Pulmonary pharmacokinetics of desfuroylceftiofur acetamide after nebulisation or intramuscular administration of ceftiofur sodium to weanling foals.

REASONS FOR PERFORMING STUDY: Administration of ceftiofur sodium via nebulisation has been recommended for the treatment of bronchopneumonia in horses, despite the lack of pharmacokinetic and safety data. OBJECTIVES: To compare concentrations of desfuroylceftiofur acetamide (DCA) in plasma and pulmonary epithelial lining fluid (PELF) of foals after nebulisation or i.m. administration of ceftiofur sodium and to determine if nebulisation of ceftiofur sodium induces airway inflammation. STUDY DESIGN: Randomised experimental study. METHODS: Six weanling foals received ceftiofur sodium (2.2 mg/kg bwt daily for 5 doses) by the i.m. route and 6 foals received the same dose by nebulisation. Concentrations of DCA in plasma and PELF were measured after Doses 1 and 5, and differential cell counts were performed on bronchoalveolar lavage samples obtained after Dose 5. RESULTS: Foals receiving ceftiofur sodium via nebulisation had significantly lower peak concentrations (0.15 ± 0.12 vs. 6.15 ± 0.75 mg/l) and area under the curve (1.26 ± 0.96 vs. 37.63 ± 4.01 mg●h/l) in plasma compared with those receiving the drug by the i.m. route. In contrast, foals receiving ceftiofur sodium via nebulisation had significantly higher peak concentrations (4.52 ± 2.91 vs. 0.73 ± 0.73 mg/l) and area under the curve (24.14 ± 14.09 vs. 5.91 ± 3.28 mg●h/l) in PELF compared with those receiving the drug by the i.m. route. Cell concentration and differential cell count in bronchoalveolar lavage fluid of foals nebulised with ceftiofur sodium were not significantly different from those of foals nebulised with saline. CONCLUSIONS: Administration of ceftiofur sodium via nebulisation is well tolerated and DCA concentrations in PELF remain above the minimum inhibitory concentration of the drug required to inhibit the growth of 90% of Streptococcus zooepidemicus for approximately 24 h after administration. Nebulised ceftiofur sodium warrants further investigation for the treatment of bacterial infections of the lower respiratory tract in horses.

Prediction of formulation effects on dermal absorption of topically applied ectoparasiticides dosed in vitro on canine and porcine skin using a mixture-adjusted quantitative structure permeability relationship.

Topical application of ectoparasiticides for flea and tick control is a major focus for product development in animal health. The objective of this work was to develop a quantitative structure permeability relationship (QSPeR) model sensitive to formulation effects for predicting absorption and skin deposition of five topically applied drugs administered in six vehicle combinations to porcine and canine skin in vitro. Saturated solutions (20 µL) of (14) C-labeled demiditraz, fipronil, permethrin, imidacloprid, or sisapronil were administered in single or binary (50:50 v/v) combinations of water, ethanol, and transcutol (6 formulations, n = 4-5 replicates per treatment) nonoccluded to 0.64 cm(2) disks of dermatomed pig or dog skin mounted in flow-through diffusion cells. Perfusate flux over 24 h and skin deposition at termination were determined. Permeability (logKp), absorption, and penetration endpoints were modeled using a four-term Abrahams and Martin (hydrogen-bond donor acidity and basicity, dipolarity/polarizability, and excess molar refractivity) linear free energy QSPeR equation with a mixture factor added to compensate for formulation ingredient interactions. Goodness of fit was judged by r(2) , cross-validation coefficient, coefficients (q(2) s), and Williams Plot to visualize the applicability domain. Formulation composition was the primary determinant of permeation. Compounds generally penetrated dog skin better than porcine skin. The vast majority of permeated penetrant was deposited within the dosed skin relative to transdermal flux, an attribute for ectoparasiticides. The best QSPeR logKp model for pig skin permeation (r(2) = 0.86, q(2) s = 0.85) included log octanol/water partition coefficient as the mixture factor, while for dogs (r(2) = 0.91, q(2) s = 0.90), it was log water solubility. These studies clearly showed that the permeation of topical ectoparasiticides could be well predicted using QSPeR models that account for both the physical-chemical properties of the penetrant and formulation components.

Distribution, metabolism, and excretion of toceranib phosphate (Palladia, SU11654), a novel tyrosine kinase inhibitor, in dogs.

Toceranib phosphate (Palladia, SU11654), a multireceptor tyrosine kinase inhibitor with anti-tumor and anti-angiogenic activity, has been developed for the treatment of mast cell tumors in dogs. An overview of the distribution, metabolism, and excretion of toceranib phosphate in dogs is presented. When [(14)C]-toceranib was orally administered to dogs, the majority of the radioactivity (92%) was excreted in feces and only a small portion (7%) was excreted in urine. Seven days after a single 3.25 mg/kg oral dose, radioactivity was the highest in bile and liver, with measurable concentrations in lymph nodes, colon, adrenals, bone marrow, kidneys, lungs, spleen, pancreas, and skin. Plasma protein binding of toceranib in fresh plasma ranged from 90.8% to 92.8% at concentrations between 20 ng/mL and 500 ng/mL and was independent of concentration. Microsomal and hepatocyte incubations resulted in the formation of a single metabolite. Spectrometric analysis of the metabolite was consistent with the formation of an alicyclic N-oxide of toceranib. The combination of the high rate of fecal excretion and the long elimination half-life of toceranib indicate enterohepatic recirculation of the parent compound and/or the N-oxide metabolite.

Pharmacokinetic properties of toceranib phosphate (Palladia, SU11654), a novel tyrosine kinase inhibitor, in laboratory dogs and dogs with mast cell tumors.

Toceranib phosphate (Palladia, SU11654), an oral tyrosine-kinase inhibitor, is under investigation for the treatment of mast cell tumors in dogs. The pharmacokinetics of toceranib phosphate has been characterized in dogs. Means of the following pharmacokinetic parameters were estimated following a 1.0 mg/kg i.v. dose to laboratory beagles: plasma clearance of 1.45 L/kg/h, volume of distribution of 29.7 L/kg, and terminal half-life of 17.7 h. Following single oral doses of 3.25 mg/kg administered to laboratory beagles, mean C(max) estimates ranged from 68.6 ng/mL to 112 ng/mL with t(max) ranging from 5.3 h and 9.3 h postdose. Terminal half-life was estimated at 31 h. Oral bioavailability was 76.9%. There were no statistically significant (P > 0.05) differences with any pharmacokinetic parameter due to fed/fasted state or with time during 13 weeks of every-other-day dosing at 3.25 mg/kg. Toceranib concentrations were proportional with dose over the range of 2.0 to 6.0 mg/kg. The pharmacokinetics of toceranib in client-owned dogs of a variety of pure and mixed breeds with mast cell tumors was similar to that in healthy laboratory dogs. In summary, toceranib phosphate exhibited moderate clearance, a high volume of distribution, and a moderate elimination half-life. After a single oral dose at 3.25 mg/kg, the concentration vs. time curve showed broad, sustained exposure with measurable concentrations for more than 48 h. These pharmacokinetic parameters support every-other-day administration of toceranib phosphate at an initial dose of 3.25 mg/kg for the treatment of mast cell tumors in dogs.

Pharmacokinetics of dirlotapide in the dog.

An overview of the pharmacokinetics of dirlotapide in beagle dogs is presented. The following mean parameters were observed after a 0.3-mg/kg i.v. dose of dirlotapide: plasma clearance of 7.8 mL/min/kg and volume of distribution of 1.3 L/kg. Following single oral doses of 0.05, 0.3, and 1.0 mg/kg to fed dogs and 0.3 mg/kg to fasted dogs using the commercial formulation, mean C(max) of 7.5, 46, 97, and 31 ng/mL, respectively, were observed at mean t(max) of 0.8-2.0 h. AUC and C(max) increased with increasing dose, but not proportionally. Oral bioavailability was 22-41%. Exposure, as reflected by AUC, was 54% higher in the fed than fasted state. In a 14-day repeated-dose study (0.3 mg/kg dose), the mean accumulation ratio was 3.7. In a 3-month study at doses of 0.4-2.5 mg/kg, accumulation ratios ranged from 2.0 to 6.7 at day 29 and from 1.3 to 4.1 at day 87. In summary, dirlotapide exhibited low clearance, low first-pass metabolism, moderate volume of distribution, low-to-moderate oral bioavailability, a modest food effect, and variable accumulation. Large interanimal variability in systemic exposure was noted for all routes and doses, but there were no consistent sex differences.

Absorption, distribution, metabolism, and excretion of dirlotapide in the dog.

Three once-daily oral doses of 0.2 mg/kg [(14)C]dirlotapide were administered to beagle dogs to study the absorption, distribution, metabolism, and excretion of dirlotapide. Mean (14)C recovered at 2.5 and 4.5 h after the last dose was 90%. Mean (14)C in urine, bile, and feces was <1%, 1.7%, and 56% of the dose, respectively. In tissues, 26% of the (14)C dose was present in the gastrointestinal tract, 6.0% in liver, and <1% each in kidney, gall bladder, heart, and brain. To further characterize drug disposition, a single 2.5-mg/kg oral dose of [(14)C]dirlotapide was administered to beagle dogs. More than 84% of the dose had been eliminated by 72 h in feces, with 21% of the dose present in feces as parent dirlotapide. Less than 1% of the dose was excreted in urine. In bile collected during the first 24-h postdose from three dogs, 32% and 11% of the (14)C dose was present in samples from male and female dogs, respectively. Based upon metabolite profiling of plasma, excreta, and bile samples, dirlotapide was extensively metabolized to more than 20 metabolites. Biliary/fecal excretion and the potential for enterohepatic recycling of metabolites are suggested.

Performance and optimization of a combustion interface for isotope ratio monitoring gas chromatography/mass spectrometry.

Conditions and systems for on-line combustion of effluents from capillary gas chromatographic columns and for removal of water vapor from product streams were tested. Organic carbon in gas chromatographic peaks 15 s wide and containing up to 30 nanomoles of carbon was quantitatively converted to CO2 by tubular combustion reactors, 200 x 0.5 mm, packed with CuO or NiO. No auxiliary source of O2 was required because oxygen was supplied by metal oxides. Spontaneous degradation of CuO limited the life of CuO reactors at T > 850 degrees C. Since NiO does not spontaneously degrade, its use might be favored, but Ni-bound carbon phases form and lead to inaccurate isotopic results at T < 1050 degrees C if gas-phase O2 is not added. For all compounds tested except CH4, equivalent isotopic results are provided by CuO at 850 degrees C, NiO + O2 (gas-phase mole fraction, 10(-3)) at 1050 degrees C and NiO at 1150 degrees C. The combustion interface did not contribute additional analytical uncertainty, thus observed standard deviations of 13C/12C ratios were within a factor of 2 of shot-noise limits. For combustion and isotopic analyses of CH4, in which quantitative combustion required T approximately 950 degrees C, NiO-based systems are preferred, and precision is approximately 2 times lower than that observed for other analytes. Water must be removed from the gas stream transmitted to the mass spectrometer or else protonation of CO2 will lead to inaccuracy in isotopic analyses. Although thresholds for this effect vary between mass spectrometers, differential permeation of H2O through Nafion tubing was effective in both cases tested, but the required length of the Nafion membrane was 4 times greater for the more sensitive mass spectrometer.

Carbon isotopic analysis of atmospheric methane by isotope-ratio-monitoring gas chromatography-mass spectrometry.

Less than 15 min are required for the determination of delta 13CPDB with a precision of 0.2% (1 sigma, single measurement) in 5-mL samples of air containing CH4 at natural levels (1.7 ppm). An analytical system including a sample-introduction unit incorporating a preparative gas chromatograph (GC) column for separation of CH4 from N2, O2, and Ar is described. The 15-min procedure includes time for operation of that system, high-resolution chromatographic separation of the CH4, on-line combustion and purification of the products, and isotopic calibration. Analyses of standards demonstrate that systematic errors are absent and that there is no dependence of observed values of delta on sample size. For samples containing 100 ppm or more CH4, preconcentration is not required and the analysis time is less than 5 min. The system utilizes a commercially available, high-sensitivity isotope-ratio mass spectrometer. For optimal conditions of sample handling and combustion, performance of the system is within a factor of 2 of the shot-noise limit. The potential exists therefore for analysis of samples as small as 15 pmol CH4 with a standard deviation of <1%.

Factors controlling precision and accuracy in isotope-ratio-monitoring mass spectrometry.

The performance of systems in which picomole quantities of sample are mixed with a carrier gas and passed through an isotope-ratio mass spectrometer system was examined experimentally and theoretically. Two different mass spectrometers were used, both having electron-impact ion sources and Faraday cup collector systems. One had an accelerating potential of 10kV and accepted 0.2 mL of He/min, producing, under those conditions, a maximum efficiency of 1 CO2 molecular ion collected per 700 molecules introduced. Comparable figures for the second instrument were 3 kV, 0.5 mL of He/min, and 14000 molecules/ion. Signal pathways were adjusted so that response times were <200 ms. Sample-related ion currents appeared as peaks with widths of 3-30 s. Isotope ratios were determined by comparison to signals produced by standard gases. In spite of rapid variations in signals, observed levels of performance were within a factor of 2 of shot-noise limits. For the 10-kV instrument, sample requirements for standard deviations of 0.1 and 0.5% were 45 and 1.7 pmol, respectively. Comparable requirements for the 3-kV instrument were 900 and 36 pmol. Drifts in instrumental characteristics were adequately neutralized when standards were observed at 20-min intervals. For the 10-kV instrument, computed isotopic compositions were independent of sample size and signal strength over the ranges examined. Nonlinearities of <0.04%/V were observed for the 3-kV system. Procedures for observation and subtraction of background ion currents were examined experimentally and theoretically. For sample/ background ratios varying from >10 to 0.3, precision is expected and observed to decrease approximately 2-fold and to depend only weakly on the precision with which background ion currents have been measured.

Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry.

Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO2 and N2. The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10(5); the precision actually obtained is often better than one part in 10(4). This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic delta values. Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined. Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.

Isotope-ratio-monitoring gas chromatography-mass spectrometry: methods for isotopic calibration.

In trial analyses of a series of n-alkanes, precise determinations of 13C contents were based on isotopic standards introduced by five different techniques and results were compared. Specifically, organic-compound standards were coinjected with the analytes and carried through chromatography and combustion with them; or CO2 was supplied from a conventional inlet and mixed with the analyte in the ion source, or CO2 was supplied from an auxiliary mixing volume and transmitted to the source without interruption of the analyte stream. Additionally, two techniques were investigated in which the analyte stream was diverted and CO2 standards were placed on a near-zero background. All methods provided accurate results. Where applicable, methods not involving interruption of the analyte stream provided the highest performance (sigma = 0.00006 at.% 13C or 0.06% for 250 pmol C as CO2 reaching the ion source), but great care was required. Techniques involving diversion of the analyte stream were immune to interference from coeluting sample components and still provided high precision (0.0001 < or = sigma < or = 0.0002 at.% or 0.1 < or = sigma < or = 0.2%).

Nitrogen isotopic analyses by isotope-ratio-monitoring gas chromatography/mass spectrometry.

Amino acids containing natural-abundance levels of 15N were derivatized and analyzed isotopically using a technique in which individual compounds are separated by gas chromatography, combusted on-line, and the product stream sent directly to an isotope-ratio mass spectrometer. For samples of N2 gas, standard deviations of ratio measurement were better than 0.1% (Units for delta are parts per thousand or per million (%).) for samples larger than 400 pmol and better than 0.5% for samples larger than 25 pmol (0.1% 15N is equivalent to 0.00004 atom % 15N). Results duplicated those of conventional, batchwise analyses to within 0.05%. For combustion of organic compounds yielding CO2/N2 ratios between 14 and 28, in particular for N-acetyl n-propyl derivatives of amino acids, delta values were within 0.25% of results obtained using conventional techniques and standard deviations were better than 0.35%. Pooled data for measurements of all amino acids produced an accuracy and precision of 0.04 and 0.23%, respectively, when 2 nmol of each amino acid was injected on column and 20% of the stream of combustion products was delivered to the mass spectrometer.

Nitrogen isotopic analyses by isotope-ratio-monitoring gas chromatography / mass spectrometry.

Amino acids containing natural-abundance levels of (15)N were derivatized and analyzed isotopically using a technique in which individual compounds are separated by gas chromatography, combusted on-line, and the product stream sent directly to an isotope-ratio mass spectrometer. For samples of N2 gas, standard deviations of ratio measurement were better than 0.1‰ (Units for δ are parts per thousand or per million (‰).) for samples larger than 400 pmol and better than 0.5‰ for samples larger than 25 pmol (0.1‰ (15)N is equivalent to 0.00004 atom % (15)N). Results duplicated those of conventional, batchwise analyses to within 0.05‰. For combustion of organic compounds yielding CO2/N2 ratios between 14 and 28, in particular for N-acetyl n-propyl derivatives of amino acids, δ values were within 0.25‰ of results obtained using conventional techniques and standard deviations were better than 0.35‰. Pooled data for measurements of all amino acids produced an accuracy and precision of 0.04 and 0.23‰, respectively, when 2 mnol of each amino acid was injected on column and 20% of the stream of combustion products was delivered to the mass spectrometer.

Recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach.

Study of organic matter in immature sediments from a Messinian evaporitic basin shows that consideration of structures, modes of occurrence, and carbon isotopic compositions of free and sulfur-bound carbon skeletons allow identification of biochemical precursors. Detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way. Moreover, unprecedented biochemicals were recognized; these extend the horizon of biomarker geochemistry.