Oxidative bioactivation of nitrofurantoin in rat liver microsomes.

1. Nitrofurantoin (NFT), a 5-nitrofuran derivative, has been widely used for the treatment of specific urinary tract infections. It has been reported that exposure to NFT was associated with various adverse effects, particularly hepatotoxicity and pneumotoxicity. The objective of the study was to identify reactive metabolites of NFT and explore the mechanisms of the toxicities. 2. An epoxide intermediate generated in microsomal incubations was trapped by glutathione (GSH) and 4-bromobenzyl mercaptan (BBM), and the resulting GSH and BBM conjugates were characterized by LC-MS/MS. A spontaneous denitration took place in the trapping reaction. 2-Nitrofuran and 2-hydroxyfuran as model compounds were employed to probe the mechanism of the denitration. 3. The oxidative activation of NFT was P450-dependent, and P450 3A5 and P450 2A6 were the principal enzymes responsible for the bioactivation. The findings facilitate the understanding of the mechanisms of NFT-induced toxicities.

Modeling the biotransformation of trimethoprim in biological nutrient removal system.

A pilot scale biological nutrient removal (BNR) process, batch experiments and modeling exercises were employed to investigate the removal and biotransformation of trimethoprim (TMP) in a BNR activated sludge process. The concentrations of the active microbial groups - ammonia oxidizing bacteria (AOB), ordinary heterotrophic organisms (OHOs) and polyphosphate accumulating organisms (PAOs) - in the BNR bioreactor were quantified through modeling of the pilot bioreactor. The overall TMP removal efficiency for the pilot BNR process was 64 ± 14% while the TMP biotransformation efficiencies in the anaerobic, anoxic and aerobic zones were 22 ± 20%, 27 ± 8% and 36 ± 5% respectively. Batch tests with and without nitrification inhibition showed that AOB played a role in the biotransformation of TMP in BNR activated sludge. A pseudo first order model which incorporated the contributions of PAOs, OHOs and AOB to the overall biodegradation of TMP was found to describe the biodegradation of TMP in batch tests with and without nitrification inhibition. This model showed that PAOs, OHOs and AOB contributed towards the biotransformation of TMP in aerobic BNR activated sludge with the biotransformation rate constants following the trend of kAOB > kOHOs > kPAOs.

An immunochromatographic assay for rapid and direct detection of 3-amino-5-morpholino-2-oxazolidone (AMOZ) in meat and feed samples.

BACKGROUND: Furaltadone (FTD) is a type of nitrofuran and has been banned in many countries as a veterinary drug in food-producing animals owing to its potential carcinogenicity and mutagenicity. FTD is unstable in vivo, rapidly metabolizing to 3-amino-5-methylmorpholino-2-oxazolidinone (AMOZ); thus AMOZ can be used as an indicator for illegal usage of FTD. Usually, for the determination of nitrofurans, the analyte is often a derivative of the metabolite rather than the metabolite itself. In this study, based on the monoclonal antibody (mAb) against AMOZ, a competitive immunochromatographic assay (ICA) using a colloidal gold-mAb probe for rapid and direct detection of AMOZ without a derivatization step in meat and feed samples was developed. RESULTS: The intensity of red color in the test line is inversely related to the analyte concentration and the visual detection limit was found to be 10 ng mL⁻¹. The performance of this assay was simple and convenient because the tedious and time-consuming derivatization step was avoided. The ICA detection was completed within 10 min. The ICA strips could be used for 7 weeks at room temperature without significant loss of activity. The AMOZ spiked samples were detected by ICA and confirmed by enzyme-linked immunosorbent assay. The results of the two methods were in good agreement. CONCLUSION: The proposed ICA provides a feasible tool for simple, sensitive, rapid, convenient and semi-quantitative detection of AMOZ in meat and feed samples on site. To our knowledge, this is the first report of the ICA for direct detection of AMOZ.

Stability studies of the metabolites of nitrofuran antibiotics during storage and cooking.

Nitrofuran antibiotics cannot be used in food production within the European Union because of their potential health risks to consumers. The recent discovery of their widespread use in global food industries and the finding of semicarbazide in baby food as a result of packaging contamination have focused attention on the toxicity and stability of these drugs and their metabolites. The stability of the nitrofuran marker residues 3-amino-2-oxazolidinone (AOZ), 3-amino-5-morpholinomethyl-2-oxazolidone (AMOZ), 1-aminohydantoin (AHD) and semicarbazide (SEM) were tested. Muscle and liver of nitrofuran treated pigs were cooked by frying, grilling, roasting and microwaving. Between 67 and 100% of the residues remained after cooking, demonstrating that these metabolites are largely resistant to conventional cooking techniques and will continue to pose a health risk. The concentration of metabolites in pig muscle and liver did not drop significantly during 8 months of storage at -20 degrees C. Metabolite stock and working standard solutions in methanol were also stable for 10 months at 4 degrees C. Only a 10 ng ml(-1) solution of SEM showed a small drop in concentration over this extended storage period.

[In vitro activity, serum, urine and prostatic adenoma concentrations of ofloxacin in urologic patients with complicated urinary tract infections]. / In vitro-Aktivität, Serum-, Urin- und Prostataadenom-Gewebekonzentrationen von Ofloxacin bei urologischen Patienten mit komplizierten Harnwegsinfektionen.

The minimal inhibitory concentrations (MIC) of ofloxacin against 400 isolates cultured from the urine of urological patients with complicated urinary tract infections (UTI) resulted in an inhibition of 94% (99%) of the gram-negative strains at a concentration of 1 mg/l (2 mg/l) and an inhibition of 59% (100%) of the gram-positive strains at a concentration of 1 mg/l (4 mg/l). According to the MIC 90% values, the corresponding grade of activity was as follows: ciprofloxacin, ofloxacin, norfloxacin, pefloxacin, enoxacin, pipemidic acid, enoxacin and nalidixic acid. After an oral dose of 400 mg of ofloxacin, the mean peak serum concentration of ten patients was 5.5 mg/l. The mean renal excretion during 24 hours was 41%. In ten patients undergoing transurethral resection of the prostate, the median serum concentration was 1.87 mg/l and the median prostatic adenoma tissue concentration 1.20 mg/kg 14.5 to 19 hours after oral administration of 400 mg ofloxacin. Due to the in vitro activity and the concentrations obtained in serum, urine and tissue, ofloxacin appears to be well suited for treatment of complicated UTI.

[Tissue diffusion of flumequine into human renal and prostatic tissues. Assay of flumequine by high performance liquid chromatography after administration of 800 mg/day over 48 hours, the sampling being done 12 hours after the last ingestion]. / Etude de la diffusion tissulaire de la fluméquine chez l'homme dans les tissus rénaux et prostatiques. Dosage de la fluméquine par chromatographie liquide haute performance aprés administration de 800 mg/jour pendant 48 heures, le prélèvement étant fait 12 heures aprés la derniére prise.

Diffusion of flumequine into human renal and prostatic tissues was studied. Chemical characteristics and the natural antibacterial spectrum of the compound are described and its rapidity of absorbtion emphasized, blood levels being detected 30 minutes after administration. Maximum plasma levels were reached after 2 to 3 hours and were of the order of 17 mcg/ml, half-life being approximately 10 hours. Plasma protein binding capacity was 60 to 70%, indicating liposolubility enabling diffusion into prostatic parenchyma. Flumequine was recovered in the urine 2 hours after oral administration, maximum urinary concentrations being reached after between 3 and 6 hours, and being of the order of 280 mg/ml after single-dose 40 mg administration. The product was still recovered from the urine 12 hours later, and 60 to 70% of the dose administered after 24 hours, including 20.6% of active form. To evaluate renal and prostatic tissue diffusion 2 series of patients were studied 10 after renal surgery and 14 prostatic operations. Diffusion was excellent into renal parenchyma since the mean ratio between renal tissue and plasma concentrations was 2.41. Urine concentrations were even more extraordinary since the ratio was 136. In contrast, prostatic tissue concentrations were lower than plasma concentrations, the ratio between the two being 0.26, although levels is prostatic tissue were still sufficiently elevated to be effective against germs sensitive to flumequine.

Pharmacological principles in the treatment of urinary tract infections.

The ideal antibacterial drug for urinary tract infections should eliminate most urinary pathogens but not alter the colonic flora. Levels in the urine can be attained with the beta-lactam and aminoglycoside antibiotics which are up to several powers of 10 higher than the minimal inhibitory concentration values of the causative organisms. At these levels even penicillin G eliminates many Gram-negative urinary pathogens. Trimethoprim has a lesser propensity to select resistant organisms than most other antimicrobials. It occurs in vaginal secretions and reduces the number of Enterobacteriaceae surrounding the urethral orifice, thereby diminishing the chance of an ascending reinfection, and it is often effective in the treatment of bacterial prostatitis as it reaches therapeutic concentrations in prostatic secretions. Tetracycline therapy, however, carries a substantial chance of bacterial resistance at the next reinfection of the urinary tract, as these antibiotics produce almost uniform resistance in Escherichia coli in the faecal flora. Failure to respond to single-dose therapy actually implies the presence of antibody-coated bacteria in the urine, which in turn implies an upper tract or prostatic infection. This is an easy means of indicating which patients require further evaluation by intravenous pyelography or cystoscopy.