In vitro efficacy of levofloxacin alone or in combination tested against multi-resistant Pseudomonas aeruginosa strains

Synergy of drug combinations in treating multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

With the emergence of metallo-betalactamases (MBL) in Pseudomonas aeruginosa (P. aeruginosa), the value of carbapenem, the drug of last resort, is being severely compromised. Curtailing the use of carbapenems becomes paramount if resistance is to be reined in.

AIMS

To study the role of synergy between combinations of drugs as an alternative treatment choice for P. aeruginosa. Synergy was studied between combinations of levofloxacin with piperacillin-tazobactam and levofloxacin with cefoperazone-sulbactam by time-kill and chequerboard techniques.

METHODS

P. aeruginosa were tested for antibiotic susceptibility by the disc diffusion assay (260 isolates) and E-test (60 isolates). Synergy testing by chequerboard and time-kill assays was performed with combinations of piperacillin-tazobactam with levofloxacin (11 isolates) and cefoperazone-sulbactam with levofloxacin (10 isolates).

RESULTS

Nearly all isolates were susceptible to piperacillin-tazobactam (96.1 per cent), followed by piperacillin (78.5 per cent). Seventy-one isolates (27.3 per cent) were found to be multidrug resistant and 19.6 per cent were ESBL producers. MIC50 of amikacin was 32μg/ml and MIC90 was 64μg/ml. MIC50 and MIC90 of cefoperazone-sulbactam was 32μg/ml and 64μg/ml, and for levofloxacin it was 10μg/ml and 240μg/ml, respectively. Piperacillin-tazobactam had MIC50 and MIC90 of 5μg/ml and 10μg/ml, respectively. Synergy was noted in 72.7 per cent isolates for levofloxacin and piperacillin-tazobactam combination, the remaining 27.3 per cent isolates showed addition by both chequerboard and time-kill assay. For levofloxacin and cefoperazone-sulbactam, only 30 per cent isolates had synergy, 40 per cent showed addition, 20 per cent indifference, and 10 per cent were antagonistic by the chequerboard method.

CONCLUSION

The combination of levofloxacin and piperacillin-tazobactam is a good choice for treatment of such strains.

In Vitro Synergy of Levofloxacin Plus Piperacillin/Tazobactam against Pseudomonas aeruginosa

In vitro synergy testing using levofloxacin (LVX) plus piperacillin/tazobactam (TZP) was performed by Etest and time-kill assay (TKA) for 31 unique fluoroquinolone-resistant Pseudomonas aeruginosa isolates. The Etest method showed synergy for 9/31 (29%) of isolates, while TKA showed synergy with 14/31 (45%) of isolates. When comparing the Etest method and TKA, concordant results for synergy, antagonism, and indifference were obtained for 24/31 (77%) of the isolates tested.

Intrapulmonary pharmacodynamics of high-dose levofloxacin in subjects with chronic bronchitis or chronic obstructive pulmonary disease

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered levofloxacin in subjects with stable chronic lung disease. Three doses of 1000 mg levofloxacin were administered once daily to 16 adult subjects divided into four groups of 4 subjects each. Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed at 4 h, 8 h, 12 h and 24 h following administration of the last dose. Blood was obtained for drug assay prior to drug administration, at the end of the last infusion (maximum concentration (Cmax)) and at the time of BAL. Levofloxacin was measured using a high-performance liquid chromatographic tandem mass spectrometric (HPLC/MS/MS) technique. Plasma, epithelial lining fluid (ELF) and alveolar cell (AC) pharmacokinetics were derived using non-compartmental methods. Cmax/MIC(90) and area under the concentration-time curve for 0-24 h after the last dose (AUC(0-24 h)/MIC(90) ratios were calculated for respiratory pathogens with minimum inhibitory concentrations for 90% of the organisms (MIC(90)) of 0.03-2 microg/mL. The Cmax (mean+/-standard deviation), AUC(0-24h) and half-life were, respectively, 9.2+/-2.7 microg/mL, 130 microg h/mL and 8.7 h for plasma, 22.8+/-12.9 microg/mL, 260 microg h/mL and 7.0 h for ELF and 76.3+/-28.7 microg/mL, 1492 microg h/mL and 49.5 h for ACs. Levofloxacin concentrations were quantitatively greater in ACs than in ELF or plasma at all time points, however only the differences between AC concentration and ELF or plasma concentrations in the 4-h and 8-h time groups were statistically significant. Cmax/MIC(90) and AUC/MIC(90) ratios in ELF were, respectively, 11.4 and 130 for Mycoplasma pneumoniae, 22.8 and 260 for Streptococcus pneumoniae, 91.2 and 1040 for Chlamydia pneumoniae and 760 and 8667 for Haemophilus influenzae. In ACs the ratios were 38.2 and 746 for M. pneumoniae, 76.3 and 1492 for S. pneumoniae, 305 and 5968 for C. pneumoniae and 2543 and 49 733 for H. influenzae. In conclusion, Cmax/MIC(90) and AUC/MIC(90) ratios provide a pharmacokinetic rationale for once-daily administration of a 1000 mg dose of levofloxacin and are favourable for the treatment of respiratory infection in patients with chronic lung disease.

Intrapulmonary pharmacokinetics and pharmacodynamics of high-dose levofloxacin in healthy volunteer subjects

The objective of this study was to determine the plasma and intrapulmonary pharmacokinetic parameters of intravenously administered levofloxacin in healthy volunteers. Three doses of either 750 mg or 1000 mg levofloxacin were administered intravenously to 4 healthy adult subjects (750 mg) to 20 healthy adult subjects divided into five groups of 4 subjects (1000 mg). Standardised bronchoscopy and timed bronchoalveolar lavage (BAL) were performed following administration of the last dose. Blood was obtained for drug assay prior to drug administration and at the time of BAL. Levofloxacin was measured in plasma, BAL fluid and alveolar cells (ACs) using a sensitive and specific combined high-performance liquid chromatographic tandem mass spectrometric technique (HPLC/MS/MS). Plasma, epithelial lining fluid (ELF) and AC pharmacokinetics were derived using non-compartmental methods. The maximum plasma drug concentration to minimum inhibitory concentration ratio (C(max)/MIC(90)) and the area under the drug concentration curve to minimum inhibitory concentration ratio (AUC/MIC(90)) during the dosing interval were calculated for potential respiratory pathogens with MIC(90) values from 0.03 microg/mL to 2 microg/mL. In the 1000 mg dose group, the C(max) (mean+/-standard deviation (S.D.)), AUC(0-8h) and half-life were: for plasma, 9.2+/-1.9 microg/mL, 103.6 microg h/mL and 7.45 h; for ELF, 25.8+/-7.9 microg/mL, 279.1 microg h/mL and 8.10h; and for ACs, 51.8+/-26.2 microg/mL, 507.5 microg h/mL and 14.32 h. In the 750 mg dose group, the C(max) values in plasma, ELF and ACs were 5.7+/-0.4, 28.0+/-23.6 and 34.2+/-18.7 microg/mL, respectively. Levofloxacin concentrations were significantly higher in ELF and ACs than in plasma at all time points. For pathogens commonly associated with community-acquired pneumonia, C(max)/MIC(90) ratios in ELF ranged from 12.9 for Mycoplasma pneumoniae to 859 for Haemophilus influenzae, and AUC/MIC(90) ratios ranged from 139 to 9303, respectively. The C(max)/MIC(90) ratios in ACs ranged from 25.9 for M. pneumoniae to 1727 for H. influenzae, and AUC/MIC(90) ratios ranged from 254 to 16917, respectively. The C(max)/MIC(90) and AUC/MIC(90) ratios provide a pharmacokinetic rationale for once-daily administration of a 1000 mg dose of levofloxacin and are favourable for the treatment of community-acquired respiratory pathogens.

In vitro and in vivo synergy of levofloxacin or amikacin both in combination with ceftazidime against clinical isolates of Pseudomonas aeruginosa

The aim of the present study was to explore the antibacterial activity of the levofloxacin (LVX) and ceftazidime (CAZ) combination compared with the amikacin (AMK)/CAZ combination against Pseudomonas aeruginosa. Minimum inhibitory concentrations (MICs) were determined according to NCCLS. FIC indices (Fl) were calculated by the checkerboard technique. CAZ combined with LVX or AMK yielded Fls indicating synergism (Fl < or = 0.5) for 71/102 (69.6%) and 81/102 (79.4%) (p = 0.108), indifference (FI > 0.5-4) for 24/102 (23.5%) and 12/102 (11.7%) (p = 0.027), and antagonism (Fl > 4) for 7/102 (6.8%) and 9/102 (8.8%) (p = 0.602) strains, respectively. In vivo, CAZ/LVX was as bactericidal as CAZ/AMK combination. Our results support the potential role of LVX as an alternative to AMK in the combination therapy with CAZ in the treatment of P. aeruginosa severe infections. Anyway, further investigations and clinical trials are awaited until any definitive conclusions can be drawn.

Levofloxacin disposition in cerebrospinal fluid in patients with external ventriculostomy

In vitro levofloxacin exhibits both potent or intermediate activity against most of the pathogens frequently responsible for acute bacterial meningitis and synergistic activity with some beta-lactams. Since levofloxacin was shown to penetrate the cerebrospinal fluid (CSF) during meningeal inflammation both in animals and in humans, the disposition of levofloxacin in CSF was studied in 10 inpatients with external ventriculostomy because of communicating hydrocephalus related to subarachnoid occlusion due to cerebral accidents who were treated with 500 mg of levofloxacin intravenously twice a day because of extracerebral infections. Plasma and CSF concentration-time profiles and pharmacokinetics were assessed at steady state. Plasma and CSF levofloxacin concentrations were analyzed by high-pressure liquid chromatography. The peak concentration of levofloxacin at steady state (C(max ss))was 10.45 mg/liter in plasma and 4.06 mg/liter in CSF, respectively, with the ratio of the C(max ss) in CSF to the C(max ss) in plasma being 0.47. The areas under the concentration-time curves during the 12-h dosing interval (AUC(0-tau)s) were 47.69 mg. h/liter for plasma and 33.42 mg. h/liter for CSF, with the ratio of the AUC(0-tau) for CSF to the AUC(0-tau) for plasma being 0.71. The terminal-phase half-life of levofloxacin in CSF was longer than that in plasma (7.02 +/- 1.57 and 5.51 +/- 1.36 h, respectively; P = 0.034). The ratio of the levofloxacin concentration in CSF to the concentration in plasma progressively increased with time, from 0.30 immediately after dosing to 0.99 at the end of the dosing interval. In the ventricular CSF of patients with uninflamed meninges, levofloxacin was shown to provide optimal exposure, which approximately corresponded to the level of exposure of the unbound drug in plasma. The findings provide support for trials of levofloxacin with twice-daily dosing in combination with a reference beta-lactam for the treatment of bacterial meningitis in adults. This cotreatment could be useful both for overcoming Streptococcus pneumoniae resistance and for enabling optimal exposure of the CSF to at least one antibacterial agent for the overall treatment period.

Contemporary in vitro synergy rates for aztreonam combined with newer fluoroquinolones and beta-lactams tested against gram-negative bacilli

Aztreonam has been commonly used in various combinations to enhance antimicrobial spectrum of co-drugs and produce potential synergistic activity. Although well studied in vitro over 10 years ago, aztreonam combination testing has been poorly documented with newer or commonly used agents against contemporary isolates. All MIC tests (alone or in combination) used in this experiment were reference broth microdilution methods in checkerboard tray designs. Aztreonam was combined with ciprofloxacin, gatifloxacin, levofloxacin, cefepime, ceftazidime and imipenem at clinically relevant concentrations. Interaction categories were defined by established criteria. Forty strains each of Pseudomonas aeruginosa and Enterobacteriaceae (12 species; aztreonam MIC, 1-16 microg/ml) were tested for each antimicrobial combination (480 total determinations). No antagonism or indeterminate interactions were identified. The overall rates of synergy or partial synergy for aztreonam with fluoroquinolone combinations was 63.4% versus P. aeruginosa, greatest for aztreonam with gatifloxacin (67.5%). Interaction categories varied greatly among aztreonam with beta-lactam combinations. Aztreonam with ceftazidime or cefepime versus P. aeruginosa had 75.0 - 85.0% partial or complete synergy rates, but aztreonam with imipenem showed dominant indifference (65.0%). In contrast, aztreonam with imipenem was more likely to exhibit synergy (32.5%) when tested against Enterobacteriaceae. Aztreonam, often used as an aminoglycoside substitute in antimicrobial combinations, continues to demonstrate enhanced, but variable drug activity interactions for contemporary antimicrobial combinations when tested against recent (2002) clinical isolates.

Current and future perspectives for levofloxacin in severe Pseudomonas aeruginosa infections

The question of whether levofloxacin includes Pseudomonas aeruginosa in its spectrum of clinical activity is discussed by reviewing the major findings on this issue, mainly those published in Italy. The in vitro activity of levofloxacin against P. aeruginosa is now documented on thousands of strains worldwide. The pharmacodynamic properties of levofloxacin allow for the treatment of pseudomonal infections. The levofloxacin clinical results extrapolated from published studies document the efficacy of levofloxacin in the treatment of infections sustained by P. aeruginosa.

In vitro synergy testing of levofloxacin, ofloxacin, and ciprofloxacin in combination with aztreonam, ceftazidime, or piperacillin against Pseudomonas aeruginosa

The synergistic potential of levofloxacin, ofloxacin and ciprofloxacin combined with aztreonam, ceftazidime, or piperacillin was compared using 24 strains of Pseudomonas aeruginosa with varying susceptibility profiles. Levofloxacin and ciprofloxacin demonstrated similar in vitro activity, with ofloxacin demonstrating less activity compared to the other agents. Predominantly additive effects were seen with all combinations, with no significant differences detected between the fluoroquinolone agents.

Cerebrospinal fluid penetration of levofloxacin in patients with spontaneous acute bacterial meningitis

We have assessed levofloxacin penetration in cerebrospinal fluid (CSF) and the liquor-to-plasma ratio (C(L)/C(P)) at 2 hours after dosing in 5 patients with spontaneous acute bacterial meningitis. CSF levofloxacin concentration at 2 hours after dosing was 1.99+/-0.67 microg/mL, and the C(L)/C(P) at 2 hours after dosing was 0.34+/-0.09.

Levofloxacin. Its use in infections of the respiratory tract, skin, soft tissues and urinary tract

Levofloxacin, the optically pure levorotatory isomer of ofloxacin, is a fluoroquinolone antibacterial agent. Like other fluoroquinolones, it acts on bacterial topoisomerase and has activity against a broad range of Gram-positive and Gram-negative organisms. Levofloxacin also appears to have improved activity against Streptococcus pneumoniae compared with ciprofloxacin or ofloxacin. Levofloxacin distributes well and achieves high levels in excess of plasma concentrations in many tissues (e.g., lung, skin, prostate). High oral bioavailability allows switching from intravenous to oral therapy without dosage adjustment. In patients with mild to severe community-acquired pneumonia receiving treatment for 7 to 14 days, oral levofloxacin was similar in efficacy to amoxicillin/clavulanic acid, and intravenous and/or oral levofloxacin was superior to intravenous ceftriaxone and/or oral cefuroxime axetil. With levofloxacin use, clinical success (clinical cure or improvement) rates were 87 to 96% and bacteriological eradication rates were 87 to 100%. In the 5- to 10-day treatment of acute exacerbations of chronic bronchitis, oral levofloxacin was similar in efficacy to oral cefuroxime axetil or cefaclor. Levofloxacin resulted in clinical success in 78 to 94.6% of patients and bacteriological eradication in 77 to 97%. Oral levofloxacin was also similar in efficacy to amoxicillin/clavulanic acid or oral clarithromycin in patients with acute maxillary sinusitis treated for 7 to 14 days. Equivalence between 7- to 10-day therapy with oral levofloxacin and ciprofloxacin was seen in patients with uncomplicated skin and soft tissue infections. Clinical success was seen in 97.8 and 96.1% of levofloxacin recipients and bacteriological eradication in 97.5 and 93.2%. Complicated urinary tract infections, including pyelonephritis, responded similarly well to oral levofloxacin or ciprofloxacin for 10 days or lomefloxacin for 14 days. Clinical success and bacteriological eradication rates with levofloxacin occurred in 92 to 93.3% and 93.6 to 94.7% of patients.

CONCLUSIONS

Levofloxacin can be administered in a once-daily regimen as an alternative to other fluoroquinolones in the treatment of infections of the urinary tract, skin and soft tissues. Its more interesting use is as an alternative to established treatments of respiratory tract infections. S. pneumoniae appears to be more susceptible to levofloxacin than to ciprofloxacin or ofloxacin. Other newer fluoroquinolone agents that also have enhanced in vitro antipneumococcal activity may not share the well established tolerability profile of levofloxacin, which also appears to improve on that of some older fluoroquinolones.

Bactericidal effects of levofloxacin in comparison with those of ciprofloxacin and sparfloxacin

OBJECTIVE: To investigate and compare the in vitro activity of levofloxacin with the activities of ciprofloxacin and sparfloxacin. METHODS: The following experiments were performed: (1) comparative studies of the rate of killing by the three quinolones of different strains of Streptococcus pneumoniae at a concentration corresponding to the 1-h serum level following a 500-mg dose in humans; (2) comparative studies of the rate of killing by levofloxacin and ciprofloxacin of different strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa at the same concentrations as above; (3) comparative studies of the rate of killing by levofloxacin at four different concentrations of reference and clinical strains of Streptococcus pneumoniae, Staphylococcus aureus, E. coli and P. aeruginosa. RESULTS: Levofloxacin exhibited statistically significantly higher bactericidal activity than sparfloxacin after 2 and/or 3 h against all strains of Streptococcus pneumoniae. Compared to ciprofloxacin, levofloxacin showed a statistically significantly higher bactericidal activity after 2 and/or 3 h against all strains of Streptococcus pneumoniae except the one resistant to both penicillin and cefotaxime. No differences in killing rate between levofloxacin and ciprofloxacin were seen against Staphylococcus aureus, E. coli and P. aeruginosa, with almost complete killing after 3 h of the P. aeruginosa strains and after 6 h for the E. coli strains. No concentration-dependent killing was seen at concentrations above 4xMIC of levofloxacin against Staphyloccus aureus, E. coli and P. aeruginosa. CONCLUSION: Levofloxacin was shown to be active against both Gram-positive and Gram-negative bacteria. In terms of MIC values, ciprofloxacin was the most active drug against the Gram-negative organisms, and sparfloxacin against the strains of Streptococcus pneumoniae, but levofloxacin exhibited a similar or even better bactericidal activity against the investigated strains compared with the other two fluoroquinolones when killing curves were compared.