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Topic:Biological Half-Life
Biological half-life refers to the time required for a substance to decrease by half in its concentration within the body. In horses, understanding the biological half-life of various substances, such as medications, nutrients, or toxins, is important for determining dosing schedules, withdrawal times, and potential effects on equine health. The biological half-life can vary significantly depending on the substance in question, as well as factors such as the horse's metabolism, age, and health status. This page compiles peer-reviewed research studies and scholarly articles that explore the biological half-life of different substances in horses, examining factors that influence these rates and their implications for veterinary medicine and equine management.
Prolonged presence of isoxsuprine in equine serum after oral administration. 1. Isoxsuprine [1-(4-hydroxyphenyl)-2-(1-methyl-2-phenoxyethylamino)-1- propanol] serum concentrations after single- and multiple-dose administration to horse were investigated using immunoenzymatic ELISA, HPLC-UV and thermospray HPLC-MS methods. 2. Using HPLC-MS, isoxsuprine was detected up to 72 h after a single administration (1.2 mg/kg by gastric probe) and up to 96 h after the end of serial administration (1.2 mg/kg every 12 h for 7 days). 3. ELISA detected the drug up to 96 h after a single dose and up to 6 days after the end of prolonged administration. 4. Isoxsuprine is present in hors...
Measurement of gastric emptying of water in foals by impedance epigastrography. Impedance epigastrography was used to measure gastric emptying rates on two occasions in each of three foals. After smoothing of the raw data, emptying of water appeared to obey an exponential model. The mean emptying rate constant (SEM) was 0.171 +/- 0.038 min-1 (mean emptying half time 4.9 +/- 1.0 min).
Ampicillin and its congener prodrugs in the horse. Ampicillin is an antibiotic commonly administered to horses by both the intramuscular (i.m.) and the intravenous (i.v.) route. Its physicochemical properties restrict its absorption after oral administration and explain its rapid elimination from the body. To prolong the effects of ampicillin in the horse, attempts have been made to alter its elimination and absorption rates. The alteration of urinary pH did not change the plasma disposition of the antibiotic but when probenecid was administered concurrently with ampicillin, a significant reduction of total body clearance was achieved. Ampicil...
Effect of xylazine and ketamine on the pharmacokinetics of alfentanil during halothane anaesthesia. We measured plasma concentrations of alfentanil in two horses after three different randomly ordered treatments. Each horse received halothane in oxygen by mask followed by a bolus dose of alfentanil 60 micrograms kg-1 i.v., halothane in oxygen by mask followed by an i.v. alfentanil infusion for 120 min and xylazine and ketamine followed by halothane and a bolus dose of alfentanil 60 micrograms kg-1 i.v. Halothane was maintained at 1.05-1.07% end-tidal concentration with a PaCO2 of 6-7.3 kPa. The plasma concentration-time curves were similar after bolus and infusion doses of alfentanil with ha...
Concentration of ceftiofur metabolites in the plasma and lungs of horses following intramuscular treatment. Ceftiofur sodium, a broad spectrum cephalosporin antibiotic approved for veterinary use, is metabolized to desfuroylceftiofur which is conjugated to micro as well as macromolecules. Twelve horses, weighting 442-618 kg, were injected intramuscularly with a single dose of 2.2 mg ceftiofur/kg (1.0 mg/lb) body weight. Blood was collected at various intervals over 24 h after treatment. Three groups of four horses each were euthanized and lungs were collected at 1, 12, and 24 h after treatment. The concentration of desfuroylceftiofur and desfuroylceftiofur conjugates in the plasma and lungs was dete...
Kinetic evaluation of muscle damage during exercise by calculation of amount of creatine kinase released. To quantify the extent of muscle alteration during prolonged exercise, the release rate of creatine kinase (CK) from striated muscle was measured in six horses during a rest period (6 h) and during three exercise tests (15, 30, and 60 km) at a constant speed of 200 m/min. CK clearance was measured after intravenous bolus administration (150 U/kg) of a CK solution obtained from horse muscle. The CK steady-state volume of distribution was 0.059 +/- 0.0215 l/kg, the terminal half-life was 123 +/- 28 min, and the plasma clearance was 0.36 +/- 0.10 ml.kg-1 x min-1. After an intramuscular CK adminis...
Caffeine clearance in the horse. The pharmacokinetic properties of intravenously administered caffeine were studied in 10 horses using a commercially available automated enzyme immunoassay. The harmonic mean for the distribution half-life was 5.2 min (range 1.4-18.7). The harmonic mean for the elimination half-life was 10.18 h (range 6.82-20.92). The harmonic mean of the volume of distribution was 0.32 L/kg (range 0.22-0.53). There was no correlation between the dose of caffeine/kg body weight and the elimination half-life (Spearman's coefficient of rank correlation = 0.19).
Kinetics and haematological effects of erythropoietin in horses. A plasma kinetic study of erythropoietin (EPO) was carried out in 4 horses after subcutaneous administration (30 IU/kg bwt) of recombinant human erythropoietin (rhEPO). At standardized intervals for 48 h before injection and for 60 h post-administration, the EPO plasma levels were determined with an immunoradiometric assay based on a sandwich technique. The peak plasma concentration (30-113 mIU/ml) was observed after a delay ranging from 6 to 9 h post-administration and the drug levels reached a physiological value around 60 h following rhEPO injection. Moreover, reference values for plasma EP...
Pharmacokinetics of phenylbutazone in neonatal foals. Single doses (2.2 mg/kg of body weight) of phenylbutazone (PBZ) were administered IV to 6 neonatal horses (5 to 17 hours old at time of dosing). Plasma concentrations of PBZ and its metabolite oxyphenbutazone were monitored serially for 120 hours after drug administration. Pharmacokinetic variables were calculated, using 1- and 2-compartment open models. Descriptive equations from the best model for each foal were then used to derive model-independent variables describing PBZ disposition. Median volume of distribution at steady-state was 0.274 L/kg (range, 0.190 to 0.401 L/kg). Median terminal...
Pharmacokinetics of and serum thromboxane suppression by flunixin meglumine in healthy foals during the first month of life. Age and species reportedly affect the pharmacokinetic variables of nonsteroidal anti-inflammatory drugs. We determined the effect of age on flunixin pharmacokinetic variables in foals during the first month of life. We also estimated the physiologic activity of the drug in neonatal foals by determining the effect of flunixin on thromboxane production during clotting of blood taken from the foals. Flunixin disposition and clearance were determined after IV administration of 1.1 mg of drug/kg of body weight to 5 healthy foals when they were 24 to 28 hours, 10 to 11 days, and 27 to 28 days old. T...
Pharmacokinetics of metronidazole after rectal administration in horses. Five healthy adult mares and 1 gelding were given a single dose (15 mg/kg of body weight) of metronidazole per rectum. After manual evacuation of feces from the rectum, a suspension of crushed tablets and water (40 ml) was administered via a 28-F catheter advanced 30 cm into the rectum. Blood samples were obtained by jugular venipuncture, and metronidazole concentration was measured serially for the 14 hours after drug administration. Mean serum concentration of metronidazole peaked at 4.5 micrograms/ml, 0.83 hour after administration, and decreased to 0.38 microgram/ml, 14 hours after adminis...
Pharmacokinetic values of drugs frequently used in performance horses. Tables of values of pharmacokinetic variables (volume of distribution, total body clearance, and plasma elimination half-life) of drugs frequently administered to performance horses are accompanied by explanatory notes. Drugs described include the nonsteroidal anti-inflammatory drugs, corticosteroids, anabolic steroids, central nervous system-modifying drugs, respiratory system drugs, diuretics, local anesthetics, and antibacterial drugs.
The intramuscular bioavailability of a phenylbutazone preparation in the horse. The plasma concentrations of phenylbutazone (PBZ) and its major metabolites, oxyphenbutazone (OPBZ) and gamma-OH-phenylbutazone (OHPBZ) were determined for up to 72 h in six horses, following intravenous (i.v.) and intramuscular (i.m.) administration of 4 g phenylbutazone, 20 ml Phenylarthrite Ventoquinol (Vetoquinol Spécialités Pharmaceutiques Vétérinaires, Magny-Vernois, 70200 Lure, France). After i.v. dosing the plasma disposition was best described by a two-compartment open model. The hydroxylated metabolites OPBZ and OHPBZ were present in detectable concentrations for 72 h and 48 h, r...
Effects of concurrent administration of phenylbutazone and flunixin meglumine on pharmacokinetic variables and in vitro generation of thromboxane B2 in mares. Flunixin meglumine and phenylbutazone are nonsteroidal anti-inflammatory drugs commonly used for the management of colic, endotoxemia, and musculoskeletal disorders in equids. Although it is not usually recommended, there appears to be an increasing trend to use nonsteroid anti-inflammatory drugs in combination to enhance or prolong their effects. Therefore, we studied the effect of concurrent administration of flunixin (1.1 mg/kg of body weight, IV) as flunixin meglumine and phenylbutazone (2.2 mg/kg, IV) on the pharmacokinetics of each drug and on in vitro thromboxane B2 production. Pharmaco...
Species scaling of propafenone disposition and concentration–time relationships among eight mammalian species. Usually, smaller mammals have higher clearances per unit body mass than do larger mammalian species. When clearance and other pharmacokinetic parameters are correlated with internal physiological processes, species tend to dispose of drugs at a similar pace. The first application of this concept is pharmacokinetic time, expressed with different units: Kallynochron, Apolysichron, Dienetichron, and Syndesichron. The present work describes pharmacokinetic time in these units from data obtained with propafenone in eight animal species: mouse, rat, rabbit, dog, sheep, human, cow, and horse. Additio...
Oviductal and uterine influence on the development of Day-2 equine embryos in vivo and in vitro. The objective of this experiment was to contrast the influence of the oviductal and uterine environments on development of Day-2 embryos. Embryos were transferred to oviducts or uteri of synchronous recipient mares, or were incubated in oviductal co-culture, in uterine co-culture or in defined culture medium. Significantly more (P < 0.02) embryos transferred to the oviduct versus the uterus survived until Day 11 after ovulation (5 7 vs 0 7 , respectively). Significantly more (P 0.1) in oviductal co-culture versus uterine co-culture (3 7 vs 6 7 , respectively), or in oviductal co-culture ve...
Kanamycin concentrations in synovial fluid after intramuscular administration in the horse. Six adult ponies were injected in the same intramuscular site with kanamycin sulphate (10 mg/kg). Two hours later, arthrocenteses of the right metacarpophalangeal, radio-carpal, intercarpal, tibio-tarsal and metatarsophalangeal joints were performed within 3 minutes. Arthrocenteses of the same joints on the left side were conducted 5 hours later. When expressed as a percentage of plasma drug concentration, differences in synovial fluid drug concentration between the joints sampled at 2 and 5 hours after injection were not detected.
Disposition, bioavailability and clinical efficacy of orally administered acepromazine in the horse. The pharmacokinetics and pharmacological efficacy of orally (p.o.) administered acepromazine were studied and compared with the intravenous (i.v.) route of administration in a cross-over study using six horses. The oral kinetics of acepromazine can be described by a two-compartment open model with first-order absorption. The drug was rapidly absorbed after p.o. administration with a half-life of 0.84 h, tmax of 0.4 h and Cmax of 59 ng/ml. The elimination was slower after p.o. administration (half-life 6.04 h) than after i.v. injection (half-life 2.6 h). The bioavailability of the orally admini...
Clinical pharmacokinetics of amikacin in hypoxic premature foals. The pharmacokinetics of amikacin, administered iv at 7 mg/kg, every 8 h, were evaluated over the first 48 h of hospitalisation in 7 critically ill hypoxic premature foals and compared with those in 8 full-term nonhypoxic critically ill neonatal foals. The pharmacokinetic data were used to calculate dosage schedules that would maintain the plasma amikacin concentrations in individual foals within a target range of > or = 15 micrograms/ml but < 30 micrograms/ml for peak values and < or = 3 micrograms/ml for trough values. The results indicated a statistically significant increase in the...
Induction of ovulation and superovulation in mares using equine LH and FSH separated by hydrophobic interaction chromatography. Pharmacological control of reproduction in mares requires the use of equine gonadotrophins to avoid induced immunological resistance. Crude equine gonadotrophins (CEG) have been used but the presence of equine luteinizing hormone (eLH) and follicle-stimulating hormone (eFSH) in CEG has led to disappointing results in superovulation studies. Separation of eLH and eFSH activities from CEG is necessary to overcome this problem. The hydrophobic properties of the two hormones were sufficiently different to permit their separation by hydrophobic interaction chromatography (HIC) on a phenyl Sepharose...
Pharmacokinetics and metabolism of avermectins in livestock. The kinetics of avermectin disposition and metabolism in ruminant livestock and horses are reviewed with particular emphasis on the influence of route of administration and formulation on persistence of residues in tissues and excretion in faeces. Because information is not publicly available on other compounds in this class currently under development (e.g. moxidectin, doramectin), ivermectin only is considered. The biological half-life of ivermectin in plasma is similar in cattle and sheep but because of a larger volume of distribution, plasma clearance is more rapid in sheep. However, injec...
A liquid chromatographic procedure for the analysis of yohimbine in equine serum and urine. A standardbred mare was dosed with 40 mg yohimbine intravenously. Serum and urine samples were collected and analyzed for yohimbine using solvent extraction and reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. Maximum yohimbine concentrations of 45 and 18 ng/mL were observed in serum and urine samples, respectively. Elimination was rapid, with half-lives of approximately 20 and 53 min observed for serum and urine, respectively. The presence of yohimbine in these samples was confirmed by liquid chromatography/mass spectroscopy (LC/MS/MS).
Pharmacokinetics of cefotaxime in neonatal pony foals. Serum concentrations of cefotaxime and desacetylcefotaxime were measured in 1-week-old pony foals after IV administration of a single dose of cefotaxime. The cefotaxime disposition data conformed to a two-compartment model with elimination half-life of 0.60 hour. The combined cefotaxime and desacetylcefotaxime data was best described by a four-compartment model. The apparent half-life describing the disappearance of desacetylcefotaxime was 1.69 hours. Dosage of 40 mg/kg of body weight given IV every 4 to 6 hours for neonatal foals with gram-negative septicemia and every 2 hours for foals with ...
Pharmacokinetics and concentrations of ceftiofur sodium in body fluids and endometrium after repeated intramuscular injections in mares. Each of 5 healthy mares was given 5 consecutive IM injections of ceftiofur sodium (2 mg/kg of body weight; 50 mg/ml) at 12-hour intervals. Ceftiofur concentrations were measured serially in serum, synovial fluid, peritoneal fluid, and urine, and were measured in CSF and endometrial tissue after the fifth dose. Mean elimination rate constant was 0.354 +/- 0.101 h-1 and elimination half-life was 2.49 +/- 0.49 hour. Mean serum ceftiofur concentrations peaked approximately 1 hour after each injection. The highest mean ceftiofur concentration was 5.09 micrograms/ml at 1 hour after the fifth dose fo...
Pharmacokinetics and applications of ampicillin sodium as an intravenous infusion in the horse. A regime for administration of ampicillin sodium by continuous intravenous infusions to horses was designed. The aim was to achieve plasma ampicillin concentrations between 5 and 10 micrograms/ml over a 4-h period. A 2 mg/kg bodyweight loading dose of ampicillin sodium was administered intravenously at the beginning of the infusion in order to achieve steady-state plasma concentrations rapidly. The infusion system subsequently administered ampicillin at a rate of approximately 19.2 micrograms/min/kg bodyweight. The plasma concentrations obtained over the infusion period correlated very well wi...
Effect of surgical removal of endometrial cups on concentrations of chorionic gonadotrophin and subsequent fertility in the mare. Seven pregnant mares underwent general anaesthesia, laparotomy, hysterotomy and removal of a 50-day conceptus. Eversion of the uterine horn through the hysterotomy site allowed direct visualisation and electrosurgical removal of endometrial cup tissue from 5 randomly selected mares (Nos 1-5), while cup tissue in 2 mares (Nos 6 and 7) was left intact. Two pregnant mares served as unoperated controls (Nos 8 and 9). Efforts to re-establish pregnancy were initiated 20 days after surgery. Serum samples collected before surgery and during the post-operative period were analysed for concentration of ...
Pharmacokinetic profile of sulphamonomethoxine-trimethoprim in horses after intravenous, intramuscular and oral administration. The pharmacokinetic profile of a sulphamonomethoxine-trimethoprim (SMM-TMP) combination was investigated in five horses. The combination was administered intravenously, intramuscularly and orally at a constant dose of 20 mg SMM plus 4 mg TMP kg-1 bodyweight. Following intravenous administration both drugs dispersed rapidly with distribution half-lives of about 12 minutes for SMM and about 18 minutes for TMP. Elimination half-lives for intravenous, intramuscular and oral administration were closely similar, indicating that elimination was independent of administration route. Bioavailability of ...
Clearance of infused triglyceride by resting horses. 1. Clearance of infused lipid was observed in six mature resting horses, 2 to 6 hr after receiving a meal of alfalfa hay. 2. Intralipid, a 10% triglyceride emulsion, was infused at a rate of 0.2 ml/kg into the jugular vein. 3. Blood samples were obtained for 80 min post-infusion and assayed for plasma triglyceride concentration. 4. Clearance rate of the infused lipid was very slow (mean t1/2 = 269 min). 5. The clearance rate of the infused lipid in these horses was much slower than has been observed in other species. 6. The slow clearance of infused triglyceride in horses may suggest an inabil...
