In vitro assessment of the capacity of certain mycotoxin binders to adsorb some amino acids and water-soluble vitamins.

The objective of this study was to evaluate the capacity of 6 mycotoxin binders (MTB) to adsorb 3 AA and 4 water-soluble vitamins (WSV). Two experiments were conducted in in vitro conditions to simulate postruminal digestion with pepsin, malic acid, citric acid, acetic acid, and lactic acid at pH 3.0 and intestinal digestion with bile salts and pancreatin extract at pH 6.5. Experiment 1 was conducted with AA, and experiment 2 was conducted with WSV. Within experiment, main factors were the MTB (bentonite, clinoptiolite, sepiolite, montmorillonite, activated carbon, and yeast cell walls), the substrate (AA: Lys, Met, and Thr; WSV: B1, B2, B3, and B6), and the incubation strategy (substrates alone or mixed). Data were analyzed for the effects of main factors and their interactions. In experiment 1, the adsorption average for AA when incubated separately was 44.3%, ranging from 62.4% for Thr by clinoptiolite to 20.0% for Thr by activated carbon. When incubated together, the average adsorption was reduced to 19.9%, suggesting competition among substrates for adsorption. Adsorption ranged from 29.8% for Thr by yeast cell walls to 5.6% for Met by clinoptiolite, but there were significant interactions among MTB and AA. In experiment 2, the average adsorption of WSV when incubated separately or together was 34.1 and 45.1%, respectively, suggesting possible synergies among substrates. When vitamins were incubated separately, adsorption ranged from 90.5% for vitamin B1 to 4.0% for vitamin B3 by montmorillonite. Vitamins B1 (except by yeast cell walls) and B6 (except by bentonite, sepiolite, and montmorillonite) were absorbed the most, and vitamin B3 was absorbed the least (except by activated carbon and yeast cell walls, which were least together with vitamin B2). When vitamins were incubated together, adsorption ranged from 97.0% for vitamin B1 by montmorillonite to 0% for vitamin B2 by activated carbon and vitamin B3 by bentonite. Vitamins B1 by all MTB and B6 by clinoptiolite, sepiolite, and yeast cell walls were the most adsorbed, and vitamin B3 (except by activated carbon and yeast cell wall) was the least absorbed. There were significant interactions among MTB and WSV. Mycotoxin binders have a high degree of adsorption of the AA and WSV tested in in vitro conditions, which may limit their bioavailability. Results also suggest that when substrates were incubated together some interactions for adsorption occurred, which were competitive among AA and synergic among vitamins.

Influence of a pig respiratory disease on the pharmacokinetic behaviour of amoxicillin after oral ad libitum administration in medicated feed.

The pharmacokinetic properties of amoxicillin in healthy and respiratory-diseased pigs were studied, after ad libitum administration of medicated feed. In addition, amoxicillin dose linearity and drug penetration into respiratory tract tissues were evaluated in diseased animals. The respiratory disease involves porcine reproductive and respiratory syndrome virus and bacterial agents such as Pasteurella multocida, Bordetella bronchiseptica and Streptococcus suis. Typical clinical signs and gross lesions of respiratory disease were observed. The plasma pharmacokinetic analysis was performed by means of a noncompartmental approach. After single intravenous bolus administration of amoxicillin to healthy pigs, the steady-state volume of distribution was 0.61 L/kg, the total plasma clearance was 0.83 L/h/kg and the mean residence time was 0.81 h. After oral bolus administration, the mean absorption time was 1.6 h and the peak plasma concentration (3.09 µg/mL) reached at 1.1 h postadministration. The oral bioavailability was 34%. For oral ad libitum administration, plasma concentration-time profiles were related to the feeding behaviour. Plasma concentrations at steady-state were established between 12 and 120 h. The pharmacokinetic parameters calculated (C(maxss) , C(minss) , C(avss) and AUC(24ss) ) showed significantly lower values in healthy pigs compared to diseased animals. This was in accordance with the significantly higher amoxicillin bioavailability (44.7% vs. 14.1%) and longer absorption period observed in diseased pigs. Amoxicillin dose linearity in diseased animals was established in a dose range of 4-18 mg/kg. On the other hand, tissue distribution ratio in diseased animals was 0.65 for bronchial mucosa, 0.48 for lung tissue and 0.38 for lymph nodes. Our results suggest that the pharmacokinetic properties and disposition of amoxicillin can be influenced by the disease state or by related factors such as changes in the gastrointestinal transit.

Effect of age and gender in the pharmacokinetics of albendazole and albendazole sulphoxide enantiomers in goats.

The kinetics of albendazole metabolites and albendazole sulphoxide enantiomers were studied in 2- and 14-month-old female and male goats, after a single oral dose administration (10mg/kg) of an albendazole formulation. Blood samples from the jugular vein were collected at 0.5, 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36, 42, 48 and 54h post-treatment and analyzed using a high performance liquid chromatography method. In all groups the area under the plasma concentration-time curve (AUC) and peak concentration (C(max)) values of (+)-ABZSO were significantly higher than those of (-)-ABZSO. The AUC and C(max) values obtained for (+)-ABZSO and (-)-ABZSO in adult animals were higher compared to the results in young animals, showing significant differences except for (+)-ABZSO in female animals. In young animals, independently of gender, the C(max) appeared earlier compared to adult animals. The mean residence time (MRT) values were shorter in young animals compared to adult animals for all compounds analyzed. No sex-related differences were found for any of the parameters calculated except for the (+)-ABZSO from adult animals.

Study of the enantiomeric separation of oxfendazole and cetirizine using subcritical fluid chromatography on an amylose-based column.

The enantiomeric separation of cetirizine and oxfendazole on a Chiralpak AD column using subcritical fluid chromatography has been studied in this work. The enantioseparation of cetirizine was only possible when 2-propanol was used as a modifier, obtaining better results in presence of the additives triethylamine (TEA) and trifluoroacetic acid (TFAA). On the contrary, 2-propanol provided the lowest enantioresolutions for oxfendazole, in this case the best results in terms of high resolution and short analysis time were obtained with ethanol. The study of the temperature effect revealed that in the case of cetirizine using 2-propanol, and oxfendazole using methanol, the separation was enthalpy-driven and the isoelution temperature was above the working range. Using ethanol or 2-propanol, the results showed that the oxfendazole enantioseparation was entropically driven and the isoelution temperatures were below the range studied.

PK and PK/PD of doxycycline in drinking water after therapeutic use in pigs.

A commercial doxycycline formulation was administered in drinking water to 12 pigs at the recommended dose of 10 mg/kg daily for 5 days. The mean plasma concentration at steady-state was 1.37 +/- 1.21 microg/mL, which was reached at 68 +/- 27.2 h postadministration. Absorption and elimination half-life values were 7.20 +/- 2.42 and 7.01 +/- 2.10 h, respectively. Most plasma concentrations during dosing were higher than the minimum inhibitory concentrations (MICs) described for the main porcine bacterial pathogens of the respiratory tract (Pasteurella multocida, Actinobacillus pleuropneumoniae, Bordetella bronchiseptica and Mycoplasma hyopneumoniae). It is concluded that when pigs were treated with doxycycline in drinking water at the recommended rate, therapeutically effective concentrations were achieved throughout the treatment period, supporting the clinical use of this tetracycline in the control of respiratory infections. However, inter-animal differences were marked.

Transplacental transfer of propofol in pregnant ewes.

Propofol is an injectable anaesthetic that is currently used both in veterinary and human medicine for the induction and maintenance of anaesthesia. Although little is known about the pharmacokinetics of propofol in fetuses, it is widely used in obstetric procedures, particularly in caesarean section. This study determines the pharmacokinetics of propofol in pregnant ewes in the last third of pregnancy, and placental transfer and pharmacokinetics in fetuses after the administration of a 6 mg/kg intravenous (i.v.) bolus (phase 1) or a 6 mg/kg i.v. bolus followed by continued infusion of 0.4 mg/kg/min. In ewes, the area under the blood concentration-time curve (AUC) and C(max) (8.6 mgh/mL and 9.5mg/mL, respectively) was higher than those of the fetus (1.6 mgh/mL and 1.19 mg/mL, respectively). The mean half-life was 0.5h in the dam and 1.1h in the fetus.

Albendazole sulphoxide enantiomers in pregnant rats' embryo concentrations and developmental toxicity.

Three single oral doses (8.5, 10, and 14 mg/kg) of a racemic formulation of albendazole sulphoxide (ABZSO) were administered to pregnant rats on day 10 of gestation. Mother plasma and embryo concentrations of ABZSO enantiomers and albendazole sulphone (ABZSO(2)) were determined 9 h after administration. The (-)-ABZSO enantiomer showed higher peak concentrations in both maternal plasma and embryo than the (+) enantiomer. An increase in embryo concentrations of ABZSO enantiomers and ABZSO(2) was only observed when dose rose to 14 mg/kg. There was an increase in resorption when the dose increased, but significant differences were only found in the higher dose group when compared with the other groups. The incidence of external and skeletal malformations (mostly of the tail, vertebrae and ribs) rose significantly in the 10 mg/kg group, producing almost 20% and 90% of malformed fetuses, respectively, and gross external and skeletal abnormalities in the thoracic region and limbs were also found.

Placental transfer of albendazole sulphoxide enantiomers in sheep.

Albendazole sulphoxide (ABZSO) is an anthelmintic drug used in veterinary practice. Its molecule has a chiral centre in the sulphur atom and racemic formulations are always used. The kinetics of the ABZSO enantiomers in the last third of pregnancy in ewes, and the placental transfer to the fetus, were studied after a single-dose oral administration (7.5 mg/kg) of a racemic formulation. In mothers, the area under the plasma concentration-time curve (AUC) and C(max) values of (+)-ABZSO (42.4+/-10.5 microg/mL and 1.9+/-0.4 microg/mL, respectively) were higher than those of (-)-ABZSO (15.3+/-5.1 microg/mL and 1.0+/-0.3 microg/mL). The MRT values were 17.0+/-1.6 h for (+)-ABZSO and 13.1+/-1.8 h for (-)-ABZSO. Similar kinetic parameters were obtained in the fetus for both enantiomers, but the fetal concentrations were lower compared with values for the dam. The AUC ratio between (-)-ABZSO/(+)-ABZSO in the dam was 0.36 and in the fetuses 0.64, indicating a higher impairment for the (+)-enantiomer in its placental transfer to the fetus.

Residue depletion of thiamphenicol in the sea-bass.

The residue depletion of thiamphenicol (TAP) was investigated in the sea-bass (Dicentrarchus labrax) after 5 days' treatment with medicated food at a dose of 15 or 30 mg/kg bw/day. Fish were sampled for blood and muscle + skin from 3 h until 14 days after treatment. Thiamphenicol concentrations were assayed by high performance liquid chromatography. Thiamphenicol concentrations measured 3 h after stopping treatment were 0.77 microg/mL and 0.91 (15 mg/kg dose) or 1.32 microg/mL and 1.47 microg/g (30 mg/kg dose), in plasma and muscle + skin, respectively. After a withdrawal of 3 days, plasma and tissue concentrations were: 0.08 microg/mL and 0.03 microg/g (lower dose) or 0.12 microg/mL and 0.06 microg/g (higher dose), respectively. Thiamphenicol was not detectable either in plasma or in tissues on days 7, 10 and 14 following withdrawal of the medicated food. Based on maximum residue levels (MRL) for TAP in fin fish, established at 50 microg/kg for muscle and skin in natural proportions, a withdrawal period of 5 and 6 days is proposed, after treatment at 15 or 30 mg/kg of TAP with medicated feed pellets, respectively, to avoid the presence of violative residues in the edible tissues of the sea-bass.

Albendazole sulphoxide enantiomeric ratios in plasma and target tissues after intravenous administration of ricobendazole to cattle.

The comparative concentration profiles of the (+) and (-) albendazole sulphoxide (ABZSO) enantiomers obtained in plasma and in selected target tissues/fluids after intravenous (i.v.) administration of a racemic formulation of ricobendazole (RBZ) to cattle were characterised. Fourteen Holstein calves received RBZ (racemic solution, 150 mg/mL) by i.v. administration at 7.5 mg/kg. Jugular blood samples were collected over 48 h post-treatment (plasma kinetic trial) and two animals were sacrificed at either 4, 12, 20, 28 or 32 h post-treatment to obtain samples of abomasal/small intestine mucosal tissue, abomasal/small intestine fluids, bile, liver and lung tissue (tissue distribution study). The (-)ABZSO enantiomer was depleted significantly faster from plasma compared with the (+)ABZSO antipode. The plasma AUC for (+)ABZSO (38.3 microg. h/mL) was significantly higher (P < 0.05) compared with that obtained for (-)ABZSO (20.5 microg. h/mL). The (+)ABZSO enantiomer was the predominant antipode measured in bile, abomasal fluid and abomasal mucosa. For instance, at 12 h post-treatment the (+)/(-) concentration ratios were: 12.9 (plasma), 1.62 (abomasal mucosa), 13.0 (abomasal fluid), 2.92 (intestinal mucosa), 9.87 (intestinal fluid) and 21.5 (bile). No marked differences between the concentration profiles of both enantiomers were observed in the liver tissue. Albendazole (ABZ) was recovered from the liver, lung and gastrointestinal (GI) mucosal tissues of RBZ-treated calves up to 32 h post-treatment, probably produced by a GI microflora-mediated sulphoreduction of RBZ. An enantioselective kinetic behaviour may account both for the faster depletion of the (-) enantiomer and for the higher availabilities of the (+) antipode observed in plasma and in most of the tissues/fluids investigated. The simultaneous evaluation of the plasma kinetics and tissue concentration profiles of both enantiomeric forms reported here, may help to interpret the relationship between chiral behaviour and pharmacological action for sulphoxide derivatives of benzimidazole (BZD) methylcarbamate anthelmintics.

Allometric analysis of thiamphenicol disposition among seven mammalian species.

The pharmacokinetics of thiamphenicol (TAP), a broad-spectrum antibiotic, was determined in male mice, rats, rabbits, dogs, pigs, sheep and calves. The relationship between the main pharmacokinetic parameters of TAP and body weight (W) was studied across these seven mammalian species, using double-logarithmic plots. The experimental values of volume of distribution (Vss), clearance (Cl) and elimination half-life (t(1/2)beta) were plotted, and extrapolated values were determined from corresponding allometric equations. These parameters were fitted to the following equations: Vss=0.98W0.92, Cl=15.80W0.76 and t(1/2)beta=0.94W0.20, and present good correlation (Vss: r2=0.997, P < 0.001; Cl: r2=0.976, P < 0.001, t(1/2)beta: r2=0.852, P < 0.005), that is expected of a drug eliminated primarily by renal glomerular filtration, with insignificant hepatic metabolism. For the t(1/2)beta, the extrapolated and observed values were similar. The extrapolated values of Cl were close to the experimental values, except for the mouse and pig mean percent error [(M.E.) equal to 62 and 119%, respectively], while the extrapolated and observed values for the Vss were very similar. The comparison between experimental and extrapolated values suggests that it could be possible to extrapolate, with good prediction, the kinetic parameters of this drug for mammalian species, using allometric scaling, except for the species that eliminate the drug by a combination of renal excretion and hepatic metabolism.

Effect of ruminal microflora on the biotransformation of netobimin, albendazole, albendazole sulfoxide, and albendazole sulfoxide enantiomers in an artificial rumen.

The effect of ruminal flora on the disposition of benzimidazole anthelmintic drugs was studied in dual-flow continuous-culture fermenters (artificial rumens). Six 1,320-mL artificial rumens were inoculated with ruminal fluid and fermentation conditions were maintained constant at 39 degrees C, pH 6.4, solid dilution rate of 5%/h, and liquid dilution rate of 10%/h to simulate standard ruminal fermentation conditions. The study was repeated in two consecutive periods. Two hours after the inoculation of rumen fluid, the fermenters were fed 30 g of a 60:40 forage:concentrate ration. Within each period two fermenters per treatment were immediately dosed with 104 mg of netobimin, 52 mg of albendazole, or 39 mg of albendazole sulfoxide. Concentrations of netobimin, albendazole, albendazole sulfoxide and its enantiomers, and albendazole sulfone were analyzed by high performance liquid chromatography at 0.25, 0.5, 1, 2, 4, 6, and 8 h after dosage. Reductive metabolism by the ruminal bacteria was observed, favoring the production of albendazole, the most potent anthelmintic molecule. No differences in the production or consumption of albendazole sulfoxide enantiomers were observed, indicating that the ruminal bacteria metabolism was not enantioselective. Because benzimidazole anthelmintic drugs are generally administered orally, the ruminal flora play an important role in the bioavailability of these drugs. In our study, increased concentrations of albendazole in the three treatments, due to reductive ruminal biotransformation, suggests that ruminal biotransformation may improve the efficacy of orally administered netobimin, albendazole, and albendazole sulfoxide.

Prolongation of epidural anaesthesia in dogs with bupivacaine in a lipid emulsion.

An aqueous solution and a lipid emulsion of bupivacaine were administered epidurally in doses of 1.8 mg/kg to six beagle dogs following a randomised two-phase crossover design. The aqueous solution was absorbed rapidly and the mean (sd) peak venous plasma concentration of bupivacaine, 1.4 (0.4) microg/ml, was detected after five minutes. After administration of the lipid emulsion, the peak plasma concentration of bupivacaine, 0.6 (0.2) microg/ml, was detected after 30 minutes. The mean (sd) t1/2beta of the aqueous preparation was 149.1 (32.6) minutes, and of the lipid emulsion 119.2 (34.0) minutes. Both preparations had a similar bioavailability. The mean time to the onset of motor block after the administration of the aqueous solution, 2.3 (2.2) minutes, was significantly shorter (P=0.028) than after the administration of the lipid emulsion, 9.4 (1.9) minutes, and the duration of the motor block induced by the lipid emulsion, 217.6 (26.2) minutes, was significantly longer (P=0.043) than for the aqueous solution, 158 (48.8) minutes. During anaesthesia, the plasma concentrations of bupivacaine ranged between 1.3 and 0.2 microg/ml. Non-significant changes in systolic blood pressure and heart rate were observed which coincided with the peak plasma concentrations of bupivacaine.

Pharmacokinetic behaviour of albendazole sulphoxide enantiomers in male and female sheep.

Benzimidazole anthelmintic drugs are widely used in veterinary practice. Albendazole sulphoxide (ABZSO) is a benzimidazole drug with two enantiomers, as a consequence of a chiral centre in the sulphoxide group. The kinetics of these enantiomers were studied in male and female sheep. Plasma samples were obtained from the animals between 0.5 and 72 h after oral administration of 7.5 mg/kg of a racemic formulation of ABZSO (total-ABZSO). After a liquid-liquid extraction, the samples were analysed by HPLC to determine the concentrations of total-ABZSO and of the sulphone metabolite (ABZSO2). During the chromatographic analysis, the ABZSO peak was collected and reanalysed by an HPLC technique using a Chiral AGP column to quantify the enantiomeric proportion therein. After kinetic analysis, the AUCs obtained for the (+)-ABZSO were 5.8 and 4.0 times higher than those for the (-)-ABZSO in male and female animals, respectively. The mean residence times were 23.4 and 16.1 h for (+)-ABZSO and 22.2 and 17.4 h for (-)-ABZSO for male and female animals, respectively. The only significant difference between the sexes (p < 0.05) was in the Tmax of the (-)-ABZSO. Comparing both enantiomers within each sex, significant differences were found in all the kinetic parameters. Finally, no kinetic differences were found between sex for total-ABZSO or ABZSO2.

Pharmacokinetics of indomethacin in poultry.

Indomethacin (INDO) is a nonsteroidal antiinflammatory drug widely used since the 1970s. The pharmacokinetic behavior of INDO (2 mg/kg) has been studied after intravenous (i.v.) and oral administration to broiler chickens. After i.v. administration, a first fast distribution phase and a later and slower elimination phase were observed. The elimination half-life and mean residence time (MRT) obtained were 1.0 hr and 0.8 hr, respectively. After oral administration, a flip-flop phenomenon was observed giving an elimination half-life and MRT approximately three times and six times higher, respectively, than the i.v. administration. The plasma concentrations after oral administration were sustained during 8-10 hr, giving an antinflammatory cover over the dose producing 50% of maximal effect during this time period.

Comparative disposition of ricobendazole enantiomers after intravenous and subcutaneous administration of a racemic formulation to calves.

The enantioselective disposition kinetics of the benzimidazole anthelmintic, ricobendazole (RBZ), have been characterized after its intravenous (iv) and subcutaneous (sc) administration as a racemic formulation to cattle. The (+) and (-) RBZ enantiomeric forms were recovered in plasma after iv and sc administration of the racemic RBZ formulation, using a chiral phase based HPLC method. A biexponential plasma concentration versus time curve was observed for both RBZ enantiomers following the iv treatment. Total body clearance was higher for (-) RBZ (150.4 mL/h. kg) compared with that obtained for the (+) RBZ antipode (78.1 mL/h. kg). The elimination half-life of the (-) RBZ enantiomer was shorter (T1/2beta: 2.67 h) compared with the (+) enantiomer (T1/2beta: 5.41 h). The plasma availability (expressed as AUC) was significantly higher for (+) RBZ compared with that obtained for the (-) antipode following both treatments. The enantiomeric ratio in plasma at T(0) was close to unity (50% of each enantiomer); the analysis of the concentration ratios (+) RBZ/(-) RBZ, demonstrated an increase in the proportion of (+) RBZ during the time course of the kinetics after both iv and sc treatments. The results presented herein show the enantioselective disposition kinetics of RBZ in cattle and are a further contribution to the understanding of the kinetic behaviour of these sulphoxide-containing benzimidazole anthelmintics in ruminants.

Liquid chromatographic determination of fenbendazole residues in pig tissues after treatment with medicated feed.

Fenbendazole (FBZ) is an anthelmintic widely used in farm animals to treat parasitic infestations. In pigs, it is administered in the food. The aim of this study was to validate an analytical method for the determination of FBZ and its metabolites in pig tissues. This method is based on oxidation of FBZ and its sulfoxide metabolite to the sulfone metabolite (FBZSO2). The limit of quantitation for this method is 20 ng FBZSO2/g for all tissues. The maximum residue limits (MRLs) established for FBZ and its metabolites in pig tissues are 50 ng/g for muscle, fat, and kidney and 500 ng/g for liver. This method is based on a liquid-liquid extraction followed by an oxidation with peracetic acid and a cleanup procedure based on 2 liquid-liquid extractions. Determination is achieved by high-performance liquid chromatography with ultraviolet detection. The present method is adjusted to the MRL established for FBZ and its metabolite residues. The analysis of the residues shows that after 72 h posttreatment, no FBZSO2 was detected in muscle, fat, and kidney and that liver levels were below the MRL.

Developmental toxicity in rat fetuses exposed to the benzimidazole netobimin.

Netobimin (NTB) is a prodrug of albendazole (ABZ) and is used as a broad-spectrum anthelmintic both in human and veterinary medicine. Pregnant Sprague-Dawley rats were treated po with 50, 59.5 and 70.7 mg/kg of NTB on Gestational Day (GD) 10. The results, observed on GD 20, demonstrated that NTB induced a significant increase of resorptions. Moreover, decreased fetal body weight and an increase in skeletal malformations were observed in treated groups. We report the first study in which vascular malformations are described in rats after the administration of a benzimidazole compound. An interesting relationship between intercostal vessel and rib malformations was found.