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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.
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 +/-...
Species-dependent binding of disopyramide enantiomers. Serum protein binding of the basic enantiomers of disopyramide were studied in several animal species. (S)-(+)-Disopyramide was more highly bound than the (R)-(-)-enantiomer to serum protein in the man, gorilla, and pig. The reverse was true in cow serum, and in serum and albumin from sheep. Enantioselective differences in binding were due to differences in association constants. No enantioselective differences in binding were observed in serum protein from horse and goat, or in albumin from cow and pig. Disopyramide was highly bound to two sites on horse albumin. The association constant char...
Efficacy of ivermectin in the oral paste formulation against naturally acquired adult and larval stages of Parascaris equorum in pony foals. The efficacy of ivermectin in oral paste formulation at a dosage of 200 micrograms/kg of body weight was tested against naturally acquired larval and adult stages of Parascaris equorum, in a controlled study. Twenty infected pony foals 18 to 27 weeks of age were randomly allocated to 2 groups of 10 each and were placed in dry lots. Foals in 1 group were given ivermectin on day 0. Necropsies and parasite recoveries from small intestines and lung tissues were performed on 5 foals in each group at 2 weeks after treatment (WAT) and on the remaining foals at 5 WAT. Ivermectin was 100% effective aga...
Objective assessment of detomidine-induced analgesia and sedation in the horse. The effects of detomidine, a veterinary sedative analgesic, were studied in the horse. Novel objective techniques were employed to assess the analgesic and sedative potency of this compound. Intravenous doses of 0.010, 0.020 and 0.040 mg/kg were administered to eight adult Thoroughbred racehorses according to a double-blind crossover design. Analgesia was measured by determining the latency to onset of the skin twitch and hoof withdrawal reflexes following noxious thermal stimulation of the withers and fetlock, respectively. Sedation was assessed by quantifying spontaneous locomotor activity i...
The effect of various antibacterial preparations on the in vitro morphology and chemotactic response of equine neutrophils. Two independent assay systems were used to study the effect of three antibacterial preparations on in vitro morphology and chemotaxis of equine neutrophils. Incubation of neutrophils with high (200 micrograms/ml) and medium (20 micrograms/ml) concentrations of neomycin impaired their response to standard chemoattractants. Trimethoprim/sulfadoxine (0.4/2.0 micrograms/ml-40/200 micrograms/ml) and benzylpenicillin (0.25-25 micrograms/ml) had no effect. Neutrophils collected from geldings 2 and 24 h after neomycin (5 mg/kg) administration had impaired responses to standard chemoattractants. Benzyl...
Adverse reaction to procaine penicillin G in horses. Adverse reactions to intramuscular injections of procaine penicillin G are reported in 11 horses, five of which died. The clinical findings are presented and suggest central nervous involvement in most cases. Post mortem findings in one horse were consistent with anaphylaxis whereas in other cases the clinical findings, duration of treatment, speed of onset and subsequent completion of treatment supports diagnosis of an acute procaine toxicity syndrome.
Development of a novel in vitro equine anthelmintic assay. An in vitro assay involving the use of a horse strongyle (Strongylus edentatus) and the micromotility meter has been developed to test for equine anthelmintic activity. Three commercially available equine anthelmintics (dichlorvos, ivermectin, and pyrantel pamoate) and an investigational drug (p-toluoyl chloride phenylhydrazone) were evaluated in this assay at four concentrations. After a 24-h incubation, greater than or equal to 10 micrograms/ml of all four drug treatments significantly (P less than or equal to 0.05) reduced the motility of ensheathed L-3 S. edentatus larvae, thereby indicati...
Use of a narcotic antagonist (nalmefene) to suppress self-mutilative behavior in a stallion. Nalmefene, an opioid antagonist, caused a decrease in self-mutilative behavior in a 500-kg stallion. Self-mutilative attempts were counted during a control period and on 4 subsequent occasions after the IM administration of 100 mg, 200 mg, 400 mg, or 800 mg of nalmefene. The frequency of self-mutilation decreased with increasing doses of nalmefene and was virtually abolished with the 800-mg dose.
Beta-adrenergic blockade in ponies with recurrent obstructive pulmonary disease. Ponies with recurrent airway obstruction have hyperresponsive airways during acute disease exacerbations but not during clinical remission. We examined the effect of beta-adrenergic blockade with propranolol on airway responsiveness to aerosol histamine in six ponies with recurrent airway obstruction and six age- and gender-matched controls. Measurements were made with principal ponies in clinical remission (period A) and during an acute period of airway obstruction (period B). beta-Adrenergic blockade did not change airway responsiveness, dynamic compliance (Cdyn), or pulmonary resistance (RL...
Determination of clenbuterol and mabuterol in equine plasma by ion-pair liquid chromatography with electrochemical detection. Chromatographic and electrochemical characteristics. A method for the routine determination of the beta-adrenergic drugs clenbuterol and mabuterol in equine plasma has been developed. The drugs were isolated from alkalinized plasma by liquid-liquid extraction. The organic phase was evaporated to dryness and the residue was dissolved in the mobile phase prior to injection. The recoveries were 98% and 95% for clenbuterol and mabuterol, respectively. The drugs were separated by reversed-phase high-performance liquid chromatography and quantitated by a use of a coulometric detector set at +0.75 V vs. the internal reference electrode. The influence o...
Effects of xylazine and acepromazine on bronchomotor tone of anaesthetised ponies. The effects of xylazine (an alpha 2-adrenoceptor agonist) and acepromazine (an alpha-adrenoceptor antagonist) on bronchomotor tone were investigated in seven anaesthetised, apnoeic ponies using a computer aided forced oscillation technique, which separates changes in bronchial calibre from changes in lung volume. Both agents produced bronchodilatation and a decrease in lung volume.
Cardiovascular effects of hydralazine HCl administration in horses. Six standing awake adult horses were instrumented for measurement of mean arterial, central venous, and pulmonary arterial blood pressures (mm of Hg), thermodilution cardiac output (ml/kg/min), and pulmonary arterial blood temperature (C). Total peripheral resistance was calculated from these values. Base-line data were accumulated, and a single dose of hydralazine HCl (0.5 mg/kg) was administered IV. Horses were monitored for 420 minutes after hydralazine administration. Mean arterial and central venous blood pressures did not change from the base-line values. Cardiac output and heart rate we...
Radioimmunoassay for etorphine in horses with a 125I analog of etorphine. To improve the sensitivity and specificity of screening for etorphine in horses, an 125I-labeled etorphine analog was synthesized and an antibody to etorphine was raised in rabbits. A radioimmunoassay (RIA) for etorphine was developed, using these reagents. Bound and free 125I-labeled etorphine was separated by a double-antibody method that reduced interference from materials associated with equine urine. The 125I-labeled etorphine binding was rarely greater than 250 pg of background etorphine equivalents/ml in raw urine and was 100 pg/ml in hydrolyzed urine. The 125I-RIA was capable of detect...
Effect of gentamicin sulfate and sodium bicarbonate on the synovium of clinically normal equine antebrachiocarpal joints. The effect of gentamicin sulfate, unbuffered and buffered with sodium bicarbonate, on synovial fluid and membrane of clinically normal equine joints was evaluated. Thirty-six adult horses with clinically normal antebrachiocarpal joints were allotted to 6 treatment groups of 6 horses each. One antebrachiocarpal joint in each horse was chosen for treatment. Group-1 horses were given gentamicin (3 ml; 50 mg/ml); group-2 horses were given sodium bicarbonate (3 ml; 1 mEq/ml); group-3 horses were given gentamicin (3 ml; 50 mg/ml) and sodium bicarbonate (3 ml; 1 mEq/ml); group-4 horses were not treat...
Effects of xylazine on cecal mechanical activity and cecal blood flow in healthy horses. Mechanical activity of the cecal body, lateral cecal arterial blood flow, carotid arterial pressure, and heart rate were measured in 6 conscious healthy horses 30 minutes before and for 120 minutes after IV administration of xylazine at dosages of 1.1 mg/kg of body weight, 0.55 mg/kg, and 0.275 mg/kg. Xylazine at a dosage of 1.1 mg/kg reduced the mean motility index (the product of the mean amplitude of contractions and the total duration of contractile activity divided by the recording time) of the circular and longitudinal muscle layers for the first, second, third, and fourth 30-minute peri...
Influence of the autonomic nervous system in the horse urinary bladder. alpha and beta-adrenergic receptors in detrusor muscle and bladder base of horses were investigated by in vitro responses of smooth muscle strips to exogenous agonist and antagonist drugs. Noradrenaline, isoprenaline and salbutamol induced relaxation of detrusor muscle strips which was significantly inhibited by propranolol and butoxamine suggesting that the response is mediated by beta-2 adrenergic receptors. In the urinary bladder base noradrenaline, phenylephrine and B-HT 920 induced strong contractile effects. These contractile responses were inhibited by the alpha antagonist phenoxybenzam...
Recognition and management of ileus. Ileus may occur in horses of all ages secondarily to drug administration, colic, exhaustion, peritonitis, or metabolic disorders. Ileus most commonly occurs following abdominal surgery for colic and is a significant cause of postoperative mortality in these horses. The most common clinical signs of ileus are decreased or absent intestinal sounds and gastric reflux. Ileus is treated by eliminating the initiating causes, correcting metabolic imbalances, decompressing distended bowel, providing analgesia, stimulating motility with drugs, and regulating exercise and feed and water intake.
Immunoassay detection of drugs in racing horses. IV. Detection of fentanyl and its congeners in equine blood and urine by a one step ELISA assay. We have developed and evaluated a one step enzyme-linked immunosorbent assay (ELISA) test for fentanyl as part of a panel of pre- and post-race tests for narcotic analgesics in racing horses. This ELISA test detects fentanyl with an I-50 of about 100 pg/ml. The test is economical in that it can be read with an inexpensive spectrophotometer, or even by eye. The test is rapid, and ten samples, a normal pre-race complement, can be analyzed in about twenty minutes. The test readily detects the presence of fentanyl or its metabolites in equine blood and urine from two and twenty-four hours respecti...
Hemodynamic and respiratory responses in halothane-anesthetized horses exposed to positive end-expiratory pressure alone and with dobutamine. The influence of positive end-expiratory pressure (PEEP) on the alveolar-arterial O2 tension difference [P(A-a)O2], physiologic right-to-left shunt fraction, physiologic dead space-to-tidal volume ratio, and hemodynamic variables was studied in halothane-anesthetized horses maintained in dorsal recumbency during controlled ventilation. Dobutamine was used to minimize the adverse cardiovascular consequences of PEEP. Six adult horses were anesthetized, using xylazine (2.2 mg/kg of body weight, IM), guaifenesin (50 mg/kg, IV), thiamylal Na (4.4 mg/kg, IV), and halothane (1.5 to 2% inspired) in 10...
Selected aspects of the clinical pharmacology of visceral analgesics and gut motility modifying drugs in the horse. Comparison of the visceral analgesic effects of xylazine, morphine, butorphanol, pentazocine, meperidine, dipyrone, and flunixin in a cecal distention model of colic pain indicated that xylazine produces the most relief from abdominal discomfort. Repeated administration of xylazine may reduce visceral pain so effectively that the seriousness of abdominal disease is obscured. Xylazine decreased propulsive motility in the jejunum and pelvic flexure of healthy ponies. Morphine and butorphanol also gave relief from visceral pain in the cecal distention model. Morphine may inhibit colonic, and buto...
