Population Pharmacokinetics and Absolute Oral Bioavailability of Lasalocid after Single Intravenous and Intracrop Administration in Laying Hens.

Lasalocid sodium is a polyether carboxylic ionophore agent authorized by the EU for use as a coccidiostat in broilers, turkeys, and pullets up to 16 weeks of age, except for laying hens. However, laying hens are the most common nontarget species exposed to lasalocid sodium, mainly due to cross-contamination from feed mills. This exposure may result in potential drug residue deposition in eggs, which could potentially expose consumers to the drug. The breeds commonly used for commercial egg production in Poland are Isa Brown and Green-legged Partridge hens, which have been found to significantly differ in egg-laying performance. This variability may also affect the pharmacokinetics of lasalocid. Data on lasalocid plasma pharmacokinetics in laying hens are lacking. In this study, we aimed to determine typical population pharmacokinetic parameters, absolute oral bioavailability, and how breed may influence the pharmacokinetics of lasalocid. Twenty-layer hens of the two breeds were used in this study. Lasalocid was administered orally at a single dose of either 1 mg or 5 mg/kg body weight or intravenously at a dose of 1 mg/kg body weight, in a crossover design with a three-week washout period between study periods. Blood samples were collected for 72 h, and lasalocid concentrations were measured using high-performance liquid chromatography with fluorescence detection. A population pharmacokinetic analysis was conducted using nonlinear mixed effects modeling. Standard numerical and graphical criteria were used to select the best model, and a stepwise covariate modeling approach was used to determine any influencing factors. The best model was a three-compartment mammillary model with first-order absorption, transit compartments, and linear elimination. The estimated absolute oral bioavailability was low (36%). It was found that breed significantly influenced not only absorption but also the elimination of lasalocid. This study revealed that lasalocid absorption and elimination varied between the two breeds. This variability in pharmacokinetics may result in breed-related differences in drug residue accumulation in eggs, and ultimately, the risk associated with consumer exposure to drug residues may also vary.

PHARMACOKINETICS OF A SINGLE ORAL DOSE OF PONAZURIL IN THE INDIAN PEAFOWL (PAVO CRISTATUS).

Ponazuril, a novel coccidiocidal triazinetrione, has shown promise in addressing apicomplexan diseases in mammals and birds. This study describes the pharmacokinetics of ponazuril in healthy adult Indian peafowl (Pavo cristatus) following a single oral dose administered at two different dosages. Peafowl (four males and four females) were administered compounded ponazuril at 20 or 40 mg/kg orally in a double crossover design, with a 2-wk washout period. Blood was collected from each bird at 2, 4, 8, 24, 48, 72, 96, and 120 h after administration for plasma concentration of ponazuril using high-pressure liquid chromatography. Fecals were evaluated for coccidial shedding for 3 consecutive d prior to the ponazuril trial, 1 wk after the first dose of ponazuril, and 1 wk after the second dose of the trial. After the first trial, one peafowl administered 20 mg/kg ponazuril was shedding coccidia, but no coccidia were detected by the end of the second trial. Ponazuril reached peak concentrations (Tmax) at 21.38 h + 5.25 and 22.04 h + 7.39, and peak concentration (Cmax) were 11.82 µg/ml + 3.01 and 18.42 µg/ml + 4.13, for 20 and 40 mg/kg doses, respectively. Ponazuril was detected at 120 h with a concentration of 9.48 µg/ml + 2.59 and 12.25 µg/ml + 2.89 and a half-life of 219.4 + 58.7 h and 186.7 + 58.7 h, for and 40 mg/kg doses, respectively. Ponazuril in peafowl was well absorbed orally, plasma concentrations increased with dose, and elimination was slower than current dosages for birds would suggest. No obvious adverse effects were observed at either dosage.

Pharmacokinetics, Activity, and Residue Elimination of R- and S-Diclazuril in Broiler Chickens.

Diclazuril (DIC) is widely used as a racemic mixture to prevent and treat coccidiosis in farm animals, while the pharmacokinetics, bioactivity, and toxicity of DIC enantiomers are not known at all. This study first established a simple, sensitive, and reliable liquid chromatography tandem mass spectrometry method for separation of R-DIC and S-DIC and their analyses. Then, it was applied to investigate the stereoselective pharmacokinetics and residual elimination of individual enantiomers, and their anticoccidial activity was also evaluated in broiler chickens. The results indicated that the area under the concentration-time curve (AUC) and elimination half-life (t1/2ß) were significantly different (p < 0.05) for two enantiomers in chicken plasma. The AUC and t1/2ß of S-DIC were approximately 2 and 1.4 times those of R-DIC, respectively. The residual elimination of DIC enantiomers in chicken tissues was also stereoselective. The concentrations of S-DIC in chicken muscle and liver were greater than those of R-DIC, and it is the opposite in the kidney. There was no significant difference (p > 0.05) in the anticoccidial activity of racemate and enantiomers when a single enantiomer in feed was added above 0.5 mg kg-1. However, the anticoccidial activity of R-DIC (0.25 mg kg-1) was significantly higher (p < 0.05) than that of S-DIC (0.25 mg kg-1) in the diet. It should be mentioned that in chicken small intestine and cecum, the enantiomerization rate of each enantiomer in the infection group was faster than that in the uninfected group.

Pharmacokinetics of toltrazuril and its metabolites in pregnant and nonpregnant ewes and determination of their concentrations in milk, allantoic fluid, and newborn plasma.

The objectives of this study were to determine the pharmacokinetics of toltrazuril and its metabolites in pregnant and nonpregnant ewes following a single oral dose and to determine the plasma concentrations of these compounds in milk, allantoic fluid, and newborn plasma. Eighteen healthy ewes were randomly divided into three groups (n = 6 each): pregnant ewes at 12-13 weeks of gestation (group A), nonpregnant ewes (group B), and pregnant ewes at 1-2 weeks before expected lambing date (group C). Ewes in all groups received a single oral dose of toltrazuril at 20 mg/kg body weight. In groups A and B, blood samples were collected at 1, 3, 5, 7, 9, 12, 15, 18 hr, every 6 hr to day 3, every 12 hr to day 7 and thereafter every 24 hr to day 14 post-toltrazuril administration. In group C, parturition was induced 24-36 hr after toltrazuril administration then milk, allantoic fluid, and newborn plasma samples were collected immediately after birth. Drug metabolites were assayed using ultra high-performance liquid chromatography-ultraviolet detection method (UHPLC-UV). The maximum concentration (Cmax ), area under the plasma concentration-time curve (AUC0-t) , AUC to 24 and 48 hr (AUC0-24 ), and (AUC0-48 ) were significantly higher in pregnant ewes. Longer apparent half-life (T1/2 ), significantly higher apparent volume of distribution (Vd/F) and total clearance (Cl/F) were observed in nonpregnant ewes. The time to maximum plasma concentration (Tmax ), mean residence time (MRT) and elimination rate constant (Kel ) were similar in both groups. The AUC0-24 and AUC0-48 were significantly higher in nonpregnant ewes. The AUC0-t was significantly higher in pregnant ones. The ratio of plasma toltrazuril concentrations in ewes and toltrazuril concentrations in newborn lambs' plasma, allantoic fluid, and milk were 68%, 2.3%, and 5.3%, respectively. Results of this study showed that toltrazuril is well absorbed after a single oral dose in ewes with widespread distribution in different body tissues.

Determination of ethanamizuril, a novel triazine coccidiostat, in rat plasma by ultra-performance liquid chromatography system-tandem mass spectrometry and its application in a toxicological study.

Ethanamizuril is a new triazine compound that has the potential to be a novel anticoccidial drug. Toxicological studies in experimental rats were performed to understand the safety profile of ethanamizuril for drug product development. In this study, a novel, selective and accurate ultra-performance liquid chromatography tandem mass spectrometry method has been developed for the determination of ethanamizuril concentrations in rat plasma. With 4-nitro-o-cresol as an internal standard, sample pretreatment involved a one-step extraction with acetonitrile of 100 µL plasma. The detection was carried out by electrospray ionization mass spectrometry in negative ion mode with selected ion recording. The standard curves were linear (r2 ≥ 0.999) over the concentration range of 0.1-100 µg/mL. The relative standard deviations of intra- and inter-day precisions were less than 8.4 and 8.87%, respectively. The mean extraction recovery of ethanamizuril from rat plasma was 97.68-102.57%. The method was fully validated and successfully applied to monitor plasma concentrations of ethanamizuril in a short-term toxicity study and two-generation reproduction toxicity study. The result of the study confirmed that the elimination of ethanamizuril in rats is slow.

Diclazuril nonlinear mixed-effects pharmacokinetic modelling of plasma concentrations after oral administration to adult horses every 3-4 days.

The purpose of this study was to determine if a low dose of diclazuril (0.5mg/kg of 1.56% diclazuril pellets) given to six healthy adult horses every 3-4 days for a total of five administrations would achieve steady-state plasma concentrations known to be inhibitory to Sarcocystis neurona and Neospora caninum. Blood was collected via venipuncture immediately before (trough concentrations) and 10h after (peak concentrations) each diclazuril administration and analysed by high-pressure liquid chromatography. The mean population-derived peak concentration was 0.284µg/mL and the mean terminal half-life was 1.6 days, but with a large variation. Thus, low dose diclazuril pellets produce steady-state plasma drug concentrations known to inhibit S. neurona (0.001µg/mL) and N. caninum (0.1µg/mL).

A PRELIMINARY ANALYSIS OF PROLONGED ABSORPTION RATE OF PONAZURIL IN RED-FOOTED TORTOISES, CHELONOIDIS CARBONARIA.

Coccidial disease is significant in tortoises; Testudines intranuclear coccidiosis (TINC), caused by an unnamed coccidia, causes high mortality in diverse tortoise species. There is a lack of information on anticoccidial drugs in tortoises. The drug ponazuril has demonstrated efficacy in treating mammals infected with similar coccidial disease. Previous empirical use of ponazuril in TINC cases suggests that it may be an effective treatment. In this study, 20 mg/kg of ponazuril was orally administered to tortoises with the goal of achieving blood concentrations known to be effective for anticoccidial therapy in mammals. Ponazuril was measured in tortoise plasma, and noncompartmental analyses of pharmacokinetic parameters were attempted. Ponazuril in these tortoises did not achieve the desired concentrations known to be effective for anticoccidial treatment in mammals. Tortoises showed prolonged oral absorption, and despite sampling for 168 hr (1 wk), a terminal elimination rate constant and half-life were not able to be determined. Additional studies are needed to fully characterize ponazuril pharmacokinetics in red-footed tortoises. The optimal dose for treating TINC remains to be determined.

Toltrazuril mixed nanomicelle delivery system based on sodium deoxycholate-Brij C20 polyethylene ether-triton x100: Characterization, solubility, and bioavailability study.

Toltrazuril (Tol) is a broad-spectrum anticoccidiosis drug that is widely used in the prevention and treatment of coccidiosis infection in poultry and mammals. However, the drug has poor aqueous solubility (25 °C, 0.41 µg/mL), and its dose escalation for systemic administration remains challenging. We engineered a Tol mixed nanomicelle (TMNM) delivery system based on sodium deoxycholate-Brij C20 polyethylene ether-triton x100 (NaDC-Brij58-Tx100) as surfactants by film hydration method. The physical properties of TMNM were characterized, and the pharmacokinetic parameters of Tol and TMNM were compared. The average particle size, drug loading, saturated solubility, and critical micelle concentration (CMC) of the TMNM system were 12.28 ±â€¯0.48 nm, 3.38 ±â€¯0.12%, 3921.70 ±â€¯0.01 µg/mL (8170-fold compared with Tol), and 0.0172 mg/mL, respectively. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) micrographs, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were performed, and the results showed TMNM formation. Furthermore, the TMNM had greater bioavailability (215%) than the Tol solution. The significant increase in the drug solubility and bioavailability of TMNM suggested the TMNM is a potential oral and parenteral delivery system for Tol and has wide application prospects in the clinical context.

Detection, quantifications, and pharmacokinetics of ponazuril in healthy swine.

A study on pharmacokinetics of ponazuril in piglets was conducted after a single oral dose of 5.0 mg/kg b.w. Plasma concentrations were measured by high-performance liquid chromatography assay with UV detector at 255-nm wavelength. Pharmacokinetic parameters were derived by use of a standard noncompartmental pharmacokinetic analysis. Samples from six piglets showed good plasma concentrations of ponazuril, which peaked at 5.83 ± 0.94 µg/mL. Mean ± SD area under the plasma concentration-time curve was 1383.42 ± 363.26 h/µg/mL, and the elimination half-life was 135.28 ± 19.03 h. Plasma concentration of ponazuril peaked at 42 h (range, 36-48 h) after administration and gradually decreased but remained detectable for up to 33 days. No adverse effects were observed during the study period. The results indicate that ponazuril was relatively well absorbed following a single dose, which makes ponazuril likely to be effective in swine.

Comparison of the oral bioavailability and tissue disposition of monensin and salinomycin in chickens and turkeys.

The current study describes the pharmacokinetic parameters of two carboxylic polyether ionophores: monensin in turkeys and salinomycin in chickens. These data can be used to understand and predict the occurrence of undesirable residues of coccidiostats in edible tissues of these animal species. Special attention is paid to the distribution of residues between the different edible tissues during and at the end of the treatment period. For the bioavailability studies, monensin was administered to turkeys intravenously, in the left wing vein, at a dose of 0.4 mg /kg and orally at a dose of 20 mg /kg. Salinomycin was administered to chickens intravenously, in the left wing vein, at a dose of 0.25 mg /kg and orally at a dose of 2.5 mg /kg. Residue studies were carried out with supplemented feed at the rate of 100 mg /kg of feed for monensin in turkeys and 70 mg /kg for salinomycin in chickens, respectively. Coccidiostats had a low bioavailability in poultry (around 30% for monensin in chickens, around 1% for monensin in turkeys and around 15% for salinomycin in chickens). Monensin in chickens had a longer terminal half-life (between 3.07 and 5.55 h) than both monensin in turkeys (between 1.36 and 1.55 h) and salinomycin in chickens (between 1.33 and 1.79 h). The tissue /plasma partition coefficients showed a higher affinity of both monensin and salinomycin for fat, followed by liver and muscle tissue. The depletion data showed a fairly rapid elimination of coccidiostats in all the tissues after cessation of treatment. According to the results of depletion studies, a withdrawal period of 1 day seems sufficient to avoid undesirable exposure of consumers.

Toltrazuril sulfone sodium salt: synthesis, analytical detection, and pharmacokinetics in the horse.

Toltrazuril sulfone (ponazuril) is a triazine-based antiprotozoal agent with clinical application in the treatment of equine protozoal myeloencephalomyelitis (EPM). In this study, we synthesized and determined the bioavailability of a sodium salt formulation of toltrazuril sulfone that can be used for the treatment and prophylaxis of EPM in horses. Toltrazuril sulfone sodium salt was rapidly absorbed, with a mean peak plasma concentration of 2400 ± 169 (SEM) ng/mL occurring at 8 h after oral-mucosal dosing and was about 56% bioavailable compared with the i.v. administration of toltrazuril sulfone in dimethylsulfoxide (DMSO). The relative bioavailability of toltrazuril sulfone suspended in water compared with toltrazuril sulfone sodium salt was 46%, indicating approximately 54% less oral bioavailability of this compound suspended in water. In this study, we also investigated whether this salt formulation of toltrazuril sulfone can be used as a feed additive formulation without significant reduction in oral bioavailability. Our results indicated that toltrazuril sulfone sodium salt is relatively well absorbed when administered with feed with a mean oral bioavailability of 52%. Based on these data, repeated oral administration of toltrazuril sulfone sodium salt with or without feed will yield effective plasma and cerebrospinal fluid (CSF) concentrations of toltrazuril sulfone for the treatment and prophylaxis of EPM and other protozoal diseases of horses and other species. As such, toltrazuril sulfone sodium salt has the potential to be used as feed additive formulations for both the treatment and prophylaxis of EPM and various other apicomplexan diseases.

Pharmacokinetics of toltrazuril and its metabolites, toltrazuril sulfoxide and toltrazuril sulfone, after a single oral administration to pigs.

Toltrazuril (TZR) is a triazine-based antiprotozoal agent. Following a single oral administration of TZR at 10 and 20 mg/kg to male pigs, the mean TZR concentration in plasma peaked at 4.24 and 8.18 microg/ml at 15.0 and 12.0 hr post-dose, respectively. TZR absorbed was rapidly converted to the short-lived intermediary metabolite toltrazuril sulfoxide (TZR-SO), and then metabolized to the reactive toltrazuril sulfone (TZR-SO2). TZR-SO2 was actually more slowly eliminated, with average half-lives of 231 and 245 hr, compared with TZR (48.7 and 68.9 hr) or TZR-SO (51.9 and 53.2 hr) in the 10 and 20 mg/kg groups, respectively. This study demonstrates that TZR metabolizes to TZR-SO2 having a long-terminal half-life, enabling the persistent clinical efficacy in the treatment of I. suis infection. In contrast, special consideration should be given to the residual of TZR-SO2.

Plasma disposition of toltrazuril and its metabolites, toltrazuril sulfoxide and toltrazuril sulfone, in rabbits after oral administration.

The objective of this study was to evaluate the pharmacokinetic profiles of toltrazuril (TZR), and its major metabolites toltrazuril sulfoxide (TZR x SO) and toltrazuril sulfone (TZR x SO(2)) in rabbits after oral administrations. Rabbits were dosed once with 10 and 20mg/kg TZR via stomach tube with manual restraint. The plasma concentrations of TZR, TZR x SO and TZR x SO(2) were determined by liquid chromatography/mass spectrometry. Plasma concentration-time data after single oral administration were analyzed by a non-compartmental analysis. Plasma peak concentrations of TZR, TZR x SO and TZR x SO(2) were 30.2+/-1.5microg/mL at 20.0+/-6.9h, 8.9+/-1.3microg/mL at 20.0+/-6.9h and 14.7+/-3.9microg/mL at 96.0+/-0.0h after oral administration of TZR with 10mg/kg bw, respectively. The terminal elimination half-lives for TZR, TZR x SO and TZR x SO(2) after oral dose of 10mg/kg were 52.7+/-3.6, 56.1+/-10.7 and 76.7+/-7.5h, respectively. Plasma peak concentrations of TZR, TZR x SO and TZR x SO(2) were 39.4+/-1.2microg/mL at 28.0+/-6.9h, 12.5+/-3.9microg/mL at 20.0+/-6.9h and 24.9+/-8.74microg/mL at 112.0+/-6.9h after oral administration of TZR with 20mg/kg bw, respectively. The terminal elimination half-lives for TZR, TZR x SO and TZR x SO(2) after oral dose of 20mg/kg were 56.7+/-1.9, 68.8+/-12.5 and 82.3+/-12.6h, respectively. In conclusion, TZR was very well-absorbed through the gastrointestinal tract and rapidly metabolized to TZR x SO and TZR x SO(2) in rabbits after oral administration. TZR x SO(2) was actually more slowly eliminated than TZR and TZR x SO.

Pharmacokinetic of sulfaclozine in broiler chickens.

In this study, 30-day-old, 14 male broiler chickens were used. Two groups, each comprising 7 animals, were established. While each animal included in the first group was administered sulfaclozine at a dose of 60 mg/kg bw by intravenous route (IV), group 2 was administered sulfaclozine at the same dose but by intracrop route (IC). In group 1, serum sulfaclozine concentrations at 0.083, 0.50, 2, 6, 24 and 72h were determined to be 99.62+/-3.31, 83.50+/-4.22, 72.68+/-5.02, 58.43+/-5.39, 38.66+/-4.04 and 13.14+/-1.64 microg/ml, respectively, via HPLC. In group 2, serum drug concentrations at 0.083, 0.50, 2, 6, 24 and 72h were determined as 4.33+/-0.45, 7.95+/-0.72, 16.46+/-2.68, 22.88+/-3.00, 16.03+/-3.53 and 5.74+/-0.98 microg/ml, respectively. Statistical analyses revealed that, of all the parameters studied, only A(1)( *), A(2)( *), alpha, beta, t(1/2)(alpha), t(1/2)(beta), MRT, Vd(area), k(12), k(21), AUC(0-->72) and AUC(0-->infinity) differed significantly between the groups (p<0.05). Compared to intravenous administration, significant increase in t(1/2)(alpha), t(1/2)(beta), MRT and Vd(area), and significant decrease in A(1)( *), A(2)( *), alpha, beta, k(12), k(21), AUC(0-->72) and AUC(0-->infinity) were observed in the group, which was administered sulfaclozine by intracrop route.

Bioavailability, distribution and depletion of monensin in chickens.

The pharmacokinetics of monensin including apparent volume of distribution, total body clearance, systemic bioavailability, partition coefficients and tissue residues were determined in chickens. The drug was given by intravenous injection in the left wing vein at the dose of 0.46 mg/kg and by intracrop administration at the dose of 4 mg/kg according to a destructive sampling. The pharmacokinetic variables were compared after noncompartmental, naïve averaged, naïve pooled and nonlinear mixed-effects modelling analyses. Partition coefficients and tissue residues were determined after a treatment with feed additives (125 mg/kg of feed) of 33 days. The clearance, volume of distribution and bioavailabilty were approximately 2.2 L/h/kg, approximately 9 L/kg and approximately 30% respectively except with nonlinear mixed effects models that presented values of 1.77 L/h/kg, 14.05 L/kg and 11.36% respectively. Tissue/plasma partition coefficients were estimated to 0.83, 3.39 and 0.51 for liver, fat and thigh muscle respectively. Monensin residues after treatment were not detected 6 h after withdrawal except for fat where monensin was still quantifiable 12 h after. Pharmacokinetic variables seem to be inaccurate when assessed with non linear mixed-effects modelling associated to destructive sampling in chickens. Values varied slightly with noncompartmental, naïve averaged and naïve pooled analyses. The absorption, elimination and partition parameters will be incorporated into a physiologically based pharmacokinetic model and the depletion study will be used to test the ability of this model to describe monensin residues in edible tissues under different dosage regimens.

Detection, quantifications and pharmacokinetics of toltrazuril sulfone (Ponazuril) in cattle.

Toltrazuril sulfone (Ponazuril) is a triazine-based anti-protozoal agent with highly specific actions against apicomplexan group of organisms, which are undergoing intensive investigation. Toltrazuril sulfone may have clinical application in the treatment of Neospora. caninum and other protozoal infections in cattle. To evaluate absorption, distribution, and elimination characteristics of toltrazuril sulfone in cattle, a sensitive validated quantitative high-pressure liquid chromatography method for toltrazuril sulfone in bovine biological fluids was developed. After a single oral dose of toltrazuril sulfone at 5 mg/kg (as 150 mg/g of Marquis; Bayer HealthCare, Shawnee Mission, KS, USA), samples from six cows showed good plasma concentrations of toltrazuril sulfone, which peaked at 4821 ng/mL +/- 916 (SD) at 48 h postadministration. Thereafter, plasma concentration declined to 1950 ng/mL +/- 184 (SD) at 192 h after administration with an average plasma elimination half-life of approximately 58 h. Following oral dose of toltrazuril sulfone, the observed peak plasma concentrations were in relatively close agreement ranging from the lowest 3925 ng/mL to the highest of 6285 ng/mL with the mean peak plasma concentration being 4821 ng/mL. This study shows that toltrazuril sulfone is relatively well absorbed after oral dose in cattle. These results are therefore entirely consistent with and support the reported clinical efficacy of toltrazuril sulfone in the treatment of experimentally induced clinical cases of N. caninum and other protozoal-mediated bovine diseases.

Synthesis and detection of toltrazuril sulfone and its pharmacokinetics in horses following administration in dimethylsulfoxide.

Triazine-based antiprotozoal agents are known for their lipophylic characteristics and may therefore be expected to be well absorbed following oral administration. However, although an increase in lipid solubility generally increases the absorption of chemicals, extremely lipid-soluble chemicals may dissolve poorly in gastrointestinal (GI) fluids, and their corresponding absorption and bioavailability would be low. Also, if the compound is administered in solid form and is relatively insoluble in GI fluids, it is likely to have limited contact with the GI mucosa, and therefore, its rate of absorption will be low. Based on the above considerations, we sought a solvent with low or no toxicity that would maintain triazine agents in solution. As the oral route is most preferred for daily drug therapy, such a solvent would allow an increased rate of absorption following oral administration. In present study, it was demonstrated that dimethylsulfoxide (DMSO) increased the oral bioavailability of toltrazuril sulfone (Ponazuril) threefold, relative to oral administrations of toltrazuril sulfone suspended in water. The cross-over study of toltrazuril sulfone formulated in DMSO indicated that the absolute oral bioavailability of toltrazuril sulfone in DMSO is 71%. The high bioavailability of the DMSO-preparation suggests that its daily oral administration will routinely yield effective plasma and cerebral spinal fluid (CSF) concentrations in all horses treated. Also, this improved formulation would allow clinicians to administer loading doses of toltrazuril sulfone in acute cases of Equine Protozoal Myeloencephalitis. Another option would involve administration of toltrazuril sulfone in DMSO mixed with feed (1.23 kg daily dose) meeting the US Food and Drug Administration (FDA) recommendations for the levels of DMSO permissible in pharmaceutical preparations.

Pharmacokinetic study of clazuril (Appertex) in eggs and plasma from laying hens after single or multiple treatments, using a new HPLC method for detection.

1. Anticoccidials are widely used as food additives to prevent and treat coccidiosis. They are licensed for use in a prescribed concentration and during a specific time interval with broilers and pullets, but not for laying hens. 2. This study was set up to develop a new high pressure liquid chromatography (HPLC) method to detect clazuril (CZ: (+/-)-2-chloro-alpha-(4-chlorophenyl)-4-(4,5-dihydro-3,5-dioxo-1,2,4-triazin-2(3H)-yl)-benzeneacetonitrile) in egg yolk and albumen and in plasma; to investigate both the presence of residues of CZ in eggs and its pharmacokinetic behaviour in laying hens. 3. A single oral dose (3 mg/kg BW) and multiple oral doses (3 mg/kg BW for 5 d) were investigated. The analytical method gave very good recovery (64 to 74%) in the three different matrices (yolk, albumen and plasma); precision and accuracy were within 11%. 4. After a single dose no residue was detected in eggs collected for up to 10 d, while following multiple dose treatment, CZ residues were detected until 10 d after the end of treatment. The concentration of the drug was higher in yolk than in albumen with a maximum ratio of 10 : 1. 5. Pharmacokinetics of CZ in laying hens after a single dose showed a detectable concentration of the drug up to 24 h. It reached a steady state after the third administration in multiple dosing. 6. Although further studies are necessary, these results indicate that a single oral dose of CZ could be used as an anticoccidial for laying hens due to the lack of residues in eggs.