Objectives – Ceftriaxone is a semi-synthetic cephalosporin with a high level of protein binding to albumin. The authors wanted to determine whether the bound fraction was actively bactericidal.

Objectifs – Évaluer si la fraction liée de la ceftriaxone participe à son action bactéricide.

OBJECTIVE:The purpose of this study was to investigate and characterize in vitro the post-beta-lactamase inhibitor effect (PLIE) of clavulanic acid against two beta-lactamase-producing species of bacteria.METHODS:The PLIE was investigated against one strain of Klebsiella pneumoniae and one strain of Haemophilus influenzae. A stationary-phase inoculum of about 107 colony-forming units per mL of each bacterium was pre-exposed for 2 h to clavulanic acid, either alone or in combination with amoxicillin at various concentrations. After pre-exposure, the dilution required to remove the beta-lactamase inhibitor was 1:100 or 1:1000 according to the bacterial species and their susceptibilities to clavulanic acid. Bacteria were counted hourly after drug removal, on solid agar medium.RESULTS:Control cultures exposed to amoxicillin alone after dilution, showed a delay in growth, which may be inherent to the time required to synthesize sufficient beta-lactamase after the dilution steps. Control experiments clearly distinguished the post-antibiotic effect and the growth delay from the PLIE.CONCLUSION:The PLIE could be one of several factors explaining why beta-lactam/beta-lactamase inhibitor combinations remain effective throughout the dosing interval, even if a few hours after in vivo administration, serum concentrations of beta-lactamase inhibitor fall below levels that are active in vitro.

L'Effet Post-Inhibiteur de Beta-Lactamases (EPIBLA) est peut-etre l'un des facteurs permettant d'expliquer pourquoi les associations β-lactamine/inhibiteur de β-lactamases demeurent actives in vivo pendant tout l'intervalle separant deux administrations, alors que les concentrations seriques de l'inhibiteur, mesurees dans les dernieres heures avant l'administration suivante, sont inferieures a celles necessaires a l'activite in vitro. L'etude de l'EPIBLA ne peut etre envisagee sans avoir prealablement recherche l'existence d'un eventuel effet post-antibiotique (EPA) dont il faudra tenir compte dans l'evaluation de l'EPIBLA. La determination precise de la duree de l'EPIBLA passe egalement par l'etude de tous les retards a la recroissance bacterienne inherents aux techniques operatoires. Une souche d'H. influenzae, une souche de K. pneumoniae et six souches d'E. coli de phenotypes de resistance differents, ont ete testees in vitro pour mettre en evidence un retard de recroissance lie a la pre-exposition a un inhibiteur de β-lactamases, l'acide clavulanique (AC), seul ou associe a l'amoxicilline (AMX). L'EPIBLA prend des valeurs de 0 a 5 h pour K. pneumoniae et de 0 a 15 h pour H. influenzae. Aucun Effet Post-Antibiotique, Retard de Croissance ou EPIBLA n'ont ete mis en evidence sur la souche d'E. coli productrice de penicillinase a bas niveau. Par contre, un EPIBLA a ete mesure apres pre-exposition a l'association amoxicilline-acide clavulanique ou a l'acide clavulanique seul sur les cinq autres souches d'E. coli productrices de β-lactamases a niveau intermediaire ou a haut niveau. D'une facon globale, l'EPIBLA est plus long apres un contact avec l'inhibiteur seul et peut atteindre des valeurs superieures a 22 heures chez E. coli, La concentration de l'amoxicilline, ajoutee apres l'elimination de l'AC, semble intervenir sur un allongement de l'EPIBLA, a condition que la concentration de l'inhibiteur ait ete suffisante pendant la phase de pre-exposition.

Objectives - From July 1997 to June 1998, 15 microbiological laboratories, set up as a regional survey unit in Alsace, collected S. pneumoniae strains to assess their susceptibility to antibiotic agents.Method - The strains were isolated from various clinical samples (blood cultures, pulmonary samples, cerebrospinal fluid, otitis media).Results - 599 strains were collected and the prevalence of Pneumococci with a Decreased Susceptibility to Penicillin G (PDSP) reached 32.9% (197 strains, MIC > 0.06 mg/L) but included a very small percentage of high level resistance strains to penicillin G (10 strains with MIC > 1 mg/L). Amoxicillin and cefotaxime remained active (3 and 0 resistant strains, respectively). The percentage of DPSP was much higher in the isolates of children (45.3%) than in those of adults (28.2%). The PDSP were rather resistant to erythromycin (76.6%), cotrimoxazole (65.2%), and fosfomycin (18.4%). Among PDSP, the most prevalent serotypes were 23, 14, and 9.Conclusion - This epidemiological survey allowed to assess the local impact of pneumocaccal resistance to antibiotics thanks to extensive collection and study. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

In vivo, serum concentrations of beta-lactamase inhibitors measured during the last part of the dosing interval are below the levels associated with in vitro activity. Nevertheless, beta-lactam plus beta-lactamase inhibitor combinations remain active in vivo throughout the dosing interval. One of the many reasons for this contradiction may be the PLIE, The PLIE can be evaluated only in the light of the postantibiotic effect (PAE). Also, accurate determination of the PLIE requires a careful investigation of all bacterial regrowth delays (BRDs) inherent to the technical procedures used. The purpose of the study reported herein was to determine the true in vitro PLIE of clavulanic acid (CA) against two beta-lactamase-producing strains, a Klebsiella pneumoniae strain (amoxicillin [AMX] MIC > 256 mg/L; CA MIC=64 mg/L; and AMX+CA MIX=4 mg/L) and a Haemophilus influenzae strain (AMX MIC=32 mg/L; CA>32 mg/L; AMX-CA=1 mg/L). For each strain, a stationary phase inoculum of 10(7) was preexposed for 2 h to either CA alone or CA + AMX in various concentrations. Dilution to 10(-2) or 10(-3) was performed to eliminate the CA and/or AMX after the preexposition phase. Hourly bacterial counts were done between 0 and 8 h and after 24 h. Control cultures exposed to AMX after dilution showed a growth delay possibly ascribable to the time needed for bacteria to produce a large enough amount of beta-lactamases. control experiments were done to unequivocally differentiate PLIE from PAE and BRD. The true PLIE values thus obtained ranged from 0 to 4.5 h for K. pneumoniae and from 0 to 15 h for H. influenzae. For both strains, a PLIE was demonstrated after exposure to CA alone.

Extended-spectrum beta-lactamases (ESBLs) are found in numerous Enterobacteriaceae, mainly in Klebsiella pneumoniae. We investigated the pharmacodynamics of two new extended-spectrum cephalosporins, cefepime and cefpirome, alone and combined with either amikacin or gentamicin or ciprofloxacin by means of time-kill curves against ESBL-producing, aminoglycoside-resistant K. pneumoniae. When used alone, cefepime (8 and 16 mg/l) resulted in a 2 and 3 log decrease at 6 h, respectively, but at 24 h regrowth occurred. The combination of cefepime (8 mg/l) with amikacin (4 mg/l) resulted in a 4 log decrease at 6 h, but there were no surviving bacteria at 6 h when combined with amikacin (8 mg/l). The combination of cefepime (16 mg/l) with gentamicin (4 mg/l) resulted in a 4 log decrease in 24 h. The antimicrobial combination of cefepime (32 mg/l) with ciprofloxacin (2 mg/l) resulted in a 4 log decrease in 24 h. Cefpirome (8 mg/l) induced a 2 log decrease at 4 h; 32 mg/l cefpirome resulted in a 3 log decrease followed by regrowth at 24 h. The regrowth observed in the late phase with cefpirome alone disappeared when combined with aminoglycoside. When cefpirome (32 mg/l) was used in combination with ciprofloxacin (1 mg/l), it resulted in a 4 log decrease in 24 h.

Three female Yucatan micropigs were included and received a single dose of amikacin (15 mg/kg) by short infusion (30 min) combined either with a single dose of cefepime or cefpirome (30 mg/kg/12 h) or meropenem (7 mg/kg/8 h). The beta-lactams were administered either by intravenous intermittent injection or by continuous infusion. The mean elimination half-life and clearance value of amikacin were 1.88 h and 2.15 ml/min.kg(-1) respectively. These pharmacokinetic parameters were similar to those obtained in man (t1/2 = 2,42 h et Cl = 1,61 ml/min kg(-1)). Furthermore, they were not affected by coadministration of cefepime, cefpirome and to meropenem. While resistant to cefepime, cefpirome and amikacin, Klebsiella pneumoniae producing ESBL was susceptible to combination of these cephalosporins with amikacin in an in vitro/ex vivo micropig model. For the six dosage regimens used in this study, the killing activities were similar and resulted in at least 4 log decrease at 6h after drug exposure. For antimicrobial combination consisting of bolus dosing of amikacin plus continuous infusion of cefepime or cefpirome, the 12 h serum bactericidal titers (SBTs) were 1:8 for cefepime and 1:2 for cefpirome dosage regimen. When each drug administered intermittently, the 12 h SBTs were 1.4 for cefepime and 1:2 for cefpirome. The 8 h SBTs for dosing schedule containing meropenem combined with amikacin were 1:4 and 1:16 after 30 min short infusion and continuous infusion respectively. In conclusion, our study showed that the micropig model is a reliable model for pharmacokinetic investigation of amikacin. It was concluded that beta-lactam antibiotics tested with amikacin may be coadministered by using the standard recommended dosing regimen of amikacin. Continuous infusion of beta-lactams combined with once dosing of amikacin seems to be as or more effective than intermittent injection of each drug.

A simple, rapid, specific and sensitive high-performance liquid chromatographic method was developed for the determination of cefepime 1-[[(6R, 7R)-7-[2-(2-amino-4-thiazolyl) glyoxylamido]-2-carboxy-8-oxo-5-thia-1-azabicyclo- [4.2.0]oct-2-en-3-yl]methyl]-1-methylpyrrolidinium hydroxide, inner salt, 7(2)-(Z)-(O-methyloxime) in human serum. Separation was achieved on a reversed-phase Ultrasphere XL-ODS column (75 x 4.6 mm I.D.). The mobile phase was 7% acetonitrile in 20 mM ammonium acetate (pH 4). Cefepime eluted in the range of 1.8-2.2 min. Detection was by UV absorbance at 254 nm. The lower limit of quantitation of cefepime in plasma was 0.5 microgram/ml. The average absolute recovery was 106.2 +/- 2.1%. The linear range was from 0.1 to 50 micrograms/ml, with a correlation coefficient greater than 0.999. The within-day C.V.s for human samples were 4.9 and 2.3% for 1 and 50 micrograms/ml, respectively. The between-day C.V.s for human serum samples were 14.5, 7.4 and 6.7 for 1, 25 and 50 micrograms/ml, respectively. Cefepime was found to be unstable in serum at room temperature. For delayed assay, samples must be stored at -80 degrees C.

Le porc miniature est un modèle non rongeur qui suscite beaucoup d'intérêt en recherche biomédicale. Il est, par de multiples aspects physiologiquement, proche de l'homme. Malgré les avantages qu'il procure, le micropore reste paradoxalement peu utilisé en pharmacocinétique. Cependant des données cinétiques sont nécessaires dans le but d'établir des comparaisons inter-espèces. C'est pourquoi nous avons entrepris une étude pharmacocinétique de quatre β-lactamines (ceftriaxone, céfépime, cefpirome, méropénème). A l'exception de la ceftriaxone administrée uniquement par une injection en bolus, les autres molécules sont administrées à la fois en bolus (ou perfusion courte pour le méropénème) et en perfusion continue. Les prélèvements sanguins sont obtenus sur une période de 12 heures à travers un cathéter placé dans la veine jugulaire externe. Les antibiotiques ont été dosés par CLHP. Concernant la ceftriaxone, des différences notables apparaissent entre le micropore et l'homme. La demi-vie d'élimination est d'environ une heure chez le microporc, soit 6 à 9 fois plus courte que chez l'homme. La pharmacocinétique du céfépime et du cefpirome chez le microporc est proche de celle observée chez l'homme à la même posologie (2 g). Les demi-vies d'élimination sont pour l'homme : 1,8 h et 1,8 h; pour le microporc 1,59 h et 1,44 h respectivement. Les valeurs de la clairance pour l'homme sont 1,82 et 1,80; pour le microporc 1,97 et 1,57 ml/min.kg−1 respectivement. La pharmacocinétique du méropénème est aussi proche de celle trouvée chez l'homme. Le méropénème administré par perfusion continue semble être plus rapidement éliminé que lorsqu'il est administré par perfusion courte. Dans l'étude présente nous concluons que le microporc est une espèce adaptée à l'étude pharmacocinétique du céfépime, cefpirome et méropénème.

Nosocomial infections encountered in intensive care units are frequently due to Gram negative bacilli among which Stenotrophomonas maltophilia, Acinetobacter sp., and Enterobacter sp. The aim of the present study was to evaluate the in vitro bactericidal activity of the new broad spectrum cephalosporins cefepime (FEP) and cefpirome (CPO) alone or in combination with amikacin (AKN), gentamicin (GTN) or ciprofloxacin (CIP) against Acinetobacter baumannii, Stenotrophomonas maltophilia and Enterobacter cloacae producing a derepressed cephalosporinase. This study was performed by using the time-kill curve method on 24 h with a starting inoculum of 10(6) - 10(7) cfu/ml. The combination of FEP (4 mg/l) with AKN (4 mg/l) against A. baumanii only results in about 1 log decrease at 24 h, but when FEP is combined at 8 mg/l, the decrease reaches 4 log in 24 h. The combination of FEP (16 and 32 mg/l) with clavulanic acid (4 mg/l) resulted in 3 log decrease at 24 h. When combined with CIP 2 mg/l, FEP (16 and 32 mg) resulted in 5 and 6 log decrease in 24 h respectively, There were no survival bacteria at 6 h when FEP (32 mg/l) was combined with clavulanic acid (4 mg/l) and GTN (8 mg/l) at 6 h. Used alone FEP (1 mg/l) or CPO (1 mg/l) against E. cloacae, a 3 log decrease occurs at 6 h followed by a regrowth at 24 h. Combined with AKN (2 mg/l), FEP (1 mg/l) results in a 6 log decrease at 24 h, when CPO at 2 mg/l is needed for an equivalent result. These data show synergistic bactericidal activity of both new extended cephalosporins combined with ARN, GTN or CIP. at concentrations achievable in biological fluid with adaptative dosage regimen.

Nosocomial infections encountered in intensive care units are frequently due to Gram negative bacilli among which Stenotrophomonas maltophilia, Acinetobacter sp., and Enterobacter sp. The aim of the present study was to evaluate the in vitro bactericidal activity of the new broad spectrum cephalosporins cefepime (FEP) and cefpirome (CPO) alone or in combination with amikacin (AKN), gentamicin (GTN) or ciprofloxacin (CIP) against Acinetobacter baumannii, Stenotrophomonas maltophilia and Enterobacter cloacae producing a derepressed cephalosporinase. This study was performed by using the time-kill curve method on 24 h with a starting inoculum of 10(6) - 10(7) cfu/ml. The combination of FEP (4 mg/l) with AKN (4 mg/l) against A. baumanii only results in about 1 log decrease at 24 h, but when FEP is combined at 8 mg/l, the decrease reaches 4 log in 24 h. The combination of FEP (16 and 32 mg/l) clavulanic acid (4 mg/l) resulted in 3 log decrease at 24 h. When combined with CIP 2 mg/l, FEP (16 and 32 mg) resulted in 5 and 6 log decrease in 24 h respectively. There were no survival bacteria at 6 h when FEP (32 mg/l) was combined with clavulanic acid (4 mg/l) and GTN (8 mg/l) at 6 h. Used alone FEP (1 mg/l) or CPO (1 mg/l) against E. cloacae, a 3 log decrease occurs at 6 h followed by a regrowth at 24 h. Combined with AKN (2 mg/l), FEP (1 mg/l) results in a 6 log decrease at 24 h, when CPO at 2 mg/l is needed for an equivalent result. These data show synergistic bactericidal activity of both new extended cephalosporins combined with AKN, GTN or CIP at concentrations achievable in biological fluid with adaptative dosage regimen.

High-performance liquid chromatographic procedures have been developed for the measurement of three new fluoroquinolones, fleroxacin, temafloxacin and A-64730, in serum, urine and bile. The sample treatment consists of a two-step chemical extraction. The three molecules are chromatographed on a C18 reversed-phase analytical column with spectrofluorimetric detection. At a signal-to-noise ratio of 4, the detection limits in serum are 2.5, 10 and 20 ng/ml, for fleroxacin, temafloxacin and A-64730, respectively. The calibration curves are rectilinear between these detection limits and 20 micrograms/ml. The intra- and inter-assay coefficients of variation are in the ranges 0.8-5.4 and 2.2-7.6%, respectively. These simple and reliable assay procedures will be of great interest for further pharmacokinetic studies and drug monitoring in hospital use.