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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.
Effects of halothane anesthesia on equine liver function. Effects of halothane anesthesia were investigated in ponies prepared surgically with chronic external biliary fistulas (T tubes) to determine the effects on liver function and biliary excretion during 2 hours of anesthesia. Four studies were performed on 2 ponies, 2 to 6 months after surgery with the enterohepatic circulation held intact between studies. Intravenous bile acid infusion was used to maintain steady-state bile flow, bilirubin, and bile acid excretion during each study. Compared with the immediate 2-hour preanesthesia values (base line), halothane caused a 138% increase in bilirubi...
Benzimidazole resistance of equine strongyles: critical tests of several classes of compounds against population B strongyles from 1977 to 1981. From 1977 to 1981, critical tests were conducted on 10 horses naturally infected with population B strongyles. Drugs tested were: oxibendazole (OBZ), 10 mg/kg of body weight (n = 1); albendazole, 10 mg/kg (n = 1); a mixture of thiabendazole (TBZ), 44 mg/kg and trichlorfon, 40 mg/kg (n = 1); a mixture of TBZ at 44 mg/kg with piperazine (PPZ) at 55 mg of base/kg (n = 1); febantel (FBT), 6 mg/kg (n = 3), 12 mg/kg (n = 1), or 24 mg/kg (n = 1); and pyrantel (PRT) pamoate, 6.6 mg of base/kg (n = 1). Large strongyles, Strongylus vulgaris (9 horses) and S edentatus (5 horses), were effectively removed...
Effects of isoflurane anesthesia on equine liver function. The acute 2-hour effects of isoflurane anesthesia on liver function and biliary excretion were examined in 2 ponies prepared surgically with chronic external biliary fistulas (T-tubes). Studies were conducted 2 to 8 months postoperatively with the enterohepatic circulation held intact between studies. Bile acid infusion IV (8.1 to 8.8 mumol/min) helped maintain bile flow and bile acid and bilirubin excretion during complete biliary diversion throughout each study. Following 3-hour control periods, anesthesia was induced and maintained at 1.3 to 1.5 minimal alveolar concentration plus O2 (spont...
Motility of the distal portion of the jejunum and pelvic flexure in ponies: effects of six drugs. Bipolar stainless steel electrodes were surgically implanted in 4 ponies to record myoelectrical and mechanical activity of the distal portion of the jejunum and pelvic flexure. After determining normal activity, the effects of neostigmine, xylazine, flunixin meglumine, dipyrone, panthenol, and atropine sulfate were determined. Flunixin meglumine, dipyrone, and panthenol had no effect on the motility of the jejunum or pelvic flexure. Xylazine and atropine sulfate decreased motility of the distal portion of the jejunum and pelvic flexure, with atropine sulfate having a greater effect and lastin...
3-methylindole as a model of equine obstructive lung disease. 3-methylindole was administered orally and intravenously to horses and ponies in order to determine the ability of this chemical to provide a model of equine pulmonary disease. Both routes produced a severe and sometimes fatal pulmonary disease, characterised by bronchiolitis. Clinical signs developed 48 to 72 h after dosing and were most severe between Days 4 and 10 post dosing. Intravenous administration of 3-methylindole produced lung injury more rapidly and at a lower dose rate than the oral route. It is suggested that the respiratory condition induced by this chemical could become a metho...
Active-site titration of horse urinary kallikrein. Horse urinary kallikrein was titrated with the reagent 4-nitrophenyl 4-guanidino-benzoate. The titration was shown to be dependent upon the concentration of the titrant. This finding, which distinguishes horse urinary kallikrein from other enzymes, is explained by the relatively small ratio between its rate of acylation and deacylation (k2/k3 = 16.8) and by a low affinity of the reagent (Km = 1.16 microM). By an appropriate kinetic treatment, it was possible to establish the relationship between the hydrolysis of 4-nitrophenyl 4-guanidinobenzoate and the actual concentration of the active enzy...
Predominantly beta-adrenergic control of equine sweating. Single equine sweat glands were found to secrete for more than 1 h in vitro in response to pharmacologic secretagogues. The adrenergic agonists epinephrine and norepinephrine evoked maximal sweat rates of 2.0 nl X gland-1 X min-1. However, the concentration of norepinephrine (10(-5) M) required to evoke the maximal response was 10 times higher than that for epinephrine. Maximal sweat rates also were stimulated with the beta 2-adrenergic agonist terbutaline. This stimulation was blocked by the beta-adrenergic antagonist propranolol. Moderate sweating responses were also obtained with the alpha-...
The effects of combinations of selected antibiotics on the growth of Corynebacterium equi. The minimal inhibitory concentrations of penicillin G, ampicillin, gentamicin, erythromycin and rifampicin were determined for nine strains of Corynebacterium equi. The effect of combinations of any two of these antibiotics on the killing of these strains was determined at antibiotic concentrations achievable in horses using recommended drug dosages (ampicillin 4.0 microgram/ml, gentamicin 1.0 microgram/ml using recommended drug dosages (ampicillin 4.0 microgram/ml, gentamicin 1.0 microgram/ml and erythromycin 0.25 microgram/ml). Penicillin G was used at 4.0 microgram/ml and rifampicin at 0.06...
A sampling protocol for the thyrotropin-stimulation test in the horse. A study was designed to assess the secretory response of thyroid glands in horses to an economically feasible dose (5 IU) of thyrotropin injected IV, and to establish valid blood sampling periods in cases in which thyroxine concentrations were different from base-line values. Significant (P less than 0.001) response (doubling or near-doubling of base line) occurred as early as 3 hours after thyrotropin administration, with peak response at 4 to 5 hours. It was concluded that administration of 5 IU of thyrotropin is economical and effective in the horse, with collection of a second blood sample...
Effects of butorphanol, flunixin, levorphanol, morphine, and xylazine in ponies. The analgesic and behavioral effects of butorphanol (0.22 mg/kg), flunixin (2.2 mg/kg), levorphanol (0.033 mg/kg), morphine (0.66 mg/kg), and xylazine (2.2 mg/kg), given IM were observed in 8 ponies. These ponies were instrumented to measure response objectively to painful superficial and visceral stimuli. Effects on the cardiopulmonary system and rectal temperature also were evaluated in 6 of these ponies. Observations were conducted before drug injection (base-line values) and after injection at 30, 60, 120, 180, and 240 minutes. Xylazine provided the highest pain threshold for the first 60 ...
The identification of C-18 neutral steroids in normal stallion urine. As part of a continuing research program associated with the detection of anabolic steroid residues in horse urine, normal samples from entire male horses have now been investigated. Isomers of three C-18 neutral steroids; 4-estren-17-ol-3-one (1), estrane-3,17-diol (2) and an unsaturated estranediol having a possible structure (3), have been identified in urine samples from two male horses aged 8 and 14 years. Of these three steroids, compound (2) was not detected in the urine of a 2.5 yr old entire male nor in the majority of post-race urine samples from entire male horses average age 3.8 yr...
Intra-articular corticosteroid- and exercise-induced arthropathy in a horse. Methylprednisolone acetate was injected repeatedly into both intercarpal joints of a horse that had a 3rd carpal bone fracture in 1 limb. Synovial fluid from intercarpal and radiocarpal joints of both limbs were obtained serially for study. Arthropathy developed in the fractured joint following prolonged corticosteroid therapy and exercise. In the corticosteroid-injected normal joint, the hyaluronic acid concentration initially decreased, then increased. A depletion in cartilage matrix was seen at necropsy, 175 days after onset of treatment. Determination of total protein content in synovial f...
Xylazine causes transient dose-related hyperglycemia and increased urine volumes in mares. Xylazine given IV at doses of 0.5, 1.0, and 1.5 mg/kg to mares caused a significant (P less than 0.05) dose-related increase in serum glucose concentration and urine volume. Serum glucose concentrations as much as 150 mg/dl were recorded in mares after they were given the largest xylazine dose. The greatest urine volume, similar to changes in peak glucose concentration, always occurred during the first hour after dosing with xylazine and averaged 1.82, 3.93, and 5.68 ml/kg/hour after the 0.5-, 1.0-, and 1.5-mg/kg doses, respectively, were given. Urine osmolality and specific gravity were signi...
Analgesic effects of butorphanol in horses: dose-response studies. The analgesic effects of butorphanol (0.05, 0.1, 0.2, and 0.4 mg/kg), pentazocine (2.2 mg/kg), and butorphanol vehicle (0.04 ml/kg) were observed in 6 horses. These horses were instrumented to measure response objectively to painful superficial and visceral stimuli. The tested drugs were given IV according to a Latin square design. After preinjection base-line measurements were made, the analgesic effects were observed at 15 and 30 minutes and then at 30-minute intervals until postinjection minute 240. Analgesic effects of butorphanol were dose-related, with durations between 15 and 90 minutes...
Combined use of sedatives and opiates in horses. The effects of four intravenous combinations, xylazine (0.7 mg/kg)/methadone (0.1 mg/kg), xylazine (0.7 mg/kg)/buprenorphine (0.004 and 0.006 mg/kg) and acepromazine (0.05 mg/kg)/buprenorphine (0.006 mg/kg) on arterial blood pressure, central venous pressure, heart rate, respiratory rate and blood gases were studied in four experimental ponies. With xylazine/buprenorphine and xylazine/methadone onset of sedation was rapid and obvious and although no surgical or diagnostic procedures were carried out, sedation was judged to be satisfactory for the next 30 to 40 minutes. Onset of sedation after ...
[Anesthesia in the horse]. The paper describes the problems of injection anaesthesia in the horse. Different commonly used methods, drugs and drug combinations are explained. Their actions and side-effects are compared and discussed.
Effect of ivermectin treatment on eosinophilic pneumonia and other extravascular lesions of late Strongylus vulgaris larval migration in foals. Eighteen parasite-free pony foals were infected orally with 500 third stage larvae of Strongylus vulgaris. At 56 days after infection, six ponies were treated with intramuscular ivermectin (22, 23-dihydroavermectin B1); six were treated with oral ivermectin; and six were not treated. Necropsy was done 91 days after infection to study the pathologic effects of migrating S. vulgaris larvae and to determine the efficacy of ivermectin in attenuation of S. vulgaris-induced lesions. Larval migration induced eosinophilic inflammation of the liver, spleen, mesenteric, colic and cecal lymph nodes, and ...
[Cardiovascular complications during anesthesia in horses]. This paper summarizes causes of cardiovascular complications. Treatment of drug related hypotension as well as etiology and therapy of cardiac arrest are discussed.
Adrenergic receptors in the urethra and prostate of the horse. The presence and types of alpha and beta adrenergic receptors in the urethra and prostate of the horse were studied in vitro using adrenergic agonist and antagonist drugs. The existence of these receptors was shown. This finding was based on the observation that the contractile action was mediated by adrenergic receptors of alpha-1 type, although in the prostate alpha-2 type receptors also participated. Relaxation in both tissues was controlled by receptors of the beta-2 type.
Pharmacokinetics of ascorbic acid in horses. The pharmacokinetics of ascorbic acid were studied in 29 horses after intravenous (iv), subcutaneous, intramuscular (im) and oral administration. Following iv injection of 5 and 10 g ascorbic acid, respectively, a biphasic decline of ascorbic acid serum levels was found, indicating that the vitamin distributes in the body according to a two-compartment open model. The apparent volume of distribution (average value for Vd(ss) = 0.6 litre/kg) was approximately equivalent to the volume of total body water. The terminal half-life of the biexponential serum level-time curve (t1/2 beta) varied betwe...
Inhibition of equine S-adenohomocysteine hydrolase by 2′-deoxyadenosine. 2'-Deoxyadenosine and 9-beta-D-arabinofuranosyladenine (ARA) are apparent suicide inhibitors for equine S-adenosylhomocysteine hydrolase. In initial velocity studies of the synthetic reaction converting adenosine and homocysteine to S-adenosylhomocysteine, adenine, adenosine 5'-triphosphate, and 9-beta-D-arabinofuranosyladenine were found to be competitive inhibitors with Kis of 3.8 microM, 1.1 mM, and 30 microM, respectively. In contrast, linear mixed inhibition was observed for 2'-deoxyadenosine, indicating that 2'-deoxyadenosine must bind in more than one fashion to the enzyme.
Critical tests of morantel-trichlorfon paste formulation against internal parasites of the horse. Critical tests were completed on six horses to evaluate the antiparasitic activity of a paste formulation mixture of morantel citrate and trichlorfon, administered intraorally at the dose rate of 6 mg morantel base kg-1 and trichlorfon at 30 mg kg-1. Aggregate average removals were: 78% for two horses infected with 2nd instar Gasterophilus intestinalis; 100% for one infected with 2nd instar G. nasalis; 96% for six infected with 3rd instar G. intestinalis; 100% for four infected with 3rd instar G. nasalis; 100% for five infected with Parascaris equorum; 100% for one infected with mature Oxyuris...
Hyperglycemia and hypoinsulinemia during xylazine-ketamine anesthesia in Thoroughbred horses. Plasma glucose and serum insulin concentrations in Thoroughbreds administered xylazine hydrochloride (1.1 mg/kg; IV) and ketamine hydrochloride (2.2 mg/kg; IV) at dosages sufficient to induce short periods of recumbency and anesthesia were measured. Samples of blood were collected from 6 adult horses before, during, and after the anesthetic period. Plasma glucose (mg/dl) was significantly increased above control (-30 minute concentration) from 15 to 150 minutes after xylazine administration with the peak value occurring at 30 minutes. Serum insulin (microU/ml) was significantly decreased from ...
Muscle perfusion in the horse. Muscle perfusion was studied in conscious and anaesthetised horses by monitoring the clearance of a locally injected bolus of saline containing radioactive xenon (133Xe). The mean of all the measurements made from the brachiocephalicus and semimembranosus muscles in conscious subjects was 1.29 ml/min/100 g while in anaesthetised subjects it was 0.40 ml/min/100 g. The significance of these results is discussed in relation to the clinical occurrence of post anaesthetic myositis.
The elimination of equine strongyles and hematological and pathological consequences following larvicidal doses of thiabendazole. Twelve horses were divided into three groups and given various doses of a mixed species strongyle inoculum, representing light, moderate, and heavy infections. Three weeks after the larval inoculations, three animals from each group were given larvicidal doses of thiabendazole (TBZ) (440 mg kg-1 on two consecutive days); one animal from each group served as a non-medicated control. Treatment was repeated three weeks later. One treated animal from each group was designated for long-term study; others were necropsied to study adult and larval parasite loads. Six of the twelve animals with strong...
Efficacy of ivermectin in injectable and oral paste formulations against eight-week-old Strongylus vulgaris larvae in ponies. A controlled test method was used to evaluate the efficacy of injectable micelle and oral paste formulations of ivermectin (22,23-dihydroavermectin B1) against 8-week-old Strongylus vulgaris larvae in experimentally infected pony foals. The dosage level of the drug in both formulations tested was 0.2 mg/kg. Ponies were euthanatized and necropsied 5 weeks after treatment. Based on the recovery of live vs dead S vulgaris from mesenteric arteries, both formulations were greater than 99% effective. Increased weight gains and marked reductions in the severity of arterial lesions were observed in tr...
