Application of an enzyme immunoassay for the determination of sulphamethazine (sulphadimidine) residues in swine urine and plasma and their use as predictors of the level in edible tissue

Development of a sensitive monoclonal antibody-based ELISA for the detection of sulfamethazine in cow milk, honey, and swine urine

A specific monoclonal antibody (MAb) against sulfamethazine was produced with hybridoma technology. This assay shows very high sensitivity with IC50 of 0.4 ng/mL and LOD of 0.05 ng/mL when it was run in 0.02 mol/L PBS (pH 7.5). This MAb has shown high specificity to sulfamethazine, with little cross reactivity for sulfamerazine (5.27%) and sulfadimethoxypyrimidine (1.12%) and very low cross reactivity values for the other test compounds (≤0.1%). Sulfamethazine was spiked in milk, honey, and swine urine. After a simple extraction procedure the extracts at appropriate dilution were analyzed by ELISA. Satisfactory results were obtained by this assay, with average recoveries of 95-116% and coefficients of variation (CVs) of 5-9%. These results suggests that the MAb-based ELISA will be a feasible quantitative/screening method for sulfamethazine residue in real samples.

Development of a physiologic-based pharmacokinetic model for estimating sulfamethazine concentrations in swine and application to prediction of violative residues in edible tissues

OBJECTIVE

To develop a flow-limited, physiologic-based pharmacokinetic model for use in estimating concentrations of sulfamethazine after IV administration to swine.

SAMPLE POPULATION

4 published studies provided physiologic values for organ weights, blood flows, clearance, and tissue-to-blood partition coefficients, and 3 published studies provided data on plasma and other tissue compartments for model validation.

PROCEDURE

For the parent compound, the model included compartments for blood, adipose, muscle, liver, and kidney tissue with an extra compartment representing the remaining carcass. Compartments for the N-acetyl metabolite included the liver and the remaining body. The model was created and optimized by use of computer software. Sensitivity analysis was completed to evaluate the importance of each constant on the whole model. The model was validated and used to estimate a withhold interval after an IV injection at a dose of 50 mg/kg. The withhold interval was compared to the interval estimated by the Food Animal Residue Avoidance Databank (FARAD).

RESULTS

Specific tissue correlations for plasma, adipose, muscle, kidney, and liver tissue compartments were 0.93, 0.86, 0.99, 0.94, and 0.98, respectively. The model typically overpredicted concentrations at early time points but had excellent accuracy at later time points. The withhold interval estimated by use of the model was 120 hours, compared with 100 hours estimated by FARAD.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of this model enabled accurate prediction of sulfamethazine pharmacokinetics in swine and has applications for food safety and prediction of drug residues in edible tissues.

Preliminary evaluation of a lateral flow immunoassay device for screening urine samples for the presence of sulphamethazine

A lateral flow immunoassay (LFIA) device was developed and applied to testing urine samples for residues of the antimicrobial sulphamethazine (SMZ). This report describes the preparation of a rat monoclonal antibody to SMZ and its characterisation in an ELISA format. Apart from SMZ, the antibody showed high (> or =50%) cross-reactivity to N4-acetyl-sulphamethazine (55%), sulphamerazine (59%) and sulphisoxazole (50%) and lower cross-reactivity of 18% to sulphachlorpyridazine and sulphadiazine. The LFIA device consisted of a nitrocellulose membrane spotted with SMZ-ovalbumin and goat anti-mouse antibody as capture line and control line, respectively. Mouse anti-rat IgG F(ab')2 fragment specific antibody, adsorbed to colloidal carbon, was used as the detection ligand in the LFIA. The LFIA device had a cut-off value of 6.3 ng/ml in diluted (1/10) urine. Urine samples from SMZ-treated pigs, and bovine and porcine urine samples fortified with SMZ were used for a blind, four-laboratory evaluation of the performance of the LFIA device. Concentrations of SMZ in the test samples (n=29), as determined by LC-MS/MS, ranged from 0 (<3) to 1174 ng/ml. The evaluation of the LFIA device showed an overall sensitivity of 100%, a specificity of 71%, and positive and negative prediction values of 73% and 100%, respectively. The LFIA device has been fabricated as a test kit for determining SMZ residues in animals produced for slaughter.

Rapid and sensitive screening of sulfamethazine in porcine urine with an enzyme-linked immunosorbent assay and a field-portable immunofiltration assay

An enzyme-linked immunosorbent assay (ELISA) and an enzyme-linked immunofiltration assay (ELIFA) were developed for the screening of sulfamethazine (SMZ) in porcine urine. Incurred urine samples were measured by ELISA with a working range of 0 to 10 ng of SMZ per ml. The assay showed good accuracy and precision, with recoveries above 99.8% and intra- and interassay coefficients of variation (CVs) ranging from 2.6 to 5.6% and from 5.9 to 12.7%, respectively. Good agreement was observed when the results of the immunoassay were compared with those of liquid chromatography/tandem mass spectrometry analysis. For the ELIFA, a nylon membrane is placed on top of an absorbent material and covalently coated with rabbit anti-rat immunoglobulins. Free binding sites are blocked, and monoclonal anti-SMZ antibodies, SMZ standard or urine, and SMZ-horse radish peroxidase conjugate are subsequently dropped onto the membrane. During the assay, the reactants are drawn through the membrane because of its close contact with the absorbent pad. Finally, a substrate solution is added for blue color development. The blue spot produced can be visually evaluated or instrumentally measured (numeric deltaE*ab value), and the intensity of its color is inversely proportional to the analyte concentration. When a blue dot appears on the membrane, even if its color is less intense than that of the negative control, the sample is considered "negative," i.e., it is thought to contain a concentration of SMZ that is below the visual detection limit. If no color appears on the test membrane, the sample is considered "positive," i.e., it is thought to contain a concentration of SMZ that is equal to or above the visual detection limit. Validation of the assay showed good inter- and intra-assay precision (CV < 10%). Because samples can be analyzed after a simple dilution in <30 min with this assay format, it has strong potential for application in the field.

Development of an ELISA for sulfachlorpyridazine and investigation of matrix effects from different sample extraction procedures

The development of an enzyme-linked immunosorbent assay (ELISA) for the detection of residues of sulfachlorpyridazine (SCP) is described for the first time. The assay is highly specific for SCP, is simple to perform and has a lower detection limit of 0.65 ng/ml in assay buffer. In potential application of the assay to detect residues of SCP at the 0.1 mg/kg level in eggs, milk, beef, lamb, pork, chicken, turkey, porcine kidney, porcine liver and pig feedstuffs is discussed with regard to the effects of sample extracts on the standard curves. The antibody exhibits a rare stability in assay buffers containing up to 30% methanol. It is concluded that the ELISA for SCP has the appropriate characteristics for development into a robust method for the detection of this sulphonamide in agri-food materials.

Liquid chromatography tandem mass spectrometric quantitation of sulfamethazine and its metabolites: direct analysis of swine urine by triple quadrupole and by ion trap mass spectrometry

This work describes a new method for the quantitation of trace amounts of sulfamethazine (SMZ) and its main metabolite, N4-acetylsulfamethazine (Ac-SMZ), in swine urine, using high-performance liquid chromatography (HPLC) tandem mass spectrometric analysis of crude urine after addition of internal standard and simple dilution with water. The aim was to determine whether residues of this sulfamidic drug, normally administered to swine in order to prevent infectious diseases, were present in urine at levels lower than those permitted by regulatory authorities before human consumption (EU Project SMT, contract number CT 96-2092). A 10 microL volume of diluted urine was injected into a very short, narrow-bore chromatographic column (Zorbax SB-C18 2.1 i. d. x30 mm length, 3.5 microm pore size). Elution of the analytes of interest was achieved in less than seven minutes using a rapid gradient (from 20 to 80% methanol in 3 minutes). Either a PE Sciex API 365 triple quadrupole (QqQ), operated in the selected reaction monitoring (SRM) mode, or a Finnigan LCQ ion trap (IT) mass spectrometer, operated in narrow-range product ion scan, was used as the final detector. Electrospray (ESI) was used as the ionization technique. A comparison of the two tandem mass spectrometers was performed by analyzing the same set of test samples, at three concentration levels, on three different days. Linearity of responses of the calibration standards, intra- and inter-assay precision of the samples, specificity and limits of detection were evaluated for both systems. Both the QqQ and the IT instrument was suitable for rapid, sensitive and specific determination of the analytes, although the overall performance of the QqQ was slightly superior in terms of linearity, precision and sensitivity.