Topic:Absorption
Absorption in horses refers to the process by which drugs and nutrients are taken up from the gastrointestinal tract into the bloodstream. This page compiles peer-reviewed research that examines the mechanisms underlying uptake, bioavailability, and the factors influencing absorption rates in horses. The studies explore pharmacokinetic profiles, the impact of different formulations, and how physiological conditions affect dietary absorption.
Lymphocytic-plasmacytic enteritis in two horses. The primary hematologic abnormalities in 2 adult horses with chronic weight loss were hypoalbuminemia and hyperglobulinemia. One horse was anemic, had subclinical disseminated intravascular coagulation, and prolonged plasma sulfobromophthalein half-life. Small-intestinal dysfunction with malabsorption was indicated by abnormal D-xylose absorption test results. Clinicopathologic and pathologic findings were consistent with a diagnosis of malabsorption and protein-losing enteropathy, attributable to lymphocytic and plasmacytic infiltration of the intestine.
Pharmacokinetic studies of cimetidine hydrochloride in adult horses. Histamine type II (H2) antagonists inhibit gastric acid secretion and are useful in treating gastric and duodenal ulcer disease. To provide some information on the pharmacokinetics of the H2 antagonist cimetidine, adult horses were given 3.3 mg/kg cimetidine intravenously (iv) or 3.3 and 10 mg/kg orally. Plasma cimetidine concentrations after 3.3 mg/kg orally were too low to measure. Following 3.3 mg/kg iv, cimetidine displayed two-compartment characteristics with a t1/2 of 0.083 +/- 0.039 h and t1/2 of 2.23 +/- 0.64 h. The total body clearance was 0.443 +/- 0.160 litre/h/kg and the mean resid...
Pharmacokinetic disposition of an immediate-release aminophylline and a sustained-release theophylline formulation in the horse. The pharmacokinetic disposition of theophylline was determined by high-performance liquid chromatographic analysis of plasma samples from six healthy, adult horses following the administration of intravenous aminophylline (dosed at 9.94 mg/kg as theophylline), immediate-release aminophylline tablets (dosed at 9.94 mg/kg as theophylline), and sustained-release theophylline tablets (dosed at 20 mg/kg). The elimination rate constant (lambda z), apparent volume of distribution (Vz), and clearance (Cl) determined by compartmental analysis of the intravenous data were 0.07 +/- 0.01 h-1, 0.80 +/- 0.0...
Effect of food deprivation on D-xylose absorption test results in mares. A D-xylose absorption test was conducted on 4 healthy mares deprived of food for 12, 36, 72, and 96 hours before the test, with a 13- to 15-day adjustment period between each test. Maximal plasma concentrations after 72 and 96 hours of food deprivation were approximately 36% lower than those obtained after the 12- and 36-hour periods (P = 0.0001). Absorption curves were flatter and the decrease in plasma concentration was slower after the 72- and 96-hour periods of food deprivation. The rate of D-xylose absorption (P = 0.0108) and the initial rate of urinary excretion (P = 0.0117) were slower ...
Performance of horse-riding helmets in frontal and side impacts. Cases of head injury are reviewed in which riders wearing jockey skull caps have suffered impacts to the front, back or side of their helmets. The design and constructional materials of such helmets are assessed. Impact tests that simulate the accidents confirm the low energy absorption potential of some helmets for lateral impacts. Most pedal or motorcycle helmet designs afford better lateral impact protection.
Pharmacokinetics and estimated bioavailability of amoxicillin in mares after intravenous, intramuscular, and oral administration. The pharmacokinetics and estimated bioavailability of amoxicillin were determined after IV, intragastric, and IM administration to healthy mares. After IV administration of sodium amoxicillin (10 mg/kg of body weight), the disposition of the drug was best described by a 2-compartment open model. A rapid distribution phase was followed by a rapid elimination phase, with a mean +/- SD half-life of 39.4 +/- 3.57 minutes. The mean volume of distribution was 325 +/- 68.2 ml/kg, and the mean body clearance was 5.68 +/- 0.80 ml/min.kg. It was concluded that frequent IV administration of sodium amoxic...
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...
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...
Absorption of neomycin from the equine uterus: effect of stage of oestrous cycle and volume of vehicle. Plasma concentrations of neomycin were measured following intrauterine infusion of 3.3 mg/kg bodyweight neomycin sulphate. Mares in oestrus absorbed approximately 6 per cent of neomycin infused whereas mares in a luteal phase absorbed 56 per cent. The volume of infusate also affected absorption as increased volume resulted in decreased absorption. The decreased absorption both during oestrus and when large volumes were used was probably due to reflux of antibiotic through the cervix.
The bioavailability of phenylbutazone in the horse. [phenyl-14C]-Phenylbutazone was administered to 2 horses p.o. and i.v. on separate occasions. Plasma levels and urinary and faecal elimination of 14C were monitored for up to 7 days after dosing. Phenylbutazone was rapidly and extensively absorbed after oral administration, and its bioavailability was 91% assessed by comparison of plasma AUCs of unchanged drug after p.o. and i.v. administration. The plasma elimination half-life of phenylbutazone was 9.7 h and this was independent of the route of administration. The pattern of elimination of phenylbutazone was independent of the route of admini...
Chronic inflammatory and lymphoproliferative lesions of the equine small intestine. A retrospective study was made of 20 horses with severe and extensive chronic disease of the small intestine. Many of the animals had clinical evidence of malabsorption, with progressive loss of weight, hypoalbuminaemia and sometimes anaemia. All but two of the horses were Thoroughbreds. The pathology was diverse. Nine of the cases were alimentary lymphomas (Platt, 1986) and five had lymphocytic and eosinophilic infiltrations in the bowel wall which were considered to be probable reactions to parasitic invasion. One had acute thrombosis associated with partial occlusion of the anterior mesente...
Absorption of phenylbutazone from a paste formulation administered orally to the horse. The absorption pattern of phenylbutazone was studied in five horses during administration of the drug in a paste formulation on days 1, 5, 8 and 12 of a 12-day dosing schedule. Since two or more plasma concentration peaks were usually obtained following each oral dose, it was concluded that phasic absorption was a particular feature of the oil:water formulation of the product. Possible causes of this unusual absorption pattern are discussed and the therapeutic implications of both phasic absorption and the recorded values of Cmax, tmax and AUC024 for phenylbutazone and its active metabolite ox...
D-xylose absorption in the growing foal. Seven healthy foals (five ponies and two horses) were maintained on grass pasture with their dams. All foals had normal faeces at the time of testing. An oral xylose absorption test was performed on each foal at one, two and three months of age. Following an 8 h fast, 0.5 g/kg D-xylose as a 10 per cent solution was given via a nasogastric tube. Control and 30 min interval plasma samples were collected for 3 h and the plasma was analysed for xylose using the phloroglucinol microassay technique. Maximum xylose concentration levels were reached between 30 and 60 mins for each of the foals. The me...
Gentamicin dosage in foals aged one month and three months. The absorption and disposition kinetics of gentamicin were compared at two dosage levels (2 and 4 mg/kg bodyweight [bwt]) in one- and three-month-old foals. Following intramuscular (im) injection of single 2 mg/kg bwt doses, the drug was absorbed rapidly and produced peak serum concentration (18.2 mu 5.3 +/- g/ml, n = 8) at 30 mins. Much wider variations were associated with the amount of drug absorbed and the serum gentamicin concentrations after administration at the higher dosage level. The half-life of gentamicin was similar in the one-month-old (3.7 +/- 1.7 h, n = 8) and three-month-old (...
Absorption and pharmacokinetics of phenylbutazone in Welsh Mountain ponies. The disposition of phenylbutazone (4.4 mg/kg), administered intravenously to six Welsh Mountain ponies, was described by a two-compartment open model. Pharmacokinetic parameters were not significantly different after morning dosing in comparison with afternoon dosing. When phenylbutazone (4.4 mg/kg) was administered orally to the same ponies, marked variations in time to peak concentrations were produced with different feeding schedules. When access to hay was permitted before and after dosing, the mean time to peak concentration was 13.2 +/- 1.2 h and double peaks in the plasma concentration-...
[14C]monensin balance in bile-fistulated ponies. To measure absorption of monensin or its metabolites and its elimination from the body, [14C]monensin sodium was given orally (1 mg/kg body wt) to two bile-fistulated ponies and iv (8.7 mg) to one bile-fistulated pony. For one orally-dosed pony, 4.7% of the 14C was eliminated in bile, 52% in feces, .7% in urine and 33% remained in the gastrointestinal (GI) tract after 3 d. Total 14C recovery was 90%. For the other orally-dosed pony, 18.3% of the 14C was eliminated in bile, 69% in feces, 1.7% in urine and 7% remained in the GI tract after 4 d. Total 14C recovery was 98%. For the iv-dosed pony, ...
Pharmacokinetics of probenecid and the effect of oral probenecid administration on the pharmacokinetics of cefazolin in mares. The pharmacokinetics and bioavailability of probenecid given IV and orally at the dosage level of 10 mg/kg of body weight to mares were investigated. Probenecid given IV was characterized by a rapid disposition phase with a mean half-life of 14.0 minutes and a subsequent slower elimination phase with a mean half-life of 87.8 minutes in 5 of 6 mares. In the remaining mare, a rapid disposition phase was not observed, and the half-life of the elimination phase was slower (172 minutes). The mean residence time of probenecid averaged 116 minutes for all 6 mares and 89.2 minutes for the 5 mares with...
Effects of oral cimetidine on plasma concentrations of phenylbutazone in horses. Phenylbutazone was administered to six Thoroughbred horses in a cross-over study in which the horses received cimetidine pretreatment or no cimetidine pretreatment. Blood samples were collected at various times for 48 h after phenylbutazone administration and the plasma was analysed for phenylbutazone. Cimetidine pretreatment elevated phenylbutazone plasma concentrations during the first 8 h after phenylbutazone administration. The absorption rate, maximum phenylbutazone plasma concentrations and AUC were significantly greater with cimetidine pretreatment. The half-life of phenylbutazone did n...
Pharmacokinetics of small doses of 3-methylindole given to horses. The pharmacokinetics of 3-methylindole (3MI) given orally in 2 doses (10 mg/kg and 20 mg/kg) to horses were determined. The pharmacokinetic plasma-concentration profiles for 3MI (10- and 20-mg/kg dosages) in horses were represented by a 2-compartment open model with first-order absorption, as determined by nonlinear least-squares regression analysis. Absorption of 3MI at both dosages was rapid. Comparisons of the peak plasma concentrations, the postdistribution half lives, total clearances, and areas under the curve of the plasma-concentration profiles between the 10- and the 20-mg/kg dosages ...
Rifampin in the horse: comparison of intravenous, intramuscular, and oral administrations. The plasma concentrations and pharmacokinetics of rifampin disposition were determined after a single IV, IM, or oral dose of 10 mg/kg of body weight and an oral dose of 25 mg/kg. The overall elimination rate constants per minute were similar for the 10 mg/kg dose (0.0021 +/- 0.0004, IV; 0.0017 +/- 0.0002, IM; and 0.0023 +/- 0.0006, orally). The apparent bioavailability was moderate to low for IM and oral administrations (59.8% +/- 3.2% and 39.5% +/- 5.0%, respectively). The rate of absorption was most rapid for oral administration with an absorption half-life of 249.7 +/- 71.6 minutes as comp...
Pharmacokinetics and bioavailability of theophylline in horses. The pharmacokinetics and bioavailability of theophylline in horses were investigated following both intravenous and intragastric administration of aminophylline solutions at doses corresponding to 15 and 10 mg/kg theophylline base. A rapid distributive phase with a half-life of approximately 15-30 min was followed by a slower elimination half-life averaging 15-17 h. The apparent volume of distribution averaged 850-900 ml/kg. Theophylline, administered as aminophylline solution, was both rapidly and completely absorbed from the equine digestive tract. Based on the bioavailability and dispositio...
Drug disposition in the neonatal animal, with particular reference to the foal. Differences between neonatal and adult animals in their response to drugs can usually be attributed to altered disposition (ie, distribution, metabolism and excretion) processes during the neonatal period. These alterations affect the plasma concentrations as well as the concentrations of drug attained at the receptor site. Some characteristics of the neonatal period include greater absorption from the gastrointestinal tract, lower extent of plasma protein binding, increased apparent volume of distribution of drugs that distribute in extracellular fluid or total body water, increased permeabil...
Studies on prolactin: conformational comparison of human, equine, and porcine pituitary prolactins. The conformations of human, equine, and porcine pituitary prolactins, as evidenced by various optical properties, have been compared. The alpha-helix contents of all three proteins are essentially identical to each other (60 +/- 5%), as well as to prolactins isolated from other mammalian species. Direct absorption (zero and second-order), difference absorption, fluorescence emission, and circular dichroism spectra suggest that the majority of tyrosine and tryptophan side chains in these three proteins exist in very similar microenvironments within the folded forms of the hormones. Thus, the ge...
A pharmacokinetic study of digoxin in the horse. Digoxin was administered orally and intravenously to seven healthy adult mares and geldings in two separate trials. At a dose of 44 microgram digoxin/kg body weight, the oral study was characterized by an absorption phase with a mean (+/- 1 standard deviation) peak serum digoxin concentration of 2.21 ng/ml (+/- 0.45) at a mean of 2.29 h (+/- 1.52) after administration. A second rise in serum digoxin concentration started about 6-8 h after administration and extended to about 20 h after administration. The mean bioavailability (F) was 23.38% (+/- 5.96). At a dose of 22 microgram digoxin/kg body...
Warfarin pharmacokinetics in the horse. The pharmacokinetics of racemic warfarin were studied in 6 adult horses. After IV administration, the plasma concentration of warfarin showed a biphasic decline in time. Analysis of the data, according to 2-compartment kinetics, revealed the following constants: biological half-life was 13.3 hours, apparent volume of distribution was 0.46 L X kg-1, body clearance was 25.3 ml X hour-1 X kg-1. Warfarin was bound (91.5%) to plasma proteins. Unchanged warfarin was not detected in the urine. Absorption from the gastrointestinal tract was almost complete. Concentrations of warfarin in tissue were ex...
The pharmacokinetics, plasma protein binding and time response relationships of 2-amino-5-phenyl-2-oxazolin-4-one (pemoline) in the horse. The disposition kinetics of pemoline after iv and oral administration of 2.4 mg/kg of the drug were studied. The elimination half-life was 39.4 hr. The mean volume of distribution was 1.5 liters/kg indicating extensive tissue distribution and sequestration for an amphoteric drug. Plasma protein binding determined by in vitro equilibrium dialysis was concentration dependent. The mean binding capacity was found to be 0.80 mu-mol/g, an apparent dissociation constant of 3.73 X 10(-5) molar, and a total plasma protein concentration of 64.7 g/liter. The mean systemic availability by oral administrat...