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.

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.

Evidence for (+)-cicletanine sulfate as an active natriuretic metabolite of cicletanine in the rat.

It was previously shown that the urinary sulfo-conjugate metabolite of cicletanine (cicletanine sulfate), and not free cicletanine, is salidiuretic in rats. Here we investigated potential differences between the resolved (+/-) enantiomers of cicletanine sulfate. Two groups of rats (n = 10) received either (+)- or (-)-cicletanine p.o. High performance capillary electrophoresis revealed that the 24-h urinary excretion of (+)-cicletanine sulfate was 5 times higher than that of (-)-cicletanine sulfate (18.9% vs. 3.8% of the oral dose). The same relative trend was observed after 5 and 10 days of oral administration. Following direct administration into the renal artery of anesthetized rats, (+)-cicletanine sulfate was 3-4 times more potent, in terms of active doses, than (-)-cicletanine sulfate to increase sodium excretion (ED50 = 1.86 +/- 0.28 mg/kg vs. 6.1 +/- 1.0 mg/kg, mean +/- S.E.M., n = 4). The maximal natriuretic potency of (+)-cicletanine sulfate was intermediate between that of furosemide and DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonate). In rat erythrocytes, (+)-cicletanine sulfate was between 2 and 3 times more potent to inhibit the Na(+)-dependent Cl-/HCO3- anion exchanger than (-)-cicletanine sulfate (IC50 = 61 +/- 3 microM vs. 142 +/- 31 microM, n = 4). In conclusion, (+)-cicletanine was more sulfo-conjugated and more potent natriuretic agent in rats than (-)-cicletanine. These results strongly suggest that (+)-cicletanine sulfate is the active natriuretic metabolite of racemic cicletanine in rats. This compound may probably act by inhibiting the Na(+)-dependent Cl-/HCO3- anion exchanger at the cortical diluting segment.

Continuous sampling of cerebrospinal fluid in the conscious rabbit.

A cannulation technique for continuous sampling of cerebrospinal fluid (CSF) in unanesthetized freely moving rabbits is described. A permanent stainless steel cannula constructed easily and inexpensively from commercially available material is placed into the third ventricle and fixed to the skull by anchoring screws and dental cement. This procedure allows a continuous CSF sampling with a flow rate of 11.2 +/- 4.5 microliters/min without any sign of disturbing the animal. The penetration of the third ventricle or the periodic drainage of CSF, during a one month period, does not result in a variation of CSF protein (356 +/- 20 mg/l), glucose (4.5 +/- 0.2 mmol/l) or lactate (1.80 +/- 0.05 mmol/l) concentrations. Our technique has some advantages for pharmacological or pharmacokinetic investigations. The third ventricle CSF data will complete that of cisterna magna or lateral ventricle CSF. This method allows studies in the same animal during a period of one month without any problem. Moreover, it lends itself to experiments in which physiological conditions are required.

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.

Comparative pharmacokinetics of two diastereoisomers dexamethasone and betamethasone in plasma and cerebrospinal fluid in rabbits.

The two diastereoisomers dexamethasone (DXM) and betamethasone (BTM) were infused at two different doses (2, 10 mg.kg-1) in anesthetized rabbits. Samples of plasma and cerebrospinal fluid were collected over a 180-min period. Steroid concentrations were measured by high performance liquid chromatography. The terminal half life (85.7 +/- 20.8 min and 102.2 +/- 29.6 min for DXM; 117.6 +/- 19.8 min and 118.5 +/- 15.8 min for BTM) and the mean residence time (121.4 +/- 27.7 min and 146.1 +/- 41.3 min for DXM; 168.6 +/- 28.1 min and 172.2 +/- 20.6 min for BTM) were unchanged between the doses. Dose-dependent changes in the area under the curve normalized by the dose, then volume distribution and clearance were observed. The average percentage of DXM and BTM bound to plasma proteins were 78.1 +/- 11.5% and 88.3 +/- 5.1% respectively at the lower dose, and decreased significantly with 10 mg.kg-1. DXM appeared more rapidly in the CSF, the highest concentrations of DXM were obtained within 15 min after the end of the injection. The CSF levels were lower than that of plasma unbound and the passage through the blood-brain barrier was saturable. These results will complicate pharmacokinetic and pharmacodynamic analysis.

Influence of sex and oestrogen replacement on the disposition of dexamethasone in rats.

The disposition of dexamethasone (DXM, 2 mg/kg, iv) was studied in ovariectomized female rats treated with oestrogen (0.1 mg and 1 mg of oestradiol benzoate) and in male rats. Oestradiol replacement had no effect on body or liver weights or on the DXM pharmacokinetic parameters (CL, Vdss, AUC, MRT and t1/2) of the female groups. If the Vdss seemed slightly greater in male than in female rats, this difference disappeared after normalization based on body weight. In contrast, CL was greater in the male rats even after normalization. For all the animals, significant correlations were observed between body weight and Vdss (r = 0.731, P less than 0.001) or CL (r = 0.639, P less than 0.001). Terminal half life and MRT were negatively correlated with CL (r = -0.481, P less than 0.01 and r = -0.575, P less than 0.01, respectively) but not with Vdss. Although oestrogen replacement did not seem to affect the pharmacokinetics of DXM, the increase in the CL in male rats should be the main determinant observed between the sexes. These results are consistent with a slower metabolism found for various drugs metabolized by the cytochrome P-450 in female rats.

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.

KINFIT: a non linear least-squares computer program for the estimation of pharmacokinetic parameters after intravenous administration.

KINFIT is a nonlinear least-squares computer program designed to allow pharmacokinetic modeling of experimental data and to obtain pertinent parameter estimates based on the derived values. It is written in Visual BASIC for the Microsoft Windows graphical environment. Drug concentrations in blood, plasma, or serum with time following intravenous administration are input and a linear or semi-logarithmic plot of the data appears on the display. On command, polyexponential coefficients and exponents are computed and a non linear curve is fitted through the data set. Results from statistical tests are printed to determine goodness of fit. Commonly calculated pharmacokinetic parameters are also calculated and appear on the output. The execution of KINFIT is demonstrated for time courses of ampicillin in man. KINFIT was compared with the widely available ESTRIP and RSTRIP computer programs and gave parameter estimates that were very similar, although not identical.

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.

Clinical pharmacology of gallium chloride after oral administration in lung cancer patients.

Pharmacokinetic parameters were determined in 18 lung cancer patients after a single administration of 800 mg/24 h of GaCl3: Cmax = 123 +/- 61 mu/l; Tmax = 5.2 +/- 5.5 h; AUCO-96h = 4690 +/- 3358 micrograms.l-1.h; AUCO - infinity = 6394 +/- 5352 micrograms.l-1.h; T 1/2 beta = 43 +/- 19 h. Serum Ga concentrations at the steady-state (Css) were then determined in these patients after a daily oral administration of 800 mg/24 h of GaCl3 for 15 days: Css = 274 +/- 167 micrograms/l. No correlation was found between Css and the previous pharmacokinetic parameters in each patient. Various doses of GaCl3 were administered daily to 45 patients to correlate Css and dosage. Serum Ga concentrations increased with dosage from 100 to 400 mg/24 h (p less than 0.05), but not with further dosages up to 1400 mg/24 h. The optimal daily dose of GaCl3 in lung cancer patients seems to be 400 mg/24 h. In 2 patients, Ga was assayed after death in tissues. Ga concentrations were more than 10 micrograms/g in metastases, 3.6 +/- 2.9 micrograms/g in the primary tumor and 2.3 +/- 0.9 micrograms/g in the kidney. Due to the lack of renal and hematological toxicities and the significant uptake of Ga by the tumor, GaCl3 can be used orally in conjunction with other cytotoxic agents. We intend to evaluate its efficacy according to a randomized study comparing chemotherapy versus chemotherapy plus 400 mg/24 h of GaCl3.

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.

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.

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.

Toloxatone pharmacokinetics in the plasma and cerebrospinal fluid of the rabbit.

The pharmacokinetics of toloxatone (5 and 10 mg kg-1, i.v.) was studied in anaesthetized rabbits. There was a biexponential decline in plasma concentration with time. No differences were observed in the pharmacokinetic parameters with the increase of the dose. The terminal half-life was short (47.4 +/- 2.8 and 41.5 +/- 4.2 min for 5 and 10 mg kg-1, respectively). The total clearance was 79 +/- 18 mL min-1 after a dose of 5 mg kg-1 and 106 +/- 40 mL min-1 after a dose of 10 mg kg-1. The volume of distribution was 5.8 +/- 2.8 (5 mg kg-1) and 5.4 +/- 1.8 L (10 mg kg-1). The average percentage of toloxatone bound to plasma protein was 30% and was not affected by concentrations within the investigated range. In cerebrospinal fluid (CSF), the highest concentrations of toloxatone were obtained within 15 min after the end of the injection. The CSF level of toloxatone was equal to that of plasma unbound toloxatone and declined at a rate similar to toloxatone in plasma. These results suggest that the toloxatone passage through the blood-brain barrier may be completed by passive diffusion. In addition, the unbound plasma concentration would accurately reflect the toloxatone concentration in CSF and could be a useful tool for drug monitoring.

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.

[Pharmacokinetics of dexamethasone administered orally in obese patients]. / Pharmacocinétique de la dexaméthasone par voie orale chez le sujet obèse.

Dexamethasone pharmacokinetics was studied after oral administration of two Décadron tablets in six healthy controls and in eight obese patients whose weight was at least 20% above that of the ideal body weight. The absorption (0.30 +/- 0.09 h and 0.29 +/- 0.08 h) and elimination (4.52 +/- 0.57 h and 3.71 +/- 1.05 h) half-lives were not significantly different. Maximum plasma concentrations were similar (11.95 +/- 1.00 micrograms/l and 10.93 +/- 0.94 micrograms/l) but the lag-time was significantly higher in the obese patients (0.49 +/- 0.12 h and 0.13 +/- 0.04 h). A positive correlation was observed between the AUC and the total body weight (r = 0.738, p less than 0.01). Mean predexamethasone cortisol level was significantly lower in the obese patients (189.20 +/- 52.7 micrograms/l and 256.90 +/- 58 micrograms/l). The pharmacokinetics modifications were not sufficient to explain the increased false positive frequency in the dexamethasone suppression test of the hypothalamic-pituitary-adrenal axis in obesity.

[Chronopharmacokinetics of dexamethasone in young subjects]. / Chronopharmacocinétique de la dexaméthasone chez le sujet jeune.

Dexamethasone chronopharmacokinetics was studied in six young subjects 20 to 30 years old. The randomized cross-over study consisted of evening (11.00 p.m.) or morning (08.00 a.m.) dose separated by a period of one week. After the evening administration of the drug, only Tmax (1.77 +/- 0.74 à 11.00 p.m. and 0.99 +/- 0.64 à 08.00 a.m.) and Cmax/Tmax were higher than those determined at 08.00 a.m. This difference might be related to a cyclic variation of the absorption phase of dexamethasone. Thus, in our study, the time of administration has only a weak effect on the pharmacokinetics of dexamethasone.

[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.