Antibiotics assay interference

Pulse polarography has also been used to measure dantrolene in plasma [181] and trimethoprim [192] and nitroimidazoles in blood [193,194]. The overall recovery of the trimethoprim assay was reported to be 81.7 6.3% (SD) with a detection limit of 0.5-0.75 fxg/mL of blood. There was no interference from the sulfamethoxazole, which is administered simultaneously. Glibomuride [195], phenobarbital, and diphenylhydantoin [97] have all been determined as their nitro derivatives after extraction from blood. The recovery of phenobarbital and diphenylhydantoin from blood was 72.3 6.5% (SD) and 76.6 2.3% (SD), respectively, with a detection limit of 1-2 fxg/mL. A modified assay [97] for the determination of both compounds in blood with TLC separation was also described. A differential pulse polarography determination of cephalosporin antibiotics in human serum samples has recently been described [196]. 

The amount of label bound to the MIP in the absence of the analyte is known as B0 and B is the amount of label bound to the MIP in the presence of each concentration of analyte. The plot of the ratio B/B0 as a function of the log[analyte], or the log [interferent], is a sigmoid curve such as the one shown in Fig. 7 for the penicillin G assay described above. As the concentration of penicillin G increases in the sample, the amount of bound PAAP decreases as does the B/B0 ratio. Another p-lactam antibiotic not derived from penicillin, such as cephapirin, did not show any cross-reactivity (Fig. 7). 

Modifications of the standard battery may be necessary for some classes, e.g., antibiotics which are toxic to bacteria or e.g., for compounds like topoisomerase inhibitors which interfere with the mammalian cell replication system. A selection of additional assays is being proposed, further modifications may be acceptable via discussion in the ICH Maintenance Process. Alternative strategies may consider assays like the in vivo Comet assay (single cell gel electrophoresis measuring DNA strand breaks) or gene mutation tests with transgenic animals or in vivo DNA adduct studies. 

The Ames test is recommended by the International Conference on Harmonisation Guidelines as part of a standard genetic toxicology battery. The other assays include the mouse lymphoma and micronucleus tests. This bacterial mutation test may not be appropriate for the evaluation of certain classes of chemicals, for example highly bactericidal compounds (e.g., certain antibiotics), any compounds that may interfere with cell division or replication, and possibly some peptides. In such cases, mammalian mutation tests may be more appropriate. 

Caf,Tb,Tp,8ClTp Sulfamethoxazole,am- Interference Tp assay picillin.par.Acsal, sal,various antibiotics ... 

An important consideration is the applicability of the rapid test to the range of sample matrices, and its susceptibility to naturally occurring interference. In a study conducted by Andrew et al., the performance of rapid antibiotic residue screening tests including the Penzyme test were evaluated in presence of different milk compositions and qualities. Metabolic changes that occur because of disease affect the composition and quality of the milk produced. Mastitis is the major disease for which antibiotic treatment is used and after which antibiotic residue screening assays are employed. 

In summary, rapid tests, either immunoassay or enzymatic formats, are the methods of choice when qualitative or semi-quantitative results are required within a short timescale, specifically, around 30 min for targeted residue screening. In general, these assay formats are portable (suitable for in situ testing) and simple to both operate and interpret. A wide variety of test formats are commercially available, many of which are applicable for the detection of classes of antibiotics, such as P-lactams and tetracyclines with detection capabilities at or below the appropriate RLs. As with other test kits, it is important to determine the applicability of the assay for the specific matrix type prior to use as certain matrices are known to contain interference that causes elevated false non-compliant/compliant rates. 

The turbidimetric technique has advantages and disadvantages as in the case of the plate diffusion assay. It is fortunate that some of the disadvantages of one method are found to be no problem in the other. Within limits, turbidimetric methods are not affected by most solvents, surface active agents, organic salts, and impurities which may change an antibiotic s diffusion characteristics. Interference is encountered with highly... 

The addition of either actinomycin or puromycin to the incubation mediam has been found to inhibit the FSH release in response to either crude rat hypothalamic extract or partially purified ovine FRF (38). The additions produced a somewhat more reproducible effect if a 30 min preincubation period in the presence of the antibiotic preceded the 6 hrs of incubation in the presence of both hypothalamic extract and antibiotic however, significant results were obtained by either procedure. Approximately equal effects were obtained by doses of 10-40jLtg/ml of actinomycin and lO-lOOjLtg/xnl of puromycin. These dosages are in the range found to be effective in blocking the response of adrenal cortex to ACTH in vitro (39,40) and were effective in blocking protein synthesis in the pituitary in the case of puromycin and RNA synthesis in the case of actinomycin. They did not interfere with the assay of the... 

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