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.
The pharmacokinetics, pharmacological responses and behavioral effects of acepromazine in the horse. After intravenous (i.v.) injection, acepromazine was distributed widely in the horse (Vd = 6.6 litres/kg) and bound extensively (greater than 99%) plasma proteins. Plasma levels of drug declined with an alpha half-life of 4.2 min, while the beta phase or elimination half-life was 184.8 min. At a dosage level of 0.3 mg/kg acepromazine was detectable in the plasma for 8 h post dosing. The whole blood partitioning of acepromazine was 46% in the plasma phase and 54% in the erythrocyte phase. Penile prolapse was clearly evident at doses from 0.01 mg/kg to 0.4 mg/kg i.v., and the duration and extent...
Body fluid concentrations of ampicillin trihydrate in 6 horses after a single intramuscular dose. Six adult mares were given a single dose of ampicillin trihydrate (250 mg/ml) intramuscularly at a dosage of 20 mg/kg body weight. Serum, synovial fluid, peritoneal fluid and urine ampicillin concentrations were measured serially over a 48 h period. The mean peak serum ampicillin concentration was 2.49 micrograms/ml at 6 h. Ampicillin was found in synovial fluid and peritoneal fluid, which obtained mean peak ampicillin concentrations of 1.65 micrograms/ml and 1.81 micrograms/ml at 6 h and 4 h respectively. These concentrations declined in parallel with serum concentrations and were still detec...
Plasma and tissue concentrations of oxytetracycline in the horse after intravenous administration. Oxytetracycline (OTC) was administered IV to 3 clinically normal horses at a dosage of 10 mg of OTC/kg of body weight. Plasma OTC concentrations were determined at 30-minute intervals until postinjection minute (PIM) 240. At PIM 240, the mean OTC concentration in pulmonary tissue was 3.96 microgram/g of tissue (wet weight) and in renal tissue was 25.47 micrograms/g. diluted bronchial fluid had a mean concentration of 0.288 microgram of OTC/ml at PIM 240. The data demonstrated that OTC has adequate tissue distribution in horses.
The pharmacokinetics of some aminoglycoside antibiotics in the horse. The disposition kinetics and bioavailability of streptomycin, kanamycin and neomycin were determined following their administration as parenteral preparations to horses. Single doses (10 mg/kg) of each aminoglycoside were given by the intravenous (i.v.) and intramuscular (i.m.) routes and, at a later time, seven intramuscular doses were injected at 12-h intervals. The pharmacokinetic behaviour of the three aminoglycosides was similar, in that a rapid distribution phase was followed by a relatively short half-life. The half-life (mean +/- SD, n = 6) of kanamycin (1.80 +/- 0.17 h) was significan...
Serum concentrations of trimethoprim and sulfadiazine following oral paste administration to the horse. Two fasted and 2 fed horses were dosed orally with a combined trimethoprim and sulfadiazine paste formulation at a dose of 35 mg (1:5 combined active ingredients)/kg. Serum concentrations of each drug were determined periodically for 3 consecutive days for the 4 horses. The extent and rate of absorption for trimethoprim were variable, but peak serum concentrations occurred generally within 3 hours; sulfadiazine absorption was slower, reaching peak concentrations by 6 hours. Fasting did not have a consistent effect on the serum concentration profiles for either drug. Both drugs achieved serum c...
Kanamycin sulfate in the horse: serum, synovial fluid, peritoneal fluid, and urine concentrations after single-dose intramuscular administration. Six healthy adult mares were given a single dose of kanamycin sulfate (200 mg/ml) IM at a dosage rate of 5 mg/kg of body weight. Kanamycin concentrations in serum, synovial fluid, peritoneal fluid, and urine were measured serially over a 48-hour period. The mean peak serum kanamycin concentration was 12.55 microgram/ml at 1 hour. Mean peak kanamycin concentrations in synovial fluid and peritoneal fluid were 7.25 microgram/ml and 9.27 microgram/ml at 2 hours and 3 hours, respectively. These concentrations decreased steadily in parallel with serum concentrations and were still measurable at 48 h...
Sodium oxacillin in the horse: serum, synovial fluid, peritoneal fluid, and urine concentrations after single-dose intramuscular administration. Six healthy adult mares were given a single dose (25 mg/kg of body weight) of sodium oxacillin IM. Oxacillin concentrations in serum, synovial fluid, peritoneal fluid, and urine were measured serially over a 48-hour period. The mean peak serum oxacillin concentration was 9.75 microgram/ml at 0.5 hour after injection. Mean peak oxacillin concentrations in synovial and peritoneal fluids were 1.45 microgram/ml and 2.60 microgram/ml at 1 hour and 2 hours, respectively. These concentrations decreased in parallel with serum values and were not measurable at 48 hours. Urine concentrations of oxacilli...
Pharmacology of narcotic analgesics in the horse: quantitative detection of morphine in equine blood and urine and logit-Log transformations of this data. Morphine was detected in equine biological fluids by a combination of liquid-liquid extraction and column chromatography, followed by derivatization and gas-liquid chromatographic assay, using electron capture detector. Recovery of morphine from the equine biological samples was poor. However, despite an overall recovery of less than 20%, this method had a detection limit of 0.2 ng/ml. Addition of 5,000 U of bovine liver beta-glucuronidase/ml of urine enabled detection of the drug in urine for up to 144 hours after horses were given 0.1 mg of morphine/kg of body weight. Morphine was found for ...
Immunochemical and biological properties of horse parathyroid hormone. No abstract available
Pharmacokinetics of a single, orally administered dose of digoxin in horses. Digoxin (elixir, 0.022 mg/kg) was administered via stomach tube to healthy horses of mixed breeding and sexes. Serum digoxin concentrations reached a peak (2.21 +/- 0.6 ng/ml) at approximately 1 hour after dosing and had a half-life of 28.8 +/- 10.7 hours. Digoxin kinetics followed a triexponential curve, indicating that at least a 2 compartmental model is required to characterize the serum concentration-time curve after this route of administration. It was calculated that to achieve average serum concentrations of 1.1 ng/ml, an oral dose of 17.4 microgram of digoxin elixir/kg/day and an IV do...
Pharmacokinetic analysis of intravenously and orally administered quinidine in horses. A pharmacokinetic study was made, using 7 healthy adult horses (weighing between 400 and 560 kg) given quinidine gluconate IV and quinidine sulfate orally. The apparent volume of distribution of quinidine base was 3.10 +/- 0.79 L/kg, total body clearance was 5.49 +/- 2.40 ml/minute/kg, and plasma half-life was 6.65 +/- 3.00 hours. The systemic availability of quinidine sulfate after oral administration of a 10 mg/kg dose was 48.5 +/- 20.4%. Oral administrations of quinidine sulfate in doses of 10 mg/kg and 10 g produced peak plasma concentrations of 0.79 microgram/ml at 146 minutes and 1.47 mi...
The pharmacokinetics of xylazine hydrochloride: an interspecific study. The pharmacokinetic disposition of xylazine hydrochloride is described after both intravenous and intramuscular injection of a single dose, in four domestic species: horse, cattle, sheep and dog, by an original high performance liquid chromatographic technique. Remarkably small interspecific differences are reported. After intravenous administration, systemic half-life (t1/2 beta) ranged between 22 min (sheep) and 50 min (horse) while the distribution phase is transient with half-life (t1/2 alpha) ranging from 1.2 min (cattle) to 5.9 min (horse). The peak level of drug concentration in the pla...
The pharmacokinetics of meclofenamic acid in the horse. The pharmacokinetics of meclofenamic acid were studied in Thoroughbred horses and in ponies. After intravenous (i.v.) administration of either 2 mg/kg or 4 mg/kg sodium meclofenamate the elimination half-life was of the order of 0.9 h while the volume of distribution was found to be 0.128 litre/kg. Elimination was in accordance with a one-compartment model. Following oral administration of either meclofenamic acid (4 mg/kg) or sodium meclofenamate (4 mg/kg) a much longer terminal half-life than that calculated for Kel from i.v. data was found. This anomaly indicated that the 'flip-flop' phenom...
Pharmacokinetics and behavioral effects of methylphenidate in Thoroughbred horses. In horses given (rapid IV) methylphenidate (Ritalin, alpha-phenyl-2-piperidinacetic acid methyl ester; 0.70 mg/kg), plasma concentrations of the drug decreased rapidly at first, with an apparent alpha half-life of about 19 minutes, and then more slowly, with an apparent beta half-life of about 2.4 hours. These data were well fitted by a 2-compartment open model. In blood, about 40% of the methylphenidate present was in the plasma fraction, and of this, about 80% was plasma-protein bound. If given by subcutaneous or IM injection, plasma concentrations of methylphenidate peaked in about 1 hour a...
Intravascular neutrophilic granulocyte kinetics in horses. Intravascular granulocyte kinetics in 4 healthy horses were determined with chromium-51 as the cell label. The disappearance rate of labeled granulocytes was an exponential function. Mean total blood granulocyte pool (+/- 1 SD) was 5.65 +/- 1.514 X 10(8) granulocytes/kg of body weight, of which 2.71 +/- 0.715 X 10(8) granulocytes/kg were circulating and 2.94 +/- 0.876 X 10(8) granulocytes/kg were marginated along blood vessel walls. The mean disappearance half-life (T1/2) was 10.5 +/- 1.33 hours and the mean granulocyte turnover rate was 8.84 +/- 1.495 X 10(8) granulocytes/kg/day. A granulokin...
Aqueous procaine penicillin G in the horse: serum, synovial, peritoneal, and urine concentrations after single-dose intramuscular administration. Six adult mares were given a single dose of aqueous suspension procaine penicillin G (300,000 IU/ml) IM at a dosage of 22,000 IU/kg of body weight (15.4 mg of penicillin G/kg). Serum, synovial fluid, peritoneal fluid, and urine penicillin concentrations were measured serially over a 48-hour period. The mean peak serum penicillin concentration was 1.42 microgram/ml at 3 hours. Penicillin was detected in synovial fluid and peritoneal fluid, which obtained mean peak penicillin concentrations of 0.62 microgram/ml and 0.58 microgram/ml, at 4 hours and 3 hours, respectively. These concentrations ste...
Oxytetracycline hydrochloride in the horse: serum, synovial, peritoneal and urine concentrations after single dose intravenous administration. Six adult mares were given a single intravenous injection of oxytetracycline HCl (50 mg/ml) at a dosage of 5 mg/kg. Serum, synovial fluid, peritoneal fluid, and urine oxytetracycline concentrations were measured serially over a 48-h period. The highest measured serum oxytetracycline concentration was 8.01 mcg/ml at 1/2 h. Oxytetracycline was detected in synovial fluid and peritoneal fluid, which obtained mean peak oxytetracycline concentrations of 4.43 mcg/ml and 4.20 mcg/ml, at 1/2 h and 1 h, respectively. These concentrations steadily declined in parallel with serum concentrations and were n...
Physico-chemical properties of pregnant mare serum gonadotropin. Pregnant mare serum gonadotropin exhibits a dissociation at acid pH as shown by the drop of s20,w values from 3.52 S at pH 8.1 to 2.52 S at pH 2.0. The dissociation is accompanied by an absorbance change with a maximum at 287 nm and a parallel loss of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activities as followed by radioreceptor assays. The apparent pKa of the acid transition is 3.45 with an extremely slow and temperature-dependent rate at pH 2.0 (1.8 . 10(-4) s-1 at 37 degrees C). By gel filtration the molecular weight of the active hormone is estimated to be 45 ...
Variations in the properties of equine chorionic gonadotropin. The objectives of this paper are to review the chemical and biological properties of equine chorionic gonadotropin (eCG, PMSG) isolated from the serum. Comparisons are made with eCG isolated from endometrial cups, trophoblast cell culture medium, and low titer serum. The results show that eCG can vary, depending on the source, in both chemical and biological (LH and FSH activity) properties.
Volume of the synovia in certain joint cavities in the horse. A method of determining the volumes of synovia in certain articular cavities in the horse is described. The method is based on the degree of dilution of human serum albumin labelled with I that is injected into the joint. It is shown that uniform distribution of the injected substance is attained within 20 min post injection. The elimination of the labelled substance was found to follow the pattern of a single exponential function. The following volumes of synovia were determined (mean ± s) : hock, 39.8 ± 2.1 ml; radio-carpal, 12.6 ±1.5 ml; intercarpal, 14.9 ± 0.6 ml; foreleg fetlock joint...
In vivo metabolism of [3H]equilin in the pregnant mare. [3H]Equilin [3H-labeled 3-hydroxy-1,3,5(10), 7-estratetraen-17-one] was administered iv to a pregnant mare in the 10th month of gestation. Maternal urine was collected for 3 days, and blood samples were taken 35 min and 3, 6, 12, and 24 h after the injection. The half-life of the disappearance of radioactivity from the blood was approximately 2.5 h. Over 90% of the administered dose was excreted in the first 24 h. The urine was extracted, hydrolyzed, and fractionated. The bulk of the radioactive material (75%) was present in the phenolic sulfate fraction from which radiochemically pure equilin...
The metabolism of promazine and acetylpromazine in the horse. Promazine hydrochloride and acetylpromazine maleate were administered intravenously at clinical dose levels to horses. In urine from horses given promazine hydrochloride, the parent drug and four metabolites were detected. The two major metabolites, present as conjugates were identified after hydrolysis by beta-glucuronidase/arylsulfatase as 3-hydroxypromazine and 3-hydroxydesmonomethyl-promazine. Conjugated 3-hydroxypromazine has been previously identified as a major metabolite in the horse. Two minor metabolites isolated in this study were primaizine N-oxide and promazine N-oxide sulfoxide. ...
Selected ion monitoring assay for bromhexine in biological fluids. A method has been developed for quantification of bromhexine in plasma using gas chromatography mass spectrometry with selected ion monitoring. A deuterium labelled analogue was synthesized and used as the internal standard. To evaluate the gas chromatographic electron capture detection method described earlier, 23 plasma samples have been analysed by both techniques. Although a good correlation was shown, selected ion monitoring was superior to the electron capture detection method for levels below 3 ng ml-1. The mass spectrometric method has also been used to set up a pharmacokinetic study o...
Turnover of 131I-labelled albumin in horses with gastrointestinal disease. Four horses with a history of chronic diarrhoea and weight loss were studied. Three of them revealed malabsorption, as indicated by decreased absorption of D(+)-xylose. Three patients had distinct hypoalbuminaemia, and 131I-albumin turnover rates of these three horses were increased, compared to two normal control horses. However, the increases were not very marked, probably because actual signs of enteric disease were few in the patients, all of which were studied during convalescence. It is suggested that the observed hypoalbuminaemia is due to a gastrointestinal protein loss during the chro...
The disposition and metabolism of the synthetic prostaglandin fluprostenol (ICI 81,008) in the horse. 1. Following single intramuscular doses of [14C]fluprostenol (0.5--2.4 micrograms/kg) to three female horses and to three gelded male horses, radioactivity was present in the plasma within 5 min; peak concn. (0.32--1.30 ng/ml fluprostenol equiv.) occurred 5 to 90 min after injection. Radioactivity was still present in the plasma of the females after three days. About 88% of fluprostenol is bound to plasma proteins. 2. Radioactivity was present in the parotid saliva of the gelded male horses within 10 min. Peak concn. (45--91 pg/ml fluprostenol equiv.) occurred from 5 min to 1 h after injection...
Digoxin pharmacokinetics, bioavailability, efficacy, and dosage regimens in the horse. The pharmacokinetics of IV administered digoxin and the bioavailability of intragastrically administered powdered digoxin tables suspended in water were investigated in 6 clinically normal adult horses by 125I radioimmunoassay. The effect of 3 to 5 sequential IV doses of 5 micrograms of digoxin/kg of body weight at 2-hour intervals on a left ventricular index of contractility (Vmax) was assessed in 5 clinically normal horses. Standard pharmacokinetic equations and mean pharmacokinetic variables were used to derive parenteral and oral (loading and maintenance) doses for digoxin in horses. The c...