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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.
Doxapram: cardiopulmonary effects in the horse. The cardiopulmonary effects of 3 dosages of doxapram hydrochloride (0.275 mg/kg, 0.55 mg/kg, and 1.1 mg/kg, IV) were studied in 6 adult horses. Doxapram given IV significantly (P less than 0.05) decreased PaCO2 and increased respiratory rate, cardiac output arterial blood pressures (systolic, mean, and diastolic) arterial pH, and PaO2 at 1 minute after each dose was administered. Heart rate and mean and diastolic pulmonary arterial blood pressure were significantly (P less than 0.05) increased 1 minute after the 2 larger dosages of doxapram were given (0.55 mg/kg and 1.1 mg/kg, IV), but not af...
Critical test and safety evaluations of an oral paste preparation of mebendazole and trichlorfon in horses. Critical tests were done on 24 naturally parasitized horses to compare the antiparasitic activity of an oral paste preparation of mebendazole and trichlorfon with that of the marketed powder formulation. Each formulation was administered at the recommended dosages of 8.8 mg of mebendazole and 40 mg of trichlorfon/kg of body weight. Efficacy of the paste formulation ranged from 97.7% to 100% against 2nd- and 3rd-stage Gasterophilus spp, adult Strongylus vulgaris, S edentatus, Parascaris equorum, small strongyles; and larval and adult forms of Oxyuris equi. Adverse effects were generally limited...
Phenylbutazone and oxyphenbutazone distribution into tissue fluids in the horse. The clinically recommended dose rate of phenylbutazone (4.4 mg/kg) was administered intravenously as a single dose to five Welsh Mountain ponies. Distribution of phenylbutazone and its active metabolite oxyphenbutazone into body fluids was studied by measuring concentrations in plasma, tissue-cage fluid, peritoneal fluid and acute inflammatory exudate harvested from a polyester sponge model of inflammation. The ready penetration of phenylbutazone into inflammatory exudate was demonstrated by the relatively high mean value for Cmax of 12.4 micrograms/ml occurring at a time of 4.6 h and a mean A...
Activity of ivermectin against natural infections by abomasal nematodes in lambs in controlled tests: evaluation of equine and bovine injectable formulations administered intraorally. The efficacy of 2 injectable formulations of ivermectin, administered intraorally at the dosage of 200 micrograms/kg of body weight, was evaluated against naturally occurring infections by abomasal nematodes in lambs in 2 controlled tests. One test (A) included 17 lambs treated with the equine formulation and 16 nontreated lambs. For the other test (B), 14 lambs were treated with the bovine formulation, and 12 were nontreated. In controlled test A, only mature nematodes were recovered, and removals were 98% to 100% for Haemonchus contortus, Ostertagia circumcincta male, O trifurcata male, Oste...
Iopamidol myelography in the horse. The use of the non-ionic, water-soluble contrast agent iopamidol for myelography in seven horses is described. Contrast columns of diagnostic quality were produced in all seven cases and the procedure did not invoke any adverse reactions in the five cases which were recovered from general anaesthesia. It is concluded that iopamidol is a safe and effective contrast agent for myelography in the horse.
Effects of warfarin on blood rheology in navicular disease. A preliminary investigation has been undertaken of blood rheology in horses and ponies, its variation in navicular disease and the changes following treatment with warfarin. Erythrocyte flexibility, measured by a centrifuge packing technique, is higher in horses (30 per cent min-1) than in ponies (23.8 per cent min-1). There are corresponding differences in blood viscosity. The high erythrocyte flexibility in horses is caused by an unknown factor present in plasma. The erythrocyte flexibility in horses with navicular disease is even higher, at 38.5 per cent min-1. Treatment with warfarin reduc...
Radioimmunoassay screening for etorphine in racing horses. A commercially available radioimmunoassay kit was used to screen for the presence of etorphine in post-race urines from horses racing in Kentucky. Most horse urines contained small amounts of materials which reacted positively in this immunoassay. These materials are apparently endogenous to the horse and were called apparent etorphine equivalents. The levels of these apparent etorphine equivalents in post-race urines from 70 horses were estimated. Their modal level averaged 0.1 ng/ml, the population distribution was log normal, and individual horses showed levels of up to 0.8 ng/ml.
Effects of acetylpromazine on the hemodynamics of the equine metatarsal artery, as determined by two-dimensional real-time and pulsed Doppler ultrasonography. Heart rate, blood velocity, volumetric blood flow, and arterial diameter for 10 horses given acetylpromazine were determined from measurements of the dorsal metatarsal artery 3 (the great metatarsal artery), using 2-dimensional real-time and gated pulsed Doppler ultrasonography. Acetylpromazine induced significant increases in arterial diameter (P less than 0.01) and volumetric flow rate (P less than 0.05)--all compatible with adrenergic blockade. There was a trend indicating that there was increased blood velocity. Heart rate was unchanged.
Evaluation of leukapheresis and thrombocytapheresis in the horse. Continuous-flow centrifugation leukapheresis techniques were used to collect 300-ml volumes of leukocyte-rich plasma from 5 nonmedicated horses and from 5 corticosteroid-stimulated horses. White blood cell counts and differential counts were performed on the horses before (base line) and up to 48 hours after leukapheresis. Systemic administration of hydrocortisone increased numbers of total WBC and neutrophils and improved harvest of these cells. Nonmedicated horses had a mean yield of 3.38 X 10(10) leukocytes in the 300-ml volume. Stimulated horses yielded a mean of 6.88 X 10(10) leukocytes. ...
Neuromuscular and cardiovascular effects of atracurium in ponies anesthetized with halothane. Atracurium besylate, a recently developed, intermediate-duration acting, neuromuscular-blocking agent, was given to 15 halothane-anesthetized ponies to produce surgical relaxation (95% to 99% reduction of hoof twitch). All 15 ponies were given 3 injections; 8 of the 15 ponies were given 2 additional injections. Initial dosage of 0.11 +/- 0.01 mg/kg (mean +/- SD) and all subsequent injections of 0.052 mg/kg produced desired relaxation. Paralysis phase (maximum twitch reduction to 10% twitch recovery) lasted 24 +/- 5 minutes for the initial injection. Paralysis from subsequent injections lasted ...
Gentamicin tissue concentrations in equine small intestine and large colon. Gentamicin sulfate (2.2 mg/kg of body weight, IV) was given to anesthetized horses. Jejunal and large colon tissue samples (1 g), serum, and urine were collected over a 4-hour period. Maximum gentamicin concentrations in serum (10.06 +/- 2.85 micrograms/ml) occurred at 0.25 hours after injection. Maximum gentamicin concentrations in the large colon (4.13 +/- 1.80 micrograms/ml) and jejunum (2.26 +/- 1.35 micrograms/ml) occurred in horses at 0.5 and 0.33 hours, respectively. Tissue concentrations decreased in parallel with serum concentrations and were still detectable at the end of the 4-hour ...
Development of a gas chromatographic-mass spectrometric method using multiple analytes for the confirmatory analysis of anabolic steroids in horse urine. I. Detection of testosterone phenylpropionate administrations to equine male castrates. A gas chromatographic-mass spectrometric (GC-MS) method using three analytes to detect and confirm the administration to equine male castrates of veterinary pro-drugs based upon esters of testosterone is described. The method involves extraction of steroid conjugates from horse urine by C18-bonded cartridges and fractionation into glucuronic acid and sulpho-conjugates by Sephadex LH-20 column chromatography. After deconjugation, the free neutral steroids were partially purified by thin-layer chromatography and following derivatization (methyloxime-trimethylsilyl ether) were analysed by capilla...
Anti-strongyle activity of a propylene glycol-glycerol formal formulation of ivermectin in horses (mares). Four groups of 10 horses (mares) each were treated with a 1% solution of ivermectin (200 micrograms/kg of body weight) in a propylene glycol-glycerol formal base orally, a 1% solution of ivermectin (200 micrograms/kg) in a propylene glycol-glycerol formal base via nasogastric tube, a 1.87% paste of ivermectin (200 micrograms/kg) orally, or a 22.7% paste of oxibendazole (10 mg/kg) orally. Fecal examinations were done before treatment and on posttreatment days (PTD) 14, 28, 42, 56, and 70. Strongyle egg per gram counts and sugar flotation fecal examinations were performed. Results of fecal exami...
Effects of phenobarbital treatment on 3-methylindole toxicosis in ponies. To study the role of cytochrome P-450-dependent mixed function oxidase reactions in equine 3-methylindole (3MI) toxicosis, ponies were given 20 mg of phenobarbital/kg of body weight at 72, 60, 48, 36, and 24 hours before 100 mg of oral 3MI/kg to induce cytochrome P-450 or no treatment (controls). Maximal 3MI plasma concentration was decreased and clearance was faster in phenobarbital-treated ponies. Plasma 3MI was still detectable 12 and 36 hours after dosing in phenobarbital-treated and control ponies, respectively. Phenobarbital treatment induced a distribution phase with transition from a 1...
Dermal reactivity to histamine, serotonin and bradykinin in relation to allergic skin reactions of the horse. The reactivity of horse skin to intradermal inoculation of histamine, serotonin and bradykinin was investigated, and the resulting reactions compared with those produced in the same horses by a 1% whole-body extract of Culicoides. Both histamine and bradykinin produced large reactions, but there was no significant correlation between the dermal responsiveness to insect allergen and either histamine or bradykinin. Two anti-histamine drugs (promethazine hydrochloride and tripelennamine hydrochloride) were effective in reducing the reaction produced by the insect extract.
Effectiveness of oxfendazole against early and later 4th-stage Strongylus vulgaris in ponies. Twenty pony foals (reared worm free), 6.5 to 10 weeks of age, were inoculated with Strongylus vulgaris and allocated to 5 groups, each with 4 foals. One week after inoculation, 1 group of 4 foals was given oxfendazole (OFZ) at a dosage rate of 10 mg/kg of body weight, another group was given 2 such treatments 48 hours apart, and a 3rd group was given a placebo. All treatments were administered by stomach tube. Three weeks later, foals were euthanatized and necropsied in a test for efficacy against early 4th-stage larvae. Oxfendazole was 80% and 94.9% effective against early 4th-stage S vulgari...
Effects of flunixin meglumine, phenylbutazone and a selective thromboxane synthetase inhibitor (UK-38,485) on thromboxane and prostacyclin production in healthy horses. The efficacy of three agents which alter the metabolism of arachidonic acid was investigated in normal, conscious horses. A dose response evaluation was made of flunixin meglumine and phenylbutazone, two cyclo-oxygenase inhibitors, and of a selective thromboxane synthetase inhibitor, UK-38,485. Radioimmunoassay of thromboxane B2 (TxB2) and 6-keto prostaglandin F1 alpha (PGF1 alpha) was used to assess the concentrations of thromboxane A2 (TxA2) and prostacyclin (PGI2) respectively, in serum. Flunixin was the most potent inhibitor of serum TxB2 and 6-keto PGF1 alpha production. UK-38,485 also de...
Pressures in the right side of the heart and esophagus (pleura) in ponies during exercise before and after furosemide administration. Pressures in the right side of the heart and esophagus (pleural) have not been determined in the exercising equine subjects. In the present study, 8 healthy ponies were examined to determine the changes in these variables caused by 2 degrees of exercise done on a treadmill (heart rate:183 +/- 5 beats/min [trot] and 220 +/- 6 beats/min [canter]). Measurements were also made during both degrees of exertion 10 minutes and 120 minutes after furosemide (1.0 mg/kg) administration. It was observed that both gaits resulted in significant increases in pulmonary artery, right ventricular, and right atri...
Effects of xylazine on renal function and plasma glucose in ponies. The intravenous administration of xylazine (1.1 mg/kg bodyweight) in six ponies resulted in a significant increase in urine output over two hours, with maximum flow occurring between 30 and 60 minutes after injection. Urine specific gravity, osmolality and glucose concentration decreased. Renal clearance of endogenous creatinine was unchanged. Significant increases in the excretion of potassium and chloride occurred. Plasma glucose concentration was increased 30 minutes after the administration of xylazine by a mean value of 37 per cent. Serum osmolality and sodium, potassium and chloride conc...
[Flunixin and its use in horses]. Flunixin is a non-steroidal anti-inflammatory agent, with a potent analgesic activity and a slight toxicity. It is largely used in horses, in the form of meglumine salt, for the treatment of inflammatory diseases or colics, and often identified in dopage cases. Physical and chemical properties of the drug, its pharmacological and toxicological properties, and its use in equine species are depicted.
Novel environment suppression of stallion sexual behavior and effects of diazepam. Pony stallions were given sexual behavior trials in experimental "home" and "novel" environments, similar in all major features except location. In the novel environment, erection latency was increased and erection time decreased. Treatment with an anxiolytic benzodiazepine derivative (diazepam) appeared to block these effects.
