Effect of collisions with a second fluid on the temporal development of nonlinear, single-mode, Rayleigh-Taylor instability

Goncharov's [Phys. Rev. Lett. 88, 134502 (2002)0031-900710.1103/PhysRevLett.88.134502] nonlinear model of a single-mode Rayleigh-Taylor instability (RTI) is investigated for a partially ionized plasma in a predominantly neutral background. Terminal bubble and spike velocities are derived from the nonlinear equations in the case where the RTI dynamics is dominated by collisions between neutrals and ions. Direct numerical simulations are used to justify the use of Goncharov's model in this regime and observe its limitations.

Supersonic-jet experiments using a high-energy laser

In this Letter, laboratory astrophysical jet experiments performed with the LULI2000 laser facility are presented. High speed plasma jets (150 km.s(-1)) are generated using foam-filled cone targets. Accurate experimental characterization of the plasma jet is performed by measuring its time evolution and exploring various target parameters. Key jet parameters such as propagation and radial velocities, temperature, and density are obtained. For the first time, the required dimensionless quantities are experimentally determined on a single-shot basis. Although the jets evolve in vacuum, most of the scaling parameters are relevant to astrophysical conditions.

Observation of laser driven supercritical radiative shock precursors

We present a supercritical radiative shock experiment performed with the LULI nanosecond laser facility. Using targets filled with xenon gas at low pressure, the propagation of a strong shock with a radiative precursor is evidenced. The main measured shock quantities (electronic density and propagation velocity) are shown to be in good agreement with theory and numerical simulations.

Pharmacokinetics and pharmacodynamics of sequential intravenous and subcutaneous teicoplanin in critically ill patients without vasopressors

OBJECTIVE

To compare the pharmacokinetic parameters of sequential intravenous and subcutaneous teicoplanin in the plasma of surgical intensive care unit patients.

DESIGN AND SETTING

Prospective, randomized, crossover study in the surgical ICU of a university hospital.

PATIENTS

Twelve patients with a suspected nosocomial infection, a serum albumin level higher than 10 g/l, body mass index less than 28 kg/m(2), and estimated creatinine clearance higher than 70 ml/min.

INTERVENTIONS

Teicoplanin was first administered intravenously as a loading dose of 6 mg/kg per 12 h for 48 h and then continued at a daily dose of 6 mg/kg. On the fourth day patients were randomized in two groups according to the order of the pharmacokinetic studies.

MEASUREMENTS AND RESULTS

Serial plasma samples were obtained to measure teicoplanin levels. Compared with a 30-min intravenous infusion the peak concentration of teicoplanin after a 30-min subcutaneous administration occurred later (median 7 h, range 5-18) and was lower (16 micro g/ml, 9-31; vs. 73, 53-106). Despite large and unpredictable interindividual differences no significant differences between subcutaneous and intravenous administration were observed in: trough antibiotic concentrations (10 micro g/ml, 6-24; vs. 9, 5-30), the area under the teicoplanin plasma concentration vs. time curves from 0 to 24 h (AUC(0-24h); 309 micro g/ml per minute, 180-640; vs. 369, 171-955), the proportion of the dosing interval during which the plasma teicoplanin concentration exceeded 10 micro g/ml (96%, 0-100%; vs. 79%, 13-100%), and the ratio of AUC(0-24h) to 10 (77, 45-160; vs. 92, 43-239).

CONCLUSIONS

In critically ill patients without vasopressors a switch to the subcutaneous teicoplanin after an initial intravenous therapy seems to give comparable pharmacodynamic indexes of therapeutic success.

Pharmacokinetic-pharmacodynamic modeling of electroencephalogram effect of imipenem in rats with acute renal failure

The epileptogenic activity of imipenem was investigated in rats with experimental renal failure induced by uranyl nitrate injection by using electroencephalogram (EEG) recording and a pharmacokinetic-pharmacodynamic model including an effect compartment. Results previously obtained with healthy rats were used to estimate the dose of imipenem required to induce an observable but nonlethal EEG effect on the assumption that only the pharmacokinetic parameters of the model would be affected by renal failure. Good agreement was observed between the predicted and observed effects.

A pharmacokinetic/pharmacodynamic approach to show that not all fluoroquinolones exhibit similar sensitivity toward the proconvulsant effect of biphenyl acetic acid in rats

The proconvulsant effect of biphenyl acetic acid (BPAA) on several fluoroquinolones (FQs) was investigated in vivo, by measuring drug concentrations in the biophase at the onset of convulsions. Male Sprague-Dawley rats (n = 134) were given BPAA orally, at various doses 1 h before starting FQ infusion, which was maintained until the onset of maximal seizures, when cerebrospinal fluid (CSF) and plasma samples were collected for drug concentration determination. The FQ-BPAA interactions in the biophase (CSF) were adequately described on most occasions by an inhibitory Emax effect model with a baseline effect parameter. The efficacy of the proconvulsant effect was characterized by the ratio of the CSF concentrations of FQs at the onset of convulsant activity when BPAA was absent (CCSF0, FQs) and as BPAA CSF concentrations tended toward infinity (CCSFbase, FQs). This ratio varied from 15 for enoxacin to 1.9 for sparfloxacin. The potency of the proconvulsant effect was characterized by the CSF concentration of BPAA corresponding to a proconvulsant effect half of its maximum. This parameter varied between 0.18 +/- 0.06 micromol/L with enoxacin and 15.0 +/- 12.1 micromol/L with sparfloxacin. The CSF diffusion of all FQs was apparently non-linear, as well as the plasma protein binding of BPAA, complicating interpretation of plasma data. The important variability in the proconvulsant effect of BPAA demonstrated in this study between various FQs suggests that in vitro gamma-aminobutyric acid (GABA) binding experiments conducted in the presence of BPAA are unlikely to be good predictors of FQ convulsant risk in clinical practice.

Pharmacokinetic-pharmacodynamic modeling of the electroencephalogram effect of imipenem in healthy rats

A pharmacokinetic-pharmacodynamic (PK-PD) modeling approach was developed to investigate the epileptogenic activity of imipenem in rats. Initially, animals received an intravenous infusion of imipenem at a rate of 2.65 mg min(-1) for 30 min. Blood samples were collected for drug assay, and an electroencephalogram (EEG) was recorded during infusion and postinfusion. A dramatic delay was observed between concentrations of imipenem in serum and the EEG effect; this effect was accompanied by tremors and partial seizures. Indirect-effect models failed to describe these data, which were successfully fitted using an effect compartment model. The relationship between effect and concentration at the effect site was best described by a spline function. The elimination rate constant from the effect compartment was severalfold lower than that from the central compartment. The robustness of the model was then confirmed after administering the imipenem dose over 60 and 90 min. In conclusion, the successful PK-PD modeling of the imipenem EEG effect in rats constitutes a major improvement for better prediction of the epileptogenic risk associated with this antibiotic.

Effects of inhaled salbutamol in exercising non-asthmatic athletes

BACKGROUND

Beta-2 agonists such as salbutamol are used, not only by asthmatic athletes to prevent exercise induced asthma, but also by non-asthmatic athletes as a potentially ergogenic agent. We have investigated whether inhaled salbutamol enhances endurance performance in non-asthmatic athletes.

METHODS

A prospective double blind, randomised, three way crossover design was used to study the effects of 200 microg and 800 microg inhaled salbutamol versus a placebo in 12 trained triathletes. The treatments were compared in three identical cycle ergometer sessions at 85% of the predetermined maximal oxygen uptake. Lung function, endurance time, metabolic parameters (glucose, potassium, lactate, free fatty acid, and glycerol), and psychomotor performance were evaluated.

RESULTS

Neither endurance time nor post-exercise bronchodilation were significantly different between the treatments. Metabolic parameters were affected by exercise but not by treatment.

CONCLUSIONS

Inhaled salbutamol, even in a high dose, did not have a significant effect on endurance performance in non-asthmatic athletes, although the bronchodilating effect of the drug at the beginning of exercise may have improved respiratory adaptation. Our results do not preclude an ergogenic effect of beta2 agonists given by other routes or for a longer period.

Effects of inhaled salbutamol in exercising non-asthmatic athletes

BACKGROUND

Beta-2 agonists such as salbutamol are used, not only by asthmatic athletes to prevent exercise induced asthma, but also by non-asthmatic athletes as a potentially ergogenic agent. We have investigated whether inhaled salbutamol enhances endurance performance in non-asthmatic athletes.

METHODS

A prospective double blind, randomised, three way crossover design was used to study the effects of 200 μg and 800 μg inhaled salbutamol versus a placebo in 12 trained triathletes. The treatments were compared in three identical cycle ergometer sessions at 85% of the predetermined maximal oxygen uptake. Lung function, endurance time, metabolic parameters (glucose, potassium, lactate, free fatty acid, and glycerol), and psychomotor performance were evaluated.

RESULTS

Neither endurance time nor post-exercise bronchodilation were significantly different between the treatments. Metabolic parameters were affected by exercise but not by treatment.

CONCLUSIONS

Inhaled salbutamol, even in a high dose, did not have a significant effect on endurance performance in non-asthmatic athletes, although the bronchodilating effect of the drug at the beginning of exercise may have improved respiratory adaptation. Our results do not preclude an ergogenic effect of β2 agonists given by other routes or for a longer period.

In vitro and in vivo investigations on fluoroquinolones; effects of the P-glycoprotein efflux transporter on brain distribution of sparfloxacin

The role of mdr1a-encoded P-glycoprotein on transport of several fluoroquinolones across the blood-brain barrier was investigated. In vitro, P-glycoprotein substrates were selected by using a confluent monolayer of MDR1-LLC-PK1 cells. The inhibition of fluoroquinolones (100 microM) on transport of rhodamine-123 (1 microM) was compared with P-glycoprotein inhibitors verapamil (20 microM) and SDZ PSC 833 (2 microM). Subsequently, transport polarity of fluoroquinolones was studied. Sparfloxacin showed the strongest inhibition (26%) and a large polarity in transport, by P-glycoprotein activity. In vivo, using mdr1a (-/-) and wild-type mice, brain distribution of pefloxacin, norfloxacin, ciprofloxacin, fleroxacin and sparfloxacin was determined at 2, 4, and 6 h following intra-arterial infusion (50 nmol/min). Brain distribution of sparfloxacin was clearly higher in mdr1a (-/-) mice compared with wild-type mice. Sparfloxacin was infused (50 nmol/min) for 1, 2, 3 and 4 h in which intracerebral microdialysis was performed. At 4 h, in vivo recovery (dynamic-no-net-flux method) was 6.5+/-2.2 and 1.5+/-0.5%; brain(ECF) concentrations were 5.1+/-0.2 and 26+/-21 microM; and total brain concentrations were 7.2+/-0.3 and 23+/-0.3 microM in wild-type and mdr1a (-/-) mice, respectively. Plasma concentrations were similar (18.4+/-0.7 and 17.9+/-0.5 microM, respectively). In conclusion, sparfloxacin enters the brain poorly mainly because of P-glycoprotein activity at the blood-brain barrier.

Comparative cerebrospinal fluid diffusion of imipenem and meropenem in rats

The main objective of this study was to compare the cerebrospinal fluid (CSF) diffusion of imipenem and meropenem at steady state, following intravenous infusions at various rates in rats. A preliminary experiment was conducted to estimate the elimination half-lives of these two carbapenem antibiotics, and then to evaluate the infusion duration necessary to reach steady state. CSF diffusion of imipenem was essentially linear over the wide range of infusion rates (66-1,320microg min(-1)) and corresponding steady-state plasma concentrations (11.7-443.0 microg mL(-1)). Conversely the CSF diffusion of meropenem was saturable, with a predicted maximum CSF concentration equal to 1.3 microg mL(-1). Extrapolation of these data to the clinical situation may not be possible since the rats had normal blood-brain and blood-CSF barriers whereas patients with diseases such as meningitis may not. However, it is suggested that the observed differences in the diffusion characteristics of imipenem and meropenem may be partly responsible for their differences in toxicity and efficacy at the central level.

Imipenem but not meropenem induces convulsions in DBA/2 mice, unrelated to cerebrospinal fluid concentrations

Imipenem and meropenem CSF diffusion was comparable in DBA/2 mice but only imipenem induced convulsions, not related to CSF concentration.

Intranasal midazolam in piglets: pharmacodynamics (0.2 vs 0.4 mg/kg) and pharmacokinetics (0.4 mg/kg) with bioavailability determination

Intranasal midazolam was studied in two series of piglets: series 1, n = 20 (18 +/- 3 kg), a randomized double blind pharmacodynamic study to compare doses of 0.2 mg/kg and 0.4 mg/kg; series 2, n = 9 (42 +/- 8 kg), a pharmacokinetic study with a 0.4 mg/kg dose administered either intravenously (i.v.) or intranasally (i.n.) in a cross-over protocol with a one-week wash-out period between each. In series 1, midazolam caused significant anxiolysis and sedation within 3 to 4 min, without a significant difference between 0.2 and 0.4 mg/kg doses for any of the studied parameters. In series 2, after intranasal midazolam administration of 0.4 mg/kg, plasma concentrations attained a maximum (Cmax) of 0.13 +/- 0.04 mg/l at 5 min (median Tmax) and remained higher than 0.04 mg/l until 60 min. The bioavailability factor (F) in this study was F = 0.64 +/- 0.17 by the intranasal route. The terminal half-life (T1/2 lambda z) = 145 +/- 138 min was comparable with the i.v. administration half-life (158 +/- 127 min). In conclusion, optimal intranasal midazolam dose in piglets was 0.2 mg/kg, which procures rapid and reliable sedation, adapted to laboratory piglets.

Pharmacokinetic-pharmacodynamic contributions to the convulsant activity of fluoroquinolones in rats

The in vivo convulsant activities in rats of five representative fluoroquinolones (FQs), norfloxacin, enoxacin, sparfloxacin, fleroxacin, and pefloxacin, were compared. The experimental approach allowed distinction between the drugs' ability to reach the pharmacological receptors at the level of the central nervous system (pharmacokinetic contribution) and their ability to interact with these receptors (pharmacodynamic contribution). The presence of a methyl group on the piperazine moiety decreased the pharmacodynamic contribution to the convulsant activity by severalfold, and the ratios of concentrations of the FQs in cerebrospinal fluid (CSF) to concentrations of unbound FQs in plasma varied from about 5 to 75% as a function of lipophilicity. Interestingly, FQs with the highest intrinsic convulsant activities had the lowest levels of diffusion in CSF and vice versa. This in vivo approach provides information complementary to that of in vitro experiments and should be recommended for early preclinical assessment of a new FQ's epileptogenic risk.

A new approach for early assessment of the epileptogenic potential of quinolones

The epileptogenic potential of pefloxacin and norfloxacin, two quinolone antibiotics, was investigated in vivo in three different animal species by measuring drug concentrations in cerebrospinal fluid (CSF), which is part of the biophase, at the onset of convulsions. Interestingly, the pefloxacin-to-norfloxacin concentration ratios in CSF were virtually constant across the species (7.0, 6.6, and 6.0 in mice, rats, and rabbits, respectively), suggesting that this approach could be used to predict the relative epileptogenic potential of quinolones in humans.

Development of a new quantitative approach for the isobolographic assessment of the convulsant interaction between pefloxacin and theophylline in rats

PURPOSE

A new mathematical approach was developed to quantify convulsant interaction between pefloxacin and theophylline in rats.

METHODS

Animals received each compound separately or in different combination ratios. Infusion was stopped at the onset of maximal seizures. Cerebrospinal fluid (CSF) and plasma samples were collected for HPLC drug determination. The nature and intensity of the pharmacodynamic (PD) interaction between drugs was assessed with a new modeling approach which includes (a) data transformation to create an essentially error-free X-variable and (b) estimation of an interaction parameter a by fitting a nonlinear hyperbolic model to the combination data with unweighted nonlinear regression.

RESULTS

Drug disposition to the biophase was linear within the range of administered doses. The estimates of a suggested a Loewe antagonistic interaction between pefloxacin and theophylline at the induction of maximal seizures in rats. Similar intensity of PD interaction was observed at the dose and biophase level (alpha was -0.415 +/- 0.069 and -0.567 +/- 0.079, respectively).

CONCLUSIONS

The suitability of the proposed model was assessed by Monte Carlo simulation. This new mathematical approach enabled the characterization of the Loewe antagonistic nature of the PD (convulsant) interaction between pefloxacin and theophylline, whereas previously used methodologies failed to do so.

Pharmacokinetic-pharmacodynamic contributions to the convulsant activity of pefloxacin and norfloxacin in rats

The purpose of this investigation was to compare the convulsant activity of two quinolones differing, respectively, by the presence (pefloxacin) or absence (norfloxacin) of a methyl group on the piperazine moiety at the position 7 of their parent nuclei and consequently by their lipophilicity. An in vivo model was used, which can distinguish between ease in reaching pharmacological receptors at the central nervous system level, and ability to interact with these receptors. Male Sprague-Dawley rats (approximately 230g-300g) received an i.v. infusion of pefloxacin or norfloxacin at one of four different rates: 480, 960, 1440 and 1920 micromol/hr, until the onset of maximal seizures. This occurred after an average of 12.7 to 69.4 min. We found enough evidence to suggest that in these conditions the contribution of pefloxacin metabolites, including norfloxacin, to its convulsant activity was negligible. Doses of pefloxacin and concentrations in cerebrospinal fluid and plasma (total and unbound) at the pharmacodynamic endpoint were all independent of infusion rate, whereas only cerebrospinal fluid concentrations of norfloxacin were independent of infusion rate. The overall cerebrospinal fluid concentration of norfloxacin (47.3 +/- 9.9 micromol/liter) was about 8-fold lower than that of pefloxacin (380 +/- 27 micromol/liter), indicating that on average the "intrinsic convulsant activity" of norfloxacin is 8-fold greater than that of pefloxacin. However, total doses of pefloxacin and norfloxacin at the onset of maximal seizures were in the same order of magnitude (1500-2000 micromol/kg), suggesting that the higher ability of the more lipophilic pefloxacin to reach central nervous system compensates for its lower intrinsic convulsant activity.

Effect of tamoxifen on the pharmacokinetics of theophylline in rats

The effect of tamoxifen on the pharmacokinetics of theophylline was investigated in male Sprague-Dawley rats. The oral administration of tamoxifen at a dose equal to 40 mg kg-1 48 h before the intravenous injection of theophylline 10 mg kg-1, significantly (P < 0.05) increased the clearance of theophylline by 39%, with no apparent effect on the volume of distribution. As a consequence, the elimination half-life of theophylline was significantly (P < 0.05) shortened in the tamoxifen-treated rats (3.56 +/- 0.39 h vs 5.25 +/- 0.48 h) as well as its mean residence time (5.04 +/- 0.60 h vs 7.50 +/- 0.75 h). Although these data cannot be directly extrapolated to the clinical situation, they provide experimental support to suggest that more attention should be paid to the potential risk of pharmacokinetic interactions in the presence of tamoxifen.

Nephrotoxicity of gentamicin and vancomycin given alone and in combination as determined by enzymuria and cortical antibiotic levels in rats

The purpose of this study was to compare the nephrotoxicity of gentamicin and vancomycin alone and in combination. Thirty-two male Sprague-Dawley rats were randomized into 4 groups of 8 animals. Each group received 200mg/kg gentamicin (G) i.m., or 300 mg/kg vancomycin (V) i.v., or an association of 200 mg/kg gentamicin + 300 mg/kg vancomycin (i.m. and i.v., respectively), or 0.9% NaCl solution i.m. and i.v. (controls). To determine AAP, GGT, and NAG enzyme excretions, urine samples were taken over 24-h periods before and after the start of the experiment. A single renal cortical sample was obtained at necropsy for quantitation of antibiotic levels. No significant modifications of urinary excretions of creatinine and enzymuria were noted during the 24-h period before each drug administration or in controls. AAP, GGT, and NAG excretions were significantly increased after G and G + V injections (p < 0.001), whereas only AAP and GGT were statistically higher in rats receiving V (p < 0.05). NAG elimination (mean +/- SD) was higher in G + V (16.0 +/- 0.2 IU/mmol creatinine/24 h; p < 0.001) than g (8.8 +/- 0.6) or V (1.7 +/- 0.2). Surprisingly, mean vancomycin cortical levels decreased in the combination (827 +/- 131 vs. 1964 +/- 23 micrograms/g for V alone; p < 0.001), whereas gentamicin concentration was unchanged (826 +/- 66 vs. 839 +/- 28 micrograms/g for G alone). Determination of enzymuria allowed the nephrotoxicity of the antibiotics to be graded in the following order: vancomycin + gentamicin > gentamicin > vancomycin.

Pharmacokinetics of lidocaine with epinephrine in piglets following epidural anaesthesia

The time course of arterial plasma lidocaine concentration, following an epidural anaesthesia via the sacrococcygeal or the S4-S5 trans-sacral approach, was studied in nine healthy piglets (7.8 +/- 1.3 weeks). Plasma lidocaine concentrations were measured for up to six hours after administration (5 mg/kg). Peak plasma concentration was 1.83 +/- 0.17 mg/l. Pharmacokinetic parameters determined from an independent compartment model were not different from those observed after an epidural administration of lidocaine via the sacrococcygeal space in children, except for a wide variability in the time taken to reach the maximum concentration (27.3 +/- 7.4 min) and a shorter half-life of elimination (82.8 +/- 7.0 min). The total body clearance of lidocaine was similar in piglets (17.3 +/- 1.6 ml/min/kg) to that in children. The shorter half-life of elimination was therefore attributed to a smaller volume of distribution in piglets (2.0 +/- 0.2 l/kg).

Fluvoxamine and fluoxetine: interaction studies with amitriptyline, clomipramine and neuroleptics in phenotyped patients

The in vivo pharmacokinetic interaction between two selective serotonin reuptake inhibitors (SSRI) (fluvoxamine, fluoxetine) and tricyclic antidepressants (TCAs) (amitriptyline, clomipramine) or neuroleptics (haloperidol, cyamemazine, levomepromazine, propericiazine) was assessed in 29 in-patients. They were phenotyped twice with dextromethorphan and mephenytoin: first in steady state conditions while under treatment with TCAs or neuroleptics; and also 10 days after an associated treatment with fluvoxamine (150 mg day(-1)) or fluoxetine (20 mg day(-1)). A clear and statistically significant increase in the mean urinary metabolic ratio (MR) of dextromethorphan/dextrorphan and in the mean mephenytoin S/R ratio (S/R) was seen with the fluvoxamine and fluoxetine treatment. The mean MR increased from 0.13 to 0.27 (P<0.01) with fluoxetine and from 0.34 to 0.84 with fluvoxamine (P<0.05). The (dextromethorphan) 'extensive metabolizer' phenotype switched to the 'poor metabolizer' phenotype in six patients by the 10-day fluoxetine treatment, and in two patients by the fluvoxamine treatment. The mean S/R increased from 0.24 to 0.34 (P<0.05) with fluoxetine, and from 0.33 to 0.58 (P<0.002) with fluvoxamine. These results are in agreement with the observed modification of TCA plasma levels after the SSRI association. During fluvoxamine treatment, amitriptyline and clomipramine plasma levels (P<0.06 both) tendentially increased, and those of demethylclomiprarnine decreased (P<0.06). Fluoxetine addition lead to a significant increase (P<0.02) of the desmethylclomipramine plasma levels. Fluvoxamine induced a moderate augmentation of the plasma levels of haloperidol and its reduced metabolite and no change in the plasma levels of cyamemazine and levomepromazine. But patients treated with neuroleptics are to few to draw any firm conclusion. This study suggests, that fluoxetine and fluvoxamine differ in their interaction with the metabolism of some other basic psychotropic drugs, by a mechanism which implies CYP2D6 and CYPmeph and possibly other isoformes of cytochrome P-450. Moreover, the interactions produced varied with the TCA prescribed.

[Cytochrome p450 IID6, its role in psychopharmacology]

Cytochrome P450 IID6 has got typical features (genetical polymorphism, competitive inhibition, saturability) which can be at the origin of pharmacokinetic modifications of molecules using it for their metabolism. In the field of pharmacology, many molecules are substrates or inhibitors of this cytochrome. They are presented. The results of a study of the dextromethorphan variation test performed before and after 28 days of clomipramine therapy with depressed patients are explained. They show a significant decreasing of the cytochrome P450 IID6 oxidation capacities between both of these times. A patient has passed from the phenotype "effective metabolizer" to the one of "poor metabolizer" with clomipramine.

[Cocaine contact anesthesia for endonasal surgery. Kinetics and clinical tolerance of a concentrated solution]

OBJECTIVE

To assess the pharmacokinetics and clinical tolerance of a 33% cocaine solution administered topically for intranasal surgery.

STUDY DESIGN

Clinical prospective open trial.

PATIENTS AND METHODS

Twelve ASA I patients scheduled for intranasal surgery were sedated with midazolam 2 mg and fentanyl 50 micrograms. Topical anaesthesia was obtained with aqueous 33% cocaine HCl 360 mg, lidocaine HCl 140 mg, adrenaline 0.04 mg and naphazoline 0.4 mg. Venous blood samples were taken before cocaine application and 15, 30, 45, 60, 90, 120, 150, 180, 240 min later. The plasma was immediately separated and the samples were frozen. The concentration of cocaine was measured by HPLC. Potential cardiotoxic and neurotoxic effects were clinically monitored.

RESULTS

The mean dose of cocaine applied was 5.85 +/- 1.3 mg.kg-1 and the dose actually delivered was 4 +/- 1.5 mg.kg-1. The Cmax was 859 +/- 503 ng.mL-1 after a Tmax to 47 +/- 17 min. The mean elimination half-life was 87 +/- 19 min (mean +/- SD). The total clearance and the volume of distribution were respectively 4,521 +/- 1,858 mL.min-1 and 568 +/- 273 L. No clinical evidence of toxicity was found.

CONCLUSIONS

This study shows that it is possible to perform major intranasal surgery under topical anaesthesia with a concentrated solution (33%) of cocaine at a high dose (6 mg.kg-1). These results differ completely with data obtained in addicts.

Rifampin-induced nonresponsiveness of giant cell arteritis to prednisone treatment

Rifampin is an enzymatic inducer known to increase steroid metabolism. We studied two patients with giant cell arteritis in whom rifampin caused nonresponsiveness to prednisone treatment. A prednisone pharmacokinetics study was done. When rifampin-prednisone treatment must be used in giant cell arteritis, we propose increasing the prednisone dosage to 2 mg/kg per day.

Pharmacokinetic and pharmacodynamic study of suriclone imipramine interaction in man

Suriclone is a novel cyclopyrrolone exhibiting anxiolytic activity. Twelve healthy Caucasian male volunteers participated in the study. A single dose of suriclone 0.4 mg, imipramine 75 mg, suriclone 0.4 mg + imipramine 75 mg, or placebo was given according to a 4 x 4 Latin-square design in order to assess the effect of drug association on pharmacokinetics and psychomotor performances. Visual analogue scale ratings, critical flicker frequency, choice visual reaction time, and Pauli, picture memory and Sternberg tests were performed before and 1.5, 6 and 9 h after drug administration. Suriclone, with the exception of the Pauli test, had no effect on psychomotor performances. The imipramine-suriclone association appeared to disturb some performances (no statistical significance), probably due to the effect of imipramine. Blood samples were collected for determination of imipramine and suriclone plasma levels respectively by high-performance liquid chromatography and radioimmunoassays. Suriclone AUC, Cmax and Tmax were not affected by imipramine, and reciprocally.

Minor and clinically non-significant interaction between toloxatone and amitriptyline

The possibility of a pharmacokinetic interaction between amitriptyline and toloxatone (a new MAOI-A) has been studied in 17 depressed in-patients. Amitriptyline and its demethylated and hydroxylated metabolites in blood and urine were measured at steady state after the administration of amitriptyline with and without toloxatone in steady state. The metabolic status of patients was determined using the dextromethorphan phenotyping test. There was only a minor pharmacokinetic interaction between amitriptyline (AMT) and toloxatone, with a small increase in the AMT/NT (nortriptyline) plasma ratio: 0.68 before and 0.78 after toloxatone. The urinary excretion and plasma levels of AMT and its metabolites were not affected by the co-therapy. Three of the patients were poor metabolisers, but this did not predict the magnitude of the drug interaction. The interaction does not justify plasma level monitoring of amitriptyline as the change in pharmacokinetics was so small.

A comparative study of enzymuria, in the rat, of the drug combinations amikacin/vancomycin and amikacin/teicoplanin

The aim of this study was to compare nephrotoxicity of the combinations amikacin/vancomycin and amikacin/teicoplanin. Eighteen male Wistar rats were divided into 3 groups of 6 animals each. The first group received 50 mg.kg-1 of amikacin (i.m. route) and 100 mg.kg-1 of vancomycin (i.p. route). The second group received 50 mg.kg-1 of amikacin (i.m. route) and 40 mg.kg-1 of teicoplanin (i.p. route). The third group received an isotonic solution of sodium chloride. The antibiotics were injected for a period of 6 days. Urine samples of animals were taken 24 h before the beginning of the experiment, then every day, throughout the duration of the treatment (6 days), continuing for an additional 3 days following completion of the administration of the drugs. There were no significant modifications in the urinary excretions of alanine aminopeptidase and the creatinine between the 3 groups; but in the group receiving amikacin/teicoplanin, we observed between days 3 and 8 an increase in the excretion of N-acetyl-beta-D- glucosaminidase when compared to the group receiving amikacin/vancomycin (p < or = 0.05) and to the control group (p < or = 0.01).

Chrononephrotoxicity in Rat of a Vancomycin and Gentamicin Combination

The effect of time of administration on excretion of two brush border enzymes--alanine aminopeptidase (AAP) and gamma-glutamyl transferase (gamma GT), and a lysosomal enzyme, N-acetyl-beta-D-glucosaminidase (NAG) with a single high dose of vancomycin, gentamicin or a combination of vancomycin and gentamicin was studied in male Wistar rats and compared with elimination of a control group. The rats received vancomycin intraperitoneally (200 mg.kg-1), gentamicin intramuscularly (100 mg.kg-1) or the combination of the drugs by the same route. A control group received isotonic NaCl solution. The four groups of animals received a single injection at 8 a.m., 2 p.m., 8 p.m., and 2 a.m. and urine excretion values for AAP, gamma GT and NAG were determined 24 hr later. The results show that the nephrotoxicity of gentamicin + vancomycin is greater than that observed with gentamicin, which again is greater than that observed with vancomycin. Furthermore, circadian variations in renal toxicity were observed, the least occurring at 8 a.m.

[Drug interactions of cyclosporine. Literature review]

The cyclosporine is widely used as an immuno-suppressive agent in association with others drugs. Its narrow therapeutic range requires frequent monitoring. We suggest a literature review of suspected or confirmed drug interactions. The classification is presented as: absorption interactions; pharmacokinetic interactions in antiinfectious, anticonvulsants, cardiovascular drugs, H2 antagonists agents, hormonotherapy; pharmacodynamic interactions associated to increased cyclosporine nephrotoxicity.

Debrisoquine and dextromethorphan phenotyping and antidepressant treatment

The correlation between debrisoquine and dextromethorphan oxidation polymorphism was studied in 16 depressed in-patients. There was a close correlation between both phenotypes (r = 0.81 p less than 0.0017). During a treatment with amitriptyline during two weeks there was no significant modification of the dextromethorphan polymorphism. In the same way, the association of amitriptyline and toloxatone during two other weeks did not change this polymorphism in a significant way, even if there was a non significant shift towards higher values of the dextromethorphan metabolic ratio.

A study of the interaction of viloxazine with theophylline

The effect of viloxazine on the pharmacokinetics of theophylline was studied in eight healthy volunteers. Theophylline 200 mg/day (théophylline Bruneau 100 mg tablets) was administered on day 1; after a 3-day washout period, viloxazine 300 mg/day (Vivalan 100 mg tablets) was administered orally from days 5 to 7. On day 8, theophylline 200 mg and viloxazine 100 mg were concomitantly administered. The pharmacokinetic parameters of theophylline alone and after coadministration of viloxazine were determined. Viloxazine significantly increased the plasma concentrations (p less than 0.01) and the area-under-the-curve values (p less than 0.01) of theophylline and decreased its body clearance (p less than 0.05). Our results suggest that the dosage of theophylline should be decreased and its plasma concentrations monitored when viloxazine is prescribed.

[Clinical pharmacokinetics of viloxazine chlorhydrate. Practical implications]

Pharmacokinetic data of an antidepressant agent: Apparent half-life (T1/2 elim), time of peak plasma concentration (Tmax), bioavailability, have a major contribution to determine optimal dosage in accordance with a low modification of steady-state levels. Viloxazine is a second generation antidepressant drug with a short apparent half-life (T1/2 elim: 2 to 5 h (3.4 h), which requires once a day 3 h i.v. infusion or three intakes of 100 mg oral standard formulation. The recent development of a new 300 mg slow-release form seems justified by a best compliance. Pharmacokinetic properties [Tmax = 3 to 9 h (5.2 h), T1/2 term = 6 to 7 h], suggest once a day dosage without risk of accumulation in chronic treatment. The relationships between plasma levels and the clinical improvement were not clear in literature. The recent therapeutic use of a 300 mg slow-release tablet has not permitted to change precedent findings.

Oral pharmacokinetics and ascitic fluid penetration of ofloxacin in cirrhosis

Plasma and ascitic fluid concentrations of ofloxacin were determined in 12 cirrhotic patients after a single dose and repeated 200 mg oral doses. The single dose kinetics were compared to those obtained in 12 healthy volunteers. Mean plasma elimination half-life was 11.6 h in cirrhotics and 7.0 h in controls. Mean total clearance was 2.3 times lower in patients than in controls, due to a significant decrease of renal clearance of the drug, unrelated to creatinine clearance. Mean apparent volume of distribution was 1.2 l/kg in patients and 1.8 l/kg in controls. Estimated by the ratio of AUC in peritoneal fluid and plasma, ascitic fluid penetration was 80% after the first oral dose. Ascitic fluid concentrations equaled corresponding plasma concentrations after 10 h, without pronounced accumulation of ofloxacin in ascites. We may conclude that, in cirrhotic patients with normal serum creatinine, a significant impairment of renal tubular handling of ofloxacin could be observed and led to a delayed elimination half-life of the drug. Because of its broad spectrum of activity, low side-effect profile, and large ascitic fluid penetration after oral administration, ofloxacin appears to be a new therapeutic approach of severe infections in cirrhotic patients, in particular spontaneous bacterial peritonitis.

Chlorophacinone intoxication. A biological and toxicological study

Plasma chlorophacinone determinations were performed in three cases of intoxication. The data collected in this study confirm the particularly prolonged anticoagulant effect of this compound and show that the knowledge of plasma concentrations may be very useful for clinicians since it allows to confirm the diagnosis and to evaluate the duration of the treatment. The determination of half-lives was investigated and the results indicate that the greater the quantity absorbed, the longer the half-life. The effect of phenobarbital on the elimination of cholorophacinone could be studied in one case. An increased elimination was noted when phenobarbital was administered.

[Demonstration of seasonal variations of circadian rhythm in gentamicin-induced chrono-nephrotoxicity in rats]

The present study investigates the chronobiological approach of the gentamicin-induced nephrotoxicity in rats treated with a single sublethal dose administered at different times of day and season of year. The nephrotoxicity is appreciated by gamma-glutamyl-transferase and alanine-amino-peptidase, two enzymes of the brush border cells and N-acetyl-beta-D-glucosaminidase, a lysosomal enzyme. These excretions peak out at 8 p.m. and reach a through at 8 a.m. for the experimentation in january-february. In contrast, for the experimentation in June-July, we evidence gamma-glutamyl-transferase and alanine aminopeptidase excretion increased at 2 p.m. and decreased at 8 p.m. So, we evidence with gentamicin not only a circadian but also a seasonal susceptibility in rats.

Circadian variations in the renal toxicity of gentamicin in rats

The hypothesis that sublethal doses of aminoglycosides cause renal tubule disorders resulting in changes of urine enzyme levels was investigated. The renal status following injection of a single sublethal dose of gentamicin (200 mg/kg) at different times during a 24 h cycle was studied. Increased excretion of gamma-glutamyl transferase, alanine aminopeptidase and N-acetyl-beta-D-glucosaminidase, used clinically as markers for tubule toxicity of aminoglycosides, was maximal when gentamicin was administered to rats at 2 p.m. and was minimal when injected at 8 p.m. These significant differences in enzyme excretion as a function of injection time are correlated with the concentration of gentamicin in the urine and in the renal cortex.