Ceftiofur

Ceftiofur (57) differs from the preceding cephalosporin derivatives in that it ha.s a thioester moiety at C-3. This can be introduced by displacement of the C-3 acetyl group of 7-aminocepha-losporanic acid (40) with hydrogen sulfide and esterification with 2-furylcarboxylic acid to give synthon 5reacted with trimethylsilylated oximinoether derivative 55 (itself obtained from the corresponding acid by reaction with dicyclohexylcarbodiimide and 1-hydroxy-benzotriazole) to produce, after deprotecting, ceftiofur (57) [18]. 

A monoclonal antibody-based ELISA has been utilized to determine ceftiofur levels in milk. The authors noted that matrix interference occurred, but a 1 100 dilution lowered the interference, and a 1 1000 dilution eliminated the matrix interference. Because of the high dilution, samples could not be measured below l.Opgkg The assay measured ceftiofur, its major metabolite desfuroylceftiofur, and ceftiofur protein conjugates and has been utilized to measure residues in milk from cows treated with therapeutic doses of the drug. The results from the incurred residue correlated well with a previous study using radiolabeled ceftiofur, confirming the detection of a metabolite that was not detected by HPLC. 

Cephalosporin Ceftiofur and cephapirin Gastrointestinal upset, diarrhea, nausea and allergic reactions... 

Ceftiofiir is absorbed poorly after oral administration but rapidly after intramuscular injection. In all species, ceftiofur was rapidly metabolized to desfuroyl-ceftioftir and fiiroic acid. Desfiiroylceftiofur occurred in the free form in the plasma of treated cattle but was covalently bound to plasma proteins in rats (82). Maximum blood concentrations of ceftiofiir-related residues were achieved within 0.5 and 2 h of dosing. Unmetabolized ceftiofur was generally undetectable in blood within 2-4 h of dosing (83). More than 90% of the administered dose was excreted within 24 h of administration, mostly in urine. Residues in urine and feces were composed primarily of desfiiroylceftiofur and desfiiroylceftiofur cysteine disulfide, with small amounts of unmetabolized ceftiofur. 

After intramuscular injections of radiolabeled ceftiofur to cattle and swine, the compound was absorbed rapidly into the blood and eliminated mostly in urine (84). The tissue in which highest residue concentrations were observed at 12 h after the last dose was the kidney. Most of the radioactivity was found in the form of the microbiologically active primary metabolite, desfiiroylceftiofur, conjugated to macromolecules in plasma and tissues. Desfiiroylceftiofur cysteine was also found in tissues, plasma, and urine, whereas the desfiiroylceftiofur dimer was found in urine. It was suggested that since the binding of desfiiroylceftiofur to biological molecules is reversible, all of the ceftiofiir-related residues that contain the desfuroylceftiofur moiety have the potential to be microbiologically active. 

Residue depletion studies in pigs after intramuscular administration of ceftiofur showed total residue concentrations of 590, 1190, 250, 400, and 1320 ppb in liver, kidney, muscle, skin/fat, and injection site, respectively, at 12 h after dosing. In cattle, intramuscular administration of radiolabeled ceftiofur resulted in total residue concentrations of 1294, 250, 60, and 60 ppb equivalents in liver 3508, 853, 159, and 159 ppb equivalents in kidney 208, 20, 10, and 10 ppb... 

Milk from lactating cows intramuscularly injected with radiolabeled ceftiofur was found to contain 103 and 50 ppb of total residues at 12 and 24 h, respectively, postdosing. No parent ceftiofur could be detected in milk (85). Therefore, use of ceftiofur at the approved dosage and route is not expected to result in ceftiofiir-related residues exceeding maximum residue limit (MRL) at any time postdosing, and no milk withdrawal periods need to be assigned for ceftiofur. In addition, ceftiofur residues are not hazardous to industrial cheese and yogurt starter cultures. 

European Agency for the Evaluation of Medicinal Products (EMEA), in Ceftiofur, Summary Report, Committee for Veterinary Medicinal Products, EMEA/MRL/498/... 

Ceftiofur 556.113 Ceftiofur Cattle, swine. Edible tissues - Not required... 

However, recent investigations on the effect of the tissue matrix on the detection limits attained by this test have indicated that ceftiofur, sulfonamides, streptomycin, and some macrolide antibiotics cannot be detected in intact meat with the plates and the bacterial strains prescribed in the European four-plate test (81, 82). Two plates of this system were not found suitable for screening sulfamethazine or streptomycin at levels far above the MRL the third plate detected tetracyclines and -lactams up to the MRL levels whereas the fourth was sensitive to -lactams and some but not all macrolides. Detection, on the other hand, of the fluoroquinolones enrofloxacin and ciprofloxacin could only be made possible by an additional Escherichia coli plate not included in the four-plate test. 

It has been recently reported (109) that use of both Penase and lactamase II hydrolysis and screening assays prior to chromatographic analysis can tentatively classify -lactams into three subgroups the first group includes a ceftiofur metabolite represented by desfuroyl-ceftiofur-cysteine the second, cephapirin and the third, penicillin G, ampicillin, amoxicillin, and cloxacillin. In this approach, portions of aqueous extracts of tissues are treated separately with Penase and lactamase II, and results are compared with those of untreated samples and positive controls. Bioactive ceftiofur metabolites are present, provided that the extracts retain inhibitory activity after Penase treatment but lose activity after lactamase II treatment and are positive in response to the immunochemical Lac-Tek-Cef test but negative to the Lac-Tek-Bl test (113). This approach can eliminate a large number of negative samples and, therefore, increases the efficiency of the assay. 

Higher specificity and selectivity can be obtained by reacting -lactams with suitable reagents to form derivatives with improved ultraviolet chromophores. Thus, precolumn derivatization of penicillins with triazole-mercuric chloride and ultraviolet detection at 325 nm (71, 90, 112, 114, 115, 121, 122), 340 nm (123), or 345 nm (116) has become the method of choice for more selective detection and matrix interferences reduction. An alternative precolumn reaction using iodoacetamide as derivatizing reagent has been described in ceftiofur analysis (124), while imidazole-mercuric chloride has also been suggested for on-line postcolumn derivatization of penicillin G (69). 

Straub et al. (76) reported a method for the identification and quantification of penicillin G, ampicillin, amoxicillin, cephapirin, cloxacillin, and ceftiofur residues in milk using perfusive-particle liquid chromatography combined with ultrasonic nebulization electrospray mass spectrometry. According to this method, a 0.5 ml milk sample is diluted with an equal volume of a solution consisting of acetonitrile/water (1 1), and ultrafiltrated in a microseparation system with a 10000 da molecular mass cut-off filter. An aliquot of the ultrafiltrate is then analyzed on a 15 cm porous II R/H LC (7-8 m) perfusion analytical column using the chromatographic conditions shown in Table 29.3. Concentrations as low as 10 ppb could be readily determined in milk by electrospray mass spectrometric detection. 

Amoxycillin (AMO), ampicillin (AMP), penicillin-G (PenG), penicillin-V (PenV), oxacillin (OXA), cloxacillin (CLO), and dicloxacillin (DICL) are the main representatives of penicillins cephapyrin (CEP), ceftiofur (CEF), and cefadroxil (CFD) are the main representatives of cephalosporins. Other /3-lactams could be found in the food samples, e.g., methicillin (MET), piperacillin (PIP), nafcillin (NAF), and ticarcillin (TIC), among others. 

PG Schermerhorn, PS Chu, MA Ngoh. Determination of ccphapyrin and ceftiofur residues in bovine milk by liquid chromatography with ultraviolet detection. J AOAC Int 81 973 -977, 1998. 

PJ McNeilly, VB Reeves, EJI Deveau. Determination of ceftiofur in bovine milk by liquid chromatography. J AOAC Int 79 844-847, 1996. 

J Keever, RD Voyksner, KL Tyczkowska. Quantitative determination of ceftiofur in milk by liquid chromatography-electrospray mass spectrometry. J Chromatogr A 794 57-62, 1998. 

WA Moats, S A Buckley. Determination of free metabolites of ceftiofur in animal tissues with a liquid chromatographic cleanup. J AOAC Int 81 709-713, 1998. 

Salter, R.S., D. Legg, N. Ossanna, et al. 2001. Charm safe-level 3-lactam test for amoxicillin, ampicillin, ceftiofur, cephapirin, and penicillin G in raw commingled milk. J. AOAC Int. 84 29-36. 

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