Concentration-Dependent Enrichment of Linezolid-Resistant Staphylococcus aureus in an in vitro Dynamic Model.

To establish the relationships between the enrichment of resistant Staphylococcus aureus mutants and the ratio of daily area under the concentration - time curve (AUC24) to the MIC of linezolid, a mixed inoculum of linezolid-susceptible and -resistant cells of three strains of S.aureus was exposed to twice daily linezolid in an in vitro dynamic model. Simulated pharmacokinetic profiles mimicked five-day treatments with linezolid dosing over a 32-fold range of the AUC24/MIC ratio. Population analysis of linezolid-exposed staphylococci was performed daily over 120 h after the start of the treatments. Minor if any enrichment of mutants resistant to 2X, 4X and 8XMIC of antibiotic was observed at the lowest and the highest AUC24/MIC ratios in contrast to pro- nounced enrichment of resistant mutants at the intermediate AUC24/MICs. An integral parameter AUBCm, the area under the time course of resistance mutants, was shown to be a more appropriate endpoint to establish AUC24/MIC relationships with resistance than postexposure number of mutants (NM).

[PK/PD Modeling as a Tool for Predicting Bacterial Resistance to Antibiotics: Alternative Analyses of Experimental Data].

Postexposure number of mutants (NM) is a conventional endpoint in bacterial resistance studies using in vitro dynamic models that simulate antibiotic pharmacokinetics. To compare NM with a recently introduced integral parameter AUBC(M), the area under the time course of resistance mutants, the enrichment of resistant Staphylococcus aureus was studied in vitro by simulation of mono(daptomycin, doxycycline) and combined treatments (daptomycin + rifampicin, rifampicin + linezolid). Differences in the time courses of resistant S. aureus could be reflected by AUBC(M) but not N(M). Moreover, unlike AUBC(M), N(M) did not reflect the pronounced differences in the time courses of S. aureus mutants resistant to 2x, 4x, 8x and 16xMIC of doxycycline and rifampicin. The findings suggested that AUBC(M) was a more appropriate endpoint of the amplification of resistant mutants than N(M).

Nanofabricated media with negative permeability at visible frequencies.

A great deal of attention has recently been focused on a new class of smart materials--so-called left-handed media--that exhibit highly unusual electromagnetic properties and promise new device applications. Left-handed materials require negative permeability micro, an extreme condition that has so far been achieved only for frequencies in the microwave to terahertz range. Extension of the approach described in ref. 7 to achieve the necessary high-frequency magnetic response in visible optics presents a formidable challenge, as no material--natural or artificial--is known to exhibit any magnetism at these frequencies. Here we report a nanofabricated medium consisting of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits a strong magnetic response at visible-light frequencies, including a band with negative micro. The magnetism arises owing to the excitation of an antisymmetric plasmon resonance. The high-frequency permeability qualitatively reveals itself via optical impedance matching. Our results demonstrate the feasibility of engineering magnetism at visible frequencies and pave the way towards magnetic and left-handed components for visible optics.

Two-dimensional gas of massless Dirac fermions in graphene.

Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

[Pharmacokinetics of n-(5-oxynicotinoyl)-L-glutamic acid calcium salt upon bolus administration in rats and rabbits: interspecies extrapolation].

The pharmacokinetics of N-(5-oxynicotinoyl)-L-glutamate (ONG) was studied in rats (doses, 20, 100 and 500 mg/kg) and rabbits (50 mg/kg) after bolus administration of calcium salt of N-(5-oxynicotinoyl)-L-glutamic acid (Ampasse preparation). The ONG concentration in the blood serum was determined by HPLC assay with fluorimetric detection. The lower limit of accurate detection for ONG was 100 ng/ml. The ONG pharmacokinetics in rats was linear at relatively small doses (20-100 mg/kg) but nonlinear at a large dose (500 mg/kg). The ONG concentration decay had a two-phase character in both rats and rabbits, so that the pharmacokinetic profiles were fitted to a biexponential equation of the two-compartment model. Systemic pharmacokinetic parameters determined in rats and rabbits, respectively, were as follows: total clearance, 18 and 15 ml/(min kg); steady state distribution volume, 330 and 880 ml/kg; mean retention time, 0.3 and 1.0 h; half-life, 0.73 and 2.3 h. Using the allometric approach to the interspecies extrapolation of the pharmacokinetic data, the half-life of ONG in humans is predicted to be 4 h.

Comparative anti-staphylococcal effects of gemifloxacin and trovafloxacin in an in vitro dynamic model in terms of AUC/MIC and dose relationships.

To compare the antimicrobial effects of gemifloxacin and trovafloxacin on Staphylococcus aureus, their pharmacodynamics were studied in an in vitro dynamic model. A series of pharmacokinetic profiles of gemifloxacin and trovafloxacin with half-lives of 7.4 and 9.2 h, respectively, were simulated in vitro over an eightfold range of area under the curve (AUC)-to-MIC ratio, from 58 to 466 h. The relationships observed between the intensity of antimicrobial effect (I(E)) and log AUC/MIC were linear, species- and strain-independent and were distinct (not superimposed) for both gemifloxacin and trovafloxacin (r(2) = 0.99 in both cases). At AUC/MICs > 100 h, trovafloxacin had greater effects than gemifloxacin. For example, at an AUC/MIC of 250 h, the antimicrobial effect of trovafloxacin was 17% higher than gemifloxacin. However, due to its higher intrinsic activity, gemifloxacin may be as efficient as trovafloxacin at their clinical doses (320 and 200 mg, respectively): the I(E)s on a hypothetical strain of S. aureus with gemifloxacin's and trovafloxacin's MICs corresponding to the MIC(50)s were similar-290 and 310 (log CFU/mL)x h, respectively. This analysis suggests that both AUC/MIC and dose relationships of the antimicrobial effect are needed for comprehensive comparisons of fluoroquinolone pharmacodynamics.

Gemifloxacin and ciprofloxacin pharmacodynamics in an in-vitro dynamic model: prediction of the equivalent AUC/MIC breakpoints and doses.

To compare the antimicrobial effects (AMEs) of gemifloxacin (GEM) and ciprofloxacin (CIP) on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, a series of pharmacokinetic profiles of GEM (a single dose with the half-life (T(1/2)) of 7.4 h and CIP (two 12 h doses with T(1/2) of 4 h) were simulated in vitro over eight-fold ranges of the AUC/MIC ratio. Species- and strain-independent linear relationships observed between the intensity of AME (I(E)) and log AUC/MIC were not superimposed for GEM and CIP (r(2)=0.99 and 0.98, respectively). The predicted ratio for GEM that might be equivalent to a clinically established breakpoint value of AUC/MIC=125 (mg h/l)/(mg/l) for CIP was estimated at 110 (mg h/l)/(mg/l). It was calculated, that a daily dose of CIP that might provide the same AME as a clinical dose of GEM (320 mg) on a hypothetical strain of S. aureus with MICs=MIC(50)s would be as high as 2 x 3200 mg.

In vitro dynamic model for determining the comparative pharmacology of fluoroquinolones.

An in vitro model for determining the comparative pharmacology of fluoroquinolones is presented. The true therapeutic potential of fluoroquinolones against bacterial pathogens may be best understood before clinical testing with the use of in vitro dynamic models. These models simulate pharmacokinetics in humans and can be used to compare different drugs in the same class over a wide range of dosages with respect to the antimicrobial effect (AME). Two models for evaluating AME are described. In one (a two-compartment model), a simple bacterial killing curve is generated after exposure to simulated clinical doses of antimicrobial. In the other (a one-compartment model), AME is defined as the area between the control bacterial growth curve in the absence of drug and the curve that represents bacterial killing and regrowth. This area can be readily measured and is referred to as the intensity of the effect (I(e)). In general, AME is correlated with drug exposure, as simulated in the model at different ratios of the area under the concentration-time curve (AUC) to the minimum inhibitory concentration (MIC) for the organism under study. With this in vitro dynamic model, several fluoroquinolones were tested over a range of AUC/MIC ratios for their AMEs against Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. The data generated illustrate the usefulness of in vitro dynamic models for comparing AMEs of different fluoroquinolones. Because the model incorporates pharmacokinetic variables, it provides a method for comparing various dosage regimens or schedules of administration and is useful in preclinical drug development.

[Pharmacokinetic validation of the antitumor efficacy of aclarubicin administered by various routes in CBF1 mice with Ca 755 carcinoma]. / Farmakokineticheskoe obosnovanie protivoopukholevoiéffektivnosti aklarubitsina pri razlichnykh sposobakh primeneniia u myshei linii CBF1 s kartsinomoi Ca 775.

Aclarubicin was established to be more active against murine mammary gland carcinoma Ca 755 after its intravenous injection as compared to oral administration. Pharmacokinetics of aclarubicin and its biologically active metabolites MA 144 N1, MA 144 T1 and MA 144 M1 was studied by HPLC in the tumour tissues. Not only quantitative but also qualitative differences in the ratios of the unchanged antibiotic and its metabolites in tumour Ca 755 were detected after aclarubicin administration by these methods. Diverse therapeutic activity was shown to be due to these differences.

Relationship between the blood concentration of the drug and its cumulative effect: a pharmacokinetic analysis of the nephrotoxic action of gentamicin and streptomycin.

The general principle of dependence of cumulative effects on drug concentration in the blood is proposed. The registered response is regarded as a result of the dual effect of drug blood level and duration of action. The corresponding experimental design consists in maintaining the serum concentration values at several definite levels and determining the response values for each of them. The constant serum level of the drug could be achieved by means of continuous infusion calculated according to the pharmacokinetic model. This principle was proved in the acute experiments on cats which established a relationship between the nephrotoxic effect of gentamicin and streptomycin on the one hand and their concentration in the serum and duration of action on the other.

In vitro simulated pharmacokinetics profiles: forecasting antibiotic optimal dosage.

Sisomicin (SMN) and cefotaxime (CTX) antimicrobial effect (AME) kinetics were studied under in vitro stimulation the drug monoexponential pharmacokinetic profiles mimicking normal and impaired elimination of SMN or CTX administered in various doses to humans. Similar general shape of the AME intensity or duration vs the SMN and CTX AUC curves, i.e. the appearance of the "bacteriostatic" and "bactericidal" phases, was established irrespective of the antibiotic elimination rate. At the same time the AME vs AUC curves simulated normal and delayed drug elimination did not match. Thus, AME is defined not only the AUC value but also the peculiarities of the pharmacokinetic profile and, subsequently, the term of "antibiotic efficient concentration" is unseparable of the pharmacokinetic profile.

Correlations between aminoglycoside pharmacokinetic parameters and patient's factors: from statement to implication for individual dosage design.

Amikacin pharmacokinetics was studied in 20 critically ill patients after a single i.v. bolus dose (500 mg). The amikacin pharmacokinetic profiles were characterized by marked intra-individual variability. Stepwise multivariate regression analysis made it possible to establish statistically significant correlations between the amikacin total clearance (Cl) and 8 patient's factors such as the, age, sodium plasma content, plasma osmolarity, partial pressure of oxygen and carbon dioxide, volumes of transfused plasma and blood, application of artificial lung ventilation (r2 = 0.98). The multiple regression equation for the Cl prediction provides reliable indirect estimation of the parameter. Thus, it appears possible to adjust the aminoglycoside dosage by taking into account 8 patient's factors, until the amikacin plasma concentration, time data are available.

Age dependence of erythromycin rectal bioavailability in children.

Erythromycin pharmacokinetics was studied in neonates (less than 1 month), infants (1-12 months) and other children (1-12 years) after the drug rectal and intravenous administration. The areas under the erythromycin serum concentration-time curves (AUC) were practically independent on children's age following the intravenous drug administration, but not its rectal administration. There was a distinct age dependency of the AUC parameter in the latter case. The increase of children's age was resulted in enhancement of the erythromycin total clearance, reduction of the steady-state volume of distribution and of the mean residence time. The extent of absolute bioavailability of rectally administered erythromycin was increased from 28 per cent in neonates to 36 per cent in infants and to 54 per cent in children greater than 1 year. Alteration of the mean absorption time parameter was reflected the delayed absorption of erythromycin in neonates.

[Correlation of dose-antimicrobial effect in modeling in vitro pharmacokinetic profiles of normal and impaired elimination of antibiotics]. / Sootnosheniia kontsentratsii/antimikrobnyi éffekt pri modelirovanii in vitro farmakokineticheskikh profilei normal'noi i narushennoi éliminatsii antibiotikov.

Relationships between concentration and antimicrobial effect (AME) of sisomicin (SMN) and cefotaxime (CTX) were established by simulating their pharmacokinetic profiles in an in vitro dynamic model. The AME duration (TE, time shift between the curves of bacteria heat output in the presence and absence of the antibiotics) or intensity (IE, area between the above curves) for both the antibiotics depended in the same way on the area under the concentration/time curve (AUC, mimicing of intravenous administration of the antibiotics in various doses). At low and moderate values of the AUC the dependences of IE or TE vs the AUC (the bacteriostatic phase of the AME development) were of the sigmoid shape while at high values of the AUC there was a marked increase in IE or TE (the bactericidal phase). The patterns of the IE or TE vs AUC curves in impaired antibiotic elimination were analogous. At the same time the IE or TE vs AUC curves for both the antibiotics under simulation of normal elimination (T 1/2, SMN-2.1 h, T 1/2, CTX-1.2 h) and impaired one (T 1/2, SMN-8.3 h, T 1/2, CTX-4.6 h) did not match. In the first case the AMESMN was on the whole higher and the AMECTX was lower than in the second case. Therefore, in patients with renal failure the efficient concentration of the aminoglycoside in blood can be higher and that of the cephalosporin on the contrary can be lower than the normal.

[Pharmacokinetic monitoring of antibiotic therapy]. / Farmakokineticheskii monitoring v antibiotikoterapii.

The general strategy in optimization of antibiotic dosage regimens included development of population or common regimens for an "average" patient (the 1st approximation), subpopulation regimens for patients of certain categories on the basis of interactions between the pharmacokinetic parameters and "patient factors" (the 2nd approximation) and individual regimens on the basis of the data of the pharmacokinetic monitoring (the 3rd approximation). Characteristics of every of the approximations in antibiotic therapy of adults and children were analyzed. Out of the peculiarities of the strategy use in pediatrics+ and micropediatrics+ the following should be indicated: (1) pharmacokinetic heterogeneity of the population requiring grouping of the patients and consequently development of subpopulation dosage regimens omitting stage I, (2) possible development of dosage regimens on the basis of the ration between the pharmacokinetic parameters or immediate drug concentration values and the "patient factors" not only in chronic but also in transitory impairment of some functions and (3) the necessity of considering systematic changes in "pharmacokinetic status" of every child during individualization of the dosage regimens by the data of the pharmacokinetic monitoring.

[Pharmacokinetics of protegentin, a combined preparation]. / Farmakokinetika kombinirovannogo preparata protégentin.

Protegentin is a combined preparation in the form of ointment containing 0.1 per cent of gentamicin, 0.25 per cent of erythromycin and 0.1 per cent of protease C. Pharmacokinetic studies on the preparation were conducted. Protegentin and gentamicin ointment, currently manufactured in this country, were applied to the surface of experimental pure cutaneous wounds in guinea pigs in a dose of 1 g. It was shown that inspite of the same contents of gentamicin in the ointments, the mean maximum concentration of the antibiotic in the underlying muscular tissue after the protegentin application was somewhat higher than that after the use of the gentamicin ointment. The differences in the drug concentration maintained during the whole observation period of 24 hours. However, they were not statistically significant. The gentamicin concentrations in serum after the use of protegentin were also somewhat higher than those after application of the gentamicin ointment (the differences were not statistically significant). Still, in no case the concentrations reached the potentially toxic ones. The erythromycin concentrations in the muscular tissue were much higher than those in the blood.

[Microcalorimetric study of the kinetics of the antibacterial effect of third generation cephalosporins in an in vitro dynamic system]. / Mikrokalorimetricheskoe izuchenie kinetiki antibakterial'nogo éffekta tsefalosporinov tret'ego pokoleniia v dinamicheskoi sisteme in vitro.

The antimicrobial effect (AME) kinetics of cefotaxime and ceftizoxime was studied with respect to 4 bacterial strains (E. coli, S. aureus, K. pneumoniae and P. aeruginosa) in an in vitro dynamic model. The mean integral concentrations, i.e. the AUC values divided by the dosing interval observed in blood of humans after the drug single intravenous administration in doses of 0.25, 0.5, 1 2 and 4 g. were simulated. The simulated concentrations of cefotaxime and ceftizoxime were 6.25 and 6.75, 12.5 and 13.5, 25 and 27, 50 and 54 and 100 and 108 mg/kg, respectively accounting for the differences in their pharmacokinetics. The changes in the microbial count were recorded microcalorimetrically by the rate of heat output with the BioActivity Monitor LKB 2277-202. The AME was expressed by TE reflecting the shift of the microbial growth curve in the presence of the cephalosporins against the control growth curve (in the absence of the drugs). It was noted that in simulating the concentrations observed after the drugs administration in various doses cefotaxime was mainly superior to ceftizoxime in terms of the TE, the value of the TE correlating with the respective values of the MICs. Some discrepancies between the TE and MICs were explained by the complicated shape of the TE vs. concentration or AUC curve observed earlier in regard to cefotaxime as well as by the differences in the steady state and dynamic conditions of the experiment.

[Pharmacokinetic monitoring during aminoglycosides: optimal therapy method of individual amikacin dosing]. / Farmakokineticheskii monitoring pri lechenii aminoglikozidami: optimal'nyi sposob individualizatsii dozirovaniia amikatsina.

One of the most successful approaches to adjustment of dosage regimens on the basis of single determinations of drug contents in blood specimens provides the blood sampling at the "ideal" moment (t*), i. e. at the time equal to the inverse value of the elimination rate constant. The above version of the one-point method is applicable to drugs obeying the one-compartment model. In practice, however, it is never known a priori whether the individual pharmacokinetic profile (PKP) is monoexponential or not. An attempt was made to apply the one-point method to individual amikacin (Am) intravenous bolus dosing in 27 patients with PKPs described not only by mono- but also by biexponential equations. The individual doses (Dc) estimated on the basis of Am concentrations recorded at the "ideal", point (2.75 hours after the administration) by the equation Dc = Dp.Cp(t*)/Ci(t*) were compared to the doses (DCl) found on the basis of greater than or equal to 4 determinations of the Am concentration (within 0.5 to 6 hours after the administration), i. e. by the equation DCl = Dp.Cli/Clp, where: Dp is the population value of an Am dose (7.5 mg/kg); Cp (t*) is the population value of an Am concentration at t* (6.7 mg/l), Clp is that of the total clearance [81.2 ml/(h.kg)] and Ci (t*) and Cli are the individual values of an Am concentration and clearance, respectively. The correlation coefficient of the DCl vs. Dc estimates was equal to 0.87. In 17 patients with monoexponential PKPs it was higher (r = 0.99).(ABSTRACT TRUNCATED AT 250 WORDS)

[Age-related characteristics of ceftazidime pharmacokinetics in children]. / Vozrastnye osobennosti farmakokinetiki tseftazidima u detei.

To reveal possible age-dependent variations in the ceftazidime pharmacokinetics, the drug plasma concentrations were determined by HPLC in 10 children aged 2 to 13 years with peritonitis. The blood specimens were collected 0.25, 0.5, 1, 3, 6 and 8 hours after intravenous bolus administration of ceftazidime (Kefadym, Eli Lilly) in a single dose of 20 mg/kg. The mean values of the model-independent parameters were: total clearance (Cl), 3.3 +/- 0.8 ml/min.kg; steady-state distribution volume, 0.32 +/- 0.06 ml/kg; mean residence time, 1.7 +/- 0.4 hours. The C-coordinate of the gravity center was equal to 26 +/- 7 mg/l. A noticeable age-dependent decrease in Cl was detected by comparing the Cl estimates in our study for the children aged 7.0 +/- 3.0 years with earlier findings in children aged 12 years as well as in adults (18 and 26 years) and elderly patients (77 years): 2.5, 2.2, 2.0 and 1.1 ml/min.kg, respectively. A similar trend was observed for the ceftazidime volume of distribution (Varea). Due to the described reduction in Cl and Varea the age-induced changes in the half-life of ceftazidime were negligible. The age-dependent differences in ceftazidime pharmacokinetics should be taken into account in designing rational dosage regimens for the drug administration.

[Pharmacokinetic monitoring of aminoglycoside therapy: an optimal method of administration of individualized doses of gentamicin and sisomicin]. / Farmakokineticheskii monitoring pri lechenii aminoglikozidami: optimal'nyi sposob individualizatsii dozirovaniia gentamitsina i sizomitsina.

One of the most promising approaches to design the optimal schedule for TDM provides a single determination of a drug content in the blood specimen being collected at the "ideal" sampling time equaled to the inverse value of the elimination rate constant. Three versions of the one-point method when the specimen was collected at the "ideal" time point (3 h after a single i.m. drug administration), as well as at the times of "maximum" (1 h after injection) and "minimum" (6 h after injection) concentrations were compared by the retrospective analysis of the routine TDM data obtained with HPLC-techniques in 47 patients treated with gentamicin or sisomicin. As optimal individualized doses were considered ones calculated on the base of three subsequent determinations of the aminoglycoside concentrations, i.e. 1, 3 and 6 h after injection, and the estimation of individual clearance values (Cli). The optimal doses (DCl) were calculated according to equation DCl = Dp.Cli/Clp, where Dp and Clp are population values of the dose (1 mg/kg) and Cl 72.4 ml/(h.kg), respectively. The approximate values of the individual doses (D) were calculated according to equation D = Dp.Cp/Ci, where Ci is the individual drug serum concentration 1, 3 or 6 h after administration and Cp is the corresponded population value (4.8, 1.9 and 0.8 mg/l, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)