The topic of medication in horses encompasses the study and application of pharmaceutical substances used to treat, manage, or prevent diseases and conditions in equine patients. This field involves understanding the pharmacokinetics and pharmacodynamics of various drugs, including their absorption, distribution, metabolism, and excretion in horses. Medications commonly administered to horses include non-steroidal anti-inflammatory drugs (NSAIDs), antibiotics, anthelmintics, and sedatives. The appropriate use of these medications is critical for ensuring therapeutic efficacy and minimizing adverse effects. Research in this area focuses on dosage optimization, drug interactions, resistance development, and withdrawal times to ensure both the health of the horse and compliance with regulatory standards. This page aggregates peer-reviewed studies and scholarly articles that explore the pharmacological aspects, clinical applications, and regulatory considerations of equine medications.
Zullian C, Menozzi A, Pozzoli C, Poli E, Bertini S.The effects of selective α(2)-agonists (xylazine, detomidine and medetomidine) and antagonists (yohimbine and atipamezole) on in vitro small intestine motility in the horse were evaluated. Samples of equine jejunum were placed in isolated organ baths and drug-induced modifications of motility were measured by means of an isotonic transducer. All tested α(2)-agonists dose-dependently reduced both spontaneous and electrically-evoked phasic contractions. Conversely, α(2)-antagonists were ineffective when tested alone, and showed a heterogeneous and dose-independent ability to inhibit agonist a...
Andrews FM, Reinemeyer CR, Longhofer SL.Eighteen mature, healthy horses were divided into three groups (six per group) receiving either no treatment, 15 consecutive days of phenylbutazone (PBZ), or 15 consecutive days of suxibuzone (SBZ) at recommended label doses. Horses underwent endoscopy before and after the treatment period and were assigned gastric ulcer scores. Gastric ulcer number and severity scores were similar across treatment groups. These findings suggest that when administered at the recommended label dose for 15 days, neither PBZ nor SBZ causes an increase in the number or severity of gastric ulcers over what would be...
Houghton E, Maynard S.This chapter reviews drug and medication control in equestrian sports and addresses the rules of racing, the technological advances that have been made in drug detection and the importance of metabolism studies in the development of effective drug surveillance programmes. Typical approaches to screening and confirmatory analysis are discussed, as are the quality processes that underpin these procedures. The chapter also addresses four specific topics relevant to equestrian sports: substances controlled by threshold values, the approach adopted recently by European racing authorities to control...
Tsujimura K, Yamada M, Nagata S, Yamanaka T, Nemoto M, Kondo T, Kurosawa M, Matsumura T.We investigated the pharmacokinetics of penciclovir after oral administration of its prodrug famciclovir to horses. Following an oral dose of famciclovir at 20 mg/kg, maximum plasma concentrations of penciclovir occurred between 0.75 and 1.5 hr (mean 0.94 + or - 0.38 hr) after dosing and were in the range 2.22 to 3.56 microg/ml (mean 2.87 + or - 0.61 microg/ml). The concentrations of penciclovir declined in a biphasic manner after the peak concentration was attained. The mean half-life of the rapid elimination phase was 1.73 + or - 0.34 hr whereas that of the slow elimination phase was 34.34 +...
Love EJ, Taylor PM, Clark C, Whay HR, Murrell J.In the UK butorphanol has a marketing authorisation for administration to horses for sedation in combination with detomidine, and at a higher dose (0.1 mg/kg bwt), for the alleviation of pain. There is only a limited number of clinical studies designed to examine the analgesic effects of butorphanol administration following surgery. Objective: To investigate the effect of premedication with butorphanol on post operative pain following castration under general anaesthesia in ponies. Objective: Ponies receiving butorphanol would experience less pain after castration than ponies that did not rece...
Cordes B.The research article titled, “Effects of compounding and storage conditions on stability of pergolide mesylate” investigates the importance of adhering to the official US Pharmacopeia (USP) when formulating pergolide mesylate […]
Ho EN, Leung DK, Leung GN, Wan TS, Wong AS, Wong CH, Soma LR, Rudy JA, Uboh C, Sams R.Administration studies of levamisole in horses were carried out using two different levamisole preparations, namely, levamisole hydrochloride oral bolus and levamisole phosphate injectable solution. These preparations were analysed in detail for the presence of aminorex-like impurities. Both levamisole preparations were found to contain 1-(2-mercaptoethyl)-4-phenyl-2-imidazolidinone (I) and 4-phenyl-2-imidazolidinone (II) as degradation impurities, but neither aminorex nor rexamino was detected in these preparations. After the administration of these preparations to horses, aminorex, rexamino,...
De Clercq D, van Loon G, Tavernier R, Verbesselt R, Deprez P.To investigate effects of IV administration of propafenone for naturally occurring and experimentally induced chronic atrial fibrillation in horses. Methods: 2 horses with naturally occurring atrial fibrillation and 4 horses with pacing-induced atrial fibrillation. Methods: Horses received a bolus of propafenone (2 mg/kg, IV over 15 minutes). If atrial fibrillation persisted after 20 minutes, a continuous infusion of propafenone (7 microg/kg/min) was given for 120 minutes. Before, during, and after treatment, plasma propafenone concentrations, hematologic and serum biochemical values, and elec...
Schwarz B, Burford J, Knottenbelt D.This case report describes a 4-year-old-horse with two cutaneous masses on the right crest of the neck. Biopsy revealed chronic nodular pyogranulomatous dermatitis and panniculitis. Giemsa and periodic acid-Schiff stains showed focal spherical, yeast-like organisms. A diagnosis of cutaneous fungal granuloma was made. The size of the masses decreased after oral treatment with fluconazole for 10 days combined with potassium iodide for 30 days, and the remaining masses were excised by laser. Lesions did not recur at the site. Fungal granuloma should be considered as a differential diagnosis in ho...
Hilton H, Affolter VK, White SD.The response to treatment with four topical preparations was evaluated in an 11-year-old Morgan horse mare with histologically confirmed quadrilateral cannon hyperkeratosis. Each limb was treated for 30 days with 0.1% tacrolimus ointment, 0.1% adapalene gel, 0.2% phytosphingosine spray or a water-based emollient. Response to treatment was evaluated both histologically and visually. A water-based emollient and 0.1% tacrolimus ointment produced encouraging clinical responses. Pre-treatment histopathology identified marked, mostly compact, hyperkeratosis and follicular hyperkeratosis, most promin...
Lezica FP, Filip R, Gorzalczany S, Ferraro G, de Erausquin GA, Rivas C, Ladaga GJ.In the present study, we determined the incidence and effects of season and weather on clinical manifestations of endophyte-infected ryegrass toxicity, performed chemical detection and pharmacological bioassays on ryegrass extracts, and conducted trials on: (i) effects of domperidone or metochlopramide on ovarian inactivity induced by endophyte-infected ryegrass; (ii) efficacy of buspirone or dihydrochloro phenyl piperazine (m-CPP) for preventing suppressed milk production induced by endophyte-infected ryegrass; and (iii) efficacy of domperidone to induce ovulation during winter anestrus. Mare...
Okamura K, Sasaki N, Yamada M, Yamada H, Inokuma H.Although extensive work has been done to elucidate the beneficial and unfavorable effects of gastrointestinal prokinetic agents in humans, little is known on the effects of these agents in horses. In this study, we compared the effects of mosapride, metoclopramide, cisapride, and lidocaine on equine gastric emptying, jejunal and caecal motility and evaluated these agents' adverse drug reactions (ADRs). Methods: Seven healthy adult Thoroughbreds. Methods: Mosapride 1.0mg/kg and 2.0mg/kg, metoclopramide 0.2mg/kg, and cisapride 1.0mg/kg were dissolved in 100mL distilled water for oral administrat...
Longhofer SL, Reinemeyer CR, Radecki SV.The efficacy of top-dress antiinflammatory drugs ultimately depends on a patient's willingness to consume treated feed. The current study compares the palatability of two phenylbutazone top-dress formulations (Equipalazone Powder, Dechra Pharmaceuticals, and Pro-Dynam, VetXX, Ltd.) and a suxibuzone top-dress formulation (Danilon Equidos, Janssen Animal Health). Results of a three-period, crossover study on 18 healthy horses showed that Pro-Dynam was significantly less palatable, with significantly less consumption of treated feed compared with either Equipalazone Powder or Danilon Equidos. The...
Rendle DI, Durham AE, Hughes KJ, Lloyd D, Summerhays GE.Five horses with sabulous cystitis were managed for up to three years. They were treated by emptying the bladder through a urinary catheter and saline lavage with cytoscopic guidance to remove residual sabulous material. The cystitis was treated with antimicrobial and anti-inflammatory medications, and bethanechol chloride was also administered. Frequent catheterisation and emptying of the bladder was an alternative to regular cystoscopic examination with saline lavage but it resulted in the development of a urethral stricture in one case. Four of the horses returned to work and one was retire...
Durham AE, Rendle DI, Newton JE.Laminitis in equids is a very common debilitating disease, and insulin resistance (IR) and hyperinsulinaemia are increasingly recognised as important predisposing factors. Pharmacological modification of IR and hyperinsulinaemia might reduce the risk of laminitis. Objective: Metformin, a drug commonly prescribed for treatment of human IR, may also decrease IR in equids. Methods: Eighteen horses and ponies with IR and recurrent laminitis were treated with 15 mg/kg bwt metformin per os q. 12 h. Each animal served as its own control by comparing pre- and post treatment proxies for IR, insulin sen...
Pauwels FE, Schumacher J, Castro FA, Holder TE, Carroll RC, Sega GA, Rogers CW.To determine whether clinically effective concentrations of methylprednisolone or triamcinolone can be achieved in the navicular bursa after injection of methylprednisolone acetate (MPA) or triamcinolone acetonide (TA) into the distal interphalangeal joint (DIPJ) and whether clinically effective concentrations of these drugs can be achieved in the DIPJ after injecting the navicular bursa with the same doses of MPA or TA. Methods: 32 healthy horses. Methods: Horses in groups 1 through 4 received 40 mg of MPA in the DIPJ, 10 mg of TA in the DIPJ, 40 mg of MPA in the navicular bursa, and 10 mg of...
Hallowell GD.Cases with a history of colic due to a large colonic impaction were recruited retrospectively to assess the treatment efficacy and complications of oral and parenteral fluid therapy regimes for correction of primary large colon impactions. Oral isotonic fluids had been administered at varying intervals following initial treatment with magnesium sulphate and water. There was no significant difference in complication rates between groups. Considering complication rates with impaction clearance, hourly administration of oral fluids appears to be the most appropriate treatment regime of those inve...
Javsicas LH, Sanchez LC.Administration of omeprazole paste per os to healthy neonatal foals has been shown to effectively increase intragastric pH, but has not been evaluated in sick neonatal foals. Objective: To determine the effect of orally administered omeprazole paste on intragastric pH in clinically ill neonatal foals requiring nasogastric intubation. Methods: Intragastric pH was measured continuously for 24 h using an indwelling electrode and continuous data recording system in hospitalised neonatal foals age < or =2 days. Intragastric pH was measured for 12 h prior to (pretreatment period) and 12 h followi...
Wooldridge AA, Eades SC, Hosgood GL, Moore RM.To compare effects of oxytocin, acepromazine maleate, xylazine hydrochloride-butorphanol tartrate, guaifenesin, and detomidine hydrochloride on esophageal manometric pressure in horses. Methods: 8 healthy adult horses. Methods: A nasogastric tube, modified with 3 polyethylene tubes that exited at the postpharyngeal area, thoracic inlet, and distal portion of the esophagus, was fitted for each horse. Amplitude, duration, and rate of propagation of pressure waveforms induced by swallows were measured at 5, 10, 20, 30, and 40 minutes after administration of oxytocin, detomidine, acepromazine, xyl...
Park SC, Yun HI.The pharmacokinetic properties of norfloxacin-glycine acetate (NFLXGA) were determined in six horses following a single intravenous (i.v.) and intramuscular (i.m.) dose of 4 mgkg(-1) body weight. Following i.v. and i.m. administration, the plasma drug concentrations were best fitted by an open two-compartment model with a rapid distribution phase. After i.v. NFLXGA administration, the distribution (t(1/2alpha)) and elimination half-life (t(1/2beta)) were 0.42 (0.05) and 5.44 (1.36)h. The volume of distribution of NFLXGA at steady state (Vd(ss)) was 2.19 (0.53) Lkg(-1). After NFLXGA i.m. admini...
Estell KE, Knych HK, Patel T, Edman JM, Magdesian KG.To the authors' knowledge, there have been no studies evaluating the pharmacokinetics of chloramphenicol administered orally to horses at the currently recommended dose of 50 mg/kg PO q6 h for multiple days. The published antimicrobial susceptibility breakpoint is 8.0 ug/mL; it is unknown if this concentration is achievable at the recommended dose rate in horses. The aim of this prospective multi-dose pharmacokinetic study was to perform pharmacokinetic analysis of chloramphenicol after multiple doses. The authors hypothesize that the antimicrobial susceptibility breakpoint will not be reached...
Smith LCR, Wylie CE, Palmer L, Ramzan PHL.There is a need for investigation of associations between intrasynovial medication and fracture risk in racehorses. Objective: To document the proportion and type of fracture occurring following intrasynovial medication. Methods: Retrospective longitudinal study. Methods: Review of clinical records from all Thoroughbred flat racehorses receiving intrasynovial medication under the care of a first-opinion veterinary practice between 2006 and 2011. Fractures pre- and post-medication were categorised by location, type, and severity; analysis of fractures sustained within 56-days of medication was ...
Littlewood JD, Rose JF, Paterson S.A single blind controlled clinical trial of oral ivermectin paste at a dose rate of 0.1 mg/kg daily for seven days for the treatment of chorioptic mange in horses was carried out. There was a statistically significant reduction in the numbers of mites in the samples taken from the treated horses compared with the untreated horses, but the mites were not eliminated from all the treated animals. Two further groups of horses were treated, one at a dose rate of 0.1 mg/kg daily for 10 days and the other with two doses of 0.2 mg/kg given two weeks apart. There were no statistically significant diffe...
Brouwer GJ.A total of 103 anaesthetic inductions were performed in horses for a variety of elective procedures. All cases were premedicated with acepromazine maleate (0.02 to 0.05 mg/kg body weight [bwt] intramuscularly [im]). In 50 cases (Group A) anaesthesia was induced by a single intravenous (iv) bolus of thiopentone sodium (11.1 mg/kg bwt or 1 g/90 kg bwt) followed immediately by a bolus of suxamethonium chloride (0.1 mg/kg bwt). In 53 cases (Group B) anaesthesia was induced using iv guaiacol glycerine ether (GGE) (approximately 50 mg/kg bwt) followed by a bolus of thiopentone at half the usual dose...
Mouncey R, Arango-Sabogal JC, de Mestre A, Verheyen K.The study aimed to (1) describe the use of reproductive therapeutics; (2) estimate the incidence of disease and injury; and (3) describe non-reproductive medications administered during pregnancy in Thoroughbred broodmares. A prospective birth cohort was established on seven farms across the UK and Ireland. Details of dams' signalment, breeding history, reproductive management during the breeding season(s) and veterinary-attended episodes of illness or injury and medication usage during gestation were retrieved retrospectively for 275 pregnancies in 235 mares over two breeding seasons. Results...
Lotfollahzadeh S, Mokhber-Dezfouli MR, Tajik P, Bokaie S, Watson DG.The present survey evaluated the use of prohibited substances cases in the first 2 years of medication regulation in horseracing in Iran so that the impact of these regulations on the level of positive cases over the period could be assessed. Objective: To determine the prevalence of positive tests for prohibited substances in horse races during 2 years of a drugs testing programme in Iran. Methods: A total of 656 horses that were winners or second in races were tested during the 2 year study. In the first year 354 horses (209 males and 145 females) and in the second year 302 horses (155 males...
Javsicas LH, Sanchez LC.Administration of omeprazole paste per os to healthy neonatal foals has been shown to effectively increase intragastric pH, but has not been evaluated in sick neonatal foals. Objective: To determine the effect of orally administered omeprazole paste on intragastric pH in clinically ill neonatal foals requiring nasogastric intubation. Methods: Intragastric pH was measured continuously for 24 h using an indwelling electrode and continuous data recording system in hospitalised neonatal foals age < or =2 days. Intragastric pH was measured for 12 h prior to (pretreatment period) and 12 h followi...
Fortier LA.Systemic therapies for joint disease may be prescribed when a single joint is involved or when multiple sites are affected. The precise therapeutic regimen recommended depends on the duration,cause, and site(s) of injury and is often an adjunct to intra-articular or supportive therapies. If the clinical signs of joint disease are acute and moderate in severity, nonsteroidal anti-inflammatory drugs are often administered to alleviate pain and inflammation. When aiming for more of a generalized maintenance or chondro-protective regimen, an alternative medication, such as hyaluronan,polysulfated ...
Nieto JE, Van Hoogmoed LM, Spier SJ, Vatistas NJ, Snyder JR, Timmerman BL.To use an extracorporeal circuit to evaluate effects of intraluminal distention on the jejunum of healthy horses. Methods: 2 jejunal segments from each of 5 horses. Methods: Jejunal segments were harvested and maintained in an extracorporeal circuit. One segment was subjected to distention (intraluminal pressure, 25 cm H2O) followed by decompression, and 1 segment was maintained without distention. The influence of distention-decompression on vascular resistance was calculated. Mucosal permeability was evaluated by measuring the clearance of albumin from blood to lumen. After distention and de...
Karns PA, Luther DG.In a survey of 13 Louisiana equine practices, it was determined that 366 of 3,316 horses developed adverse reactions following use of ivermectin, with 3 of the horses having more than 1 reaction. Almost all of the reactions were of minor to moderate concern; however, 1 death was reported. Three hundred and thirty-two (91% of all reactions) were reported as ventral midline pruritus or edema (10% of all doses). Fifteen (0.45%) were transient injection site swelling and/or stiffness. Eleven horses (0.33%) developed limb edema. Eyelid edema was reported in 4 horses (0.12%). Two horses (0.06%) had ...
Pirie RS, McGorum BC, Owen C, Carr O, Oakley H, McLachlan G.Despite frequent use of metered dose inhalers (MDIs) and spacers in equine practice, limited information exists on the efficiency of aerosol delivery using such devices. We determined the particle size distribution within an MDI-generated salbutamol aerosol delivered via an equine spacer using 'best practice' delivery technique and assessed the effect of variations in MDI use technique (shaking prior to each actuation, rapid repetitive actuations, and MDI angulation) on aerosol delivery efficiency. Under optimal conditions, only 53(±18) μg salbutamol per 100 μg actuation was delivered bey...
Tsujimura K, Yamada M, Nagata S, Yamanaka T, Nemoto M, Kondo T, Kurosawa M, Matsumura T.We investigated the pharmacokinetics of penciclovir after oral administration of its prodrug famciclovir to horses. Following an oral dose of famciclovir at 20 mg/kg, maximum plasma concentrations of penciclovir occurred between 0.75 and 1.5 hr (mean 0.94 + or - 0.38 hr) after dosing and were in the range 2.22 to 3.56 microg/ml (mean 2.87 + or - 0.61 microg/ml). The concentrations of penciclovir declined in a biphasic manner after the peak concentration was attained. The mean half-life of the rapid elimination phase was 1.73 + or - 0.34 hr whereas that of the slow elimination phase was 34.34 +...
Duvivier DH, Votion D, Vandenput S, Lekeux P.Inhalation therapy plays an increasing role in the management of equine respiratory disorders. This alternative to systematic treatment permits a high concentration of medication to act locally while minimizing side effects and residues. In human medicine, literature in this field is prolific and continuously renewed, whereas in veterinary medicine, applications of aerosol therapy are less extensive. This review considers the principles of action of the different types of devices used for inhalation, i.e., nebulization, metered-dose inhalation and dry powder inhalation, describes the technical...
Muir WW, McGuirk SM.The rational therapy of cardiovascular disease in horses requires a thorough knowledge of the pharmacology and pharmacokinetics of several specific drugs (digitalis, digoxin). Calcium solutions, dopamine, and dobutamine are frequently used to treat congestive heart failure in horses. Quinidine, procainamide, lidocaine, and propranolol are used to treat a variety of supraventricular and ventricular arrhythmias. Furosemide, a highly potent loop diuretic, is used to eliminate edema and promote diuresis. A thorough understanding of the applied pharmacology, dosage recommendations, toxicity, and pr...
Popot MA, Jacobs M, Garcia P, Loup B, Guyonnet J, Toutain PL, Bailly-Chouriberry L, Bonnaire Y.Tiludronate is a bisphosphonate drug marketed to treat different bone conditions in horses. Objective: The goal of this study was to measure the plasma concentrations of tiludronate in a population of race and sport horses under field conditions, and using pharmacokinetic population modelling, to estimate detection times for doping control. Methods: Prospective cohort. Methods: This study was conducted under field conditions on 39 race or sport horses diagnosed with bone conditions based on a lameness examination and treated with tiludronate. Each horse received 1 mg/kg of tiludronate (Tildren...
Deutsch J, Ekiri A, de Vries A.To compare alfaxalone as continuous intravenous (IV) infusion with intermittent IV injections for maintenance of anaesthesia in ponies undergoing castration. Methods: Prospective, randomized, 'blinded' clinical study. Methods: A group of 33 entire male Welsh ponies undergoing field castration. Methods: After preanaesthetic medication with IV detomidine (10 μg kg) and butorphanol (0.05 mg kg), anaesthesia was induced with IV diazepam (0.05 mg kg) followed by alfaxalone (1 mg kg). After random allocation, anaesthesia was maintained with either IV alfaxalone 2 mg kg hour (group A; n ...
Miller TR.Topical administration of drugs is the treatment of choice for diseases of the anterior segment. Drug levels attained by this means are usually of short duration, however, necessitating frequent therapy or continuous perfusion if prolonged drug levels are required. A drug-delivery device (collagen shield or contact lens) or subconjunctival injections can be used to augment topical therapy if frequent treatment is not possible. Subconjunctival injections are recommended for drugs that have low solubility and, hence, low corneal penetration. Retrobulbar injections are seldom indicated, except fo...
Bergstrom TC, Sakai RR, Nieto JE.A mare was euthanized because of gastric rupture secondary to complete duodenal obstruction by 2 bezoars located in the pylorus and proximal duodenum. Infrared spectroscopy showed that the bezoars were composed of psyllium. The mare had been receiving treatment with a pelleted psyllium product at 4 times the recommended dosage. Veterinarians should be aware that treatment of colic in horses with pelleted psyllium products could be associated with gastric impaction. Rupture gastrique catastrophique secondaire à des pharmacobézoards de psyllium en boulettes chez un cheval. Une jument a été e...
McReynolds CB, Yang J, Guedes A, Morisseau C, Garcia R, Knych H, Tearney C, Hamamoto B, Hwang SH, Wagner K, Hammock BD.There are few novel therapeutic options available for companion animals, and medications rely heavily on repurposed drugs developed for other species. Considering the diversity of species and breeds in companion animal medicine, comprehensive PK exposures in the companion animal patient is often lacking. The purpose of this paper was to assess the pharmacokinetics after oral and intravenous dosing in domesticated animal species (dogs, cats, and horses) of a novel soluble epoxide hydrolase inhibitor, EC1728, being developed for the treatment of pain in animals. Results: Intravenous and oral adm...
