geiser D, Carter W, Tobin T.To compare the effect of orally delivered detomidine on head posture when administered alone or in combination with two different food items, and to determine the serum concentrations of detomidine after oral delivery. Methods: Prospective randomized experimental study. Methods: Fifteen adult grade mares weighing 328-537 kg. Methods: The horses were randomly assigned to one of the three treatment groups (five horses each). The groups were given detomidine (0.06 mg kg): alone; mixed with 3 mL of an apple sauce and gum mixture; or mixed with 3 mL molasses. Head droop, measured before treatment a...
Machnik M, Kaiser S, Koppe S, Kietzmann M, Schenk I, Düe M, Thevis M, Schänzer W, Toutain PL.Methylxanthines positives in competition samples have challenged doping control laboratories and racing jurisdictions since methylxanthines are naturally occurring prohibited substances and often constituents of feed. For theobromine, an international threshold (renamed in International Residue Limit, IRL) of 2 µg/mL in urine has been established. On the basis of the data presented herein, a threshold or rather an IRL for theobromine in plasma of 0.3 µg/mL was proposed and was thereupon approved by the International Federation of Horseracing Authorities (IFHA). Official recommendations f...
Burkett BN, Thomason JM, Hurdle HM, Wills RW, Fontenot RL.Determine the effects of nonsteroidal anti-inflammatory drugs (NSAID) on platelet function and thromboxane synthesis immediately after drug administration and following 5 days of NSAID administration in healthy horses. Methods: Randomized cross-over study. Methods: Healthy adult horses (n=9; 6 geldings and 3 mares). Methods: Horses received either flunixin meglumine (1.1 mg/kg IV every 12 hours), phenylbutazone (2.2 mg/kg IV every 12 hours), or firocoxib (loading dose of 0.27 mg/kg IV on day 1, then 0.09 mg/kg IV every 24 hours for 4 days) for a total of 5 days. Blood samples were collected pr...
Rodríguez-Pozo ML, Armengou L, Monreal L, Viu J, Cesarini C, Jose-Cunilleras E.To assess whether an oral direct factor Xa inhibitor (DiXaI) anticoagulant drug used at the low end of the recommended dose in people achieves presumed prophylactic plasma concentrations and does not induce bleeding in horses. Methods: Experimental study. Methods: Field study. Methods: Ten healthy adult horses. Methods: A DiXaI was administered at a dose of 0.125 mg/kg every 24 h orally for 4 days. Following a wash-out period of 2 weeks, 8 of 10 horses received daily subcutaneous doses of a low molecular weight heparin (dalteparin) for 4 consecutive days at 50 IU/kg. In both trials, antifactor...
Easton S, Pinchbeck GL, Bartley DJ, Hotchkiss E, Hodgkinson JE, Matthews JB.The aim of this study was to determine practices, attitudes and experiences of UK prescribers of anthelmintics for horses and livestock. A questionnaire was sent by direct email to groups licenced to prescribe these medicines. These were veterinarians, Suitably Qualified Persons (SQPs, registered with the Animal Medicines Training Regulatory Authority) and veterinary pharmacists. The survey was also advertised through social media. It comprised questions relating to demographics, training experiences, current prescribing practices, as well as personal opinions on anthelmintic selection, diagno...
Guan F, Robinson MA, Soma LR.Etanercept is a protein-based medication for the treatment of human patients with rheumatoid arthritis and other autoimmune-based diseases; its pharmacological action is to inhibit and antagonize tumour necrosis factor alpha. Etanercept was rumoured to be used in horse racing in North America. To detect such use, the aim of this study was to develop a liquid chromatography-mass spectrometry (LC-MS) method for confirmation of etanercept in equine plasma. Etanercept was extracted from plasma by anti-human IgG antibody linked to magnetic beads. The analyte was reduced and alkylated, and then dige...
Pezzanite L, Chow L, Hendrickson D, Gustafson DL, Russell Moore A, Stoneback J, Griffenhagen GM, Piquini G, Phillips J, Lunghofer P, Dow S....Septic arthritis causes significant morbidity and mortality in veterinary and human clinical practice and is increasingly complicated by multidrug-resistant infections. Intra-articular (IA) antibiotic administration achieves high local drug concentrations but is considered off-label usage, and appropriate doses have not been defined. Using an equine joint model, we investigated the effects of amikacin injected at three different doses (500, 125, and 31.25 mg) on the immune and cartilage responses in tibiotarsal joints. Synovial fluid (SF) was sampled at multiple time points over 24 h, the cell...
Lowe JE, Sellers AF, Brondum J.Pelvic flexure fistulas (2.5 cm diameter) were established in eight 160 kg Shetland X ponies. Impaction was induced at the pelvic flexure 25 times in the 8 animals through partial obstruction by a 1 litre rubber rebreathing bag fixed at the fistula site. Blood flow probes were implanted on the dorsal and ventral colic arteries (right colic artery and colic branch of ileocolic artery) in two of the ponies. Intraluminal pressure changes were measured at 8 different locations in the large colon during episodes of colic and following administration of flunixin or xylazine. Episodes of colic charac...
Meschter CL, Gilbert M, Krook L, Maylin G, Corradino R.Phenylbutazone, a non-steroidal anti-inflammatory drug known to produce intestinal erosions, was administered intravenously (13.46 mg/kg bodyweight) to 12 horses which were killed after 24, 48, 72 and 96 h. Eight untreated horses served as controls. Annular erosions in the duodenum and mucosal necrosis in the colon were seen after 48 h which progressed in severity. The erosions were characterised by sloughing of the surface epithelium, subepithelial cleft and bleb formation, necrosis of the lamina propria, degeneration of the walls of subsurface capillaries and microthrombosis. Large numbers o...
Geor RJ, Weiss DJ, Burris SM, Smith CM.The effects of furosemide and pentoxifylline on blood flow properties in horses were investigated. Hematologic and rheologic changes were examined in 4 horses before and 3 minutes after administration of epinephrine (1 mg, IV). The next day, hemorheologic changes were determined before and 3 hours after administration of furosemide (1 mg/kg of body weight, IM), and after administration of epinephrine at the sampling at 3 hours. Hematologic and rheologic changes were evaluated weekly in 3 horses given pentoxifylline (8.5 mg/kg, q 12 h, PO) for 28 days. In addition, hemorheologic responses to ep...
Autefage A, Alvinerie M, Toutain PL.Synovial fluid and plasma kinetics of methylprednisolone acetate (MPA) and methylprednisolone (MP) after a single intra-articular administration of MPA at a therapeutic dose (111 mg in toto) was measured in five horses. MPA was detected in synovial fluid for two to six days post injection and MP, which results from synovial MPA hydrolysis, was present in pharmacologically significant concentrations for 4.8 to 39 days, depending on the horse. MPA synovial concentration was maximal (289 +/- 284 micrograms/ml) at the first sampling time (2 h after administration) and MP synovial concentration was...
Winther L, Guardabassi L, Baptiste KE, Friis C.Sulfadiazine (SDZ) and trimethoprim (TMP) concentrations were examined in plasma and pulmonary epithelial lining fluid (PELF), following intravenous and oral administration and compared to minimum inhibitory concentrations (MICs) of common bacterial isolates from equine lower airway infections. SDZ/TMP (25/5 mg/kg) was administered intravenously, intragastric or per os to fed horses, and blood samples were collected before and 11 times, over 24 h, after administration. PELF samples were collected via a tampon device four times after drug administration and analysed for drug concentrations. Add...
Hall TL, Tell LA, Wetzlich SE, McCormick JD, Fowler LW, Pusterla N.Ceftiofur, a third generation cephalosporin, demonstrates in vitro efficacy against microorganisms isolated from septicemic neonatal foals. This pharmacokinetic study evaluated the intravenous and subcutaneous administration of ceftiofur sodium (5 mg/kg body weight; n = 6 per group) and subcutaneous administration of ceftiofur crystalline free acid (6.6 mg/kg body weight; n = 6) in healthy foals. Plasma ceftiofur- and desfuroylceftiofur-related metabolite concentrations were measured using high performance liquid chromatography following drug administration. Mean (±SD) noncompartmental pharma...
Broome TA, Brown MP, Gronwall RR, Casey MF, Meritt KA.Six healthy adult horses (5 mares and 1 stallion) were given a single dose of acetylsalicylic acid (ASA), 20 mg/kg of body weight, by intravenous (IV), rectal, and intragastric (IG) routes. Serial blood samples were collected via jugular venipuncture over a 36-h period, and plasma ASA and salicylic acid (SA) concentrations were determined by high-performance liquid chromatography. After IV administration, the mean elimination rate constant of ASA (+/- the standard error of the mean) was 1.32 +/- 0.09 h(-1), the mean elimination half-life was 0.53 +/- 0.04 h, the area under the plasma concentra...
Swanson CR, Muir WW, Bednarski RM, Skarda RT, Hubbell JA.The hemodynamic changes induced by constant infusions of dopamine or dobutamine (each 3, 5, and 10 micrograms/kg/min) were observed in halothane-anesthetized horses. Left ventricular dp/dt and cardiac output were increased in horses given dobutamine at dosage of 3 micrograms/kg/min and in those given either of the drugs at dosages of 5 and 10 micrograms/kg/min. Concomitant increases in systemic arterial blood pressure occurred at lower infusion dosage rates of dobutamine than those of dopamine and were modulated by dosage-related changes in peripheral vascular resistance that were different be...
Chen CL, Sailor JA, Collier J, Wiegand J.Seven mature thoroughbred horses, weighing between 400 and 541 kg, were each injected intra-articularly into three joints with 6 mg/joint of triamcinolone acetonide (Vetalog). The fourth joint, the control, was injected with saline. Synovial fluid was taken from all four legs of the horses on days 1, 2, 3, 4, 5, 6, 7, 8, 11, and 15 following the injections. Triamcinolone acetonide was assayed by a radioimmunoassay. Blood was collected at 1, 2, 4, 6, 12 h and on days 1, 2, 3, 4, 5, 6, 7, 8, 11, and 15 following injection of either triamcinolone or saline. Both cortisol and triamcinolone were as...
Ekstrand C, Ingvast-Larsson C, Olsén L, Hedeland M, Bondesson U, Gabrielsson J.The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC-MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accu...
Carregaro AB, Freitas GC, Ribeiro MH, Xavier NV, Dória RG.Continuous-rate infusion (CRI) of drugs results in more stable plasma drug concentrations than administration of intermittent boluses, thus providing greater stability of physiological parameters. The aim of this study was to evaluate the physiologic and analgesic effects of the administration of morphine, butorphanol, tramadol or methadone by CRI in horses with induced synovitis of the radiocarpal joint. Results: Increased values of cardiorespiratory parameters and body temperature were observed in all groups after initiation of opioid administration, and these increases were sustained throug...
Zhang XY, Zhu FX, Olszewski MA, Robinson NE.The beta 2-agonists currently used as bronchodilators are racemic mixtures of R- and S-enantiomers. In the present study, we examined the effects of enantiomers of the beta 2-agonists albuterol and formoterol on acetylcholine (ACh) release from equine trachealis parasympathetic nerves. ACh release was evoked by electrical field stimulation (20 V, 0.5 ms, 0.5 Hz) and measured by high-performance liquid chromatography coupled with electrochemical detection. We also tested the effects of enantiomers of albuterol and formoterol on equine tracheal smooth muscle (TSM) contraction in response to exog...
van Duijkeren E, Ensink JM, Meijer LA.The distribution of trimethoprim (TMP) and sulfadiazine (SDZ) into subcutaneously implanted noninfected tissue chambers was studied in healthy adult ponies. Six ponies were given an oral TMP/SDZ paste formulation at a dose of 5 mg/kg TMP and 25 mg/kg SDZ at 12 h intervals for 2 days in order to reach steady-state concentrations. Plasma concentrations and tissue chamber fluid (TCF) concentrations of both drugs were measured at regular intervals during a period commencing 24 h after the last oral administration. The peak concentration of TMP (mean +/- SD) was 2.92 +/- 0.86 microg/mL for plasma a...
Bousquet-Mélou A, Formentini E, Picard-Hagen N, Delage L, Laroute V, Toutain PL.The present study aimed to characterize the adrenal response to ACTH. A model was developed that coupled the nonlinear disposition of cortisol with a physiologically based model for cortisol secretion by the adrenals. It was assumed that the response to ACTH resulted from two mechanisms: a stimulation of the cortisol secretion rate and control of the duration of the secretion. Seven dose levels of ACTH were tested in horses, a species similar to man as regards adrenal function. The main result was that the secretion rate of the adrenal gland can be modelized by a zero order process that is max...
Mendoza FJ, Serrano-Rodriguez JM, Perez-Ecija A.Nonsteroidal anti-inflammatory drugs are administered in horses for several systemic diseases. Selective cyclooxygenase-2 inhibitors are preferred because of lower risk of adverse effects. Several meloxicam formulations have been tested in horses, but a recently marketed granule oral formulation has not been studied. Objective: To characterize the pharmacokinetics of a novel granule meloxicam formulation in fasted and fed horses, and to compare pharmacokinetic features with oral suspension and tablets. Methods: Seven healthy adult horses. Methods: Meloxicam was administered at 0.6 mg/kg in fas...
Chapuis RJJ, Smith JS, French HM, Toka FN, Peterson EW, Little EL.Doxycycline (DXC) is a broad-spectrum antibacterial antimicrobial administered to horses for the treatment of bacterial infections which may also affect donkeys. Donkeys have a different metabolism than horses, leading to differences in the pharmacokinetics of drugs compared to horses. This study aimed to describe the population pharmacokinetics of DXC in donkeys. Five doses of DXC hyclate (10 mg/kg) were administered via a nasogastric tube, q12 h, to eight non-fasted, healthy, adult jennies. Serum, urine, synovial fluid and endometrium were collected for 72 h following the first administratio...
Grimsrud KN, Mama KR, Thomasy SM, Stanley SD.Detomidine is commonly used i.v. for sedation and analgesia in horses, but the pharmacokinetics and metabolism of this drug have not been well described. Objective: To describe the pharmacokinetics of detomidine and its metabolites, 3-hydroxy-detomidine (OH-detomidine) and detomidine 3-carboxylic acid (COOH-detomidine), after i.v. and i.m. administration of a single dose to horses. Methods: Eight horses were used in a balanced crossover design study. In Phase 1, 4 horses received a single dose of i.v. detomidine, administered 30 microg/kg bwt and 4 a single dose i.m. 30 microg/kg bwt. In Phase...
Chiavaccini L, Claude AK, Lee JH, Ross MK, Meyer RE, Langston VC.The study objective was to compare butorphanol pharmacokinetics and physiologic effects following intravenous and subcutaneous administration in horses. Ten adult horses received 0.1 mg/kg butorphanol by either intravenous or subcutaneous injections, in a randomized crossover design. Plasma concentrations of butorphanol were measured at predetermined time points using highly sensitive liquid chromatography-tandem mass spectrometry assay (LC-MS/MS). Demeanor and physiologic variables were recorded. Data were analyzed with multivariate mixed-effect model on ranks (P ≤ 0.05). For subcutaneous i...
Steckler D, Naidoo V, Gerber D, Kähn W.To determine the intercyclic effect of oxytocin and carbetocin on equine myometrial tissue, the effect of the drugs was evaluated through pharmacokinetic and pharmacodynamic studies. The complete pharmacokinetic profile for oxytocin was unknown and had to be established. To do so, 25 IU of oxytocin were administered intravenously to six cycling mares and blood samples were collected before and 2, 4, 8, and 15 min after administration. The half-life of oxytocin was determined to be 5.89 min, the clearance rate 11.67 L/min, mean residence time (MRT) 7.78 min. The effective plasma concentration w...
Kelmer G, Tatz AJ, Famini S, Bdolah-Abram T, Soback S, Britzi M.Regional limb perfusion (RLP) significantly decreases morbidity and mortality associated with distal limb injuries in horses. There is an urgent need for finding additional effective antimicrobial drugs for use in RLP. In this study, we tested the pharmacokinetics (PK) of chloramphenicol in RLP. Eight horses participated in the study, which was approved by the University Animal Care and Use Committee. The cephalic and the saphenous veins were used to perfuse the limbs. Synovial samples were collected from the metacarpo/metatarsophalangeal (MCP/MTP) joint. The Friedman Test was applied for asse...
Knych HK, Arthur RM, Mitchell MM, Holser I, Poppenga R, Smith LL, Helm MN, Sams RA, Gaskill CL.Cobalt has been used by human athletes due to its purported performance-enhancing effects. It has been suggested that cobalt administration results in enhanced erythropoiesis, secondary to increased circulating erythropoietin (EPO) concentrations leading to improvements in athletic performance. Anecdotal reports of illicit administration of cobalt to horses for its suspected performance enhancing effects have led us to investigate the pharmacokinetics and pharmacodynamic effects of this compound when administered in horses, so as to better regulate its use. In the current study, 18 horses were...
Spadavecchia C, Arendt-Nielsen L, Andersen OK, Spadavecchia L, Schatzmann U.To investigate the action of a single IV administration of romifidine on the thresholds of the nociceptive withdrawal reflex (NWR) and temporal summation in conscious horses. Methods: 10 adult horses. Methods: Single electrical stimulations were applied on the digital nerves to evoke NWR from the left forelimb and hind limb. Repeated electrical stimulations (10 stimuli, 5 Hz) were given to obtain temporal summation. Surface electromyographic reflex activity was recorded from the common digital extensor and cranial tibial muscles. After baseline assessment of NWR and temporal summation threshol...
Sun WC, Moore JN, Hurley DJ, Vandenplas ML, Linden JM, Murray TF.To evaluate anti-inflammatory effects of several novel adenosine receptor agonists and to determine their specificity for various adenosine receptor subtypes on neutrophils, cells heterologously expressing equine adenosine receptors, or equine brain membranes. Methods: Neutrophils isolated from 8 healthy horses. Methods: Radioligand binding experiments were performed to compare binding affinities of adenosine receptor agonists to equine adenosine A(1), A(2A), and A(3) receptor subtypes. Effects of these agonists on endotoxin-induced production of reactive oxygen species (ROS) by equine neutrop...
Jean D, Vrins A, Lavoie JP.To determine temporal variations of pulmonary function in horses without respiratory tract disease (controls) and horses with chronic obstructive pulmonary disease (COPD) and determine whether reversibility of airway obstruction after environmental control can be predicted by response to atropine administration. Methods: 7 COPD-affected and 5 control horses. Methods: Pulmonary function testing was performed monthly during 3 consecutive months, daily for 5 consecutive days, and at 6-hour intervals for 24 hours before and after administration of atropine (0.02 mg/kg of body weight, i.v.) and aft...
Uney K, Altan F, Altan S, Erol H, Arican M, Elmas M.The plasma and synovial fluid pharmacokinetics and safety of cefquinome, a 2-amino-5-thiazolyl cephalosporin, were determined after multiple intravenous administrations in sixteen healthy horses. Cefquinome was administered to each horse through a slow i.v. injection over 20 min at 1, 2, 4, and 6 mg/kg (n = 4 horses per dose) every 12 h for 7 days (a total of 13 injections). Serial blood and synovial fluid samples were collected during the 12 h after the administration of the first and last doses and were analyzed by a high-performance liquid chromatography assay. The data were evaluate...
Soma LR, Uboh CE, Luo Y, Guan F, Moate PJ, Boston RC.To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses. Methods: 6 Thoroughbreds. Methods: In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry. Results: A 5-compartment pharmacokinetic-pharmacodynamic model was used to des...
