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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.
Scanning electrons and light microscopy of the equine seminiferous tubule. Changes within the equine seminiferous tubules during the cycle of the seminiferous epithelium were studied light and scanning electron microscopy (SEM). Once observed with SEM, tubules were sectioned and staged using light microscopy. As viewed by SEM, the weblike, spongy cytoplasm of germ cells or Sertoli cells in stages I and II extended over the entire height of the germinal epithelium. The cytoplasm of the basal portion of the germinal epithelium in stages III to VIII was similar to that in stages I and II. However, the cytoplasm which occupied the luminal third of the epithelium in stage...
Physicochemical and biological characterizations of pregnant mare serum gonadotropin and its subunits. Pregnant mare serum gonadotropin and its subunits have been further characterized. Ultracentrifugation of the gonadotropin at pH 1.3 and 11.5 showed little evidence of dissociation compared to pH 8.2. Highly purified subunits are obtained by urea dissociation and ion-exchange chromatography followed by gel-filtration. Circular dichroism spectra of the gonadotropin and its subunits are much like those of ovine lutropin and its subunits in that there is little evidence for secondary structure and one or more tyrosine residues are inaccessible in the intact gonadotropin compared to the subunits. ...
Therapeutic use of gentamicin in horses: concentrations in serum, urine, and synovial fluid and evaluation of renal function. Serum, synovial fluid, and urine concentrations of gentamicin were measured in normal mature horses which had been given a single dose of the drug. Mean peak serum concentration (16.8 microgram/ml) occurred in horses 30 minutes after they were given a single intramuscular dose of 4.4 mg of gentamicin/kg of body weight. In horses given a smaller dose of gentamicin (1.7 mg/kg), mean peak serum concentrations of gentamicin (10.2 microgram/ml) appeared at 1 hour. Synovial fluid concentration was maximum at 2 hours for both doses; in horses given the larger dose, mean peak concentration was 6.4 mic...
The urinary excretion of synthetic corticosteroids by the horse. A radioimmunoassay method has been developed that enables the administration of therapeutic doses of synthetic corticosteroids to be detected in horse urine. Fourteen proprietary preparations of these steroids have been given by intramuscular injection to ponies and thoroughbreds. The administration of some preperations could still be detected six days after a single intramuscular injection of a therapeutic dose. The route of injection of dexamethasone-21-sodium phosphate, whether intramuscular, intravenous or intra-articular, did not appear to alter the length of time over which the steroid o...
A review of drug “clearance times” in racehorses. A review is presented of published and some unpublished work dealing with aspects of drug clearance from horses. This work includes plasma half-lives and urinary clearance times for specified drugs, as well as a consideration of more general factors likely to influence these values. The review is presented primarily as a guide to the veterinary surgeon in practice, to assist in the drug therapy of horses without contravening the Rules of Racing relating to doping.
[Studies on the effects of intravenous administration of glucose, fructose, invertose and sorbitol on various blood constituents of blood plasma (monosaccharides, insulin, lactate, pyruvate and free fatty acids as well as glutamate-oxaloacetate transaminase) in the horse]. Horses were examined for the behaviour of various blood constituents prior to and following infusions of solutions of glucose, fructose, invertose, and sorbitol. Infusion of 0.5 g/kg live weight glucose to six horses was followed by half-life variation between eleven and 23 minutes. Subsequent infusion of invertose to the same animals usually caused prolongation of glucose half-life. Half-life values were between 17 and 33 minutes for fructose and between 21 and 80 minutes for glucose. Infusion of 0.5 g/kg live weight fructose to two horses was followed by half-life values between 17 and 18 mi...
Drug interactions in the horse: effects of chloramphenicol, quinidine, and oxyphenbutazone on phenylbutazone metabolism. The plasma half-life of phenylbutazone in horses was not increased after pretreatment with chloramphenicol or quinidine, but was increased after oxyphenbutazone. This increased plasma half-life after oxyphenbutazone is consistent with observations in other species and suggests that oxyphenbutazone inhibits the metabolism of phenylbutazone in horses. Lack of inhibition of phenylbutazone metabolism in the horse by chloramphenicol and quinidine is inconsistent with results obtained in other species.
Pharmacology of procaine in the horse: procaine esterase properties of equine plasma and synovial fluid. Procaine added to whole equine blood or diluted plasma was hydrolyzed with half times of approximately 9 and 12 minutes, respectively, at 37 C. This hydrolytic activity was sensitive to heating and physostigmine, but did not affect procainamide. At pharmacologic concentrations of procaine, the rate of the hydrolytic reaction depended directly on the concentrations of plasma or procaine in the system and was less in whole blood than in plasma. These properties are consistent with hydrolysis being due to plasma esterases operating at less than saturating procaine concentrations. These esterases ...
Drug interactions in the horse: effect of furosemide on plasma and urinary levels of phenylbutazone. Horses pretreated with 6.6 mg/kg of phenylbutazone were injected with 1 mg/kg of furosemide intravenously. Furosemide had no clinically significant effect on either plasma levels or plasma half-life of phenylbutazone. Furosemide reduced urinary levels of phenylbutazone 18-fold to concentrations which may result in inconsistent drug detection in routine screening tests. The results show that it is not possible to monitor compliance with phenylbutazone medication rules by means of urinalysis alone if the use of furosemide is permitted. Furosemide treatment, however, does not interfere with monit...
A review of the pharmacology, pharmacokinetics and behavioral effects of procaine in thoroughbred horses. Since procaine has both local anaesthetic and central stimulant actions its presence in the blood or urine of racing horses is forbidden. After rapid intravenous injection of procaine HC1 (2.5 mg/Kg) in thoroughbred mares plasma levels of this drug fell rapidly (t 1/2 alpha = 5 min) and then more slowly (t 1/2 beta = 50.2 min). These kinetics were well fitted by a two compartment open model (Model I). This model gave an apparent Vdbeta for procaine in the horse of about 3,500 litres. Since procaine was about 45% bound to equine plasma protein this gives a true Vdbeta for procaine of about 6,50...
The excretion of ibuprofen by the horse – a preliminary report. The anti-inflammatory drug Ibuprofen [(+/-)-2-(p-isobutylphenyl) propionic acid] was estimated in the blood and urine of a horse using gas-liquid chromatography of the silylated derivative. Levels of the drug in the two body fluids were measured over a period of about 24 hours after administering a 12 gm dose of Ibuprofen. Plasma peak levels were observed within 30 to 60 min, and the drug was no longer detectable in the plasma by 8 hr. Urinary peak levels were observed 200 to 300 min after dosing, and the drug was no longer detectable in the urine by about 28 hr. It was observed that only 2% t...
Pharmacology of procaine in the horse: a preliminary report. Rapid intravenous injection of 1 g of procaine hydrochloride in Thoroughbred mares produced variable signs of central nervous system excitation for as long as 4 minutes. Plasma concentrations of procaine were similarly variable and transient, decreasing with a half-life of approximately 25 minutes. In vitro, plasma from freshly collected equine blood hydrolyzed procaine with a half-life of approximately 7.5 minutes. This hydrolysis was apparently due to plasma esterases. Penicillin, when added free or complexed as procaine-penicillin, did not protect procaine against hydrolysis by these plasma...
Mefanamic acid blood and urine levels in the horse determined by derivative gas-liquid chromatography-electron capture. Mefenamic acid is extracted from biological fluids and is acylated with pentafluoropropionic anhydride to form a derivative possessing high electron affinity. The derivative is analyzed by gas-liquid chromatography with an electron capture detector. The method is particularly valuable for determining drug levels in blood where small sample and/or drug concentrations are available.
Studies on metabolism and effects of estrogen on pituitary prolactin and LH secretion. The effect of a subcutaneous injection of estradiol on the secretion of pituitary prolactin in the rat and the relationship between serum estradiol level and luteinizing hormone (LH) secretion in mare were reviewed. In addition, the effect of estradiol injection on LH secretion and the metabolism of [14C] estradiol in intact and bile duct fistulated pony mares were studied. Low (0.1 mug/day/rat) to moderate dose (5 mug/day/rat) of estradiol benzoate injected subcutaneously to mature or immature rats significantly increased pituitary content of prolactin and serum prolactin level five- to tenfo...
Comparison of the pharmacokinetics of penicillin G and ampicillin in the horse. The affinity and the binding capacity of horse serum proteins for ampicillin and penicillin G were measured by equilibrium dialysis or ultrafiltration technique. From the figures thus obtained it may be concluded that in the range of therapeutic concentrations the protein-bound fraction accounts for 6 X 8-8 per cent of the total ampicillin concentration and for 52-54 per cent of the total penicillin G concentration in serum. The rate of elimination of ampicillin and penicillin G in horses was assessed by following serum concentrations after a single intravenous injection. The biological half l...
Muscle structure and function–an explanation. The structure of vertebrate skeletal muscle is reviewed. The mechanism of muscular contraction and its control is then discussed from the point of view of molecular structure. Contraction takes place by a sliding filament mechanism produced by cross-bridges which form between thick and thin filaments. Control is exercised by tropomyosin and troponin. When the calcium concentration is low, these proteins interfere with the formation of cross-bridges and prevent contraction, but when the calcium concentration is increased, they no longer interfere and contraction proceeds.
Pharmacological experiments as a basis for the administration of digoxin in the horse. It is shown that the concentration of ouabain necessary for 50 per cent inhibition of the Na+K activated membrane ATPase of red cells is similar in man and horse. This is taken to indicate that the two species have similar sensitivity towards cardiac glycosides in general. In five adult healthy horses plasma digoxin concentration was measured with a radioimmunoassay technique after a single intravenous injection of 1 mg/100 kg body weight digoxin. The half time of elimination was 23 h and the apparent volume of distribution 7.3 litres/kg. An approximate estimate of plasma protein binding of di...
Plasma concentrations, plasma protein binding and residues of sulfamonomethoxine in pigs, horses and cattle. The protein binding, the plasma half-life and the residue depletion of sulfamonomethoxine (SMM) after intramuscular administration were investigated in pigs, horses and cattle. Protein binding was weakly concentration-dependent. The bound fraction in plasma in the therapeutic range amounted to approximately 45, 40 and 50% for pigs, horses and cattle respectively, and the plasma half-lives were approximately 5.1, 5.7 and 3.1 hours respectively. SMM levels were less than 1 mug/g in muscle tissue after 36, 20 and 12 hours in pigs, horses and cattle respectively. In the kidney SMM levels were not ...
Immunoglobulin metabolism in the neonatal foal. The proteins IgG and IgG(T) are the predominant immunoglobulins in equine colostrum. Their distribution and catabolism were studied in the newborn foal using an isotopic tracer technique. More precise quantitation of the absorption of these immunoglobulins from colostrum is now possible.
Effect of exogenous progesterone on its endogenous levels: biological half-life of progesterone and lack of progesterone binding in mares. The disappearance rate of progesterone from blood plasma of an ovariectomized mare was rapid and occurred in three phases. The half-life of the first component was 2-5 min and that of the second was 20 min; the half-life of the much slower third component was not measured. Progesterone, administered to ovariectomized and deeply anoestrous mares at the rate of 150 or 300 mg/day, maintained maximal peripheral levels of 6 to 8 ng/ml. Physiological levels were reached in 21 days using a dose of 150 mg and in 11 days with 300 mg daily. After withdrawal, circulating levels dropped rapidly. Blood pla...
Plasma LH levels in the mare during the oestrous cycle. Plasma levels of LH were determined by heterologous radioimmunoassay utilizing highly purified equine LH as standard. Samples were taken regularly from eleven mares for twenty-six oestrous cycles over a period of 10 weeks. The mean cycle length was 20-5 +/- 3-1 (S.D.) days, and ovulation occurred on average 4-3 +/- 1-6 (S.D.) days from the time heat was first detected. Levels of LH were persistently low from Days 5 to 16 of the cycle (ovulation = Day 0). They then increased slowly over a number of days and continued to rise beyond the levels observed at any time during the immediate preovulato...
Relationship between luteal function and metabolic clearance and production rates of progesterone in the mare. The functional activity of the equine CL was measured by its ability to convert [4-14C]3beta-hydroxy-5-en-20-one to [4-14C]pregn-4-en-3,20-dione. The capacity of homogenates of CL of different ages followed the temporal pattern of plasma progestagen concentrations. In ten mares which ovulated twice at intervals of 0 to 9 days in the same cycle, the conversion capacity of the CL from the second ovulation was similar to that from the first ovulation. After adjusting for age, the CL from the first of two ovulations had a similar conversion capacity as that resulting from a single ovulation. Plasm...
