Objective—To investigate the pharmacokinetics of fentanyl administered transdermally and IV in sheep.
Animals—21 adult female sheep.
Procedures—Fentanyl was administered IV to 6 healthy sheep. Transdermal fentanyl patches (TFPs) were applied to 15 sheep 12 hours prior to general anesthesia and surgery. Seria blood samples were collected for 18 hours after IV injection and 84 hours after TFP application. Fentanyl concentrations were quantified via liquid chromatography-mass spectrometry, and pharmacokinetic values were estimated.
Results—All sheep completed the study without complications. Following a dose of 2.5g/kg administered IV, the half-life was 3.08 hours (range, 2.20 to 3.36 hours), volume of distribution at steady state was 8.86 L/kg (range, 5.55 to 15.04 L/kg), and systemic clearance was 3.62 L/kg/h (range, 2.51 to 5.39 L/kg/h). The TFPs were applied at a mean dose of 2.05 g/kg/h. Time to maximum plasma concentration and maximal concentration were 12 hours (range, 4 to 24 hours) and 1.30 ng/mL (range, 0.62 to 2.73 ng/mL), respectively. Fentanyl concentrations were maintained at > 0.5 ng/mL for 40 hours after TFP application.
Conclusions and Clinical Relevance—IV administration of fentanyl resulted in a short half-life. Application of a TFP resulted in stable blood fentanyl concentrations in sheep. (Am J Vet Res 2010;71:1127—1132)
Objective—To investigate the pharmacokinetics and behavioral effects of aminorex administered IV and PO in horses.
Procedures—In a cross-over design, aminorex (0.03 mg/kg) was administered IV or PO. Plasma and urinary aminorex concentrations were determined via liquid chromatography– mass spectrometry.
Results—Decrease of aminorex from plasma following IV administration was described by a 3-compartment pharmacokinetic model. Median (range) values of α, β, and γ half-lives were 0.04 (0.01 to 0.28), 2.30 (1.23 to 3.09), and 18.82 (8.13 to 46.64) hours, respectively. Total body and renal clearance, the area under the plasma time curve, and initial volume of distribution were 37.26 (28.61 to 56.24) mL·min/kg, 1.25 (0.85 to 2.05) mL·min/kg, 13.39 (8.82 to 17.37) ng·h/mL, and 1.44 (0.10 to 3.64) L/kg, respectively. Oral administration was described by a 2-compartment model with first-order absorption, elimination from the central compartment, and distribution into peripheral compartments. The absorption half-life was 0.29 (0.12 to 1.07) hours, whereas the β and γ elimination phases were 1.93 (1.01 to 3.17) and 23.57 (15.16 to 47.45) hours, respectively. The area under the curve for PO administration was 10.38 (4.85 to 13.40) ng·h/mL and the fractional absorption was 81.8% (33.8% to 86.9%).
Conclusions and Clinical Relevance—Aminorex administered IV had a large volume of distribution, initial rapid decrease, and an extended terminal elimination. Following PO administration, there was rapid absorption, rapid initial decrease, and an extended terminal elimination. At a dose of 0.03 mg/kg, the only effects detected were transient and central in origin and were observed only following IV administration.
OBJECTIVE To evaluate plasma interleukin 6 (IL-6) concentration in Standardbred racehorses by means of a novel ELISA following validation of the assay for use with equine plasma samples.
SAMPLE Plasma samples obtained from 25 Thoroughbreds for use in assay validation and from 319 Standardbred racehorses at rest 2 to 2.5 hours prior to warm-up and racing.
PROCEDURES A sandwich ELISA was developed with equine anti–IL-6 polyclonal antibody and the biotin-streptavidin chemical interaction to enhance sensitivity. The assay was validated for specificity, sensitivity, precision, and accuracy by use of both recombinant and endogenous proteins.
RESULTS For the assay, cross-reactivity with other human and equine cytokines was very low or absent. Serial dilution of plasma samples resulted in proportional decreases in reactivity, indicating high specificity of the method. Partial replacement of detection antibody with capture antibody or pretreatment of samples with capture antibody caused assay signals to significantly decrease by 55%. The inter- and intra-assay precisions were ≤ 13.6% and ≤ 9.3%, respectively; inter- and intra-assay accuracies were within ranges of ± 14.1% and ± 8.6%, respectively, at concentrations from 78 to 5,000 pg/mL, and the sensitivity was 18 pg/mL. Plasma IL-6 concentration varied widely among the 319 Standardbreds at rest (range, 0 to 193,630 pg/mL; mean, 6,153 pg/mL; median, 376 pg/mL).
CONCLUSIONS AND CLINICAL RELEVANCE This ELISA method proved suitable for quantification of IL-6 concentration in equine plasma samples. Plasma IL-6 concentration was high (> 10,000 pg/mL) in 9.1% of the Standardbred racehorses, which warrants further investigation.
Objective—To compare pharmacokinetics of triamcinolone acetonide (TA) following IV, intra-articular (IA), and IM administration and determine its effect on plasma concentrations of hydrocortisone and cortisone.
Procedures—TA (0.04 mg/kg) was administered IV, IM, or IA, and plasma TA, hydrocortisone, and cortisone concentrations were determined.
Results—IV administration of TA was fitted to a 2-compartment model. Median distribution half-life was 0.50 hours (range, 0.24 to 0.67 hours); elimination half-life was 6.1 hours (range, 5.0 to 6.4 hours). Transfer half-life of TA from joint to plasma was 5.2 hours (range, 0.49 to 73 hours); elimination half-life was 23.8 hours (range, 18.9 to 32.2 hours). Maximum plasma concentration following IA administration was 2.0 ng/mL (range, 0.94 to 2.5 ng/mL), and was attained at 10 hours (range, 8 to 12 hours). Maximum plasma concentration following IM administration was 0.34 ng/mL (range, 0.20 to 0.48 ng/mL) and was attained at 13.0 hours (range, 12 to 16 hours); concentration was still quantifiable at 360 hours. Hydrocortisone plasma concentrations were significantly different from baseline within 0.75, 2, and 1 hours after IV, IA, and IM administration, respectively, and remained significantly different from baseline at 96 and 264 hours for IV and IA administration. Following IM administration of TA, plasma concentrations of hydrocortisone did not recover to baseline concentrations by 360 hours.
Conclusions and Clinical Relevance—Pharmacokinetics of TA and related changes in hydrocortisone were described following IV, IA, and IM administration. A single administration of TA has profound effects on secretion of endogenous hydrocortisone.
Objective—To determine whether prolonged administration of clenbuterol results in tachyphylaxis, specifically regarding its bronchoprotective properties and effect on sweating in horses.
Animals—8 Thoroughbreds with inflammatory airway disease.
Procedures—In a crossover design, horses received clenbuterol (0.8 μg/kg, PO, q 12 h) or placebo for 21 days, with a washout period of ≥ 30 days between the 2 treatments. Airway reactivity was evaluated by use of flowmetric plethysmography and histamine broncho-provocation before (day 0; baseline) and every 7 days after the start of treatment. Sweat function was evaluated via response to epinephrine administered ID before and every 10 days after the start of treatment.
Results—The concentration of histamine required to increase total airway obstruction by 35% (PC35) was significantly reduced during treatment with clenbuterol (mean change, 11.5 mg/mL), compared with during administration of the placebo (mean change, −1.56 mg/mL), with a peak effect at 14 days. Tachyphylaxis was evident by day 21, with 7 of 8 horses having a PC35 below the baseline value (mean change, −0.48 mg/mL), which returned to baseline values during the washout period. No effect of clenbuterol was seen in sweat response to epinephrine administration.
Conclusions and Clinical Relevance—Clenbuterol initially reduced airway sensitivity to inhaled histamine, but tachyphylaxis that resulted in increased airway reactivity was evident by day 21. Although no effects on sweating were detected, the technique may not have been sensitive enough to identify subtle changes. Prolonged administration of clenbuterol likely results in a clinically important reduction in its bronchodilatory effects.
Objective—To determine the pharmacokinetics of methylprednisolone (MP) and develop a pharmacokinetic-pharmacodynamic model of the related changes in plasma concentrations of endogenous hydrocortisone (HYD) and cortisone (COR) following intra-articular administration of methylprednisolone acetate (MPA) in horses.
Procedures—In each horse, 200 mg of MPA was injected intrasynovially into a carpal joint, and plasma MP, HYD, and COR concentrations were determined via liquid chromatography-mass spectrometry.
Results—A 5-compartment pharmacokinetic-pharmacodynamic model was used to describe the concatenated changes in the plasma concentrations of MP, HYD, and COR and to estimate the instantaneous rate of endogenous HYD production. The median transfer half-life (t1/2t) of methylprednisolone from the joint to plasma and elimination half-life (t1/2e) from plasma were 1.7 and 19.2 hours, respectively. Maximum plasma concentration of methylprednisolone was 7.26 ± 3.3 ng/mL at 8 hours, which decreased to 0.11 ± 0.08 ng/mL at 144 hours after injection. At 3 hours after MPA administration, plasma COR and HYD concentrations were significantly decreased from baseline values (from 2.9 ± 0.28 ng/mL to 2.10 ± 1.0 ng/mL and from 61.1 ± 18.9 ng/mL to 25.7 ± 12.1 ng/mL, respectively).
Conclusions and Clinical Relevance—The sensitivity of the analytic method used allowed complete description of the related kinetics of MP, HYD, and COR following intra-articular administration of MPA. A single intra-articular administration of MPA profoundly affected the secretion of HYD and COR in horses; secretion of endogenous corticosteroids remained suppressed for as long as 240 hours after injection.
Objective—To evaluate whether urine supernatant contains amplifiable DNA and to determine factors that influence genotyping of samples from racehorses after storage and transportation.
Sample Population—580 urine, 279 whole blood, and 40 plasma samples obtained from 261 Thoroughbreds and Standardbreds.
Procedures—Genomic DNA was isolated from stored blood and urine samples collected from racehorses after competition. Quantified DNA was evaluated to determine whether 5 equine microsatellite loci (VHL20, HTG4, AHT4, HMS6, and HMS7) could be amplified by use of PCR techniques. Fragment size of each amplified locus was determined by use of capillary electrophoresis.
Results—High–molecular-weight and amplifiable DNA were recovered from refrigerated blood samples, but recovery from urine varied. Deoxyribonucleic acid was recovered from both urine supernatant and sediment. Freeze-thaw cycles of urine caused accumulation of amplifiable DNA in the supernatant and clearance of naked DNA. Repeated freeze-thaw cycles significantly decreased DNA yield and induced DNA degradation, which resulted in failure to detect microsatellite loci. Select drugs detected in test samples did not affect PCR amplification. Contaminants in DNA isolates inhibited PCR amplification and resulted in partial microsatellite profiles.
Conclusions and Clinical Relevance—Properly stored urine and blood samples were successfully genotyped, but subjecting urine to freeze-thaw cycles was most detrimental to the integrity of DNA. Increasing the volume of urine used improved recovery of DNA.
OBJECTIVE To determine the anabolic and lipolytic effects of a low dosage of clenbuterol administered orally in working and nonworking equids.
ANIMALS 8 nonworking horses and 47 polo ponies in active training.
PROCEDURES Each polo pony continued training and received either clenbuterol (0.8 μg/kg) or an equal volume of corn syrup (placebo) orally twice daily for 21 days, and then was evaluated for another 21-day period. Nonworking horses received clenbuterol or placebo at the same dosage for 21 days in a crossover trial (2 treatments/horse). For working and nonworking horses, percentage body fat (PBF) was estimated before treatment and then 2 and 3 times/wk, respectively. Body weight was measured at intervals.
RESULTS Full data sets were not available for 8 working horses. For working horses, a significant treatment effect of clenbuterol was detected by day 3 and continued through the last day of treatment; at day 21, the mean change in PBF from baseline following clenbuterol or placebo treatment was −0.80% (representing a 12% decrease in PBF) and −0.32%, respectively. By day 32 through 42 (without treatment), PBF change did not differ between groups. When treated with clenbuterol, the nonworking horses had a similar mean change in PBF from baseline from day 6 onward, which peaked at −0.75% on day 18 (an 8% decrease in PBF). Time and treatment had no significant effect on body weight in either experiment.
CONCLUSIONS AND CLINICAL RELEVANCE Among the study equids, long-term low-dose clenbuterol administration resulted in significant decreases in body fat with no loss in body weight.
Objective—To determine pharmacokinetics and
excretion of phenytoin in horses.
Animals—6 adult horses.
Procedure—Using a crossover design, phenytoin
was administered (8.8 mg/kg of body weight, IV and
PO) to 6 horses to determine bioavailability (F).
Phenytoin also was administered orally twice daily for
5 days to those same 6 horses to determine steadystate
concentrations and excretion patterns. Blood
and urine samples were collected for analysis.
Results—Mean (± SD) elimination half-life following a
single IV or PO administration was 12.6 ± 2.8 and 13.9
± 6.3 hours, respectively, and was 11.2 ± 4.0 hours following
twice-daily administration for 5 days. Values for
F ranged from 14.5 to 84.7%. Mean peak plasma concentration
(Cmax) following single oral administration
was 1.8 ± 0.68 µg/ml. Steady-state plasma concentrations
following twice-daily administration for 5 days
was 4.0 ± 1.8 µg/ml. Of the 12.0 ± 5.4% of the drug
excreted during the 36-hour collection period, 0.78 ±
0.39% was the parent drug phenytoin, and 11.2 ±
5.3% was 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH). Following twice-daily administration for 5
days, phenytoin was quantified in plasma and urine
for up to 72 and 96 hours, respectively, and p-HPPH
was quantified in urine for up to 144 hours after
administration. This excretion pattern was not consistent
in all horses.
Conclusion and Clinical Relevance—Variability in F,
terminal elimination-phase half-life, and Cmax following
single or multiple oral administration of phenytoin
was considerable. This variability makes it difficult to
predict plasma concentrations in horses after phenytoin
administration. (Am J Vet Res 2001;62:483–489)
Objective—To compare the pharmacokinetics of
penicillin G and procaine in racehorses following IM
administration of penicillin G procaine (PGP) with
pharmacokinetics following IM administration of penicillin
G potassium and procaine hydrochloride (PH).
Animals—6 healthy adult mares.
Procedure—Horses were treated with PGP (22,000
units of penicillin G/kg of body weight, IM) and with
penicillin G potassium (22,000 U/kg, IM) and PH
(1.55 mg/kg, IM). A minimum of 3 weeks was allowed
to elapse between drug treatments. Plasma and urine
penicillin G and procaine concentrations were measured
by use of high-pressure liquid chromatography.
Results—Median elimination phase half-lives of penicillin
G were 24.7 and 12.9 hours, respectively, after
administration of PGP and penicillin G potassium.
Plasma penicillin G concentration 24 hours after administration
of penicillin G potassium and PH was not significantly
different from concentration 24 hours after
administration of PGP. Median elimination phase halflife
of procaine following administration of PGP (15.6
hours) was significantly longer than value obtained
after administration of penicillin G potassium and PH
Conclusions and Clinical Relevance—Results suggest
that IM administration of penicillin G potassium
will result in plasma penicillin G concentrations for 24
hours after drug administration comparable to those
obtained with administration of PGP. Clearance of procaine
from plasma following administration of penicillin
G potassium and PH was rapid, compared with clearance
following administration of PGP. (Am J Vet Res