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Topic:Pharmacokinetics
Pharmacokinetics in horses involves the study of how drugs are absorbed, distributed, metabolized, and excreted in equine species. This field of study provides insights into the time course of drug concentrations within the horse's body and helps in understanding the effects of various pharmaceuticals. Key parameters in equine pharmacokinetics include absorption rates, bioavailability, half-life, and clearance. These parameters can vary significantly due to factors such as age, breed, and health status of the horse. This page compiles peer-reviewed research studies and scholarly articles that explore the pharmacokinetic profiles of different drugs in horses, aiming to optimize dosing regimens and improve therapeutic outcomes in equine medicine.
Pharmacokinetics of sodium amoxicillin in horses. The pharmacokinetics of sodium amoxicillin were investigated after intravenous and intramuscular administration of a single dose of 15 mg kg-1 body-weight to five horses. A rapid distribution phase was noted after intravenous administration (t1/2 alpha about 20 minutes). The t1/2 beta values obtained after the intravenous and the intramuscular administration were significantly different (P less than 0.05). The bioavailability obtained was about 67 per cent. Plasma protein binding, evaluated in vitro, showed that the percentage of bound fraction was 37 to 38 per cent. It was concluded that sodi...
Pharmacokinetics of ticarcillin and clavulanic acid given in combination to adult horses by intravenous and intramuscular routes. The pharmacokinetics of ticarcillin and clavulanic acid following administration by the intravenous (i.v.) and intramuscular (i.m.) routes were investigated in six normal adult horses. Following i.v. administration, the ticarcillin disposition data conformed to a two-compartment model with an elimination half-life of 1.0 h. The disposition of clavulanic acid was described by a one-compartment model with an elimination half-life of 0.40 h. Following i.m. administration, the half-lives of both drugs were prolonged (ticarcillin 1.8 h, clavulanic acid 1.2 h). The bioavailability of ticarcillin was...
Determination of boldenone sulfoconjugate and related steroid sulfates in equine urine by high-performance liquid chromatography/tandem mass spectrometry. Sulfoconjugated anabolic steroids were separated by micro-bore high-performance liquid chromatography. The eluent was introduced into the atmospheric pressure ion source of the triple-quadrupole mass spectrometer via an ion spray liquid chromatograph/mass spectrometer interface operated in the negative ion mode. The limit of detection was 10 pg on-column by selected ion monitoring of the molecular ion and the response increased linearly over a concentration range of 2.4 orders of magnitude. Following work-up by a liquid-solid extraction procedure of equine urine samples, full-scan daughter ion...
Effect of induced synovial inflammation on pharmacokinetics and synovial concentration of sodium ampicillin and kanamycin sulfate after systemic administration in ponies. Single doses of sodium ampicillin (10 mg/kg) and kanamycin sulfate (5 mg/kg) were administered intramuscularly (i.m.) separately, and then together, to five pony mares. The plasma antibiotic concentration-time curves were constructed. The pharmacokinetic parameters of the antibiotics given separately were not altered by concurrent administration. Four of the five pony mares were then given the i.m. kanamycin/ampicillin combination 4 h after acute synovitis and fever had been induced by injection of lipopolysaccharide into the left intercarpal joint. The plasma concentration-time curves and the...
Enterohepatic circulation of lorazepam and acetaminophen conjugates in ponies. Adult female ponies (130-225 kg) with chronically implanted external biliary fistulas (T-tubes) participated in three-way cross-over studies using either i.v. lorazepam (10 mg) or acetaminophen (2 g), two model drugs biotransformed mainly by hepatic conjugative reactions. The objectives were to determine the systemic pharmacokinetics, urinary and biliary excretion and degree of enterohepatic circulation (EHC) of these compounds. Trial conditions were: A: EHC intact, with blood and urine, but not bile, collected after i.v. drug administration; B: EHC interrupted, with blood, urine and bile coll...
Probenecid infusion in mares: effect on para-aminohippuric acid clearance. Para-aminohippuric acid (PAHA, 0.1 mg/min/kg of body weight) was infused IV into 2 mares, followed by concurrent IV infusion of PAHA and probenecid (0.075, 0.15, 0.25, or 0.35 mg of probenecid/min/kg). Probenecid infusion reduced the clearance of PAHA at serum probenecid concentrations greater than 55 micrograms/ml. At 12-hour intervals, probenecid (in 5 repeated doses - 50, 75, 100, or 200 mg/kg) was administered by gavage to 2 mares. Mean serum probenecid concentration was greater than 55 micrograms/ml for all dosages. At dosages less than 200 mg/kg, accumulation of probenecid in the serum w...
Absorption of neomycin from the equine uterus: effect of bacterial and chemical endometritis. Plasma concentrations of neomycin were measured after intrauterine infusion of 3.3 mg/kg neomycin sulphate. Mares infected two hours previously with an intra-uterine infusion of beta-haemolytic streptococci absorbed approximately 12 per cent of the neomycin in both the oestrous and the luteal phases of the cycle. Normal mares in oestrus absorbed 6 per cent of the neomycin infused and luteal mares absorbed 56 per cent. In infected mares the peak plasma concentrations occurred two hours after neomycin infusion, earlier than in healthy mares. Cervical flushings after neomycin infusion in infected...
Pharmacokinetics of intravenously and intramuscularly administered ticarcillin and clavulanic acid in foals. Serum concentrations of ticarcillin and clavulanic acid were measured in healthy foals (2 to 6 months old) given the drugs in combination by intravenous and intramuscular routes of administration. Five foals were administered 50 mg of ticarcillin/kg of body weight and 1.67 mg of clavulanic acid/kg, IV. Five foals were administered 100 mg of ticarcillin/kg and 3.33 mg of clavulanic acid/kg, IV, and 4 of those 5 were given the same combined dose IM. The elimination half-life of ticarcillin for intravenous administration was 0.83 hour for the low dosage and 0.96 hour for the high dosage. After in...
The effect of oral L-carnitine supplementation on the muscle and plasma concentrations in the Thoroughbred horse. 1. L-carnitine was administered orally to thoroughbred horses for 58 days. 2. Acceptability and effects on plasma, muscle and urine concentration were studied. 3. Ten-60 g/day (as 2-3 doses) was acceptable with no deleterious effects. 4. One x 10 g L-carnitine significantly raised the plasma-free carnitine concentration (7 hr post) from 21.2 to 31.8 mumol/l; 2 x 30 g increased the mean to 36.5 mumol/l. 5. Plasma acetylcarnitine increased from approximately 1 to 5.5 mumol/l (7 hr post) on 2 x 30 g/day. 6. Muscle total carnitine was unchanged over 58 days. 7. Urinary output accounted for 3.5-7.5...
Effects of halothane anesthesia on the clearance of gentamicin sulfate in horses. Inhalation anesthetics decrease the clearance of some drugs that are eliminated by renal excretion. The purpose of the study reported here was to investigate the effects of halothane anesthesia on the pharmacokinetics and urinary excretion of gentamicin sulfate, using the horse as a model. Using a crossover design, pharmacokinetic values after a single IV dose of gentamicin (4 mg/kg) were compared in halothane-anesthetized and unanesthetized horses. Compared with unanesthetized horses, the anesthetized horses had significant decreases in total body clearance (P less than 0.01) and apparent vol...
The detection, pharmacokinetics and behavioral effects of diisopropylamine dichloroacetate (DADA) in the horse: a preliminary report. 1. Drug administration studies using diisopropylamine dichloroacetate (DADA) and diisopropylamine (DIPA) were conducted in Thoroughbred and Standardbred horses to assess physiological effects and develop detection methods. 2. Four horses received 0.08 mg DADA/kg body wt and showed no changes in heart and respiratory rates or body temperature as measured over a 1-hr period after administration. A transient diuretic effect was found to occur in 2 mares dosed with 0.80 mg DADA/kg body wt. 3. A qualitative detection method using thin-layer chromatography was developed to detect DIPA, the major met...
In vitro and in vivo binding of phenylbutazone and related drugs to equine feeds and digesta. In vitro and in vivo studies of phenylbutazone binding to equine ingesta and digesta were undertaken. In vitro binding to chopped hay and powdered pony nuts in buffer solutions at 37 degrees C was found to be time-, concentration- and pH-dependent. Percentage binding generally increased with time, decreased with concentration and varied with buffer pH in an unpredictable manner. Other non-steroidal anti-inflammatory drugs (NSAIDs) also bound to hay, the degree of binding being less for meclofenamate and least for flunixin in comparison with phenylbutazone. Phenylbutazone became bound to digest...
Plasma heparin values and hemostasis in equids after subcutaneous administration of low-dose calcium heparin. Different doses of heparin were given to equids SC to establish 0.05 to 0.20 U of heparin/ml of plasma. Plasma heparin values and antithrombin III activities were assayed, using chromogenic substrate methods. Activated partial thromboplastin and thrombin times were determined, using conventional coagulation assays. Tests were run every hour (or every 2 hours for antithrombin III) for 12 hours from 5 groups of 5 equids each after single injection of 40, 60, 80, 100, or 125 U of calcium heparin/kg of body weight and from 11 equids after injection of 150 U of calcium heparin/kg. The smaller dose ...
Evaluation of the potential for interference by dimethyl sulfoxide (DMSO) in drug detection in racing animals. Dimethyl sulfoxide (DMSO) had been postulated to be a 'masking agent' when used concurrently with therapeutic or prohibited drugs in racing animals. Eight drugs (flunixin, furosemide, caffeine, apomorphine, phenylbutazone, lidocaine, cocaine, and acepromazine maleate) were administered to six horses singly and with concurrent intravenous DMSO. Urine samples were analyzed for the presence of the drugs and/or their metabolites by thin layer chromatography. Direct comparison of thin layer chromatograms of extracts of positive urine samples with and without DMSO verified that DMSO did not interfer...
A pharmacokinetic study of phenobarbital in mature horses after oral dosing. The pharmacokinetics of phenobarbital were determined in six mature horses after a single oral dose. Horses were administered a 5.5 mg/kg of body weight oral dose of phenobarbital tablets. Based on the combined evaluation of i.v. and oral results, phenobarbital displayed two-compartment pharmacokinetics in the horse with a terminal half-life of 19.0 +/- 4.4 (mean +/- SD) h. This half-life is considerably shorter than those reported for dogs and humans. The steady-state volume of distribution (Vdss/F) and the total body clearance (Clt/F) of phenobarbital were 0.753 +/- 0.115 l/kg and 27.9 +/- 9...
Alpha- and beta-adrenergic receptors in the horse ureter. The presence of both alpha and beta adrenergic receptors in the caudal third ureter of the horse were studied in vitro under isometric conditions using adrenergic agonist and antagonist drugs. Isoprenaline and the beta 2- stimulating agent, salbutamol, elicited relaxation of the ureter smooth muscle strips. The responses were not affected by the beta 1- blocking agent, practolol, but were totally abolished by propranolol and the beta 2- blocking agent, butoxamine. The stimulation of alpha-adrenergic receptors with noradrenaline and phenylephrine evoked a contractile effect which was totally in...
Effect of ranitidine on gastric acid secretion in young male horses. Gastric cannulas were placed surgically in 5 young male horses. After a 2-week recovery period, horses were studied once a week. Horses were fasted for 24 hours, and gastric fluid output was collected for 5 continuous hours. Volumes were recorded every 15 minutes, and pH and hydrogen ion concentration were determined in an aliquot from each period. In 10 basal experiments, using 5 horses, volume, pH, and hydrogen ion concentration were continuously variable. Mean acid output was 45.1 +/- 2.02 microEq/15 min/kg (mean +/- SEM). In 6 experiments, using 3 horses, 0.5 mg of ranitidine/kg of body we...
In vitro febantel transformation by sheep and cattle ruminal fluids and metabolism by hepatic subcellular fractions from different animal species. Febantel and one of its main metabolites, febantel sulphoxide, are chemically modified to only a slight extent when incubated in vitro with sheep and cattle ruminal fluids; other major metabolites, fenbendazole and oxfendazole, are respectively, oxidized to oxfendazole and reduced to fenbendazole. Febantel is negligibly metabolized by hepatic cytosol fractions but microsome preparations effect more extensive metabolic transformations. Important differences in this respect were found between microsome preparations from rat, horse, pig, cattle, sheep, chicken and trout livers.
Pharmacokinetics of xylazine in ponies: influence of yohimbine. Twenty healthy ponies were given i.v. 1.1 mg/kg of xylazine from 2 manufacturers and the pharmacokinetic parameters calculated from the disposition curves. The disposition curves for the 2 commercial preparations were not different. Yohimbine, an antagonist of the pharmacologic effects produced by xylazine, did not alter the disposition of xylazine in the plasma. A single i.v. bolus of xylazine was completely described in 17 of 20 animals by the biexponential equation: Cp = 1.30e(-0.3955t) + 0.58e(-0.033t) where Cp represents the concentration of xylazine in the plasma at time t (min). The t1/...
Distribution of cephapirin into a tissue chamber implanted subcutaneously in horses. The pharmacokinetics of cephapirin sodium and its distribution into a tissue chamber implanted subcutaneously in the neck of mature horses are described. Cephapirin was administered as an intravenous bolus dose of 20 mg/kg. The serum concentration vs time curve was best described by a two-compartment open model. Cephapirin disappeared from serum rapidly (t1/2 beta = 18.8 min), and had only a modest volume of distribution (Vd(area) approximately equal to 346 mg/kg, Vd(ss) approximately equal to 204 ml/kg). Total clearance was also rapid (approximately equal to 13 ml/min.kg). Concentrations of t...
Pharmacokinetics of dantrolene sodium in horses. The pharmacokinetics of dantrolene sodium were investigated in horses following both intravenous (2 mg/kg) and intragastric (4 mg/kg) administration. Two ponies also received dantrolene sodium intravenously (2 mg/kg) in a pilot study to obtain preliminary kinetic data and to determine urinary and biliary excretion of the intact drug. Distribution and elimination of dantrolene was rapid, resulting in an elimination half-life of 129 +/- 8 (SEM) min and a whole body clearance of 4.16 +/- 0.52 ml/min/kg. Following intragastric administration, dantrolene rapidly acheived peak concentrations within ...
Immunoassay detection of drugs in horses. I. Particle concentration fluoroimmunoassay detection of fentanyl and its congeners. We investigated the use of particle concentration fluorescence immunoassay (PCFIA) as a technique for drug detection in racing horses. The test was constructed from an antiserum to a carboxyfentanyl-BSA conjugate and carboxyfentanyl linked to b-Phycoerythrin. Using these reagents and a PCFIA apparatus levels of fentanyl as low as 0.1 ng/ml could be detected by the assay. In addition, cross-reactivity studies on this assay showed that the anti-serum cross-reacted well with carfentanil, sufentanil and the methylated analogs of fentanyl. We therefore evaluated the ability of these agents to produ...
Analysis of detomidine in horse blood, plasma and urine samples utilizing a sensitive gas chromatography-mass spectrometry method. Chemical ionization- and electron impact ionization-selective ion monitoring provided a simple and sensitive method for measuring detomidine (Domosedan), a potent sedative-analgesic drug for horses and cattle. Chemical ionization was at least 10 times more sensitive than electron impact ionization. By using propranolol as an internal standard, we found that the recovery of detomidine from the extraction procedure used in this study was greater than 75% for plasma, whole blood, or urine samples. Approximately 68% of detomidine was bound to plasma protein and 53% was bound to red blood cells.
A review of the pharmacology and clinical uses of ivermectin. The avermectins were introduced in 1981 and constitute a potent new class of anthelmintic agents. They are naturally-derived products of microbial action displaying an exceptionally wide range of antiparasitic efficacy against internal and external parasites of domestic animals. This paper reviews their isolation and chemistry, mechanism of action, chemical efficacy and safety in cattle, sheep, swine, horses and dogs.
