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Topic:Pharmacology
Pharmacology in horses involves the study and application of drugs and medications to diagnose, treat, and prevent diseases and conditions in equine species. This field encompasses the understanding of pharmacokinetics and pharmacodynamics specific to horses, including how drugs are absorbed, distributed, metabolized, and excreted by the equine body. Commonly studied pharmacological agents in horses include non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics, sedatives, and anthelmintics. Research in equine pharmacology focuses on determining appropriate dosages, understanding drug interactions, and minimizing adverse effects. This page compiles peer-reviewed research studies and scholarly articles that investigate the efficacy, safety, and regulatory aspects of pharmacological interventions in equine veterinary practice.
Oxfendazole: activity of a two-dose treatment regimen on natural infections of internal parasites of equids, with emphasis on migrating large strongyles in controlled tests in 1986 and 1987. Oxfendazole paste formulation was administered intraorally at a dosage of 10 mg/kg of body weight, twice (48 hours between treatments) in 5 controlled tests (experiments A, B, C, D, and E) to 18 equids (14 horses and 4 ponies) that were 5 to 24 months old in 1986 and 1987. Activity was evaluated against naturally acquired infections of various internal parasites, with emphasis on migratory stages of Strongylus vulgaris and S edentatus. The number of treated and nontreated equids in each experiment (horses in experiments A to D and ponies in experiment E) was: A, 1 and 1; B, 3 and 3; C, 3 and 1...
Prednisolone binding to plasma proteins in domestic species. The binding of prednisolone to total plasma proteins of dogs, horses, cows, and sheep was characterized using equilibrium dialysis. Prednisolone was bound to a first protein with high affinity but low capacity (transcortin) and to a second protein according to a nonsaturable mechanism (albumin). Interspecies differences were observed, with cows and dogs exhibiting the lowest, and sheep and horses the highest specific binding capacities. The results are in good agreement with known pharmacokinetic properties of prednisolone in domestic species.
Purification of specific heterologous F(ab)2 fragments with DEAE-Zeta-Prep cartridges for ion-exchange chromatography. A simple two-step procedure for purifying F(ab)2 fragments of horse immunoglobulins is described. In the first step, the horse plasma is diluted, made up to 12% (w/v) with ammonium sulphate and digested with pepsin. In the second step, the previously dialyzed solution is chromatographed. Instead of a normal ion-exchange resin, a DEAE-cellulose, covalently linked to a synthetic vinyl polymer, was used (DEAE-Zeta-Prep). With this assembly it is possible to perform chromatography at a high flow-rate without the problems related to the use of large columns. The yield and purity of the final produc...
Detomidine-butorphanol sedation in equine clinical practice. Combinations of detomidine (mean dose rate 13 micrograms/kg) and butorphanol (mean dose rate 26 micrograms/kg) were used to sedate 61 horses for a variety of surgical or diagnostic procedures in general equine practice. Three horses were sedated on more than one occasion. The degree of sedation was graded from 3 to 0 (deep sedation to no effect) and any side effects were recorded. Forty-three per cent of the horses were graded 3, 46 per cent were graded 2, 8 per cent were graded 1 and 3 per cent were graded 0. Bradycardia and ataxia were the major side effects. The combination was judged to be...
Histopathologic effects of dimethyl sulfoxide on equine endometrium. Endometrial fibrosis is a major cause of infertility in broodmares. Because of the proven anti-inflammatory effects of dimethyl sulfoxide (DMSO) and its influence on collagen, the effect of DMSO on the endometrium was investigated in mares. Solutions of DMSO (25%, 50%, or 75%) were infused into the uterus of clinically normal mares. Examination of serially obtained biopsy specimens revealed epithelial ulceration and stromal inflammation that were proportional to the DMSO concentration infused, but vasodilatation was not observed. In all mares, the endometrium had returned to normal by day 21 a...
Treatment of Fasciola hepatica infection in horses with triclabendazole. Thirteen thoroughbred foals with an adult infection and a presumed immature infection with Fasciola hepatica were treated with 12 mg triclabendazole/kg bodyweight. The absence of eggs from samples of faeces examined at intervals up to 110 days after treatment showed that all the animals were cured. In a second trial the same dose of triclabendazole cured 11 of 12 foals whereas nitroxynil at 7 mg/kg cured only six of 12 foals. No side effects were observed after treatment.
Combined use of detomidine with opiates in the horse. The effects of administration of one of four opiates (pethidine 1 mg/kg bodyweight (bwt), morphine 0.1 mg/kg bwt, methadone 0.1 mg/kg bwt, and butorphanol 0.05 mg/kg bwt) given intravenously to horses and ponies already sedated with detomidine (10 micrograms/kg bwt) were investigated. Behavioural, cardiovascular and respiratory effects of the combinations were compared with those occurring with detomidine alone. Addition of the opiate increased the apparent sedation and decreased the response of the animal to external stimuli. At doses used, butorphanol produced the most reliable response. Sid...
Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone in the horse. Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone were studied in the horse. Acepromazine and xylazine produced cardiovascular effects whereas methadone mainly affected respiratory rate. Decreases in heart rate, arterial blood pressure and respiratory rate were seen. Sedation was superior to that of acepromazine, xylazine or a combination of these. No serious side effects were seen.
Detomidine (Domosedan) in foals: sedative and analgesic effects. Detomidine was administered twice to six foals (14 to 94 days old) using three different doses (10, 20 and 40 micrograms/kg bodyweight intravenously) in a double blind trial. Sedation, analgesia, heart rate and clinically observed side-effects were recorded. Detomidine showed strong sedative effects at all doses tested. Sedation deepened very little by increasing the dose from 10 to 40 micrograms/kg bodyweight, but the duration of the effect was longer. Analgesia was considered good with the largest dose (40 micrograms/kg), and moderate or non-existent with the lower doses. Detomidine caused a...
Hypovolemia, hyperosmolality, and acidosis associated with intraperitoneal infusion of nitrofurazone solution in healthy horses. Nitrofurazone solution containing 0.2% nitrofurazone and 99.8% polyethylene glycol was given to 4 healthy horses (2 L in 2 L of lactated Ringer solution, intraperitoneally). Horses developed hypovolemia, hyperosmolality, and mixed respiratory and metabolic acidosis. These changes were largely attributable to polyethylene glycol, but a contribution of nitrofurazone cannot be excluded. Intraperitoneal infusion of nitrofurazone solution in horses is contraindicated.
Dose-related effects of detomidine on autonomic responses in the horse. 1. Detomidine is a novel veterinary sedative analgesic which is thought to act by stimulation of alpha 2 adrenoreceptors. The present study was undertaken to determine the direction, time course, and dose-response relationship of detomidine on specific autonomic responses in the unanaesthetized horse. 2. Detomidine was administered intravenously to eight adult thoroughbred racehorses at doses of 0.010-0.040 mg kg-1, according to a double-blind Latin square crossover design. Cardiac and respiratory rates, pupil diameter and rectal temperature were monitored for 180 min postinjection. 3. Detomid...
Detomidine: a preliminary analysis of its duration of action in the horse by variable interval responding. Variable interval (VI) reinforcement scheduling is a specific type of operant conditioning that is sensitive to drug effects even when overt clinical signs of the drug have diminished. Six horses were conditioned to break a light beam with a head-bobbing movement and this behaviour was reinforced with a reward of clean oats (approximately 30 mg/reinforcement). Initial training procedures included familiarisation with the behavioural equipment and fixed-ratio reinforced scheduling. To establish baseline rates of behaviour, the horses were converted to a variable interval (60 secs) reinforcement...
The effect of drugs used in the treatment of osteoarthrosis on stromelysin (proteoglycanase) of equine synovial cell origin. There is increasing evidence that the proteoglycan-degrading neutral metalloproteinase, stromelysin, is a key enzyme in the pathogenesis of osteoarthrosis. Equine synovial lining cells were stimulated in vitro to produce stromelysin, and phenylbutazone, flunixin, betamethasone, sodium hyaluronate and polysulphated glycosaminoglycan (PSGAG) were tested for their ability to inhibit the action of this enzyme on 14C-labelled casein substrate. Only PSGAG possessed inhibitory activity at concentrations likely to be achieved therapeutically in the equine fetlock joint.
Immunoassay detection of drugs in racing horses. VII. Detection of acepromazine in equine urine and blood by ELISA and PCFIA. We have developed and evaluated a one step enzyme-linked immunosorbent assay (ELISA) test and a particle concentration fluorescence immunoassay (PCFIA) test for acepromazine as part of a panel of pre- and post-race tests for illegal medications in racing horses. These tests are rapid, sensitive and economical and development of the tests occurred in less than seven months. The ELISA test detects acepromazine with an I-50 of about 150 pg/ml. In vivo, it readily detects the presence of acepromazine or its metabolites in equine blood and urine from 8 to 72 hours or longer, respectively, after adm...
In vitro evaluation of a sustained-release veterinary peroral pellet preparation. In a preceding in vivo study in horses, wide interindividual variation was found in the extent of bioavailability and time to reach peak concentration after peroral administration of one specific theophylline sustained-release dosage form. The purpose of the present study was to investigate the factors of potency, the pH of dissolution medium, the enzymes in the dissolution medium, and the crushing of the pellets on in vitro performance. The results show a wide variation in potency for the individual units, an increase in release rate with increasing pH, and an increase in release rate if the ...
The effect of detomidine (Domosedan) on the maintenance of equine pregnancy and foetal development: ten cases. Detomidine was administered throughout 10 pregnancies in eight mares. An intravenous injection of 20 micrograms/kg body weight was given weekly from Day 14 to Day 60 of gestation and thereafter every four weeks until parturition. One mare suffered torsion of the large colon and was destroyed on Day 86; the foetus was normally developed. A further mare aborted at 167 days. The remaining eight pregnancies continued to full term. One foal was delivered by caesarean section because of torticollis and, of the seven foals born spontaneously, one had bilateral upward patellar fixation at one month ol...
Experimental chemotherapy in horses infected with benzimidazole-resistant small strongyles. The presence of benzimidazole-resistant strains of equine small strongyles was confirmed in horses at two properties in north west England by a series of faecal egg counts and larval cultures after treatment with mebendazole. A trail formulation of mebendazole in combination with piperazine citrate gave greater reductions in faecal egg counts than mebendazole alone but was much less effective than pyrantel embonate or dichlorvos.
Molecular mechanics calculation of geometries of NAD+ derivatives, modified in the nicotinamide group, in a ternary complex with horse liver alcohol dehydrogenase. The geometry of seven NAD+ analogues bound to horse liver alcohol dehydrogenase (LADH) modified only in their nicotinamide group, have been studied using AMBER molecular mechanics energy-minimization procedures. Starting geometries were taken from X-ray crystallographic data for NAD+/Me2SO/LADH reported by Eklund and co-workers. In this study the NAD+ analogues were encaged by the constituent amino acids of the enzyme within a range of 0.6 nm from the initial NAD+/Me2SO/Zn2+ complex. The calculational method used is able to rationalize individual substituent effects and to evaluate the essenti...
Platelet function testing in the pony. Platelet isolation techniques and platelet function were evaluated in 35 adult ponies. Platelet recovery from whole blood was consistent and the preparation of platelet rich plasma was facilitated by an enhanced erythrocyte sedimentation rate. All platelet samples aggregated in response to 10 microM ADP. However, concentrations of ADP as high as 100 microM did not elicit significant 14C-serotonin release. Collagen induced irreversible platelet aggregation and 14C-serotonin release in all samples. The threshold dose for collagen in most ponies was 1.5 micrograms. Arachidonic acid (500 microM) f...
Alpha 1-adrenergic-induced airway obstruction in ponies with recurrent pulmonary disease. We examined the response of five ponies with recurrent airway obstruction (principals) and five age- and gender-matched controls to the aerosol alpha-adrenergic agonist phenylephrine after blockade with propranolol and atropine. Measurements were made with principal ponies in clinical remission (period A) and during acute airway obstruction (period B). The blockade had no effect on base-line pulmonary mechanics in control ponies during periods A and B or in the principal ponies during period A. However, in the principal ponies during period B, blockade increased dynamic compliance (Cdyn) and d...
Severe hypoglycemia attributable to surreptitious injection of insulin in a mare. A mare with signs of hypoglycemia had high serum insulin concentrations before it was euthanatized. High pressure liquid chromatography revealed that the insulin in the mare's blood was of commercial origin. Surreptitious insulin injection has been suspected as the cause of several suspicious deaths of insured horses. The use of high-pressure liquid chromatography should help put an end to this practice.
Neuromuscular and cardiovascular effects of atracurium administered to healthy horses anesthetized with halothane. Neuromuscular and cardiovascular effects of atracurium, a nondepolarizing neuromuscular blocking agent, were evaluated in 10 halothane-anesthetized adult horses. Hind limb digital extensor tension (hoof twitch) was measured with a strain gauge to quantitate the muscle relaxant effects of atracurium. Response of facial muscles was compared with hoof twitch. Five injections of atracurium were given. Initial mean (+/- SEM) dosage of 0.07 +/- 0.01 mg of atracurium/kg of body weight caused 98.6 +/- 0.8% reduction of the preinjection hoof twitch. Subsequent dosages of 0.04 +/- 0.003 mg/kg induced a ...
Effects of flunixin meglumine on jejunal blood flow, motility, and oxygen consumption in ponies. Using isolated autoperfused intestinal segments, the effects of flunixin meglumine administration on systemic arterial blood pressure, jejunal blood flow, vascular resistance, motility, arteriovenous oxygen difference, and oxygen consumption were determined in 10 anesthetized ponies ventilated with a mixture of halothane and oxygen. Saline solution or flunixin meglumine (1.1 mg/kg of body weight) was infused as a single bolus into the left jugular vein. By 10 minutes, flunixin meglumine increased systemic arterial blood pressure and increased intestinal vascular resistance. The jejunal blood f...
Verification of ineffectual activity of ivermectin against adult Onchocerca spp in the ligamentum nuchae of horses. Ivermectin paste formulation (200 micrograms/kg) was administered orally to 27 horses (13 Thoroughbreds and 14 of mixed breeding) to evaluate activity against adult Onchocerca spp in the ligamentum nuchae. Ages, known or estimated, of the horses ranged from 1 to 22 years. Single or multiple doses (1 to 5) of the drug were given to each horse. When multiple doses were administered, the intervals between treatments ranged from 7 to 92 days. At 27 to 171 days after initial treatment (single dose or first of multiple doses), the horses were killed. Some of the horses treated more than once were ki...
Immunoassay detection of drugs in racing horses. VI. Detection of furosemide (Lasix) in equine blood by a one step ELISA and PCFIA. A one step enzyme-linked immunosorbent assay (ELISA) and a particle concentration fluorescent immunoassay (PCFIA) test for furosemide were evaluated as part of a panel of pre- and post-race tests for illegal medication of racing horses. These tests are very sensitive to furosemide with an I-50 for furosemide of about 20 ng/ml. The test is also rapid; an average pre-race complement of 10 samples can be analyzed in 90 minutes or less. The ELISA test results can be read with an inexpensive spectrophotometer, or even by eye. Both the PCFIA test and the ELISA test readily detect the presence of fur...
Possible resistance of small strongyles from female ponies in The Netherlands against albendazole. To determine resistance of small strongyles to albendazole, 3 female ponies (group 1) were grazed on a pasture from May to November 1985 and were treated with 7.5 mg of albendazole/kg of body weight, PO, 2 days before turnout in May and again in June and in July. Three other female ponies (group 2) grazed on a similar pasture from May to July, were treated with 7.5 mg of albendazole/kg, and were removed to another pasture until November. In December, ponies from both groups were treated with 7.5 mg of albendazole/kg, and 8 days later, they were euthanatized and necropsied for a critical test. ...
The effects of corticosteroid administration on the migration, phagocytosis and bactericidal capacity of equine neutrophils. Neutrophil function was evaluated in six clinically normal adult horses, immediately before and 3-6 hours after they were given one dose of hydrocortisone sodium succinate (1 mg/kg body weight). Random migration, stimulated migration to zymosan-activated serum, bacterial phagocytosis and bactericidal capacity of neutrophils were determined in vitro. The mean indices of stimulated migration (net migration and migration ratio) were significantly greater after CS administration (net migration = 62 +/- 23 micron; migration ratio = 11.5 +/- 6.7) than before CS administration (net migration = 44 +/-...
