Direct-gradient high-performance liquid chromatographic analysis and preliminary pharmacokinetics of flumequine and flumequine acyl glucuronide in humans: effect of probenecid

Liquid Chromatographic Enantioseparation of Some Fluoroquinoline Drugs Using Several Polysaccharide-Based Chiral Stationary Phases

The enantioseparation of three fluoroquinoline antibacterial drugs, namely, flumequine, ofloxacin and lomefloxacin using high-performance liquid chromatography was optimized on seven polysaccharide-derived chiral stationary phases, namely, Chiralpak® IB, chiralpak® IA, Chiralpak® AD, Chiralcel® OJ, Chiralcel® OD, Chiralcel® OD-H and Chiralcel® OZ-3 and applying different mobile phases in isocratic mode is described. The role of addition of organic additives was also investigated. A baseline separation of flumequine, ofloxacin and lomefloxacin enantiomers was achieved. Parameters influencing enantioseparation including mobile phase, organic additive and chemical nature of the chiral selector found to be highly influencing on the enantiomeric separation were investigated. Chiral recognition mechanism(s) are also presented.

Acyl glucuronides: the good, the bad and the ugly

Acyl glucuronidation is the major metabolic conjugation reaction of most carboxylic acid drugs in mammals. The physiological consequences of this biotransformation have been investigated incompletely but include effects on drug metabolism, protein binding, distribution and clearance that impact upon pharmacological and toxicological outcomes. In marked contrast, the exceptional but widely disparate chemical reactivity of acyl glucuronides has attracted far greater attention. Specifically, the complex transacylation and glycation reactions with proteins have provoked much inconclusive debate over the safety of drugs metabolised to acyl glucuronides. It has been hypothesised that these covalent modifications could initiate idiosyncratic adverse drug reactions. However, despite a large body of in vitro data on the reactions of acyl glucuronides with protein, evidence for adduct formation from acyl glucuronides in vivo is limited and potentially ambiguous. The causal connection of protein adduction to adverse drug reactions remains uncertain. This review has assessed the intrinsic reactivity, metabolic stability and pharmacokinetic properties of acyl glucuronides in the context of physiological, pharmacological and toxicological perspectives. Although numerous experiments have characterised the reactions of acyl glucuronides with proteins, these might be attenuated substantially in vivo by rapid clearance of the conjugates. Consequently, to delineate a relationship between acyl glucuronide formation and toxicological phenomena, detailed pharmacokinetic analysis of systemic exposure to the acyl glucuronide should be undertaken adjacent to determining protein adduct concentrations in vivo. Further investigation is required to ascertain whether acyl glucuronide clearance is sufficient to prevent covalent modification of endogenous proteins and consequentially a potential immunological response.

Optimization to eliminate the interference of migration isomers for measuring 1-O-beta-acyl glucuronide without extensive chromatographic separation

A highly selected reaction monitoring (SRM) method has been investigated for the determination of muraglitazar 1-O-beta-acyl glucuronide in animal and human plasma without chromatographic separation of this naturally formed acyl glucuronide from its migration isomers. In the ion source or the collision cell, glucuronides are often prone to lose the dehydrated glucuronic acid (176 Da) and convert back into the parent drug (aglycone). The extent of loss of the glucuronide moiety can differ among glucuronides. For the naturally occurring muraglitazar 1-O-beta-acyl glucuronide, or its synthetic anomer 1-O-alpha-glucuronide, the loss of the glucuronide moiety was a major fragment ion. The loss of the glucuronide moiety was greater for the 1-O-beta-acyl glucuronide than the 1-O-alpha-anomer. In addition, the loss of the glucuronide moiety was insignificant (less than 0.01%) with the other glucuronide isomers (2-, 3- or 4-O, alpha or beta). Given the fact that the 1-O-alpha-anomer was a minor impurity in the muraglitazar 1-O-beta-acyl glucuronide reference standard, and not either a conversion product of 1-O-beta-acyl glucuronide or endogenously formed, the SRM transition corresponding to the loss of the glucuronide moiety was very specific for 1-O-beta-acyl glucuronide, and practically free from interference of the other isomers under optimized collision-cell conditions. As a result, extensive chromatographic separation of 1-O-beta-acyl glucuronide from its migration isomers was not required. The use of this specific SRM transition effectively reduced the separation time from 12.0 min of a long-column high-performance liquid chromatography (HPLC) method to 2.5 min by use of a shorter column. The standard curve performance and analysis results of 1-O-beta-acyl glucuronide incubation samples showed that the short-column method could produce equivalent results to the long-column method but with a 4.5-fold improvement in sample throughput. This approach may be useful for other 1-O-beta-acyl glucuronide measurements with proper tuning of collision energy. The generation of a breakdown curve (abundance vs. collision energy) helps to define whether appropriate conditions may be selected for specific MRM transitions.

Separation of a BMS drug candidate and acyl glucuronide from seven glucuronide positional isomers in rat plasma via high-performance liquid chromatography with tandem mass spectrometric detection

A high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of a BMS drug candidate and its acyl glucuronide (1-O-beta glucuronide) in rat plasma. A 50-microL aliquot of each plasma sample was fortified with acetonitrile containing the internal standard to precipitate proteins and extract the analytes of interest. After mixing and centrifugation, the supernatant from each sample was transferred to a 96-well plate and injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Phenomenex Luna C(18), 3 mm x 150 mm, 3 microm column. The mobile phase contained 0.075% formic acid in 70:30 (v/v) acetonitrile/water. Under the optimized chromatographic conditions, the BMS drug candidate and its acyl glucuronide were separated from its seven glucuronide positional isomers within 10 min. Resolution of the parent from all glucuronides and acyl glucuronide from its positional isomers was critical to avoid their interference with quantitation of parent or acyl glucuronide. Detection was by positive ion electrospray MS/MS on a Sciex API 4000. The standard curve, which ranged from 5 to 5000 ng/mL, was fitted to a 1/x(2) weighted quadratic regression model for both the BMS drug candidate and its acyl glucuronide. Whole blood and plasma stability experiments were conducted to establish the sample collection, storage, and processing conditions. The validation results demonstrated that this method was rugged and repeatable. The same methodology has also been used in mouse and human plasma for the determination of the BMS drug candidate and its acyl glucuronide.

Validation of a liquid chromatography-tandem mass spectrometry method for the simultaneous quantification of 11 (fluoro)quinolone antibiotics in swine kidney

A LC-MS-MS method has been validated for the simultaneous quantification of 11 (fluoro)quinolone antibiotics at the maximum residue level (MRL) in swine kidney. The studied compounds were danofloxacine, cinoxacine, ciprofloxacine, noxacine, enrofloxacine, flumequine, marbofloxacine, nalidixic acid, norfloxacine, ofloxacine and oxolinic acid. The method involves solid-phase extraction of these compounds followed by LC-MS-MS analysis using an electrospray ionisation interface. Limits of quantification < or = 50 microg/kg could be obtained in swine kidney, much lower than every MRL. The validation is discussed. This work was carried out in order to support the European Union policy on consumer health

High-performance liquid chromatographic determination of oxolinic acid and flumequine in the live fish feed artemia

A high-performance liquid chromatography (HPLC) analytical method for the determination of oxolinic acid and flumequine in Artemia nauplii is described. The samples were extracted and cleaned up by a solid-phase extraction (SPE) procedure using SPE C18 cartridges. Oxolinic acid and flumequine were determined by reversed-phase HPLC using a mobile phase of methanol-0.1 M phosphate buffer, pH 3 (45:55, v/v) and a UV detection wavelength of 254 nm. Calibration curves were linear for oxolinic acid in the range of 0.2-50 microg/g (r2=0.9998) and for flumequine in the range of 0.3-50 microg/g (r2=0.9994). Mean recoveries amounted to 100.8% and 98.4% for oxolinic acid and flumequine, respectively. The quantification limit was 0.2 microg/g for oxolinic acid and 0.3 microg/g for flumequine. Quantitative data from an in vivo feeding study indicated excellent uptake of both drugs by Artemia nauplii.

Pharmacokinetics, bioavailability and absorption of flumequine in the rat

The study demonstrates that the oral extent of bioavailability of flumequine in the rat, relative to the intravenous injection, is complete (0.94 +/- 0.04) and not significantly different from that found by the intraduodenal route (0.95 +/- 0.04). The rate of oral bioavailability, however, is slow (ka = 1.20 +/- 0.07 h-1; Tmax = 2.0 h), but enough to maintain plasma levels above the minimal inhibitory concentration of the most common pathogens for an extended period of time (about 10 h). The reason for the oral absorption slowness could be a slow gastric emptying, an adsorption to the gastric mucosae, a precipitation in the gastric medium or any other feature concerning the stomach as the intraduodenal administration is very quick (kid = 38.1 +/- 4.7 h-1; Tmax = 0.05 h). A possible precipitation of flumequine cannot be discarded as the solubility of flumequine is very low in the pH range of 3 to 6 (mean pH values for rat stomach and rat intestine, respectively; T.T. Kararli, Biopharm. Drug Dispos. 16 (1995) 351-380). Flumequine was shown to be not substantially excreted in bile (2-3% of the dose). Surprisingly, plasma levels and AUC values found for animals with interrupted bile flow always surpass those found for animals with enterohepatic circulation. This could be due to experimental model features, which might bias plasmatic flumequine concentrations if the homeostatic equilibrium of the animal is not completely restored due to the volume reduction induced by biliary extraction.

Routine determination of flumequine in kidney tissue of pig using automated liquid chromatography

A high-performance liquid chromatographic assay is described as a routine analytical method for the determination of flumequine (FLU) and its hydroxylated metabolite (OH-FLU) in pig kidney tissue. Kidney samples (2 g) containing FLU and OH-FLU were extracted by liquid-liquid extraction with ethyl acetate (10 ml). Analytical separations were performed by reversed-phase HPLC with fluorometric detection at 252 nm excitation and 356 nm emission under gradient conditions. The mobile phase was acetonitrile-2.7.10(-3) M oxalic acid in water (pH 2.5). The assay is specific and reproducible within the flumequine range of 0.050-2.5 micrograms/g and recovery at 0.050 microgram/g was 94.8%.

Establishment of a microbiologically acceptable daily intake of antimicrobial drug residues

A model is presented to calculate the microbiologically acceptable daily intake (ADIm) of antibiotic residues in food products. The ADIm calculation is based on MIC values for indicator bacteria Escherichia coli, Bacteroides fragilis, Bifidobacterium spp. and Eubacterium spp., established under gut-like conditions in an in vitro simulation model. The maximum residue level (MRL) for residues in food products can be derived from the ADIm. Four phases can be distinguished in this gastro-intestinal simulation model, namely: 1. In vitro determination of the MIC for each bacterial strain by a standard method. 2. Incorporation of the drug into food (meat, milk) followed by testing of the stability of the antibiotic under gut-like conditions. 3. Adjustment of the 'gastric' fluid to the duodenal situation, inoculation with the test bacteria and anaerobic incubation at 37 degrees C for at least 18 h. 4. MIC reading confirmed by counting bacteria growing on specific solidified media. In this study the method for calculation of ADIm and MRL is given for flumequine as model drug. On the basis of MIC50 values for E. coli strains, a MRL for flumequine of 1.0 microgram/g meat or 0.25 microgram/ml milk was calculated. It is suggested that, depending on the antibacterial spectrum of the antibiotic involved, the ADIm can be determined with selected indicator bacteria, incubated under simulated gastrointestinal conditions.

Determination of furosemide with its acyl glucuronide in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis with fluorescence detection. Preliminary pharmacokinetics and effect of probenecid

Furosemide is metabolized in humans by acyl glucuronidation to the 1-O-glucuronide (Fgluc). Furosemide (F) and the conjugate can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugate was isolated by preparative HPLC from human urine samples. Furosemide and its acyl glucuronide were present in plasma. No isoglucuronides were present in acidic urine of a volunteer. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated F-acyl glucuronide. The limit of quantitation of F in plasma is 0.007 microgram/ml, Fgluc 0.010 microgram/ml. The limits of quantitation in urine are respectively: F 0.10 microgram/ml, Fgluc 0.15 microgram/ml. A pharmacokinetic profile of furosemide is shown, and some preliminary pharmacokinetic parameters of furosemide obtained from one human volunteer are given. Probenecid does not inhibit the formation of the acyl glucuronide of F, but inhibits the renal clearance of both compounds.

Probenecid inhibits the glucuronidation of indomethacin and O-desmethylindomethacin in humans. A pilot experiment

Indomethacin is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Indomethacin, its metabolite, and their conjugates can be measured directly by gradient high-pressure liquid chromatographic analysis without enzymic deglucuronidation. The pharmacokinetic profile of indomethacin and some preliminary pharmacokinetic parameters of indomethacin obtained from one human volunteer are given. In plasma only the parent drug indomethacin is present, while in urine the acyl and ether glucuronides are present in high concentrations. This confirms other reports that indomethacin and O-desmethylindomethacin may be glucuronidated in the kidney. Probenecid is a known substrate for renal glucuronidation. If indomethacin is glucuronidated in the human kidney like probenecid, then this glucuronidation might be reduced or inhibited under probenecid co-medication. This pilot experiment shows that probenecid reduced the acyl glucuronidation of indomethacin by 50% and completely inhibited the formation of O-desmethylindomethacin acyl and ether glucuronide.

Direct gradient reversed-phase high-performance liquid chromatographic determination of salicylic acid, with the corresponding glycine and glucuronide conjugates in human plasma and urine

A gradient reversed-phase HPLC analysis for the direct measurement of salicylic acid (SA) with the corresponding glycine and glucuronide conjugates in plasma and urine of humans was developed. The glucuronides were isolated by preparative HPLC from human urine samples. The concentration of the glucuronides in the isolated fraction were determined after enzymatic hydrolysis. Salicylic acid acyl glucuronide (SAAG) was not present in plasma. No isoglucuronides were present in acidic and alkaline urine of the volunteer. The limits of quantitation in plasma are: SA 0.2 microgram/ml, salicyluric acid (SU) 0.1 microgram/ml, salicylic acid phenolic glucuronide (SAPG) 0.4 microgram/ml and salicyluric acid phenolic glucuronide (SUPG) 0.2 microgram/ml. The limit of quantitation in urine is for all compounds 5 micrograms/ml. Salicylic acid acyl glucuronide is stable in phosphate buffer pH 4.9 during 8 h at 37 degrees C; thereafter it declines to 80% after 24 h. The subject's urine was therefore acidified by the oral intake of 4 x 1.2 g of ammonium chloride/day. With acidic urine, hardly any salicylic acid is excreted unchanged (0.6%). It is predominantly excreted as salicyluric acid (68.7%).

Pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans

The aim of this investigation was to assess the pharmacokinetics of naproxen in 10 human subjects after an oral dose of 500 mg using a direct HPLC analysis of the acyl glucuronide conjugates of naproxen and its metabolite O-desmethylnaproxen. The mean t1/2 of naproxen in 9 subjects was 24.7 +/- 6.4 h (range 16 to 36 h). The t1/2 of 7.4 as found in subject number 10 must, therefore, be regarded as an extraordinary case (p < 0.0153). Naproxen acyl glucuronide accounts for 50.8 +/- 7.32 per cent of the dose, its isomerized conjugate isoglucuronide for 6.5 +/- 2.0 per cent, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 3.4 per cent, and its isoglucuronide for 5.5 +/- 1.3 per cent (n = 10; 100 h collection period). Naproxen and O-desmethylnaproxen are excreted in negligible amounts (< 1 per cent). Even though urine pH of the subjects was kept acid (range pH 5.0-5.5) in order to stabilize the acyl glucuronides, isomerization takes place in blood when the acyl glucuronide is released from the liver for excretion by the kidney. Binding to plasma proteins was measured as 98 per cent and 100 per cent, respectively for the unconjugated compounds naproxen and O-desmethylnaproxen. Binding of the acyl glucuronides was less, being 92 per cent; for naproxen acyl glucuronide, 66 per cent for naproxen isoglucuronide, 72 per cent for O-desmethylnaproxen acyl glucuronide and 42 per cent for O-desmethylnaproxen isoglucuronide.

Direct gradient reversed-phase HPLC analysis and preliminary pharmacokinetics of nalidixic acid, 7-hydroxymethylnalidixic acid, 7-carboxynalidixic acid, and their corresponding glucuronide conjugates in humans

A gradient reversed-phase high pressure liquid chromatographic analysis was developed for the direct measurement of nalidixic acid with its acyl glucuronide, 7-hydroxymethylnalidixic acid with its acyl and ether glucuronides, and 7-carboxynalidixic acid in human plasma and urine. The glucuronides and 7-carboxynalidixic acid were not present in plasma after an oral dose of 1,000 mg nalidixic acid. The acyl glucuronides of 7-carboxynalidixic acid were not present in plasma and urine. The acyl glucuronides are stable in urine at pH 5.0-5.5. The subject's urine must therefore be acidified by the oral intake of 4 x 1 g of ammonium chloride per day. With acidic urine, hardly any nalidixic acid was excreted unchanged (0.2%). It was excreted as acyl glucuronide (53.4% of dose), 7-hydroxymethyl-nalidixic acid (10.0%), the latter's acyl glucuronide (30.9%), and 7-carboxynalidixic acid (4.2%).