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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.
Research needs on internal parasites of horses. The importance of the horse industry to the economy of the United States and the impact of parasitic infections on the industry are well documented. However, contemporary research activity on internal parasites of horses has not kept pace with growth of the horse population. Parasitic infections are a major facet of enteritis and colic in horses. Parasites are also associated with poor growth and development, respiratory tract disease, dermatitis, and CNS lesions. Babesia infections remain a threat to horses imported from some regions of the world. Most research activity has dealt with the dev...
Illness in horses following spraying with amitraz. Sickness occurred in 3 of 4 horses within 24 h of being sprayed with an 0.025% w/v aqueous suspension of amitraz. The latter consisted of a portion of an amitraz aqueous suspension made up some 3 weeks previously, to which some freshly prepared spray fluid had been added. It seemed likely that the amitraz in the older solution had broken down to the highly toxic N-3, 5- dimethylphenyl N-methyl formamadine derivative and that this was in fact the main cause of the untoward effects observed. The horses displayed typical clinical signs of tranquillisation, depression, ataxia, muscular incoordinat...
Developments in management of the newborn foal in respiratory distress 2: Treatment. New developments in therapy for foals in respiratory distress are discussed. Therapy is based on preservation of the foal's life by maintenance of a patent airway, resuscitation with fluids and warmth, provision of humidified oxygen to raise the fractional concentration of inspired oxygen sufficient to avoid hypoxia and provision of ventilatory support when hypercapnia becomes critical. Ventilatory support described includes assisted and controlled ventilation, positive end expiratory pressure, continuous positive airway pressure and intermittent mandatory ventilation. The aims of these techni...
Exercise-induced pulmonary hemorrhage in exercising Thoroughbreds: preliminary results with pre-exercise medication. Thoroughbreds with a confirmed history of exercise-induced pulmonary hemorrhage (EIPH) were treated pre-exercise with atropine sulfate, cromolyn, ipratropium or furosemide. Atropine prevented EIPH in 3 of 3 trials in 1 horse, while having no significant effect on bleeding status in the other 2 horses. Pre-exercise treatment with cromolyn had no significant effects in the 3 horses. Pre-exercise treatment of ipratropium was apparently responsible for preventing EIPH in 17 out of 18 trials in 2 horses. The pharmacologic properties of ipratropium in the horse have not been studied, but based on hu...
Influence of phenylbutazone on eicosanoid levels in equine acute inflammatory exudate. In a two part cross-over experiment, acute inflammatory exudates were induced in 7 ponies by subcutaneous implantation of 3 sterile carrageenin-soaked polyester sponge strips. Treatment comprised a single therapeutic geenin-soaked polyester sponge strips. Treatment comprised a single therapeutic dose of 4.4 mg/kg phenylbutazone (PBZ) administered intravenously at the time of sponge implantation. Exudates were harvested at 6, 12 and 24 hours and examined for leukocyte and erythrocyte numbers using the improved Neubauer technique; for eicosanoids by radioimmunoassay and by high performance liqui...
Effect of flunixin meglumine on prostacyclin accumulation in the equine eye. A study was performed to identify prostacyclin (PGI2) in equine aqueous humor, demonstrate an increase in PGI2 following anterior chamber paracentesis, and determine the effects of subconjunctival injection of flunixin meglumine on PGI2 accumulation. Twenty ponies were found to be normal upon ocular examination and were placed under general anesthesia. Anterior chamber paracentesis was performed in both eyes (right and left); immediately afterward, 25 mg of flunixin meglumine was injected (subconjunctivally) in the left eye. Aqueous paracentesis was performed 1.5 hours later (both eyes). Aqueo...
Anesthesia for cesarean section in large animals. Respiratory minute volume, blood volume, RBC mass and cardiac output increase while the functional residual capacity decreases during late pregnancy. General anesthetics reach the fetus in high concentrations and tend to persist in the fetus after delivery. Use of small doses of a combination of anesthetics is recommended. Ephedrine increases vascular tone and cardiac output. Glycopyrrolate and fentanyl-droperidol are used to restrain sows for cesarean section. Morphine alone or with acepromazine works well in depressed sows. Acepromazine or xylazine, used with ketamine, is good in restraining...
Preliminary study on the pharmacokinetics of phenobarbital in the neonatal foal. Pharmacokinetic characteristics of the anticonvulsant phenobarbital were studied in seven pony and two Thoroughbred foals aged between four and 10 days. A single, 20 mg/kg bodyweight (bwt) dose of phenobarbital was given intravenously over 25 mins and the serum concentrations of the drug were measured using an EMIT AED assay (coefficient of variation 1.37 per cent at 30 micrograms/ml, n = 7). Phenobarbital elimination was found to follow first order kinetics. The mean (+/- sd) peak phenobarbital serum concentration was 18.6 +/- 2.1 micrograms/ml at 1 h after initiation of infusion with a mean ...
Effects of fluprostenol administration in mares during late pregnancy. The effectiveness of the prostaglandin F analogue fluprostenol in inducing labour in the mare was examined by giving sequential injections over the last 50 days of gestation. The behavioural and endocrine changes elicited by the drug in pregnant and non-pregnant animals and in foals were also studied. Fluprostenol (250 or 500 micrograms intramuscularly) failed to induce labour before 320 days gestation; thereafter its effect was capricious. Twelve mares foaled 1 to 36 h after the last test; eight delivered normal, viable, apparently 'term' foals and four produced stillborn/premature animals. E...
Influence of calcium and cyclic nucleotides on beta-adrenergic sweat secretion in equine sweat glands. The effects of Ca2+, the cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP), and other parameters of sweat secretion from single equine sweat glands were examined in vitro. Extracellular Ca2+, the Ca2+ ionophore A23187, and the Ca2+ channel antagonist verapamil were all without effect on sweat secretion. Prolonged rinsing of the glands in Ca2+-free Ringer solution with 5 mM ethylenediaminetetraacetic acid decreased the secretion to 30% of the control sweat rate in response to the beta-adrenergic agonist isoproterenol; the sweat respon...
Maduromycosis (Madurella mycetomatis) in a horse. A case of maduromycosis mycetoma caused by Madurella mycetomatis is reported. The horse presented with multiple subcutaneous swelling over the right scapula. There were no discharging fistulae present. Macroscopically the lesion contained a black granular material embedded in a granulomatous mass. Microscopically large numbers of microcolonies were present containing segmented hyphae. No typical chlamydospores were observed. Cultures yielded a fungus identified as Madurella mycetomatis. Treatment consisted of surgical excision and local treatment with thiabendazole powder.
Critical test evaluations of oxfendazole and trichlorfon: effectiveness of a paste formulation in the horse. Critical tests were performed on 6 horses to evaluate the antiparasitic effectiveness of oxfendazole given in combination with trichlorfon in a paste formulation. Treatments were given orally as a single dose. The rates of active ingredient administration were 2.5 and 40 mg/kg of body weight for oxfendazole and trichlorfon, respectively. The combined activities of the 2 antiparasitic compounds proved 100% efficacious in the removal of adult Strongylus vulgaris, S edentatus, Oxyuris equi, and Parascaris equorum. Fourth stage O equi, and 2nd and 3rd instars of Gasterophilus nasalis also were com...
Effects of tryptamine antagonists on the anaphylactic contractions of the bovine pulmonary smooth muscles. Calves were sensitized with horse plasma (H.P.), 0.2 ml/kg, i.v., and H.P. (0.2 ml/kg) in Freund's complete adjuvant, s.c. The latter injection was repeated 1 week later and the animals were killed 10 days after the second injection. Spirally cut strips of pulmonary artery and vein and the trachealis muscle from the sensitized calves contracted to 5-hydroxytryptamine (5-HT) and specific antigen (horse plasma). Antigen-induced contractions of the pulmonary smooth muscles were significantly blocked (P less than 0.05) by the 5-HT antagonists, methysergide and ketanserin. The trachea, however, app...
A field trial of ketamine anaesthesia in the horse. Ketamine was used on 80 occasions to induce anaesthesia in 77 animals. Xylazine premedication was used alone on 75 occasions, in conjunction with methadone once, in conjunction with methadone and acepromazine once and, on three occasions, methadone and acepromazine only were used. Anaesthesia was maintained in seven cases with halothane and oxygen. Premedication with xylazine 5 mins previously or concurrently with ketamine gave similar results but an interval of more than 5 mins between the drugs produced less deep anaesthesia and this protocol is, therefore, not advised. Induction and recover...
Ivermectin and an ivermectin-penicillin combination: a comparison of anthelmintic efficacy in horses. Ivermectin given IM at 200 micrograms/kg, alone or in combination with procaine penicillin G at 600 IU/kg, to 20 randomly selected young horses of various breeds reduced fecal strongyle egg counts from 400-4100 epg (avg greater than 1000) pretreatment to zero 7 days posttreatment. There were no systemic or injection-site reactions, either immediate or delayed, in any of the horses.
Antagonism of xylazine and ketamine anesthesia by 4-aminopyridine and yohimbine in geldings. Thirty-six fasted, mixed horse breed geldings (6 groups of 6 animals each) were anesthetized with xylazine and ketamine, and when maximally sedated, were given 1 of the following antagonists: saline solution, 4-aminopyridine (4-AP), small-dose yohimbine, large-dose yohimbine, 4-AP plus low-dose yohimbine, or 4-AP plus high-dose yohimbine. Measured data included mean standing time (MST), heart rate, respiratory rate, rectal temperature, and mean total recovery time ( MTRT ). Emergence phenomena were also observed and recorded as smooth, fairly smooth, fairly rough, or rough. Groups given 4-AP a...
The acute inflammatory process, arachidonic acid metabolism and the mode of action of anti-inflammatory drugs. Arachidonic acid is a polyunsaturated fatty acid covalently bound in esterified form in the cell membranes of most body cells. Following irritation or injury, arachidonic acid is released and oxygenated by enzyme systems leading to the formation of an important group of inflammatory mediators, the eicosanoids. It is now recognised that eicosanoid release is fundamental to the inflammatory process. For example, the prostaglandins and other prostanoids, products of the cyclooxygenase enzyme pathway, have potent inflammatory properties and prostaglandin E2 is readily detectable in equine acute in...
The effects of naloxone on endotoxic and hemorrhagic shock in horses. The effects of naloxone on the cardiovascular, hematologic and metabolic derangements associated with endotoxic and hemorrhagic shock were studied in unanesthetized horses. In the first of 3 experiments blood glucose and lactate levels, hematocrit, white, red and differential white cell counts, rectal temperature and clinical signs were obtained before and after endotoxin (10 micrograms/Kg) administration in 5 horses. In the second experiment, two groups of 3 horses received either intravenous naloxone (0.04 mg/Kg) or saline, 7 minutes prior to endotoxin. In a third experiment two groups of 4 ...
Isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse by high-performance liquid chromatography. The isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse is described. The identity of the glucuronides was checked by UV and fluorescence spectrophotometry, by NMR spectrometry and by mass spectrometry after permethylation. The applicability of the procedure to pharmacokinetic studies is demonstrated.
Continuous caudal epidural anesthesia in the horse. A technique for continuous caudal epidural anesthesia in the horse was developed in trials involving 8 healthy adult horses. The injection site was the first intercaudal (intercoccygeal) space. A Huber point directional needle (Tuohy or Hustead) with a stylet was preplaced into the epidural space, used as a guide for an epidural catheter, and then removed, leaving the catheter in situ in the epidural space. A 2% solution of lidocaine hydrochloride was used as the anesthetic agent at an initial dose of 8 ml for an adult animal (474 kg to 560 kg). Repeated 4-ml doses were administered immediatel...
Hemodynamics before and after conversion of atrial fibrillation to normal sinus rhythm in horses. Hemodynamic measurements were obtained from 17 horses with atrial fibrillation or flutter. Eight horses had atrial fibrillation of unknown duration. In 7 horses, atrial fibrillation developed during anesthesia. Atrial flutter developed during recovery from anesthesia in 2 horses. Hemodynamic measurements were considered normal in 7 of 8 conscious horses with atrial fibrillation. Cardiac output was decreased and pulmonary arterial blood pressure and right atrial pressure were increased in 1 conscious horse which had signs of congestive heart failure. Arterial blood pressure decreased in 5 of 7 ...
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...
