Long-term monitoring of clodronate in equine hair using liquid chromatography-tandem mass spectrometry.

Given the potential for long-term inhibition of bone remodeling/healing and detrimental effects to horses in training, bisphosphonates are tightly regulated in horseracing. Hair has proven to be an effective matrix for detection of drug administration to horses and has been particularly effective in detecting drugs for a long period of time post administration. Thus, hair may prove to be a useful matrix for detection of administration of this class of drugs. The objective of the current study was to develop an assay and assess the usefulness of hair as a matrix for long-term detection of clodronate to horses. Seven horses received a single intramuscular administration of 1.8 mg/kg clodronate. Hair samples were collected prior to and up to 6 months post administration. A liquid chromatography-tandem mass spectrometry method was developed and concentrations of clodronate measured in hair samples. The drug was first detected on day 7 in 4/7 horses, and on days 14, 28 and 35 in the remaining three horses. In 4/7 horses, clodronate was still detectable 6 months post administration. Results of this study demonstrate that, although there was significant inter-individual variability in detection times (63 to 180 days) and several intermediate times where the drug could not be detected but was subsequently detected in later timepoints, clodronate administration was detectable in hair for a prolonged period in most of the horses (4/7) studied.

Steroid synthesis and metabolism in the equine placenta during placentitis.

Equine placentitis is associated with alterations in maternal peripheral steroid concentrations, which could negatively affect pregnancy outcome. This study aimed to elucidate the molecular mechanisms related to steroidogenesis and steroid-receptor signaling in the equine placenta during acute placentitis. Chorioallantois (CA) and endometrial (EN) samples were collected from mares with experimentally induced placentitis (n = 4) and un-inoculated gestationally age-matched mares (control group; n = 4). The mRNA expression of genes coding for steroidogenic enzymes (3ßHSD, CYP11A1, CYP17A1, CYP19A1, SRD5A1, and AKR1C23) was evaluated using qRT-PCR. The concentration of these enzyme-dependent steroids (P5, P4, 5αDHP, 3αDHP, 20αDHP, 3ß-20αDHP, 17OH-P, DHEA, A4, and estrone) was assessed using liquid chromatography-tandem mass spectrometry in both maternal circulation and placental tissue. Both SRD5A1 and AKR1C23, which encode for the key progesterone metabolizing enzymes, were downregulated (P < 0.05) in CA from the placentitis group compared to controls, and this downregulation was associated with a decline in tissue concentrations of 5αDHP (P < 0.05), 3αDHP (P < 0.05), and 3ß-20αDHP (P = 0.052). In the EN, AKR1C23 was also downregulated in the placentitis group compared to controls, and this downregulation was associated with a decline in EN concentrations of 3αDHP (P < 0.01) and 20αDHP (P < 0.05). Moreover, CA expression of CYP19A1 tended to be lower in the placentitis group, and this reduction was associated with lower (P = 0.057) concentrations of estrone in CA. Moreover, ESR1 (steroid receptors) gene expression was downregulated (P = 0.057) in CA from placentitis mares. In conclusion, acute equine placentitis is associated with a local withdrawal of progestins in the placenta and tended to be accompanied with estrogen withdrawals in CA.

Concentrations of sulphated estrone, estradiol and dehydroepiandrosterone measured by mass spectrometry in pregnant mares.

BACKGROUND: Few studies have provided a longitudinal analysis of systemic concentrations of conjugated oestrogens (and androgens) throughout pregnancy in mares, and those only using immunoassay. The use of liquid chromatography tandem mass spectrometry (LC-MS/MS) will provide more accurate concentrations of circulating conjugated steroids. OBJECTIVES: To characterise circulating concentrations of individual conjugated steroids throughout equine gestation by using LC-MS/MS. STUDY DESIGN: Longitudinal study and comparison of pregnant mares treated with vehicle or letrozole in late gestation. METHODS: Sulphated oestrogens and androgens were measured in mares throughout gestation and mares in late gestation (8-11 months) treated with vehicle or letrozole to inhibit oestrogen synthesis in late gestation. An analytical method was developed using LC-MS/MS to evaluate sulphated estrone, estradiol, testosterone and dehydroepiandrosterone (DHEAS) during equine gestation. RESULTS: Estrone sulphate concentrations peaked by week 26 at almost 60 µg/mL, 50-fold higher than have been reported in studies using immunoassays. An increase in DHEAS was detected from 7 to 9 weeks of gestation, but concentrations remained consistently low (if detected) for the remainder of gestation and testosterone sulphate was undetectable at any stage. Estradiol sulphate concentrations were highly correlated with estrone sulphate but were a fraction of their level. Concentrations of both oestrogen sulphates decreased from their peak to parturition. Letrozole inhibited estrone and estradiol sulphate concentrations at 9.25 and 10.5 months of gestation but, no increase in DHEAS was observed. MAIN LIMITATIONS: Limited number of mares sampled and available for analysis, lack of analysis of 5α-reduced and B-ring unsaturated steroids due to lack of available standards. CONCLUSIONS: Dependent on methods of extraction and chromatography, and the specificity of primary antisera, immunoassays may underestimate oestrogen conjugate concentrations in blood from pregnant mares and may detect androgen conjugates (neither testosterone sulphate nor DHEAS were detected here by LC-MS/MS) that probably peak coincident with oestrogen conjugates between 6 and 7 months of equine gestation.

5α-dihydroprogesterone concentrations and synthesis in non-pregnant mares.

In vivo and in vitro evidence indicates that the bioactive, 5α-reduced progesterone metabolite, 5α-dihydroprogesterone (DHP) is synthesized in the placenta, supporting equine pregnancy, but its appearance in early pregnancy argues for other sites of synthesis also. It remains unknown if DHP circulates at relevant concentrations in cyclic mares and, if so, does synthesis involve the non-pregnant uterus? Jugular blood was drawn daily from cyclic mares (n = 5). Additionally, ovariectomized mares (OVX) and geldings were administered progesterone (300 mg) intramuscularly. Blood was drawn before and after treatment. Incubations of whole equine blood and hepatic microsomes with progesterone were also investigated for evidence of DHP synthesis. Sample analysis for progesterone, DHP and other steroids employed validated liquid chromatography-tandem mass spectrometry methods. Progesterone and DHP appeared a day (d) after ovulation in cyclic mares, was increased significantly by d3, peaking from d5 to 10 and decreased from d13 to 17. DHP was 55.5 ± 3.2% of progesterone concentrations throughout the cycle and was highly correlated with it. DHP was detected immediately after progesterone administration to OVX mares and geldings, maintaining a relatively constant ratio with progesterone (47.2 ± 2.9 and 51.2 ± 2.7%, respectively). DHP was barely detectable in whole blood and hepatic microsome incubations. We conclude that DHP is a physiologically relevant progestogen in cyclic, non-pregnant mares, likely stimulating the uterus, and that it is synthesized peripherally from luteal progesterone but not in the liver or blood. The presence of DHP in pregnant perissodactyla as well as proboscidean species suggests horses may be a valuable model for reproductive endocrinology in other exotic taxa.

Potency and stability of compounded formulations of chlorambucil, melphalan and cyclophosphamide.

BACKGROUND: Oral chemotherapy agents are frequently compounded in veterinary medicine however, the potency of some formulations have been shown to vary from that of Food and Drug Administration (FDA)-approved products. AIMS: The objective of this study was to evaluate the potency and stability of three compounded oral chemotherapeutics commonly prescribed to be administered over time. MATERIALS & METHODS: Compounded chlorambucil 1 mg, cyclophosphamide 5 mg and melphalan 1 mg were obtained and for potency tested upon receipt and 6 weeks later. RESULTS: Potency ranged from 71 to 104% for chlorambucil and 58 to 109% for melphalan; 1/4 and 2/4 samples were <90% of labelled strength at baseline and 6 weeks, respectively, for both drugs. Potency of cyclophosphamide ranged from 92 to 107% with all samples +/-10% of labelled strength at all time points. DISCUSSION/CONCLUSION: These results demonstrate variability of compounded chemotherapy products, and highlight the need to consider both potency and stability when prescribing orally compounded chemotherapy.

Pharmacokinetics and selected pharmacodynamics of romifidine following low-dose intravenous administration in combination with exercise to quarter horses.

Romifidine is an alpha-2 adrenergic agonist used for sedation and analgesia in horses. As it is a prohibited substance, its purported use at low doses in performance horses necessitates further study. The primary goal of the study reported here was to describe the serum concentrations and pharmacokinetics of romifidine following low-dose administration immediately prior to exercise, utilizing a highly sensitive liquid chromatography-tandem mass spectrometry assay that is currently employed in many drug testing laboratories. An additional objective was to describe changes in heart rate and rhythm following intravenous administration of romifidine followed by exercise. Eight adult Quarter Horses received a single intravenous dose of 5 mg (0.01 mg/kg) romifidine followed by 1 h of exercise. Blood samples were collected and drug concentrations measured at time 0 and at various times up to 72 h. Mean ± SD systemic clearance, steady-state volume of distribution and terminal elimination half-life were 34.1 ± 6.06 mL/min/kg and 4.89 ± 1.31 L/kg and 3.09 ± 1.18 h, respectively. Romifidine serum concentrations fell below the LOQ (0.01 ng/mL) and the LOD (0.005 ng/mL) by 24 h postadministration. Heart rate and rhythm appeared unaffected when a low dose of romifidine was administered immediately prior to exercise.

Disposition of the anti-ulcer medications ranitidine, cimetidine, and omeprazole following administration of multiple doses to exercised Thoroughbred horses.

The use of anti-ulcer medications, such as cimetidine, ranitidine, and omeprazole, is common in performance horses. The use of these drugs is regulated in performance horses, and as such a withdrawal time is necessary prior to competition to avoid a medication violation. To the authors' knowledge, there are no reports in the literature describing repeated oral administrations of these drugs in the horse to determine a regulatory threshold and related withdrawal time recommendations. Therefore, the objective of the current study was to describe the disposition and elimination pharmacokinetics of these anti-ulcer medications following oral administration to provide data upon which appropriate regulatory recommendations can be established. Nine exercised Thoroughbred horses were administered 20 mg/kg BID of cimetidine or 8 mg/kg BID of ranitidine, both for seven doses or 2.28 g of omeprazole SID for four doses. Blood samples were collected, serum drug concentrations were determined, and elimination pharmacokinetic parameters were calculated. The serum elimination half-life was 7.05 ± 1.02, 7.43 ± 0.851 and 3.94 ± 1.04 h for cimetidine, ranitidine, and omeprazole, respectively. Serum cimetidine and ranitidine concentrations were above the LOQ and omeprazole and omeprazole sulfide below the LOQ in all horses studied upon termination of sample collection.

Progestin withdrawal at parturition in the mare.

Mammalian pregnancies need progestogenic support and birth requires progestin withdrawal. The absence of progesterone in pregnant mares, and the progestogenic bioactivity of 5α-dihydroprogesterone (DHP), led us to reexamine progestin withdrawal at foaling. Systemic pregnane concentrations (DHP, allopregnanolone, pregnenolone, 5α-pregnane-3ß, 20α-diol (3ß,20αDHP), 20α-hydroxy-5α-dihydroprogesterone (20αDHP)) and progesterone) were monitored in mares for 10days before foaling (n=7) by liquid chromatography-mass spectrometry. The biopotency of dominant metabolites was assessed using luciferase reporter assays. Stable transfected Chinese hamster ovarian cells expressing the equine progesterone receptor (ePGR) were transfected with an MMTV-luciferase expression plasmid responsive to steroid agonists. Cells were incubated with increasing concentrations (0-100nM) of progesterone, 20αDHP and 3α,20ßDHP. The concentrations of circulating pregnanes in periparturient mares were (highest to lowest) 3α,20ßDHP and 20αDHP (800-400ng/mL respectively), DHP and allopregnanolone (90 and 30ng/mL respectively), and pregnenolone and progesterone (4-2ng/mL). Concentrations of all measured pregnanes declined on average by 50% from prepartum peaks to the day before foaling. Maximum activation of the ePGR by progesterone occurred at 30nM; 20αDHP and 3α,20ßDHP were significantly less biopotent. At prepartum concentrations, both 20αDHP and 3α,20ßDHP exhibited significant ePGR activation. Progestogenic support of pregnancy declines from 3 to 5days before foaling. Prepartum peak concentrations indicate that DHP is the major progestin, but other pregnanes like 20αDHP are present in sufficient concentrations to play a physiological role in the absence of DHP. The authors conclude that progestin withdrawal associated with parturition in mares involves cessation of pregnane synthesis by the placenta.

Equine 5α-reductase activity and expression in epididymis.

The 5α-reductase enzymes play an important role during male sexual differentiation, and in pregnant females, especially equine species where maintenance relies on 5α-reduced progesterone, 5α-dihydroprogesterone (DHP). Epididymis expresses 5α-reductases but was not studied elaborately in horses. Epididymis from younger and older postpubertal stallions was divided into caput, corpus and cauda and examined for 5α-reductase activity and expression of type 1 and 2 isoforms by quantitative real-time polymerase chain reaction (qPCR). Metabolism of progesterone and testosterone to DHP and dihydrotestosterone (DHT), respectively, by epididymal microsomal protein was examined by thin-layer chromatography and verified by liquid chromatography tandem mass spectrometry (LC-MS/MS). Relative inhibitory potencies of finasteride and dutasteride toward equine 5α-reductase activity were investigated. Pregnenolone was investigated as an additional potential substrate for 5α-reductase, suggested previously from in vivo studies in mares but never directly examined. No regional gradient of 5α-reductase expression was observed by either enzyme activity or transcript analysis. Results of PCR experiments suggested that type 1 isoform predominates in equine epididymis. Primers for the type 2 isoform were unable to amplify product from any samples examined. Progesterone and testosterone were readily reduced to DHP and DHT, and activity was effectively inhibited by both inhibitors. Using epididymis as an enzyme source, no experimental evidence was obtained supporting the notion that pregnenolone could be directly metabolized by equine 5α-reductases as has been suggested by previous investigators speculating on alternative metabolic pathways leading to DHP synthesis in placenta during equine pregnancies.

Elimination of cetirizine following administration of multiple doses to exercised thoroughbred horses.

Cetirizine is an antihistamine used in performance horses for the treatment of hypersensitivity reactions and as such a withdrawal time is necessary prior to competition. The objective of the current study was to describe the disposition and elimination of cetirizine following oral administration in order to provide additional serum concentration data upon which appropriate regulatory recommendations can be established. Nine exercised thoroughbred horses were administered 0.4 mg/kg of cetirizine orally BID for a total of five doses. Blood samples were collected immediately prior to drug administration and at various times postadministration. Serum cetirizine concentrations were determined and selected pharmacokinetic parameters determined. The serum elimination half-life was 5.83 ± 0.841 h. Average serum cetirizine concentrations were still above the LOQ of the assay (0.05 ng/mL) at 48 h (final sample collected) postadministration of the final dose.

Pharmacokinetics of methocarbamol and phenylbutazone in exercised Thoroughbred horses.

Methocarbamol (MCBL) is commonly used in performance horses for the treatment of skeletal muscle disorders. Current regulatory recommendations for show horses and racehorses are based on a single oral dose of 5 g, although doses in excess of this are often administered. The goal of the current study was to characterize the disposition of MCBL following higher dose administration and administration in combination with another commonly used drug in performance horses, phenylbutazone (PBZ). Exercised Thoroughbred horses were administered various doses of MCBL as a sole agent and MCBL in combination with PBZ. Blood samples were collected at various times, concentrations of MCBL and PBZ measured using LC-MS/MS and pharmacokinetic parameters calculated using compartmental analysis. Following administration of 15 g of MCBL, either as part of a single- or multiple-dose regimen, a number of horses exceeded the Association of Racing Commissioners International and the United States Equestrian Federation's recommended regulatory threshold at the recommended withdrawal time. There was not a significant difference between horses that received only MCBL and those that received MCBL and PBZ. Results of the current study support an extended withdrawal guideline when doses in excess of 5 g are administered.

Pharmacokinetics of guaifenesin following administration of multiple doses to exercised Thoroughbred horses.

Guaifenesin is an expectorant commonly used in performance horses to aid in the clearance of mucus from the airways. Guaifenesin is also a centrally acting skeletal muscle relaxant and as such is a prohibited drug with withdrawal necessary prior to competition. To the authors' knowledge, there are no reports in the literature describing single or multiple oral administrations of guaifenesin in the horse to determine a regulatory threshold and related withdrawal time. Therefore, the objective of the current study was to describe the pharmacokinetics of guaifenesin following oral administration in order to provide data upon which appropriate regulatory recommendations can be established. Nine exercised Thoroughbred horses were administered 2 g of guaifenesin orally BID for a total of five doses. Blood samples were collected immediately prior to drug administration and at various times postadministration. Serum guaifenesin concentrations were determined and pharmacokinetic parameters calculated. Guaifenesin was rapidly absorbed (Tmax of 15 min) following oral administration. The Cmax was 681.3 ± 323.8 ng/mL and 1080 ± 732.8 following the first and last dose, respectively. The serum elimination half-life was 2.62 ± 1.24 h. Average serum guaifenesin concentrations remained above the LOQ of the assay (0.5 ng/mL) by 48 h postadministration of the final dose in 3 of 9 horses.

Frequency and Severity of Neutropenia Associated with Food and Drug Administration Approved and Compounded Formulations of Lomustine in Dogs with Cancer.

BACKGROUND: Compounded lomustine is used commonly in veterinary patients. However, the potential variability in these formulations is unknown and concern exists that compounded formulations of drugs may differ in potency from Food and Drug Administration (FDA)-approved products. HYPOTHESIS/OBJECTIVES: The initial objective of this study was to evaluate the frequency and severity of neutropenia in dogs treated with compounded or FDA-approved formulations of lomustine. Subsequent analyses aimed to determine the potency of lomustine obtained from several compounding pharmacies. ANIMALS: Thirty-seven dogs treated with FDA-approved or compounded lomustine. METHODS: Dogs that received compounded or FDA-approved lomustine and had pretreatment and nadir CBCs performed were eligible for inclusion. Variables assessed included lomustine dose, neutrophil counts, and severity of neutropenia. Lomustine 5 mg capsules from 5 compounding sources were tested for potency using high-pressure liquid chromatography (HPLC) with ultraviolet (UV) detection. RESULTS: Twenty-one dogs received FDA-approved lomustine and 16 dogs were treated with lomustine prescribed from a single compounding pharmacy. All dogs treated with FDA-approved lomustine were neutropenic after treatment; 15 dogs (71%) developed grade 3 or higher neutropenia. Four dogs (25%) given compounded lomustine became neutropenic, with 2 dogs (12.5%) developing grade 3 neutropenia. The potency of lomustine from 5 compounding pharmacies ranged from 50 to 115% of the labeled concentration, with 1 sample within ±10% of the labeled concentration. CONCLUSIONS AND CLINICAL IMPORTANCE: These data support broader investigation into the potency and consistency of compounded chemotherapy drugs and highlight the potential need for greater oversight of these products.

Pharmacokinetic and pharmacodynamic analysis comparing diverse effects of detomidine, medetomidine, and dexmedetomidine in the horse: a population analysis.

The present study characterizes the pharmacokinetic (PK) and pharmacodynamic (PD) relationships of the α2-adrenergic receptor agonists detomidine (DET), medetomidine (MED) and dexmedetomidine (DEX) in parallel groups of horses from in vivo data after single bolus doses. Head height (HH), heart rate (HR), and blood glucose concentrations were measured over 6 h. Compartmental PK and minimal physiologically based PK (mPBPK) models were applied and incorporated into basic and extended indirect response models (IRM). Population PK/PD analysis was conducted using the Monolix software implementing the stochastic approximation expectation maximization algorithm. Marked reductions in HH and HR were found. The drug concentrations required to obtain inhibition at half-maximal effect (IC50 ) were approximately four times larger for DET than MED and DEX for both HH and HR. These effects were not gender dependent. Medetomidine had a greater influence on the increase in glucose concentration than DEX. The developed models demonstrate the use of mechanistic and mPBPK/PD models for the analysis of clinically obtainable in vivo data.

Pharmacokinetics and pharmacodynamics of intravenous dexmedetomidine in the horse.

The aim of the study was to describe the pharmacokinetics and selected pharmacodynamics of intravenous dexmedetomidine in horses. Eight adult horses received 5 µg/kg dexmedetomidine IV. Blood samples were collected before and for 10 h after drug administration to determine dexmedetomidine plasma concentrations. Pharmacokinetic parameters were calculated using noncompartmental analysis. Data from one outlier were excluded from the statistical summary. Behavioral and physiological responses were recorded before and for 6 h after dexmedetomidine administration. Dexmedetomidine concentrations decreased rapidly (elimination half-life of 8.03 ± 0.84 min). Time of last detection varied from 30 to 60 min. Bradycardia was noted at 4 and 10 min after drug administration (26 ± 8 and 29 ± 8 beats/min respectively). Head height decreased by 70% at 4 and 10 min and gradually returned to baseline. Ability to ambulate was decreased for 60 min following drug administration, and mechanical nociceptive threshold was increased during 30 min. Blood glucose peaked at 30 min (134 ± 24 mg/dL) and borborygmi were decreased for the first hour after dexmedetomidine administration. Dexmedetomidine was quickly eliminated as indicated by the rapid decrease in plasma concentrations. Physiological, behavioral, and analgesic effects observed after dexmedetomidine administration were of short duration.

Disposition and metabolic profile of the weak androgen Dehydroepiandrosterone (DHEA) following administration as part of a nutritional supplement to exercised horses.

In order to ensure the welfare of performance horses and riders as well as the integrity of the sport, the use of both therapeutic and illegal agents in horse racing is tightly regulated. While Dehydroepiandrosterone (DHEA) is not specifically banned from administration to racehorses in the United States and no screening limit or threshold concentration exists, the metabolic conversion of DHEA to testosterone make its presence in nutritional supplements a regulatory concern. The recommended regulatory threshold for total testosterone in urine is 55 and 20 ng/mL for mares and geldings, respectively. In plasma, screening and confirmation limits for free testosterone (mares and geldings), of no greater than 0.1 and 0.025 ng/mL, respectively are recommended. DHEA was administered orally, as part of a nutritional supplement, to 8 exercised female thoroughbred horses and plasma and urine samples collected at pre-determined times post administration. Using liquid chromatography-mass spectrometry (LC-MS), plasma and urine samples were analyzed for DHEA, DHEA-sulfate, testosterone, testosterone-sulfate, pregnenolone, androstenedione, and androstenediol. DHEA was rapidly absorbed with maximal plasma concentrations reaching 52.0 ± 43.8 ng/mL and 32.1 ± 12.9 ng/mL for DHEA and DHEA sulfate, respectively. Free testosterone was not detected in plasma or urine samples at any time. Maximum sulfate conjugated testosterone plasma concentrations were 0.98 ± 1.09 ng/mL. Plasma testosterone-sulfate concentrations did not fall below 0.1 ng/mL and urine testosterone-sulfate below 55 ng/mL until 24-36 h post DHEA administration. Urine testosterone sulfate concentrations remained slightly above baseline levels at 48 h for most of the horses studied.

Pharmacokinetics of buprenorphine following intravenous and buccal administration in cats, and effects on thermal threshold.

This study reports the pharmacokinetics of buprenorphine, following i.v. and buccal administration, and the relationship between buprenorphine concentration and its effect on thermal threshold. Buprenorphine (20 µg/kg) was administered intravenously or buccally to six cats. Thermal threshold was determined, and arterial blood sampled prior to, and at various times up to 24 h following drug administration. Plasma buprenorphine concentration was determined using liquid chromatography/mass spectrometry. Compartment models were fitted to the time-concentration data. Pharmacokinetic/pharmacodynamic models were fitted to the concentration-thermal threshold data. Thermal threshold was significantly higher than baseline 44 min after buccal administration, and 7, 24, and 104 min after i.v. administration. A two- and three-compartment model best fitted the data following buccal and i.v. administration, respectively. Following i.v. administration, mean ± SD volume of distribution at steady-state (L/kg), clearance (mL·min/kg), and terminal half-life (h) were 11.6 ± 8.5, 23.8 ± 3.5, and 9.8 ± 3.5. Following buccal administration, absorption half-life was 23.7 ± 9.1 min, and terminal half-life was 8.9 ± 4.9 h. An effect-compartment model with a simple effect maximum model best predicted the time-course of the effect of buprenorphine on thermal threshold. Median (range) ke0 and EC50 were 0.003 (0.002-0.018)/min and 0.599 (0.073-1.628) ng/mL (i.v.), and 0.017 (0.002-0.023)/min and 0.429 (0.144-0.556) ng/mL (buccal).

Impact of the blood sampling site on time-concentration drug profiles following intravenous or buccal drug administration.

The aim of this study was to examine the effect of the sampling site on the drug concentration-time profile, following intravenous or buccal (often called 'oral transmucosal') drug administration. Buprenorphine (20 µg/kg) was administered IV or buccally to six cats. Blood samples were collected from the carotid artery and the jugular and medial saphenous veins for 24 h following buprenorphine administration. Buprenorphine concentration-time data were examined using noncompartmental analysis. Pharmacokinetic parameters were compared using the Wilcoxon signed rank test, applying the Bonferroni correction. Significance was set at P < 0.05. Following IV administration, no difference among the sampling sites was found. Following buccal administration, maximum concentration [jugular: 6.3 (2.9-9.8), carotid: 3.4 (1.9-4.9), medial saphenous: 2.5 (1.7-4.1) ng/mL], area under the curve [jugular: 395 (335-747), carotid: 278 (214-693), medial saphenous: 255 (188-608) ng·min/mL], and bioavailability [jugular: 47 (34-67), carotid: 32 (20-52), medial saphenous: 23 (16-55)%] were higher in the jugular vein than in the carotid artery and medial saphenous vein. Jugular venous blood sampling is not an acceptable substitute for arterial blood sampling following buccal drug administration.

Detection and pharmacokinetics of three formulations of firocoxib following multiple administrations to horses.

REASON FOR PERFORMING STUDY: The use of firocoxib in horses and its ability to affect performance and potential to allow a horse to compete when it otherwise should not, necessitates establishing appropriate withdrawal time guidelines prior to performance. OBJECTIVES: To describe plasma concentrations and characterise the pharmacokinetics of 3 firocoxib formulations following multiple administrations of the label dose, with respect to recommended plasma thresholds for performance horses. STUDY DESIGN: Balanced 3-way crossover prospective study. METHODS: Nine healthy mature horses were administered firocoxib injectable solution (0.09 mg/kg bwt i.v. s.i.d. for 5 days), firocoxib paste (0.1 mg/kg bwt per os s.i.d. for 14 days) and firocoxib tablets (57 mg s.i.d. for 14 days). Blood samples were collected at Time 0 and at various times post drug administration until plasma concentrations were below the limit of detection of the assay. Plasma samples were analysed using liquid chromatography-mass spectrometry and data analysed using noncompartmental analysis. RESULTS: The mean plasma half-life was 1.64 ± 0.737, 1.70 ± 0.800 and 1.73 ± 0.767 days for injectable, paste and tablet formulations, respectively. Plasma concentrations fell below the Racing Medication and Testing Consortium's recommended threshold for racehorses (20 ng/ml) by 7 days post administration of the final dose for all formulations. Plasma concentrations never exceeded the threshold concentration (240 ng/ml) for horse competing in US Equestrian Federation events for any of the formulations. CONCLUSIONS: This study extends current knowledge regarding the pharmacokinetics of firocoxib and provides information that can be used to establish appropriate withdrawal time guidelines following multiple administrations, with respect to already established plasma regulatory threshold concentrations.

Pharmacokinetics of fentanyl, alfentanil, and sufentanil in isoflurane-anesthetized cats.

The aim of this study was to compare the pharmacokinetics of fentanyl, alfentanil, and sufentanil in isoflurane-anesthetized cats. Six adult cats were used. Anesthesia was induced and maintained with isoflurane in oxygen. End-tidal isoflurane concentration was set at 2% and adjusted as required due to spontaneous movement. Fentanyl (10 µg/kg), alfentanil (100 µg/kg), or sufentanil (1 µg/kg) was administered intravenously as a bolus, on separate days. Blood samples were collected immediately before and for 8 h following drug administration. Plasma drug concentration was determined using liquid chromatography/mass spectrometry. Compartment models were fitted to concentration-time data. A 3-compartment model best fitted the concentration-time data for all drugs, except for 1 cat in the sufentanil group (excluded from analysis). The volume of the central compartment and the volume of distribution at steady-state (L/kg) [mean ± SEM (range)], the clearance (mL/min/kg) [harmonic mean ± pseudo-SD (range)], and the terminal half-life (min) [median (range)] were 0.25 ± 0.04 (0.09-0.34), 2.18 ± 0.16 (1.79-2.83), 18.6 ± 5.0 (15-29.8), and 151 (115-211) for fentanyl; 0.10 ± 0.01 (0.07-0.14), 0.89 ± 0.16 (0.68-1.83), 11.6 ± 2.6 (9.2-15.8), and 144 (118-501) for alfentanil; and 0.06 ± 0.01 (0.04-0.10), 0.77 ± 0.07 (0.63-0.99), 17.6 ± 4.3 (13.9-24.3), and 54 (46-76) for sufentanil. Differences in clearance and volume of distribution result in similar terminal half-lives for fentanyl and alfentanil, longer than for sufentanil.