Pharmacokinetics of gacyclidine enantiomers in plasma and spinal cord after single enantiomer administration in rats.

The purpose of this study was to determine the pharmacokinetics of gacyclidine, a non-competitive NMDA antagonist, in plasma and spinal cord extracellular fluid (ECF) after IV administration of single enantiomers in rats. After implantation of microdialysis probes in spinal cord, concentrations in plasma and ECF dialysates were determined by a chiral GC/MS assay over 5 h after administration of either (+)-gacyclidine or (-)-gacyclidine (1.25 mg/kg). Plasma protein binding was estimated in vitro by equilibrium dialysis. Plasma concentrations decayed in parallel in a biphasic manner (t(1/2)alpha approximately 9 min; t(1/2)beta approximately 90 min) with no significant difference between the two enantiomers. Clearance of (+)-gacyclidine and (-)-gacyclidine (291 versus 275 ml/min per kg, respectively), volume of distribution (Vdbeta: 38 versus 40 l/kg), and protein binding (90 versus 89%) were not stereoselective. Both gacyclidine enantiomers were quantifiable in spinal cord ECF 10 min after drug administration and their concentrations remained stable over the duration of the experiment in spite of changing blood concentrations. Penetration of the two enantiomers in spinal cord ECF was similar although highly variable between animals. Exposure of spinal cord ECF was comparable for both enantiomers, and not correlated with plasma AUCs. This study showed the absence of any pharmacokinetic difference between the two enantiomers when administered individually, and no enantiomeric inversion. Both gacyclidine enantiomers penetrate rapidly and extensively into spinal cord ECF, and their distribution may involve an active transport system.

Distribution of gacyclidine enantiomers after experimental spinal cord injury in rats: possible involvement of an active transport system.

The pharmacokinetics of gacyclidine enantiomers, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist, were studied in plasma and spinal cord extracellular fluid (ECF) after experimental spinal cord injury in rats. Spinal cord trauma was produced by introducing an inflatable balloon in the dorsal subdural space. Upon implantation of microdialysis probes in spinal cord (T9) and intravenous (iv) bolus administration of (+/-)-gacyclidine (2.5 mg/kg), concentrations in plasma and ECF were monitored over 5 h and analyzed by a stereospecific gas chromatography-mass spectrometry (GC-MS) assay. In plasma, concentrations of (+)-gacyclidine were approximately 25% higher than those of (-)-gacyclidine over the duration of the experiment and decayed in parallel (t(1/2 alpha) approximately 7 min; t(1/2 beta) approximately 90 min) with no significant difference between the two enantiomers. Clearance (CL) and volume of distribution (Vd) of (-)-gacyclidine were approximately 20% higher than those of its optical antipode (CL: 285 versus 236 mL. kg(-1). min(-1); Vd(beta): 39.3 versus 31.2 l/kg). Protein binding (approximately 91%) was not stereoselective. In spinal cord ECF, both enantiomers were quantifiable within 10 min after drug administration, and their concentration remained stable over the duration of the experiment in spite of changing blood concentrations. Repeated iv bolus injections of gacyclidine did not modify these profiles. Areas under the curves (AUCs) of concentration in ECF versus time were similar for both enantiomers and not correlated with AUCs in plasma. Penetration of (-)-gacyclidine was, however, significantly higher (approximately 30%) than that of (+)-gacyclidine. In summary, the disposition of gacyclidine enantiomers is stereoselective. Both enantiomers exhibit a high affinity for spinal cord tissue, and the drug exchange between plasma and spinal cord ECF involves an active transport system. These findings contribute to the explanation of the discrepancy between drug concentrations in plasma and spinal cord ECF.

Induction and inhibition of cicletanine metabolism in cultured hepatocytes and liver microsomes from rats.

Cicletanine, a racemic furopyridine derivative synthesized as racemate, is used as an antihypertensive agent. Its two enantiomers are involved in the pharmacological effects of the drug. Cicletanine is metabolized by conjugation enzyme systems (phase II) into sulfoconjugated or glucuroconjugated enantiomers. This study reports on the use of both the induction with 3-methylcholanthrene (3-MC) or phenobarbital (PB) and inhibition with selective compounds to determine and identify UGT isoenzymes involved in the metabolism of cicletanine enantiomers. PB and 3-MC both enhanced the cicletanine enantiomer glucuronidation. These two compounds being known as inducing agents of UGT2B1 and UGTIA6 isoforms, respectively, this suggests an implication of UGT2B1 and UGT1A6 isoforms in the metabolism of the two cicletanine enantiomers: ( + )-cicletanine and ( - )-cicletanine. The use of selective compounds for inhibition study evidenced, in addition to UGT2B1 and UGT1A6 isoforms, the involvement of other UGT isoforms such as UGT1A1, UGT2B7 and UGT2B15 in cicletanine metabolism.

Influence of schedule of administration on methotrexate penetration in brain tumours.

The influence of the administration schedule (intravenous (i.v.) bolus versus i.v. infusion) on the pharmacokinetics of methotrexate (MTX) in plasma and extracellular fluid (ECF) of a brain C6-glioma was investigated in rats. MTX concentrations were determined by high performance liquid chromatography (HPLC)-ultraviolet radiation (UV). MTX (50 mg/kg) was administered by i.v. bolus or i.v. infusion (4 h). Concentration-time profiles were fitted to a two-compartment open model. Maximum MTX concentrations ranged between 178 and 294 microgram/ml (i.v. bolus), and between 11 and 24 microgram/ml (i.v. infusion) in plasma. MTX rapidly entered the tumour tissue although its concentrations in the ECF were much lower than those observed in plasma for both modes of administration. In spite of an important interindividual variability, AUC(ECF) was approximately 5-fold higher and mean MTX penetration in tumour ECF (AUC(ECF)/AUC(Plasma)) was approximately 3-fold higher after i.v. bolus than after i.v. infusion administration. These results indicate that i.v. bolus administration schedules promote MTX delivery in brain tumour tissue.

[Inefficacy of N-methyl-D-aspartate receptor complex antagonists on behavioral and histologic consequences of global cerebral ischemia in rats]. / Inefficacité des antagonistes du complexe réceptorial N-méthyl-D-aspartate à l'égard des conséquences comportementales et histologiques d'une ischémie cérébrale globale chez le rat.

Glutamic acid, an excitatory amino acid, has been proposed to play a major deleterious influence in cerebral ischemia. However, the neuroprotective activity of various glutamate receptor antagonists is often low or absent, according to the animal model used. In the present study, we examined the effect of several antagonists acting on glutamate receptors of the N-methyl-D-aspartate (NMDA) type in rats submitted to a brief (5 minutes) global cerebral ischemia. The different compounds used were poorly active or inactive on behavioural and histologic alterations induced by ischemia. Our results suggest that, in this model, overactivation of NMDA receptor complex does not play a predominant role in the pathogenesis of ischemic brain damage.

Stereoselective biotransformation of cicletanine in cultured rat and human hepatocytes.

Cicletanine [(+/-)-C] is a racemic furopyridine derivative used as an antihypertensive agent. Pharmacokinetic and metabolic studies have shown that cicletanine is rapidly and almost fully metabolized into sulfo- and glucuro-conjugated metabolites. However, the stereoselective metabolism of cicletanine is not well-known in humans. In the present study, the stereoselective aspect of cicletanine metabolism was investigated in cultured hepatocytes from humans and rats. The two enantiomers of cicletanine were both strongly metabolized in rat hepatocytes. So, after 24 h of incubation, very low amounts of free cicletanine were found [1.2% for (+)-C and 2.7% for (-)-C], respectively. In addition (+/-)-C was mainly biotransformed into conjugated metabolites: (-)-C mainly transformed into (-)-C-glucuronide (78.3+/-6.4%) and (+)-C mainly into (+)-C-sulfate (87.4+/-3.3%). In human hepatocytes, inter-individual variations were more marked than in rat hepatocytes. In addition (+/-)-C biotransformation in human was lower than the one observed in rat. (-)-C enantiomer was more metabolized than (+)-C. After a 24-h incubation the percentages of free (+)-C and (-)-C were 32.3+/-16.4 and 8.2+/-10.3, respectively. On the contrary to rat hepatocytes, both cicletanine enantiomers in humans were mainly metabolized into glucuroconjugated metabolites. These results clearly demonstrated that cicletanine underwent stereospecific metabolism in both rat and human hepatocytes.

Distribution of gacyclidine enantiomers in spinal cord extracellular fluid.

PURPOSE: Determination of the pharmacokinetics of gacyclidine enantiomers, a non-competitive NMDA antagonist, in plasma and spinal cord extracellular fluid (ECF) of rats. METHODS: Implantation of microdialysis probes in spinal cord (T9). Serial collection of plasma samples and ECF dialysates over 5 hours after IV bolus administration of (+/-)-gacyclidine (2.5 mg/kg). Plasma protein binding determined in vivo by equilibrium dialysis. Chiral GC/ MS assay. RESULTS: Plasma concentrations of (+)-gacyclidine were approximately 25% higher than those of (-)-gacyclidine over the duration of the experiment in all animals. Plasma concentrations decayed in parallel in a biphasic manner (t1/2alpha approximately 9 min; t1/2beta approximately 90 min) with no significant difference between enantiomers. Clearance and volume of distribution of (-)-gacyclidine were approximately 20% higher than those of its optical antipode (CL: 248 vs 197 ml.kg(-1)x min(-1); Vdbeta: 31.6 vs 23.5 1/kg). Protein binding (approximately 90%) was not stereoselective. Both gacyclidine enantiomers were quantifiable in spinal cord ECF 10 min after drug administration and remained stable over the duration of the experiment in spite of changing blood concentrations. Penetration of (-)-gacyclidine was significantly higher (approximately 40%) than that of (+)-gacyclidine in all animals. Yet, exposure of spinal cord ECF was similar for both enantiomers, and not correlated with plasma AUCs. CONCLUSIONS: The disposition of gacyclidine enantiomers is stereoselective. Both enantiomers exhibit a high affinity for spinal cord tissue and their distribution may involve a stereoselective and active transport system. This hypothesis could also explain the discrepancy between drug concentrations in plasma and spinal cord ECE

Modified gas chromatographic-mass spectrometric assay for the determination of gacyclidine enantiomers in human plasma.

A modified method for the determination of gacyclidine enantiomers in human plasma by GC-MS with selected-ion monitoring using the deuterated derivative of gacyclidine (d3-gacyclidine) as internal standard was developed. Following a single-step liquid-liquid extraction with hexane, drug enantiomers were separated on a chiral fused-silica capillary column (CP-Chirasil-Dex; Chrompack). The fragment ion, m/z 266, was selected for monitoring d3-gacyclidine (retention times of 35.2 and 35.6 min for the (+)- and (-)-enantiomer, respectively) whereas the fragment ion, m/z 263, was selected for quantitation of gacyclidine (retention times of 35.4 and 35.9 min for the (+)- and (-)-enantiomer, respectively). The limit of quantitation for each enantiomer was 0.3 ng/ml, using 1 ml of sample, with a relative standard deviation (RSD) < 14% and a signal-to-noise ratio of 5. The extraction recovery of both gacyclidine enantiomers from human plasma was about 75%. The calibration curves were linear (r2 > 0.996) over the working range of 0.312 to 20 ng/ml. Within- and between-day RSD were < 9% at 5, 10 and 20 ng/ml, and < 16% at 0.312, 0.625, 1.25 and 2.5 ng/ml. Intraday and interday bias were less than 11% for both enantiomers. The chromatographic behavior of d3-gacyclidine remained satisfactory even after more than 500 injections. Applicability of this specific and stereoselective assay is demonstrated for a clinical pharmacokinetic study with racemic gacyclidine.

Effects of oxazepam and acetaminophen on cicletanine metabolism in rat hepatocytes and liver microsomes.

Cicletanine, a racemic furopyridine derivative synthesized as racemate, is used as an antihypertensive agent. Its two enantiomers are involved in the pharmacological effects of the drug. Cicletanine is metabolized by conjugation enzyme systems (phase II) into sulfoconjugated or glucuroconjugated enantiomers. As oxazepam and acetaminophen are widely prescribed, especially to elderly patients, these two drugs may be co-administered with cicletanine. The metabolic profile and the kinetics of biotransformation were studied by using rat hepatocytes and liver microsomes. Cicletanine was extensively metabolized by rat hepatocytes. More than 80% of the drug was biotransformed after a 3 h incubation. The formation of glucuroconjugated metabolites was characterized by the following kinetic parameters, i.e. Vmax = 2.05 +/- 0.21 nmol/min/mg protein and Km = 287 +/- 6.7 microM for (-)-cicletanine, and Vmax = 1.44 +/- 0.12 nmol/min/mg protein and K(m) = 171 +/- 4.1 microM for (+)-cicletanine. Oxazepam inhibited the glucuronidation of cicletanine in both rat hepatocytes and liver microsomes with a competitive-type inhibition, i.e. K(i) = 129 +/- 7.5 and 152 +/- 19.7 microM for (-)-cicletanine and (+)-cicletanine, respectively. The co-incubation of acetaminophen with cicletanine showed that only sulfoconjugation was inhibited in rat hepatocytes. Glucuronidation was not modified by acetaminophen. As natriuric activity is due to sulfoconjugated (+)-cicletanine, acetaminophen could potentially modulate in vivo the pharmacological effect of cicletanine. The data of the in vitro study reported here suggested an interaction between cicletanine and oxazepam or cicletanine and acetaminophen. However, the clinical impact of such a drug interaction needs further evaluation.

Pharmacokinetics of methotrexate in the extracellular fluid of brain C6-glioma after intravenous infusion in rats.

PURPOSE: Establishment of the pharmacokinetic profile of methotrexate (MTX) in the extracellular fluid (ECF) of a brain C6-glioma in rats. METHODS: Serial collection of plasma samples and ECF dialysates after i.v. infusion of MTX (50 or 100 mg/kg) for 4 h. HPLC assay. RESULTS: Histological studies revealed the presence of inflammation, edema, necrosis, and hemorrhage in most animals. In vivo recovery (reverse dialysis) was 10.8 +/- 5.3%. MTX concentrations in tumor ECF represented about 1-2% of the plasma concentrations. Rapid equilibration between MTX levels in brain tumor ECF and plasma. ECF concentrations almost reached steady-state by the end of the infusion (4 h), then decayed in parallel with those in plasma. Doubling of the dose did not modify MTX pharmacokinetic parameters (t1/2alpha, t1/2beta, MRT, fb, Vd, and CL(T)), except for a 1.7-fold increase of AUC(Plasma) and a 3.8-fold increase in AUC(ECF), which resulted in a 2.3-fold increase in penetration (AUC(ECF)/AUC(Plasma)). In spite of an important interindividual variability, a relationship between MTX concentrations in plasma and tumor ECF could be established from mean pharmacokinetic parameters. CONCLUSIONS: High plasma concentrations promote the penetration of MTX into brain tissue. However, free MTX concentrations in tumor ECF remain difficult to predict consistently.

Effect of acute ethanol administration on toloxatone pharmacokinetics in rabbits.

The pharmacokinetics of toloxatone and ethanol were determined in plasma and cerebrospinal fluid of conscious rabbits. According to a cross-over design, rabbits (n = 5) randomly received on three separate occasions either toloxatone (5 mg/kg), ethanol (1 g/kg), or toloxatone and ethanol (5 mg/kg and 1 g/kg, respectively) by intravenous injection. Toloxatone and ethanol concentrations were measured by HPLC with UV detection and GC with flame ionization detection, respectively. Ethanol concentration profiles in plasma were characterized by a rapid decline occurring within the first 30 min after administration followed by a linear (zero-order) phase that persisted for the length of the experiment. The maximum ethanol elimination rate was 0.31+/-0.20 g/h x kg. Toloxatone concentrations in plasma and cerebrospinal fluid were characterized by a multiexponential decay with effective half-lives of 0.39+/-0.06 and 0.56+/-0.07 hr, respectively. Toloxatone passage through the blood brain barrier was rapid and important. Our results also demonstrate that acute ethanol administration had no effect on toloxatone pharmacokinetics and that toloxatone administration had no effect on ethanol pharmacokinetics.

Sensitive gas chromatographic-mass spectrometric method for the determination of gacyclidine in rat plasma and spinal cord dialyzates.

A sensitive gas chromatographic-mass spectrometric (GC-MS) procedure is described for the selective determination of gacyclidine (a non-competitive N-methyl-D-aspartate antagonist) in rat plasma and spinal cord dialyzates. It involves a single-step liquid-liquid extraction of plasma samples and dialyzates with hexane (pH 8.0) and the use of phencyclidine as an internal standard. The compounds were separated on a GC capillary column and specifically detected by MS in the selected-ion monitoring mode. Gacyclidine and its internal standard were monitored by using the fragment ions at m/z 206 and 200, respectively. The method was accurate and reproducible (intra- and inter-day reproducibility < 12%) with a limit of quantification of 1.6 ng ml-1 using 100 microliters plasma of dialyzate samples. The calibration curves for rat plasma and Ringer's solution were linear (r2 > 0.996) over a range from 1.6 to 200 ng ml-1. The extraction efficiency was close to 100%. This simple and rapid assay (total run time < 10 min) was validated for a pilot pharmacokinetic study in healthy rats after intravenous injection of a bolus dose of gacyclidine (2.5 mg kg-1).

Arterio-venous ethanol levels in blood and plasma after intravenous injection in rabbits.

Arterio-venous ethanol concentrations in both whole blood and plasma were determined as a function of time in the rabbit. Following i.v. injection of 1.0 g/kg, both arterial and venous ethanol concentrations showed an abrupt decline occurring immediately after the end of the administration, followed by a pseudolinear phase that persisted for the length of the experiment. This work substantiates the arterio-venous ethanol concentration differences reported in the literature. It illustrates that equal arterial and venous ethanol concentrations may not be achieved readily after rapid i.v. injection. Moreover, it demonstrates a faster decay of ethanol concentrations in arterial than in venous plasma.

Determination of free extracellular levels of methotrexate by microdialysis in muscle and solid tumor of the rabbit.

PURPOSE: To determine of the pharmacokinetic profile of methotrexate (MTX) in blood and extracellular fluid (ECF) of VX2 tumor and muscle in rabbits. METHODS: Microdialysis probes were inserted into VX2 tumor and in muscle tissue. Following intravenous administration of MTX (30 mg/kg), serial collection of arterial blood samples and dialysates of muscle and tumor ECF for 4 h was carried out. Quantitation of MTX and determination of free plasma concentrations was performed by fluorescence polarization immunoassay and ultrafiltration, respectively. Correlations were established between the unbound plasma and ECF MTX concentrations. RESULTS: Total and free plasma concentrations exhibited a parallel three exponential decay in both healthy and tumorigenic animals. Total clearance (8.9 vs 6.5 ml-1.min-1.kg-1) and volume of distribution (4.0 vs 2.9 l.kg-1), however, tended to decrease in the tumor-bearing group. The ECF/plasma AUC ratio equaled 14.2 +/- 8.8% in muscle and 23.9 +/- 15.9% in tumor. The concentration-time profile of muscle ECF MTX was parallel and highly correlated (r = 0.97) to that determined in plasma. In contrast, free MTX plasma levels were not correlated with tumor ECF concentrations (r = 0.564). CONCLUSIONS: In addition to the well-known pharmacological variability in the concentration-effect relationship, the important inter-individual variability in tumor exposure to MTX may partly explain that studies in patients with solid tumors have often failed to demonstrate firm correlations between MTX blood pharmacokinetics and the chemotherapeutic response.

Determination of gacyclidine enantiomers in human plasma by gas chromatography-mass spectrometry using selected-ion monitoring.

A sensitive gas chromatographic assay using mass selective-detection has been developed for the simultaneous quantitation of the enantiomers of (+/-)-gacyclidine (a non competitive N-methyl-D-aspartate antagonist) in human plasma. Gacyclidine enantiomers and phencyclidine (PCP), the internal standard, were extracted using a single-step liquid-liquid extraction with hexane at pH 8.0. Each enantiomer was separated on a chiral gas chromatography capillary column and specifically detected by mass spectrometry (MS) in selected-ion monitoring (SIM) mode. Gacyclidine enantiomers and PCP were monitored using the fragment ions at m/z 206 and 200, respectively. No interference was observed from endogenous components. The limit of quantitation (LOQ) for each enantiomer of gacyclidine was 300 pg/ml by using plasma samples of 500 microl. The calibration curves were linear (r2=0.998) over a range of 0.3125 to 20 ng/ml. The extraction efficiency was higher than 95% for both enantiomers. Intra- and inter-day bias were less than 10% at every standard curve concentration. Intra-day precision was less than 19% for (-)-gacyclidine and 15% for (+)-gacyclidine. Inter-day precision was below 15% for both enantiomers. The assay was validated for an enantioselective pharmacokinetic study in healthy male volunteers.

Determination of free extracellular concentrations of piperacillin by microdialysis.

The tissue penetration and distribution of antibiotics is of great importance, since most of the infections occur in the tissue. At the infection site, the free, unbound fraction of the antibiotic is responsible for the antiinfective effect. These free extracellular concentrations can be measured by microdialysis. It was the aim of the study to correlate free levels of the beta-lactam antibiotic piperacillin in blood with those in tissue. In vivo microdialysis sampling was used to study the tissue distribution patterns of piperacillin in anesthetized rats after single dose iv administration of the drug. The pharmacokinetics of piperacillin in plasma were consistent with a two-compartment body model. Comparisons between calculated free concentrations in the peripheral compartment and measured free extracellular concentrations revealed excellent agreement. Microdialysis is a suitable method to evaluate unbound drug concentrations in the tissues. In case of piperacillin, predictions of the concentration time profiles of free drug in the peripheral compartment can be made on the basis of plasma data.

Modification of the blood-brain barrier permeability by vinorelbine: effect of intracarotid infusion compared with intravenous infusion.

Brain levels of the antineoplastic compound, vinorelbine, and its effects on the permeability of the blood-brain barrier (BBB) were studied. Preliminary experiments were carried out to define the dose of 10 mg/kg and the delay of 3 h after infusion required to induce BBB disruption. Vinorelbine was infused by i.c. or i.v. infusion to anesthetized male Sprague-Dawley rats. BBB disruption was evaluated qualitatively by the presence in the infused hemisphere of i.v. administered Evans blue dye (2%) and vinorelbine intratissular levels were measured by HPLC. After an i.c. infusion, there is an important variability in the degree of extravasation of Evans blue albumin complex, which is correlated with vinorelbine levels (p < 0.01). The percent of dose in brain tissue is less than 1%. After an i.v. infusion, the parenchyma is globally affected as shown by the uniform faint bluish staining of the two hemispheres. Vinorelbine levels are homogenous and similar to levels of brains graded + 1 after an i.c. infusion. These results seem to indicate that an i.c. infusion induces localized BBB disruptions while the effect of an i.v. infusion is global and that the gain in tissue level after an i.c. infusion is low compared with i.v. infusion.

Modification of the blood-brain barrier permeability following intracarotid infusion of vinorelbine.

The effects of the antineoplastic compound, vinorelbine, on the permeability of the blood-brain barrier (BBB) to the complex Evans blue/albumin were studied. Vinorelbine, at a dose range from 5 to 10 mg/kg, was infused (4 ml/kg over 2 min) into the left carotid artery of anesthetised male Sprague-Dawley rats. BBB disruption was evaluated, qualitatively, by the appearance in the infused hemisphere of intravenously administered Evans blue dye (2%). Six groups of 3 rats were studied for preliminary assays to define the dose and delay between infusion and sacrifice. Twenty four rats (12 controls and 12 test rats) were used to define the effect of vinorelbine. These effects of vinorelbine were dose dependent and after 3 hours, 10 mg/kg of vinorelbine caused Evans blue/albumin exudation in gray and white matter. This study shows that the intracarotid infusion of vinorelbine in this rat model system increases BBB permeability only with a high dose. Sufficient concentrations of drug may be obtained in cerebral tissue without significant BBB disruption.

Urinary excretion of cicletanine in the rat. Stereochemical aspects.

The metabolism of (+)-cicletanine and (-)-cicletanine (10 mg kg-1) was studied in healthy male Wistar rats 24 hr after a single dose and following daily oral administration for 25 days. Urine, collected in 24-hr intervals on days 1, 5, 10, 15, 20, and 25, was analyzed by an HPLC method for parent drug and its sulfate/glucuronide conjugates. In urine, the sulfate and glucuronide conjugates of cicletanine were the only two major components quantitated; parent drug was a minor component. Within 24 hr after the first dose of (+)-cicletanine, the sulfate conjugate was the major urinary component; the ratio of sulfate to glucuronide conjugate was 3. After oral administration of (-)-cicletanine, the glucuronide and sulfate conjugates were present in similar amounts. For each enantiomer, the ratio of sulfate/glucuronide did not change upon multiple dosing, and inversion of the enantiomers did not occur. Although sulfate and glucuronide conjugates of each enantiomer are formed, the relative amounts of each conjugate depends on the enantiomer, indicating that there is stereospecificity in the disposition of cicletanine.

Virulence factors (aerobactin and mucoid phenotype) in Klebsiella pneumoniae and Escherichia coli blood culture isolates.

We examined the presence of two virulence factors in 241 blood isolates of Klebsiella pneumoniae from patients hospitalized during 1989 and 1990 in 7 French hospitals, and 125 blood isolates of Escherichia coli from one hospital. Aerobactin was scored phenotypically and genotypically with an intragenic DNA probe of 2 kb. The mucoid phenotype was assessed by culture on trypticase soy agar and by genotypic analysis (intragenic DNA probe of 235 bp). Only 6% K. pneumoniae isolates were aerobactin-positive with no significant variation according to geographical location while 20% of K. pneumoniae isolates displayed the mucoid phenotype, with a significant variation according to hospital. Aerobactin was always associated with the mucoid phenotype. The frequency of aerobactin production but not mucoid phenotype (14%) was higher among E. coli isolates (48%). They harbored two types of large plasmids. Intraperitoneal injection into mice of 10(3) cfu of K. pneumoniae producing both virulence factors demonstrated that capsular serotype K2 was the more virulent K23 and K28.