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.
Quantitative methodology for corticosteroids based on chemical oxidation to electrophilic products for electron capture-negative chemical ionization using capillary gas chromatography-mass spectrometry. I. Assessment of feasibility in the analysis of horse urine for dexamethasone. Sensitive and specific methodology based on capillary column gas chromatography-electron capture-negative chemical ionization-mass spectrometry has been developed for the quantitative analysis of corticosteroids from biological fluids. The feasibility of this method is demonstrated in the quantitative analysis of dexamethasone in horse urine following administration of the drug. A structurally similar compound, 6 alpha-methylprednisolone, is added to the urine as an internal standard. The free dexamethasone and the internal standard are extracted and oxidized to high-electron-affinity 1,4-andr...
Effect of intra-articular gentamicin sulfate on normal equine synovial membrane. Gentamicin sulfate (3 ml; 50 mg/ml) was administered intra-articularly into 30 normal equine radiocarpal joints after arthrocentesis. Arthrocentesis alone was performed on 10 normal radiocarpal joints. Synovial fluid evaluations and gross and microscopic examinations were performed on synovial fluid and synovial membrane of designated joints at selected daily intervals over a period of 10 days. Synovial fluid from gentamicin-injected joints had greater turbidity, higher RBC and WBC counts, and higher refractive indices than did joints not injected with gentamicin. The largest increases develop...
Effects of verapamil on the smooth muscle of the horse urinary tract. The effects of verapamil, a calcium antagonist agent, were studied on smooth muscle preparations of the lower urinary tract of horses. Verapamil (2 X 10(-4) to 2 X 10(-8) M) relaxed the ureter, urethra and urinary bladder preparations contracted by potassium (127 mM), L-noradrenaline (2 X 10(-5) M), histamine (2 X 10(-5) M) and acetylcholine (2 X 10(-5) M). These results allow the conclusion that verapamil has a dose-dependent relaxing effect on smooth muscle of the lower urinary tract.
Effects of flunixin meglumine on cardiopulmonary responses to endotoxin in ponies. The effects of endotoxemia on cardiopulmonary parameters, before and after cyclooxygenase blockade, were determined in anesthetized ponies spontaneously breathing a mixture of halothane and 100% O2. Escherichia coli endotoxin was infused intravenously at 20 micrograms/kg for 1 h followed by 10 micrograms X kg-1 X h-1 the subsequent 4 h. By 15 min endotoxin increased mean pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), and alveolar dead space ventilation (VDA/VT), and these were followed by a return to base-line values by 30 min. A second increase in PVR occurred by 5 h ...
Effects of multiple intramuscular injections and doses of dexamethasone on plasma cortisol concentrations and adrenal responses to ACTH in horses. Adrenocortical function was assessed in horses given multiple IM doses of dexamethasone to determine the duration of adrenocortical suppression and insufficiency caused by 2 commonly used dosages of dexamethasone (0.044 and 0.088 mg/kg of body weight). Dexamethasone was administered at 5-day intervals for a total of 6 injections. Daily blood samples were collected. The plasma was frozen and later assayed for cortisol. An ACTH response test was determined 2 days before the first injection of dexamethasone and again 8 days after the last dexamethasone injection. Maximum suppression of plasma cor...
Effect of xylazine and ketamine on intraocular pressure in horses. Intraocular pressure was measured with a MacKay-Marg tonometer in eight horses following auriculopalpebral nerve block and topical application of lignocaine. Measurements were recorded before and after xylazine, 1.1 mg/kg intravenously, every two minutes for 16 minutes after administration of ketamine, 2.2 mg/kg intravenously, and after recovery from anaesthesia. Before xylazine, intraocular pressure was 17.1 +/- 3.9 and 18.4 +/- 2.2 mm Hg in the left and right eyes, respectively. Intraocular pressure tended to decrease after administration of xylazine and ketamine, with a significant decrease...
Visceral analgesia: effects of xylazine, butorphanol, meperidine, and pentazocine in horses. The visceral analgesic, cardiorespiratory, and behavioral effects induced by xylazine, butorphanol, meperidine, and pentazocine were determined in 9 adult horses with colic. Colic was produced by inflating a balloon in the horses' cecum. Heart rate, respiratory rate, mean arterial blood pressure, and cardiac output increased after cecal balloon inflation. Xylazine and butorphanol decreased the hemodynamic response to cecal balloon inflation. Meperidine and pentazocine had minimal effects on the cardiorespiratory changes induced by cecal balloon inflation. Xylazine produced the most pronounced ...
Enhanced biliary bilirubin excretion after heparin-induced erythrocyte mass depletion. The effect of large-dose heparin therapy on erythrocyte mass depletion in ponies was investigated to determine whether stimulation of reticuloendothelial cell activity and catabolic function would be evidenced by enhanced catabolism of heme to bilirubin. Ponies with chronic external biliary fistula were used to examine biliary excretion of bilirubin both before and after heparin loading (107 U/kg, IV, plus 320 U/kg, subcutaneously) and at maintenance dosages of 320 U/kg given (subcutaneously) at 12 and 24 hours after initial loading with heparin. Results indicated that by 48 hours after ponies...
Inhibitory effects of intravenous chloramphenicol sodium succinate on the disposition of phenylbutazone in horses. The effects of i.v. chloramphenicol sodium succinate on the pharmacokinetics of i.v. phenylbutazone in six healthy adult horses were investigated. Administration of chloramphenicol sodium succinate to mares reduced mean (+/- SD) phenylbutazone clearance from 0.600 +/- 0.222 to 0.339 +/- 0.123 ml/min per kg and increased mean (+/- SD) half life from 244 +/- 59.8 to 371 +/- 80.8 min and mean residence time from 333 +/- 86.2 to 533 +/- 124 min. The mean steady-state volume of distribution of phenylbutazone was unchanged, with mean (+/- SD) values of 187 +/- 28.9 ml/kg in control animals and 170 +...
Solubilization and characterization of [3H] 5HT high affinity binding sites (5HT1 and 5HT3). The solubilization of the serotonergic 5HT1 and 5HT3 sites was performed with digitonin and sodium cholate at 1% (final concentration). Two binding sites for [3H]5HT were observed on rat or horse brain synaptosomal membranes solubilized with these detergents. The corresponding dissociation constants (KD) were 1-3 nM and 13-30 nM respectively. These values were closely similar to those corresponding to 5HT1 and 5HT3 sites located in intact membranes. The solubilized sites specifically bound 5HT. The effect of GTP decreasing the binding to 5HT1 sites was lost on solubilized 5HT1 sites; it was re...
Immediate and long-term effects of halothane anesthesia on equine platelet function. The acute and long-term quantitative and qualitative effects of halothane anesthesia on equine platelet performance were studied in fourteen horses. Horses were anesthetized with only halothane in O2 for about 8.0 MAC hours. Platelet numbers declined during the anesthetic period but returned to normal within 24 h. Platelet aggregation was significantly diminished during the anesthetic period and for up to 4 days after anesthesia. A period of hyperaggregability occurred at the 7th day.
Anti-lipopolysaccharide toxin therapy for whole body X-irradiation overdose. Death in humans from ionising radiation overexposure in the 3-8 Gy (300-800 rad) range is in part due to the toxaemia caused by the entry of gram-negative bacteria and/or their lipopolysaccharide toxin (LPS) into the blood circulation through the walls of partially denuded gut. Anti-LPS hyperimmune equine plasma was evaluated for its ability to lower irradiation-induced lethality. Mice were irradiated with 6.3 Gy (630 rad) and six days later received equine Anti-LPS hyperimmune plasma, control plasma or saline. Mortalities in the three groups were 58%, 92% and 79% (p less than 0.01) respective...
Some dynamic and toxic effects of theophylline in horses. A single intravenous administration of theophylline as aminophylline at 10 mg/kg to four mares induced a diuresis in which maximal urine production was more than seven times the control volume. The diuretic effect was maximal within the first hour post-administration, and lasted approximately 6 h. Theophylline resulted in dose-related tachycardia, polypnoea and nervous symptoms (tactile, visual and auditory hypersensitivity, muscle tremor, sweating) in normal mares, but had only minor effects on arterial and central venous blood pressures, intrapleural pressure, red blood cell variables and pl...
Unusual response following use of succinylcholine in a horse anesthetized with halothane. A syndrome similar to malignant hyperthermia developed in a 545-kg Quarter Horse while anesthetized with halothane for cataract removal. Succinylcholine administration caused prolonged, severe muscle fasciculations followed by tachycardia, and an elevated blood pressure. Later, while the horse was still under anesthesia, its body temperature rose 2 degrees C, and respiratory acidosis developed. Myositis developed after surgery, but the horse recovered.
Total intravenous anaesthesia in the horse with propofol. The use of propofol, solubilised in a non-ionic emulsifying agent, for the induction and maintenance of anaesthesia in experimental ponies was assessed. Pilot studies revealed that premedication with xylazine (0.5 mg/kg bodyweight [bwt]) intravenously (iv) followed by propofol (2.0 mg/kg bwt) iv provided a satisfactory smooth induction. Two infusion rates (0.15 mg/kg bwt/min and 0.2 mg/kg bwt/min) were compared for maintenance of anaesthesia. An infusion rate of 0.2 mg/kg/min produced adequate anaesthesia in these ponies. Cardiovascular changes included a decrease in arterial pressure and card...
Cardiovascular and respiratory effects of acetylpromazine and xylazine on halothane-anesthetized horses. Circulatory and respiratory effects of intravenously administered acetylpromazine (0.033 and 0.067 mg/kg) and xylazine (0.5 and 1.0 mg/kg) were studied in drug cross-over fashion in eight laterally recumbent horses anesthetized only with halothane (1.06%, end-tidal) in O2. Both doses of acetylpromazine caused a significant and sustained elevation in cardiac output via a rise in stroke volume. Xylazine produced an initial significant fall in cardiac output followed by a return to control levels. Halothane anesthesia did not prevent xylazine-related atrioventricular conduction block. All treatme...
A hemodynamic model for anaphylactic shock. The treatment of cardiovascular collapse and anaphylactic shock is largely empiric. A simple animal model was developed to evaluate the hemodynamic alterations in anaphylaxis. Eight adult New Zealand white rabbits of both sexes were studied. All animals weighed 3.8 kg to 5.3 kg. Sensitization was accomplished with a 2-mL subcutaneous dose of horse serum followed in two days with a 2-mL intravenous (IV) dose. At least 14 days elapsed after the IV dose before a 1-mL challenge dose of horse serum was given. On the day of the challenge dose, a femoral arterial catheter, arterial temperature probe,...
Efficacy of furosemide in the treatment of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses. The repeatability of endoscopic observations of exercise-induced pulmonary hemorrhage (EIPH) and the efficacy of furosemide as a prophylactic treatment of horses with EIPH were studied in Thoroughbred race horses after consecutive breezes (at or near maximum speed, approx 16 m/s). Of 56 horses examined greater than or equal to 2 times, 21 (38%) had identical EIPH scores, whereas 26 (46%) and 9 (16%) had scores that differed by greater than or equal to 1 grade. In 56 nontreated horses, there was good agreement between 2 consecutive observations (K = 0.59, Z = 4.54, P less than 0.001). Similar c...
[An undesirable drug interaction in horses? Complications which can occur during the administration of coumarin derivatives and phenylbutazone]. A study of the literature was done because of questions asked in a court of justice concerning possible poisoning in a jumper, resulting from administration of both phenylbutazone and a coumarin derivative within a particular period. In view of the mechanisms of action and the pharmacokinetic characteristics of the agents, these forms of combined treatment are also highly inadvisable in horses.
[The treatment of podotrochilosis with oral anticoagulants. An instruction insert desired]. The anticoagulant, warfarin, has been reported to be effective as treatment for navicular disease in horses. Since other forms of treatment for this disease are palliative, this new anticoagulant therapy has become widely employed. Despite the fact that initiation of anticoagulant therapy is relatively simple, attending veterinary practitioners should be aware that careful monitoring of this therapy is required for both safety and efficacy. Navicular disease is an example of equine thrombotic disease, and the goal of warfarin therapy is the prevention of new thrombus formation, while at the sa...
Pharmacology and pharmacokinetics of drugs used to treat cardiac disease in horses. 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...
Effect of diuresis on urinary excretion and creatinine clearance in the horse. Endogenous creatinine clearance and renal excretion of phenylbutazone, osmotically active material, and compounds contributing to the urinary refractive index were studied in 12 Thoroughbred mares after no treatment, after water administration, or after furosemide administration. Urine was quantitatively collected, using urinary bladder catheters. On average, urine flow of the mares was 9 microliters/min/kg without treatment and increased to about 50 microliters/min/kg after water administration and to about 70 microliters/min/kg after furosemide administration. Water administration increased ...
Effects of dihydrotestosterone benzoate administration on gonadotropin secretion in ovariectomized pony mares. Eight long-term ovariectomized pony mares were treated with either dihydrotestosterone (DHT) benzoate (400 micrograms/kg body weight) in safflower oil or an equivalent amount of oil every other day for 21 d to determine the effects of DHT on follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations in blood samples drawn once daily and after administration of three successive injections of gonadotropin releasing hormone (GnRH). The GnRH injections were given at 4-h intervals on the day following the last DHT or oil injection. Treatment with DHT benzoate did not alter (P gr...