Testing for drugs in horses

Drug testing today depends primarily on post-race urine testing, with blood testing and pre-race testing as adjuncts to the testing process. Drugs are extracted from urine by a process called liquid-liquid extraction, and then screened for the presence of illegal agents. Screening is generally done by Thin Layer Chromatography (TLC analysis). If a drug is detected in the screening process, its presence in the sample is confirmed by other chromatographic methods, and most especially by Gas Chromatography-mass Spectrometry (GC-MS.) The qualitative detection of drugs in forensic samples is a well worked-out art, and most drugs can be identified in blood or urine samples with a high degree of accuracy. Drugs can be quantitated in blood or urine with an accuracy of plus or minus 25% or more. Thesescientific determinations on a sample can be independently verified in referee samples, and form the scientific basis of the regulatory process of medication control.     

Pain management in horses and farm animals

Objective: This review discusses the different analgesic drugs and routes of administration used in large animals for acute pain management. General guidelines and doses are given to assist in choosing techniques that provide effective analgesia. Etiology: Noxious stimuli are perceived, recognized, and localized by specialized sensory systems located at spinal and supraspinal levels. Diagnosis: Localizing the source of the noxious stimulus as well as understanding the behavioral aspects and physiological changes that result from such insult is important to adequately diagnose and treat pain. Pain assessment is far from being definite and objective; not only are there species differences, but also individual variation. In addition, the behavioral and physiological manifestations vary with the acute or chronic nature of pain. Therapy: Pain management should include (1) selecting drugs that better control the type of pain elicited by the insult; (2) selecting techniques of analgesic drug administration that act on pathways or anatomical locations where the nociceptive information is being processed or originating from; (3) combining analgesic drugs that act on different pain pathways; and (4) provide the best possible comfort for the animal. Prognosis: Providing pain relief improves the animal's well being and outcome; however, interpreting and diagnosing pain remains difficult. Continuing research in pain management will contribute to the evaluation of the pathophysiology of pain, pain assessment, and newer analgesic drugs and techniques.     

Pre-purchase testing for drugs in horses: A review

The use of medications to mask defects of wind, limb or temperament in horses offered for sale can be a problem for purchasers, and for veterinarians performing pre-purchase examinations. Drugs which may be used in this way include the phenylbutazone-like drugs, cotricosteroids, local anaesthetics, and tranquilizers. If skillfully used, no signssuggestive of medication by these agents will be detectable by the examining veterinarian. In the absence of information on the medications status of an animal, the usefulness of a pre-purchase examination may be limited.These limitations can be circumvented by the analysis of blood or more expecially blood and urine samples from such horses. Current analytical methodology allows the detection of many medications in blood, and of virtually all significant medications if blood and urine samples are available. Such analysis, therefore, allows the veterinary practitioner to offer a significantly better pre-purchase test, and protects both the veterinarian and the purchaser.     

Antibodies to Berne virus in horses and other animals

After inoculation into 2 foals, Berne virus induced neutralizing antibody, but did not cause clinical symptoms. In a horizontal study of seropositive mares and their offspring, a decline of maternal antibodies and a sudden synchronous seroconversion in all foals were observed, again without clinical symptoms. The virus is widespread in the Swiss horse population and has been so during the last decade; rises in antibody titers were noted in 9% of paired sera sampled at random. Positive reactions were also obtained in serum neutralization tests and ELISA using small numbers of horse sera from Germany, France and the U.S.A. The results of neutralization tests and ELISA were correlated in 83% of random samples tested; 13% were neutralization-positive and ELISA-negative and in 4% the inverse was observed. Neutralizing activity was found in the sera of other ungulates (cattle, goat, sheep and pig), laboratory rabbits and 2 species of wild mice (Clethrionomys glareolus and Apodemus sylvaticus). Inconclusive results were obtained with feline and human sera; those from dogs and foxes (Vulpes vulpes) were consistently negative. The probable occurrence of antigenic variants in Berne-type viruses is discussed.     

Cardiovascular drugs. Their pharmacology and use in horses

Knowledge of the dosage, rate and route of administration, and potential side effects of drugs used to treat cardiac disease in horses has been refined. The judicious use of these drugs can increase exercise capacity, improve health, and potentially prolong life. Currently, antiarrhythmics (quinidine, lidocaine), positive inotropies (digoxin), and diuretics (furosemide) are the primary agents used to treat cardiovascular disease in horses. The development of newer drugs (verapamil, milrinone, bumetanide) and their usefulness in therapy for horses with cardiovascular disease require further investigation.     

Transdermal fentanyl combined with nonsteroidal anti-inflammatory drugs for analgesia in horses

This study investigated the pharmcokinetics, efficacy, and safety of the fentanyl transdermal therapeutic system (TTS) in horses in which there was an inadequate analgesic response to nonsteroidal anti-inflammatory drugs (NSAIDs) alone. Nine horses with pain that was refractory to therapeutic doses of phenylbutazone (n = 3) or flunixin meglumine (n = 6) subsequently also received between 39 and 110 microg/kg of transdermal fentanyl. Blood samples were collected at 0, 1, 2, 3, 4, 5, 6, 12, 24, 36, 48, 60, and 72 hours after patch application, and a radioimmunoassay was used to determine serum fentanyl concentrations. Pharmacokinetic values were determined by noncompartmental analysis. Physical examination findings were recorded in all horses, and pain and lameness grading systems were used to assign scores to 8 and 6 horses, respectively. All horses tolerated the administration of fentanyl TTS, in that no clinically significant adverse effects attributable to fentanyl were observed. Use of the TTS resulted in variable serum concentrations of fentanyl, with a peak serum concentration of 2.2+/-1.1 ng/mL (mean+/-SD) and a time to peak serum concentration of 26+/-13 hours. After transdermal fentanyl administration, mean time to reach serum fentanyl concentrations consistent with analgesia in other species (1 ng/mL) was 14 hours. In addition, serum fentanyl concentrations of 1 ng/mL or greater were maintained in all but one horse for at least 18 hours. Pain scores were significantly decreased after fentanyl TTS and NSAID administration (P < .05), but lameness scores were not significantly different (P > .05). Overall, administration of fentanyl TTS had a favorable pharmacokinetic profile in horses with clinical pain, and the fentanyl TTS in combination with NSAIDs appeared to provide safe and effective analgesia in most of the horses with pain that was refractory to NSAID therapy alone.     

Nonsteroidal anti-inflammatory drugs: a review. New applications in hypersensitivity reactions of cattle and horses.

Nonsteroidal anti-inflammatory drugs inhibit the biosynthesis of kinins and prostaglandins and stabilize leukocyte lysosomal membranes. Nonsteroidal anti-inflammatory drugs also weakly block the biosynthesis of histamine and serotonin, and pharmacologically antagonize kinins, prostaglandins and slow-reacting substance of anaphylaxis. Nonsteroidal anti-inflammatory drugs effectively control both cardiovascular and respiratory manifestations of hypersensitivity in cattle and horses. This, coupled with the contrasting lack of effectiveness of "antiamine" drugs, suggests that bio-amines such as histamine and serotonin (5-hydroxytryptamine) may be less important than kinins, postaglandins and slow-reacting substance in the mediation of the hypersensitivity/inflammatory reaction, at least in cardiopulmonary systems of these species. Nonsteroidal anti-inflammatory drugs justify more prominence in the clinical control of acute respiratory disease in domestic herbivores.     

Potential competitive interactions between feral horses and other grazing animals

The potential impacts on vegetation and watersheds in the western U.S. by feral horses are discussed. Feral horses select open habitats with relatively large amounts of grass. Horse dietsare largely grasses but shrubs are used in some areas. Utilization levels are proportional to animal numbers but equivalent numbers of horses may consume more than cattle because of differing digestive physiology. Predicted vegetation changes under heavy feral horses use may result in range dominated by unpalatable shrubs. Watershed conditions would probably not change except underheavy use by horses when soil compaction, soil disturbance and fouling of water holes could result.     

Rational selection of antimicrobial drugs for treatment of infections of horses

The goal of antimicrobial drug use is quite specific. Consideration of many microbe-related, host-related, and drug-related factors is necessary for appropriate selection and use of antimicrobial drugs in equine patients. The concepts and data presented in this article demonstrate that fact. At the risk of oversimplification, "The bug denotes the drug, and the horse directs the course."