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1.  Efficacies of cefotaxime and ceftriaxone in a mouse model of pneumonia induced by two penicillin- and cephalosporin-resistant strains of Streptococcus pneumoniae. 
Antimicrobial Agents and Chemotherapy  1996;40(12):2829-2834.
We previously demonstrated the efficacy of ceftriaxone (CRO), at 50 mg/kg of body weight every 12 h, against a highly penicillin-resistant (MIC, 4 micrograms/ml) Streptococcus pneumoniae strain with low-level resistance to CRO (MIC, 0.5 microgram/ml) in a leukopenic-mouse pneumonia model (P. Moine, E. Vallée, E. Azoulay-Dupuis, P. Bourget, J.-P. Bédos, J. Bauchet, and J.-J. Pocidalo, Antimicrob. Agents Chemother. 38:1953-1958, 1994). In the present study, we assessed the activity of CRO versus those of cefotaxime (CTX) and amoxicillin (AMO) against two highly penicillin- and cephalosporin-resistant S. pneumoniae strains (P40422 and P40984) (MICs of 2 and 8 for penicillin, 2 and 4 for AMO, and 4 and 8 for CRO or CTX, respectively). Against both strains, a greater than an 80% cumulative survival rate was observed with CRO at a dose of 100 or 200 mg/kg every 12 h (dose/MIC ratio, 25). With CTX, a high dosage of 400 mg/kg (dose/MIC ratio, 100 or 50) administered every 8 h (TID) was needed to protect 66 and 75% of the animals, respectively, with no statistically significant differences versus CRO. Against the P40422 strain, CRO (100 mg/kg) produced the greatest bactericidal effect, from the 8th to the 24th hour after a single injection (1.8-log-unit reduction over 24 h), and the fastest bacterial pulmonary clearance during treatment; with CTX, only multiple injections at a high dosage, i.e., 400 mg/kg TID, demonstrated a significant bactericidal effect. AMO in a high dosage, 400 mg/kg (dose/MIC ratio, 200) TID, showed good activity only against the P40422 strain. Despite the identical MICs of CTX and CRO, the longer time (3.6 to 4.6 h) that serum CRO concentrations remained above the MICs for the pathogens at a dose of 100 mg/kg resulted in greater efficacy versus CTX against highly penicillin- and cephalosporin-resistant S. pneumoniae strains.
PMCID: PMC163631  PMID: 9124850
2.  Absorption of ofloxacin isomers in the rat small intestine. 
Antimicrobial Agents and Chemotherapy  1997;41(10):2274-2277.
Ofloxacin, a chiral fluoroquinolone, possesses two optical isomers. The antibacterial activity of S-(-)-ofloxacin is 8 to 128 times higher than that of R-(+)-ofloxacin. In the rat, a saturable absorption process has been described for racemic ofloxacin. In the present study we investigated the mechanism underlying the in vivo intestinal absorption of ofloxacin enantiomers in the rat. Blood samples were collected from the portal vein. Our results show that the intestinal absorption of ofloxacin isomers is pH dependent, both enantiomers being best absorbed at neutral pH. S-(-)-Ofloxacin seems to have a greater affinity for the intestinal transporter (initial concentrations at 5 min [C(init)] are 0.17 +/- 0.04 and 0.12 +/- 0.03 microg/ml for S-(-)- and R-(+)-ofloxacin, respectively). Dipeptides fail to modify ofloxacin absorption, but amino acids reduce both isomers' absorption (C(init) is reduced by 53 and 33% with glycine for S-(-)- and R-(+)-ofloxacin, respectively, and by 59 and 42% with L-leucine). Gamma amino butyric acid interferes with the absorption of ofloxacin isomers, but less seriously than do amino acids. Furthermore, ofloxacin competes with other fluoroquinolones or P-glycoprotein substrates for a common secretory pathway, resulting in an increased rate of absorption for both ofloxacin isomers; this is probably an indirect result of their reduced efflux from the apical side of intestinal cells.
PMCID: PMC164106  PMID: 9333061
3.  Influence of inducible cross-resistance to macrolides, lincosamides, and streptogramin B-type antibiotics in Enterococcus faecium on activity of quinupristin-dalfopristin in vitro and in rabbits with experimental endocarditis. 
The influence of inducible cross-resistance to macrolides, lincosamides, and streptogramin B (MLS(B)) type antibiotics (inducible MLS(B) phenotype) on the activity of quinupristin-dalfopristin was investigated against Enterococcus faecium in vitro and in rabbits with experimental endocarditis. In vitro, quinupristin-dalfopristin displayed bacteriostatic and bactericidal activities against a MLS(B)-susceptible strain similar to those against two strains with the inducible MLS(B) phenotype. In addition, induction of the two MLS(B)-resistant strains with quinupristin (0.016 to 1 microg/ml) or quinupristin-dalfopristin (0.08 to 0.25 microg/ml) increased the MICs of quinupristin from 8 microg/ml to 32 to > 128 microg/ml, but did not modify the MIC of dalfopristin (2 microg/ml) or quinupristin-dalfopristin (0.5 microg/ml). In a rabbit endocarditis model, quinupristin-dalfopristin was as active as amoxicillin against the MLS(B)-susceptible E. faecium strain. In contrast, the activity of quinupristin-dalfopristin was significantly decreased in animals infected with either of the two inducible MLS(B)-resistant strains (P < 0.05), although no mutants resistant to quinupristin-dalfopristin were detected. Against the clinical strain with the inducible MLS(B) phenotype, quinupristin-dalfopristin was not effective and was less active than amoxicillin (P < 0.001); however, the activity of the combination of amoxicillin and dalfopristin-quinupristin was superior to that of amoxicillin (P < 0.01). The different impact of the inducible MLS(B) phenotype in E. faecium on the activity of quinupristin-dalfopristin in vitro and in experimental endocarditis may be related to the reduced diffusion of dalfopristin compared with that of quinupristin into cardiac vegetations that we previously reported. This result emphasizes the importance of the constant presence of dalfopristin at the site of infection to ensure synergism with quinupristin.
PMCID: PMC163828  PMID: 9145847
4.  Use of a new mouse model of Acinetobacter baumannii pneumonia to evaluate the postantibiotic effect of imipenem. 
Acinetobacter baumannii is responsible for severe nosocomial pneumonia. To evaluate new therapeutic regimens for infections due to multiresistant strains and to study the pharmacodynamic properties of various antibiotics, we developed an experimental mouse model of acute A. baumannii pneumonia. C3H/HeN mice rendered transiently neutropenic were infected intratracheally with 5 x 10(6) CFU of A. baumannii. The mean log10 CFU/g of lung homogenate (+/- the standard deviation) were 9 +/- 0.9, 9.4 +/- 0.8, 8.6 +/- 1.2, and 7.7 +/- 1.4 on days 1, 2, 3, and 4 postinoculation. The lung pathology was characterized by pneumonitis with edema and a patchy distribution of hemorrhages in the peribronchovascular spaces of both lungs. Abscesses formed on days 3 and 4. Four days after inoculation, subacute pneumonitis characterized by alveolar macrophage proliferation and areas of fibrosis was observed. The cumulative mortality on day 4 was 85%. This new model was used to study the effects of 1, 2, or 3 50-mg/kg doses of imipenem. Imipenem concentrations in lungs were above the MIC for 2 h after the last dose. The in vivo postantibiotic effect (PAE) was determined during the 9-h period following the last dose; it decreased in duration with the number of doses: 9.6, 6.4, and 4 h after 1, 2, and 3 50-mg/kg doses, respectively. In contrast, no in vitro PAE was observed. This model offers a reproducible acute course of A. baumannii pneumonia. The presence of a prolonged in vivo PAE supports the currently recommended dosing intervals of imipenem for the treatment of human infections due to A. baumannii, i.e., 15 mg/kg three times a day.
PMCID: PMC163712  PMID: 9021190
5.  Effects of nifedipine and diltiazem on pharmacokinetics of cefpodoxime following its oral administration. 
Antimicrobial Agents and Chemotherapy  1996;40(12):2879-2881.
We compared the effects of nifedipine and diltiazem on the uptake of cefpodoxime proxetil (CP). The study was aimed at establishing the impact of increased mesenteric blood flow due to calcium channel blockers on passive transport. Twelve volunteers were given CP (200 mg) orally in a crossover design. The absorption, disposition, and elimination parameters of cefpodoxime were compared among the following three treatment groups: CP alone, CP following oral administration of diltiazem (60 mg), or CP following oral administration of nifedipine (20 mg). No statistically significant difference in pharmacokinetic parameters was observed between the three treatment groups.
PMCID: PMC163639  PMID: 9124858
6.  Resistance to amikacin and isepamicin in rabbits with experimental endocarditis of an aac(6')-Ib-bearing strain of Klebsiella pneumoniae susceptible in vitro. 
Antimicrobial Agents and Chemotherapy  1996;40(12):2848-2853.
The effect of production of the aminoglycoside 6'-N-acetyltransferase [AAC(6')-IB] in Klebsiella pneumoniae on the outcome of amikacin and isepamicin treatment of rabbits with experimental endocarditis was assessed. Isogenic high-level (Hi) and low-level (Lo) AAC(6')-Ib-producing transconjugants (T) were constructed from clinical isolates with plasmid-borne resistance determinants. The MICs of amikacin and isepamicin, their bactericidal effects, and AAC(6')-Ib production appeared to be well correlated among the clinical isolates and the transconjugants. The susceptibility data determined in vitro, with MICs (in micrograms per milliliter) of amikacin and isepamicin for LoT and HiT of 4 and 0.5 and 32 and 8, respectively, were, however, not predictive of the in vivo efficacies of the drugs. While amikacin and isepamicin caused reductions in bacterial densities (log10 CFU per gram of cardiac vegetation) of 5.1 and 4.8 of the fully susceptible recipient strain (MICs of amikacin and isepamicin, 0.5 and 0.25, respectively), the reductions in density of both LoT and HiT caused by the two drugs (2.7 and 2.4 and 2.9 and 2.2, respectively) were only marginally significant, if at all. There was no significant difference (P > 0.05) when the reductions in density of LoT and HiT by either drug were compared or when the efficacies of the two drugs in reducing the density of any strain [non-AAC(6')-producing, LoT, or HiT] were compared (P > 0.5). It is concluded that AAC(6')-Ib in K.pneumoniae, even when produced at a low level and not conferring resistance to amikacin and isepamicin in vitro, compromises the efficacies of both drugs in vivo and possibly does so beyond the experimental model studied here.
PMCID: PMC163634  PMID: 9124853
7.  Synergy between amoxicillin and gentamicin in combination against a highly penicillin-resistant and -tolerant strain of Streptococcus pneumoniae in a mouse pneumonia model. 
In vivo synergy with beta-lactam antibiotics and aminoglycosides has been studied only with penicillin-susceptible Streptococcus pneumoniae strains. We evaluated the interaction between amoxicillin (AMX) and gentamicin (GEN) on the basis of in vitro checkerboard and time-kill curves and of findings in a mouse model of acute bacteremic pneumonia due to a highly penicillin-resistant and -tolerant S. pneumoniae strain of serotype 19 (penicillin and AMX MICs of 4 micrograms/ml; gentamicin MIC of 16 micrograms/ml). Checkerboard results at 18 h of incubation showed indifference. With regard to AMX alone, in vitro time-kill curves demonstrated synergy between AMX (1 microgram/ml) and GEN (16 micrograms/ml) at 5 and 8 h of incubation and for AMX (16 micrograms/ml) in combination with GEN (16 micrograms/ml) at 3, 5, and 8 h of incubation. In leukopenic mice, pulmonary killing curves after a single drug injection demonstrated that AMX (100 mg/kg of body weight) with GEN (16 mg/kg) was more effective than AMX alone (P = 10(-4). With repeated-dose treatment, a synergy was apparent at 8 h after four injections with AMX (100 mg/kg) in combination with GEN (8 or 16 mg/kg) (P < or = 0.05). The cumulative survival rate with AMX (100 mg/kg) every 8 h, combined with GEN (4 or 8 mg/kg) every 8, 12, or 24 h, was better than with AMX alone. Combined use of AMX and GEN may be a valuable therapeutic alternative for pneumococcal pneumonia due to highly penicillin-resistant S. pneumoniae strains.
PMCID: PMC163489  PMID: 8878597
8.  Intestinal elimination of ofloxacin enantiomers in the rat: evidence of a carrier-mediated process. 
The aim of this work was to examine the mechanism involved in intestinal elimination of the two optical isomers of ofloxacin in the rat. An intestinal segment was isolated in situ and perfused with saline, while drug solution was administered via the carotid artery. Blood samples and intestinal effluents were collected and analyzed by a high-performance liquid chromatography method. We observed saturable and stereoselective intestinal elimination of the ofloxacin enantiomers. The elimination process favored the R-(+) form of the molecule. After a parenteral dose of 20 mg of racemic ofloxacin per kg of body weight, intestinal clearances were 0.23 +/- 0.03 versus 0.30 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively. Ciprofloxacin and pefloxacin interfered with ofloxacin elimination and significantly reduced the intestinal clearance of S-(-)- and R-(+)-ofloxacin. With concomitant ciprofloxacin, intestinal clearances became 0.13 +/- 0.02 versus 0.17 +/- 0.03 ml/min and 0.14 +/- 0.01 versus 0.19 +/- 0.05 ml/min with pefloxacin for S-(-)- and R-(+)-ofloxacin, respectively. Those findings argue for the presence of a common transport system in the rat intestine with variable affinities for fluoroquinolones. In addition, verapamil and quinidine, two P-glycoprotein blockers, significantly reduced the intestinal elimination of both ofloxacin isomers (with concomitant verapamil, intestinal clearances were 0.12 +/- 0.02 versus 0.18 +/- 0.03 ml/min for S-(-)- and R-(+)-ofloxacin, respectively, while with concomitant quinidine, values were 0.18 +/- 0.01 versus 0.23 +/- 0.01 ml/min without modifying their areas under the concentration-time curve in serum. Similar results were found with another fluoroquinolone, ciprofloxacin, in previous work. P-glycoprotein appears to be involved in the intestinal elimination of fluoroquinolones in rats. The characterization of fluoroquinolone intestinal elimination has significant clinical relevance for the better evaluation of the influence of this secretory pathway on antibiotic efficacy and selection of resistant bacteria within the intestinal flora.
PMCID: PMC163485  PMID: 8878593
9.  Efficacy of single-dose ceftriaxone in experimental otitis media induced by penicillin- and cephalosporin-resistant Streptococcus pneumoniae. 
We used a gerbil model of otitis media to assess the efficacy of single-dose ceftriaxone against three Streptococcus pneumoniae strains highly resistant to penicillin (MICs, 4 to 8 micrograms/ml) and with various susceptibilities to ceftriaxone (MICs, 0.5, 4, and 8 micrograms/ml). Middle ear infection was induced by bilateral transbullar challenge with 10(7) bacteria per ear. Antibiotic treatment was administered subcutaneously at 2 h postinfection. Infection status was checked 2 days later by counting the bacteria in middle ear and cerebrospinal fluid samples. With the cefriaxone-susceptible strain (MIC, 0.5 microgram/ml), we tested doses of 5 to 100 mg/kg of body weight. With a dose of 50 mg/kg, treatment outcome was equivalent to that with amoxicillin, which was used as a reference (25 mg/kg, two injections); no bacteria were recovered from 82% of the middle ear samples, and the rate of cerebrospinal fluid culture positivity was significantly reduced to 6%, relative to 59% for the untreated controls. Similar efficacy was obtained with a dose of 100 mg/kg against the two ceftriaxone-resistant strains. Pharmacokinetic study indicates that the values of the parameters in plasma after the administration of a dose of 100 mg/kg (peak level of total drug, 268 +/- 33 micrograms/ml; elimination half-life, 0.8 h; area under concentration-time curve, 488 were still suboptimal compared with the values of the parameters measured in pediatric patients after intravenous or intramuscular administration of a dose of 50 mg/kg. Our results indicate the efficacy of ceftriaxone against experimental cephalosporin-resistant pneumococcal otitis and provide a basis for the clinical use of single-dose ceftriaxone against pneumococcal otitis media.
PMCID: PMC163458  PMID: 8878566
10.  Efficacy of sparfloxacin and autoradiographic diffusion pattern of [14C]Sparfloxacin in experimental Staphylococcus aureus joint prosthesis infection. 
Using a new rabbit model of methicillin-susceptible Staphylococcus aureus knee prosthesis infection, we compared the efficacies of sparfloxacin (50 mg/kg of body weight subcutaneously, twice a day) and pefloxacin (50 mg/kg subcutaneously, twice a day). A partial knee replacement was performed with a silicone implant fitted into the intramedullary canal of the tibia, and 5 x 10(7) CFU of methicillin-susceptible S. aureus was injected into the knee. The 7-day treatment regimen was started 15 days later. The MICs and MBCs of sparfloxacin and pefloxacin were, respectively, 0.06 and 0.25 microgram/ml (MIC) and 0.25 and 1 microgram/ml (MBC). The peak levels of sparfloxacin and pefloxacin in serum were 3.6 and 21 micrograms/ml, respectively. Three weeks after the end of treatment, animals were sacrificed and tibias were removed, pulverized, and quantitatively cultured. In contrast to pefloxacin (3.61 +/- 1.64 log10 CFU/g of bone), sparfloxacin significantly reduced the bacterial density (2.12 +/- 1.1 log10 CFU/g of bone) (P = 0.01) in comparison with the level in controls (4.59 +/- 1.21 log10 CFU/g of bone), without selection of resistant variants. Sparfloxacin was significantly more effective than pefloxacin (P = 0.025). The autoradiographic pattern of [14C]sparfloxacin diffusion was studied in noninfected animals with prostheses and in infected animals 15 days after inoculation. Sixty minutes after completion of infusion of 250 microCi of [14C]sparfloxacin, in infected animals the highest levels of radioactivity were detected around the prosthesis, in femoral cartilage, and in articular ligaments. Radioactivity was slightly less intense in bone marrow and muscles and was very weak in compact bone. The distribution of sparfloxacin in uninfected rabbits was similar. Thus, sparfloxacin may represent a valid alternative therapy in these infections provided that it is carefully monitored for potential side effects.
PMCID: PMC163482  PMID: 8878590
11.  Importance of penicillinase production for activity of penicillin alone or in combination with sulbactam in experimental endocarditis due to methicillin-resistant Staphylococcus aureus. 
The activity of penicillin, alone and in combination with sulbactam, against a heterogeneously methicillin-resistant, penicillinase-producing clinical isolate of Staphylococcus aureus and its penicillinase-negative derivative was investigated in vitro and in a rabbit experimental endocarditis model. Penicillin was significantly more effective than vancomycin against the penicillinase-negative derivative in vivo (P < 0.001), and it sterilized 25% of the vegetations. The combination of penicillin and sulbactam exhibited an in vivo synergistic effect on the penicillinase-producing strain (P < 0.01) but did not produce any advantage over treatment with vancomycin, even when a high dose of sulbactam was used (100 mg/kg of body weight every 6 h). This combination was significantly less effective against the penicillinase-producing strain than was penicillin alone against the penicillinase-negative derivative (P < 0.03). In addition, the most resistant subpopulation of the surviving bacteria, which grew on agar containing 16 micrograms of methicillin per ml, was detected in 5 of 6 animals treated with penicillin and a high dose of sulbactam against the penicillinase-producing strain compared with only 1 of 12 animals treated with penicillin alone against the penicillinase-negative derivative (P < 0.01). We conclude that penicillin is highly effective against penicillinase-negative methicillin-resistant S. aureus and that penicillinase production, rather than methicillin resistance, appears to be the limiting factor for the activity of the penicillin-sulbactam combination against penicillinase-producing, methicillin-resistant S. aureus.
PMCID: PMC163295  PMID: 8723470
12.  Comparison of fluconazole and amphotericin B for treatment of experimental Candida albicans endocarditis in rabbits. 
Amphotericin B (AmB) and fluconazole, administered intraperitoneally for 7 days, were compared in a rabbit model for Candida albicans endocarditis. When given early, AmB was more effective than fluconazole for reducing CFU counts in vegetations (P < 0.01) and kidneys. Forty-eight hours after the last dose, AmB was still detected in all vegetations whereas fluconazole was detected in only one case.
PMCID: PMC163098  PMID: 8787921
13.  Excretion of ciprofloxacin into the large bowel of the rabbit. 
The intestinal elimination of ciprofloxacin in the large bowel was studied in a rabbit model. Segments from the cecum, colon, and sigmoid colon along with their intact blood vessels were isolated and perfused, and their contents were collected over a 90-min period following the administration of a single parenteral dose of 27 mg of ciprofloxacin per kg of body weight. The elimination rates of ciprofloxacin were 0.126 +/- 0.084 in the cecum and 0.264 +/- 0.126, 0.11 +/- 0.07, and 0.21 +/- 0.141 in the proximal colon, distal colon, and sigmoid colon, respectively. The calculated fraction of ciprofloxacin eliminated in the large bowel was 3% of the parenteral dose administered. The elimination pattern of ciprofloxacin in the large bowel may explain the unusual activity of this fluoroquinolone in modifying the colonic flora.
PMCID: PMC163047  PMID: 8787870
14.  Critical influence of timing of administration of granulocyte colony-stimulating factor on antibacterial effect in experimental endocarditis due to Pseudomonas aeruginosa. 
Antimicrobial Agents and Chemotherapy  1995;39(12):2702-2707.
The effect of human recombinant granulocyte colony-stimulating factor (hrG-CSF) in rabbits with aortic endocarditis due to Pseudomonas aeruginosa was investigated. hrG-CSF significantly increased the number of polymorphonuclear neutrophils in blood and in cardiac vegetations and the expression of the adhesin molecule CD11b on the surface of polymorphonuclear neutrophils compared with those of animals that had not received hrG-CSF. When treatment was started 72 h after bacterial challenge, hrG-CSF alone had no antibacterial effect and did not enhance the efficacy of ciprofloxacin when used in combination, even with the higher dosing regimen used (50 micrograms/kg of body weight subcutaneously every 12 h for 4 days), in terms of number of positive blood cultures, bacterial counts in vegetations, and survival. In contrast, when treatment was started 30 min prior to bacterial challenge, hrG-CSF (50 micrograms/kg injected every 12 h) decreased bacterial titers in vegetations 72 h later (6.5 +/- 0.9 versus 7.9 +/- 0.9 log10 CFU/g of vegetation for hrG-CSF and controls, respectively; P = prophylactic administration of hrG-CSF did not increase the antibacterial effect of ciprofloxacin. We concluded that the antibacterial effect of hrG-CSF in experimental endocarditis was related to the timing of its administration since hrG-CSF demonstrated a significant but transient antimicrobial effect only when treatment was initiated before bacterial challenge.
PMCID: PMC163016  PMID: 8593006
15.  Evaluation of high-dose regimen of paromomycin against cryptosporidiosis in the dexamethasone-treated rat model. 
In the dexamethasone-treated rat model of cryptosporidiosis, paromomycin was effective at a dosage of 50 mg/kg/day or more for ileal infection and 200 mg/kg/day or more for cecal infection. At 1 and 3 weeks after treatment, a persistent infection was demonstrated in all rats. These results confirm the anticryptosporidial activity of paromomycin and underscore the limitations of this compound because of its potential toxicity at such high dosages and its inability to eradicate the infection.
PMCID: PMC162902  PMID: 8540737
16.  Critical influence of resistance to streptogramin B-type antibiotics on activity of RP 59500 (quinupristin-dalfopristin) in experimental endocarditis due to Staphylococcus aureus. 
In order to determine the microbiological and pharmacokinetic parameters that best predicted the in vivo antistaphylococcal activity of the streptogramin RP 59500 (quinupristin-dalfopristin), we evaluated the activity in rabbit aortic endocarditis of three regimens of quinupristin-dalfopristin against five strains of Staphylococcus aureus with various streptogramin B-type antibiotic resistance phenotypes and susceptible to streptogramin A-type antibiotics. Quinupristin-dalfopristin was as active as vancomycin against three strains that were susceptible to its streptogramin B component quinupristin, including one strain that was inducibly resistant to erythromycin, but had a significantly decreased activity against two strains that were resistant to quinupristin, for all quinupristin-dalfopristin regimens tested (P < 0.05). The area under the concentration-time curve for quinupristin-dalfopristin in plasma divided by the MIC of quinupristin was the only parameter retained by multilinear regression that predicted the in vivo activity of quinupristin-dalfopristin (P = 0.0001), emphasizing the importance of determining the susceptibility to quinupristin in order to predict the in vivo activity of quinupristin-dalfopristin against S. aureus.
PMCID: PMC162550  PMID: 7726505
17.  Intestinal elimination of sparfloxacin, fleroxacin, and ciprofloxacin in rats. 
The intestinal transepithelial elimination of sparfloxacin and fleroxacin was compared with that of ciprofloxacin in a rat model following a single parenteral administration of 25 mg of each of the antibiotics per kg of body weight. All three fluoroquinolones were eliminated through the small intestine. Ciprofloxacin was eliminated in the proximal jejunum at a rate of 1.97 +/- 0.70 micrograms/cm2, while the elimination rates of fleroxacin and sparfloxacin were 0.64 +/- 026 and 0.21 +/- 0.10 micrograms/cm2, respectively, over a 90-min collection period. In the ileum, the elimination rates of ciprofloxacin, fleroxacin, and sparfloxacin over the same period were 1.44 +/- 0.77, 1.00 +/- 0.33, and 0.41 +/- 0.26 micrograms/mc2, respectively. These data suggest that these fluoroquinolones undergo a transepithelial elimination process in the small intestine. This route of elimination may be important in the therapy of bacterial diarrhea.
PMCID: PMC162492  PMID: 7695338
18.  Influence of diet on experimental toxicity of amphotericin B deoxycholate. 
The effects of pre- and postprandial levels of lipids in serum on the experimental in vivo and in vitro toxicities of amphotericin B deoxycholate (AmB-d) were studied. Normal OF1 mice were tested at baseline, after normal feeding, after 3 h of fasting, or after a sequence of feeding and fasting and vice versa. The 50% lethal dose (LD50) of AmB-d was significantly higher in fed mice than in mice which fasted or at baseline (2.38 +/- 0.12 versus 1.53 +/- 0.2 and 1.50 +/- 0.1 mg/kg of body weight, respectively; P < 0.05). When different nutritional regimens were alternated over a short period, the level of in vivo AmB-d toxicity was dictated by the last feeding regimen. Serum triglycerides, but not cholesterol in very-low-density and low-density lipoproteins, correlated significantly (P < 0.01) with the LD50 of AmB. In vitro experiments showed that the addition of human serum reduced AmB-d-induced toxicity against human erythrocytes, but serum drawn after fasting was less protective than postprandial serum. However, neither serum decreased the in vitro activity of AmB-d against Candida albicans. Circular dichroism, a method that enables the amount of free AmB to be measured, showed that both mouse and human total serum lipoproteins bound more AmB-d when serum was isolated postprandially than when it was obtained after fasting. Our results show that AmB-d toxicity is reduced by feeding-induced modifications in serum lipids. The influence of food intake on the clinical toxicity of the drug merits being investigated.
PMCID: PMC188134  PMID: 8067777
19.  Influence of antimicrobial therapy on kinetics of tumor necrosis factor levels in experimental endocarditis caused by Klebsiella pneumoniae. 
The kinetics of tumor necrosis factor (TNF) levels in serum during therapy with cell wall-active agents (ceftriaxone, imipenem) and gentamicin were investigated in rabbits with experimental endocarditis caused by an isogenic pair of Klebsiella pneumoniae strains: a TEM-3 beta-lactamase-producing strain (KpR) or its susceptible variant (KpS). In vitro, KpR was resistant to ceftriaxone and was susceptible to gentamicin and imipenem, while KpS was susceptible to all three antibiotics. Serum TNF levels were determined in control rabbits hourly after bacterial inoculation and then daily; they were determined in treated animals hourly after the first antibiotic injection and then daily during a 4-day therapy with either imipenem (60 mg/kg of body weight four times daily), ceftriaxone (75 mg/kg once daily), or gentamicin (4 mg/kg once daily) alone or in combination with ceftriaxone. After a transient peak (10.2 +/- 3.1 ng/ml) at 90 min following bacterial challenge, serum TNF levels remained low and stable in control animals. The peak in the serum TNF levels occurred 4 h after the first antibiotic injection and with ceftriaxone was significantly higher (P < 0.05) against KpS (1.99 +/- 0.52 ng/ml) than against KpR (1.40 +/- 0.17 ng/ml). Against the KpR strain, the levels observed with ceftriaxone were significantly higher (P < 0.05) than those obtained with the other therapeutic regimens (0.70 to 0.80 ng/ml). On the day of sacrifice, effective regimens were associated with low TNF levels. We concluded that TNF production depends on (i) the antiobiotic's mechanism of action and the susceptibility of the strain at the early phase of therapy, without any effect of the rapidity of bacterial killing, and (ii) the final reduction of the bacterial count at a later stage of therapy.
PMCID: PMC188143  PMID: 8067731
20.  Intestinal elimination of ciprofloxacin in rabbits. 
The intestinal transepithelial elimination of ciprofloxacin was studied in a rabbit model. Jejunal, ileal, and cecal segments along with their intact blood vessels were isolated and perfused, and their contents were collected over a 120-min period following administration of a single parenteral dose of 27 mg of ciprofloxacin per kg of body weight. The intestinal elimination rates of ciprofloxacin were 0.126 +/- 0.084, 0.235 +/- 0.22, and 0.11 +/- 0.084 for the jejunal, ileal, and cecal segments, respectively. The calculated fractions of ciprofloxacin eliminated were 3.3 mg from the jejunum and 13.8 mg from the ileum, representing 19% of the administered dose. Additional amounts of 2.5 to 3.7 mg or 4.9 to 7.3% of the administered dose were eliminated from the cecum. Elimination was probably not due to a passive diffusion process but rather due to an active transepithelial transport. This intestinal elimination pattern of ciprofloxacin may explain the unusual activity of the fluoroquinolones in modifying the intestinal flora.
PMCID: PMC284538  PMID: 8031042
21.  In vitro renal toxicity and in vivo therapeutic efficacy in experimental murine cryptococcosis of amphotericin B (Fungizone) associated with Intralipid. 
We compared the experimental toxicities and activities of deoxycholate amphotericin B (d-AmB) dissolved in glucose (Dd-AmB) or mixed with 20% Intralipid (ILd-AmB). In vitro, ILd-AmB against renal tubular cells in primary culture. In vivo, the toxicities and activities of Dd-AmB and ILd-AmB were studied in DBA2 mice with cryptococcosis. The maximum tolerated dose of intravenously administered d-AmB, i.e., the dose that induced less than 15% mortality because of toxicity, was 1.7 to 2.5 times higher when it was administered as ILd-AmB than when it was administered as Dd-AmB. Both treatments given intravenously at the same dose were equivalent for improving the survival of mice and reducing CFU counts in infected tissue, but at maximum tolerated doses, ILd-AmB (2 mg/kg of body weight) was more effective than Dd-AmB (0.8 to 1.2 mg/kg). AmB concentrations in spleen, liver, lung, and kidney were measured by high-pressure liquid chromatography 4 and 24 h after a single injection of 1.2 mg of Dd-AmB per kg, 1.2 mg of ILd-AmB per kg, or 2 mg of ILd-AmB per kg. In a given organ, AmB levels were similar after administration of 1.2 mg of Dd-AmB or ILd-AmB per kg but were significantly higher after administration of 2 mg of ILd-AmB per kg. The lower level of toxicity of ILd-AmB might be explained by circular dichroism experiments, showing that ILd-AmB contained 10-fold less soluble oligomeric AmB, which is believed to be the toxic form of the drug, than Dd-AmB. We conclude that ILd-AmB is as efficient as Dd-AmB and is better tolerated than Dd-AmB in mice with experimental cryptococcosis. By allowing higher doses of AmB to be infused, Intralipid enhances AmB concentrations in infected sites, and thus the therapeutic activity of the drug.
PMCID: PMC284422  PMID: 8192439
22.  Daptomycin or teicoplanin in combination with gentamicin for treatment of experimental endocarditis due to a highly glycopeptide-resistant isolate of Enterococcus faecium. 
Antimicrobial Agents and Chemotherapy  1992;36(12):2611-2616.
Using an experimental endocarditis model, we studied the activity of daptomycin used alone or in combination with gentamicin against an Enterococcus faecium strain that was highly resistant to glycopeptides and susceptible to gentamicin. In vitro, the MIC of daptomycin was 1 micrograms/ml. In vivo, daptomycin appeared to be effective only when it was used in a high-dose regimen, i.e., 12 mg/kg of body weight every 8 h (-2.5 log10 CFU/g versus controls; P < 0.05), particularly when it was combined with gentamicin (-5.0 log10 CFU/g versus controls; P < 0.01). Since the distribution of daptomycin into cardiac vegetations, as evaluated by autoradiography, appeared to be homogeneous, the poor in vivo activity of daptomycin was considered to be related to its high degree of protein binding, as suggested by killing curves studies. Since the MIC of teicoplanin for the vancomycin-resistant E. faecium strain used in the study was only 64 micrograms/ml and since an in vitro synergy between teicoplanin at high dose and gentamicin was observed, a high-dose regimen of teicoplanin, i.e., 40 mg/kg every 12 h, was also assessed in vivo. This treatment provided marginal activity only when it was combined with gentamicin (-2.3 log10 CFU/g versus controls; P < 0.05). These results suggest that the levels of daptomycin or teicoplanin in serum required to cure experimental endocarditis caused by a highly glycopeptide-resistant strain of E. faecium would not be achievable in humans.
PMCID: PMC245515  PMID: 1336339
23.  Optimal aminoglycoside dosing regimen for penicillin-tobramycin synergism in experimental Streptococcus adjacens endocarditis. 
Antimicrobial Agents and Chemotherapy  1992;36(11):2403-2407.
The combination of penicillin and aminoglycoside is the recommended therapy for endocarditis caused by nutritionally variant streptococci (NVS). However, the optimal aminoglycoside dosing regimen remains controversial. We compared the efficacies of four regimens of tobramycin alone or combined with procaine penicillin in the therapy of rabbits with endocarditis caused by Streptococcus adjacens, a new species of NVS. Animals were injected intramuscularly for 4 days with procaine penicillin (150,000 U/kg of body weight twice daily) or tobramycin at a low dose (3 mg/kg every 24 h) or a high dose (12 mg/kg every 24 h) either once or three times daily (t.i.d.) alone or in combination with procaine penicillin. Additional groups of animals were treated with the combination regimens for a shorter period of time (2 days) in order to demonstrate a possible difference in the rapidity of efficacy between the regimens. The MICs and MBCs were 0.015 and 1 micrograms/ml and 8 and 16 micrograms/ml for penicillin and tobramycin, respectively. The mean peak tobramycin levels in plasma were 2.4 +/- 1.3 (1 mg/kg t.i.d.), 5.4 +/- 3.7 (4 mg/kg t.i.d.), and 25 +/- 9.3 (12 mg/kg once daily). The mean penicillin levels in serum were always above the MIC. In vitro kill curves plotted at the time that peak concentrations were reached in plasma showed a concentration-dependent killing effect of tobramycin alone but not in combination with penicillin. In vivo, low-dose tobramycin was significantly less effective than the high dose. Results for the combinations of the different dosing regimens of tobramycin with procaine penicillin were not significantly different. Our results suggest that (i) against susceptible strains of streptococci, aminoglycoside alone exhibits a concentration-dependent killing effect both in vitro and in vivo; (ii) against NVS strains, combinations of penicillin and high- or low-dose tobramycin are equally effective; and (iii) aminoglycoside given once daily or at a low dose t.i.d. with penicillin could be a cost-effective alternative with reduced toxic risk for patients with NVS endocarditis when the bacteria are susceptible to the killing activities of both compounds.
PMCID: PMC284343  PMID: 1489184
25.  Piperacillin, tazobactam, and gentamicin alone or combined in an endocarditis model of infection by a TEM-3-producing strain of Klebsiella pneumoniae or its susceptible variant. 
The efficacy of tazobactam, a beta-lactamase inhibitor, in combination with piperacillin, was studied in vitro and in rabbit experimental endocarditis due to a Klebsiella pneumoniae strain (KpR) producing an extended-spectrum beta-lactamase, TEM-3, or its nonproducing variant (KpS). In vitro, piperacillin was active against KpS (MIC = 4 micrograms/ml, MBC = 8 micrograms/ml with 10(7)-CFU/ml inoculum) but not against KpR (MIC = MBC = 256 micrograms/ml). Tazobactam (1 microgram/ml) restored the activity of piperacillin against KpR (MIC = 2 micrograms/ml, MBC = 4 micrograms/ml). Gentamicin was active against both strains (MIC = 0.25 and 0.5 micrograms/ml for KpS and KpR, respectively). The piperacillin-tazobactam-gentamicin combination was synergistic in vitro. The piperacillin/tazobactam ratio in plasma and in vegetations was always lower than the 4/1 injected dose ratio. In vivo, piperacillin (300 mg/kg of body weight four times a day [QID]) was active against KpS but not against KpR. Tazobactam (75 mg/kg QID) was able to restore the in vivo effect of piperacillin (300 mg/kg QID) against KpR (-3.0 log10 CFU/g of vegetation versus that of controls). Gentamicin (4 mg/kg twice a day [BID]) was active against both strains. Compared with controls, the combination of gentamicin plus piperacillin against KpS (-5.6 log10 CFU/g of vegetation), and the gentamicin-piperacillin-tazobactam combination against KpR (-4.4 log10 CFU/g of vegetation) achieved the greatest decrease in bacterial counts in vegetations and were the only regimens that significantly increased the proportion of sterile vegetations. It is concluded that (i) tazobactam was able to restore the effect of piperacillin against a TEM-3 extended-spectrum Beta-lactamase-producing strain of K. pneumoniae, both in vitro and in a severe experimental infection with high inoculum, when used in a 4/1 piperacillin/tazobactam dose ratio; (ii) gentamicin alone was effective because of the high peak/MBC ratio in plasma; (iii) piperacillin-tazobactam-gentamicin, probably because of the effect of gentamicin in reducing bacterial inoculum in vivo, as stressed by the results obtained by piperacillin-gentamicin against KpS, may be the most effective regimen against KpR.
PMCID: PMC192204  PMID: 1329634

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