Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Veterinary Physiology, Pharmacology, and Toxicology (Veterinary Medical Sciences)

First Advisor

Steven A. Barker

Abstract

Analytical methods for extraction, detection, and quantitation of sulfadimethoxine (SDM) residues in channel catfish muscle and plasma were developed for a tiered residue monitoring program. The plasma and muscle concentrations of SDM and its primary metabolite in channel catfish, 4-N-acetylsulfadimethoxine (N-acetyl SDM), were determined in SDM medicated fish. Drug extraction methods using matrix solid phase dispersion (MSPD), drug screening methods using enzyme-linked immunoassay (ELISA), and drug residue quantitation methods using high pressure liquid chromatography (LC) are presented. All methods were developed for the simultaneous extraction and analysis of the parent compound and metabolite. MSPD extracts of muscle or plasma were reconstituted in mobile phase for LC analysis or in a buffer suitable for use in an ELISA system. The performances of four commercially available ELISAs as screening assays were evaluated using MSPD derived extracts of catfish muscle fortified at concentrations of 0, 25, 50, 100, 250 ng/g. Overall sensitivities of 98-100% and specificities of 71-94% were obtained for the four ELISAs examined. Cross-reactivity with a number of compounds was examined. All four assays reacted equally well with SDM or N-acetyl SDM. Performance results indicated that MSPD extracts can be used in these immunoassays for screening catfish muscle for violative SDM residue levels ($\ge$100 ng parent and metabolite/g). Methods for the LC analysis of MSPD derived muscle and plasma extracts are presented and evaluated. Results of the LC analysis of MSPD extracts of catfish muscle and plasma indicated that these extracts may be used for quantitation of SDM and N-acetyl SDM residues at concentrations of 50-1000 PPB. Drug concentration ratios were determined for total SDM residues in channel catfish plasma and muscle. Fish maintained in 27$\sp\circ$C water were dosed once daily for five days and sampled at intervals of 6, 12, 24, 48, 72, 96 hours after the last dose. The mean plasma:muscle total SDM residue ratio was 1.8:1. The 95% confidence interval for individual fish was (1.2:1,2.4:1). Such a tissue concentration ratio enables one to use a rapid screening method, such as an immunoassay, with a reference body fluid as an indicator of the presence of violative drug residues in an edible target tissue.

Pages

258

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