Inhalation anesthesia induced by isoflurane alters penicillin disposition in swine tissues.

Twelve healthy swine were dosed with penicillin G intramuscularly. Fluids and tissues samples were collected at the end of two periods of general anesthesia, performed 24 h apart. Tissue samples were collected by minimally invasive laparoscopy under general anesthesia at 8 and 28 h postdose. Four nonanesthetized, penicillin-treated pigs were euthanized at 8 h postdose, and a second set of four similarly treated control pigs were sacrificed 28 h postdose. Liver penicillin tissue concentrations from animals that underwent anesthesia and laparoscopic tissue collection had tissue concentrations that were higher than nonanesthetized pigs at both time points. Urine, plasma, kidney, skeletal, and cardiac muscle showed no differences between the two groups. Laparoscopic tissue collection under general anesthesia in swine induces physiological changes that cause alterations in tissue pharmacokinetics not seen in conscious animals.

Tissue/fluid correlation study for the depletion of sulfadimethoxine in bovine kidney, liver, plasma, urine, and oral fluid.

Sulfonamides are among the oldest, but still effective, antimicrobial veterinary medicines. In steers and dairy cows, the sulfonamides are effective in the treatment of respiratory disease and general infections. Sulfadimethoxine (SDM) has been approved by US Food and Drug Administration (FDA) for use in steers and dairy cows with a tolerance of 100 ng/g (ppb) in edible tissues and 10 ppb in milk. The detection of SDM residue above tolerance in the animal slaughtered for food process will result in the whole carcass being discarded. This report describes a comprehensive depletion study of SDM (and its main metabolite) in plasma, urine, oral fluid, kidney, and liver. In this study, nine steers were injected intravenously with the approved dose of SDM; the loading dose was 55 mg/kg, followed by 27.5 mg/kg dose at 24 h and again at 48 h. Fluids (blood, urine, and saliva) and tissue (liver and kidney) samples were collected at intervals after the last dose of SMD. The combination of laparoscopic serial sampling technique with the liquid chromatography/mass spectrometry method provided the data to establish the tissue/fluid correlation in the depletion of SMD. A strong correlation and linearity of the log-scale concentration over time in the depletion stage has been confirmed for kidney, liver, and plasma.

Determination of oxytetracycline in bovine kidney and medicated milk replacer by liquid chromatography.

Improvements and optimization of AOAC INTERNATIONAL Official Method 995.09 for the detection of oxytetracycline in bovine kidney at the new U.S. tolerance of 12 ppm are reported. Recoveries from kidney fortified at 4 concentrations over the range of 3-40 ppm averaged 84-98%. Results from the kidney of a calf fed medicated milk replacer containing oxytetracycline are also reported. Additionally, adaptation of this method to the detection of oxytetracycline in medicated milk replacer is discussed.

Colorimetric determination of selenium in mineral premixes .

A method is described for determination of sodium selenite or sodium selenate in mineral-based premixes. It is based on the formation of intense-yellow piazselenol by Se(IV) and 3,3'-diaminobenzidine. Mineral premixes typically contain calcium carbonate as a base material and magnesium carbonate, silicon dioxide, and iron(III) oxide as minor components or additives. In this method, the premix is digested briefly in nitric acid, diluted with water, and filtered to remove any Iron(III) oxide. Ethylenediaminetetraacetic acid and HCl are added to the filtrate, which is heated to near boiling for 1 h to convert any selenate to selenite. After heating, the solution is buffered between pH 2 and 3 with NaOH and formic acid and treated with NH2OH and EDTA; any Se present forms a complex with 3,3'-diaminobenzidine at 60 degrees C. The solution is made basic with NH4OH, and the piazselenol is extracted into toluene. The absorbance of the complex in dried toluene is measured at 420 nm. The method was validated independently by 2 laboratories. Samples analyzed included calcium carbonate fortified with 100, 200, and 300 micrograms Se in the form of sodium selenite or sodium selenate, a calcium carbonate premix containing sodium selenite, a calcium carbonate premix containing sodium selenate, and a commercial premix; 5 replicates of each sample type were analyzed by each laboratory. Average recoveries ranged from 89 to 109% with coefficients of variation from 1.2 to 13.6%.

Multi-residue confirmation of aminoglycoside antibiotics and bovine kidney by ion spray high-performance liquid chromatography/tandem mass spectrometry.

An ion spray high-performance liquid chromatographic/tandem mass spectrometric (HPLC/MS/MS) method capable of determining the following six aminoglycosides in bovine kidney is presented: spectinomycin, hygromycin B, streptomycin, dihydrostreptomycin, gentamicin C complex and neomycin B. Tobramycin was used as an internal standard. This method uses an improved matrix solid-phase dispersion (MSPD) method for tissue extraction. A gradient HPLC separation was developed with mobile phases consisting of aqueous 20 mM pentafluoropropionic acid and acetonitrile. Protonated molecules served as precursor ions for collision-induced dissociation (CID) and three product ions were chosen for each analyte for selected reaction monitoring (SRM) where possible. A validation study was conducted for the confirmation of dihydrostreptomycin, neomycin B and four major components of the gentamicin C complex through SRM HPLC/MS/MS analysis of negative control, fortified and incurred bovine kidney samples. All of the samples analyzed could be confirmed with ion ratios within 15% of the daily mean of fortified standards and 90% of the samples had ion ratios within 10%. All compounds except spectinomycin could be detected (while monitoring three ions by SRM) in bovine kidney tissue at or below the regulatory level of concern. MSPD recoveries were acceptable with the exception of the 27% value observed for spectinomycin.

Determination of gentamicin in bovine milk using liquid chromatography with post-column derivatization and fluorescence detection.

A method capable of separating and quantifying the three major and one minor components of gentamicin in milk has been developed. The method is capable of detecting 15 ng/ml gentamicin, based on a total of the four components. Milk samples are centrifuged at 4 degrees C, the fat layer removed, and the samples deproteinated with 30% trichloracetic acid. After a second centrifugation, the supernatant is passed through a C18 solid-phase extraction column. The column is washed with water, water-methanol (50:50) and methanol. Ammonium hydroxide (16%) in methanol is used to elute the gentamicin. The eluent is evaporated to near dryness and taken up with water. An aliquot of the sample is then mixed with an ion-pairing reagent for chromatography. Separation is achieved using pentanesulfonic acid in a water-methanol mobile phase on a C18 reversed-phase column. The o-phthalaldehyde fluorescence derivatives of gentamicin are formed post-column and are detected with excitation at 340 nm and emission at 430 nm. The percent recovery of gentamicin averaged 72, 78 and 88% from milk samples fortified at 15, 30 and 60 ng/ml, respectively.

Confirmation of oxytetracycline, tetracycline and chlortetracycline residues in milk by particle beam liquid chromatography/mass spectrometry.

A method using particle beam liquid chromatography/mass spectrometry was developed for the confirmation of oxytetracycline, tetracycline and chlortetracycline residues in bovine milk. This method is one of the first to apply particle beam technology to the confirmation of animal drug residues in food products for regulatory purposes. The milk is centrifuged, using molecular weight cut-off filters to remove components of 25,000 daltons and above from the milk. The filtrate is passed through a C-18 sample preparation cartridge which retains the tetracyclines. After the columns are washed with water, the tetracyclines are eluted with 0.1 M oxalic acid in methanol and concentrated. The compounds are separated on a Novapak C-18 column with a methanol-oxalic acid-acetonitrile mobile phase. Negative chemical ionization with selective ion monitoring is used to identify the tetracyclines. The procedure was used to confirm the presence of each tetracycline at 100 ng ml-1 in fortified and incurred milk samples.