Comparative in vitro activity of ciprofloxacin against aerobic and anaerobic bacteria from clinical isolates

1-Cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-piperazin-1- ylquinoline-3-carboxylic acid (ciprofloxacin, Bay o 9867, Ciprobay) is a broad spectrum antibiotic of the 4-quinolone group. It possesses a bactericidal effect attributable to the property of DNA-gyrase inhibition. The antimicrobial action comprises all grampositive strains (including Streptococcus faecalis) and gramnegative strains (including Pseudomonas aeruginosa and Serratia spp.), as well as Bacteroides fragilis and other Bacteroides species. In this comparative study the antimicrobial effect of ciprofloxacin was tested against 665 gramnegative, 412 grampositive and 274 anaerobic strains from fresh clinical isolates and compared with that of other frequently used antibiotics. The minimum inhibitory concentrations (MIC) were determined by means of a serial dilution test with micro standard plates. Within the group of gramnegative strains, ciprofloxacin was the most active antibiotic with an MIC90 of 0.12 mg/l to 0.5 mg/l for most isolates. Ciprofloxacin shows a broad spectrum of activity against gramnegative pathogenic bacteria including Escherichia coli, Klebsiella spp., Citrobacter spp., Enterobacter spp., Serratia spp. and Acinetobacter spp., and also covers resistant strains of Pseudomonas aeruginosa and Alcaligenes faecalis. Ciprofloxacin also shows a high inhibiting activity against grampositive strains (Staphylococci, Enterococci) and anaerobic pathogens.     

Comparison of azithromycin and moxifloxacin against bacterial isolates causing conjunctivitis

ABSTRACT

Objective: To examine in vitro resistance to azithromycin and moxifloxacin in bacterial conjunctivitis isolates.

Methods: MIC₉₀s (Minimum Inhibitory Concentration) and resistance rates to azithromycin and moxifloxacin were determined based upon microtiter broth dilution and/or antimicrobial gradient test strips in a multicenter phase III study and confirmed externally.

Results: The most common isolates collected from bacterial conjunctivitis patients in the phase III study were Haemophilus influenzae (40.6%), followed by Staphylococcus epidermidis (19.3 %), Propionibacterium acnes (17.3%), Streptococcus pneumoniae (16.8%), and Staphylococcus aureus (0.06%). MIC₉₀s for all of these organisms were well below established resistance breakpoints for moxifloxacin, indicating no bacterial resistance. On the other hand, the MIC₉₀ for H. influenzae was 3-fold higher than the resistance breakpoint for azithromycin, ≥ 128-fold higher for S. epidermidis, 16-fold higher for S. pneumoniae and ≥ 128-fold higher for S. aureus, indicating moderate to very high bacterial resistance to azithromycin.

Conclusions: Resistance to azithromycin is more common than resistance to moxifloxacin in clinical isolates causing bacterial conjunctivitis.     

Antibacterial activity of moxifloxacin against periodontal anaerobic pathogens involved in systemic infections

A meta-analysis was performed on five studies conducted over the last decade to demonstrate a positive effect for the drug Uro-Vaxom® compared with Placebo in double-blind studies in patients with urinary tract infection (601 women), with special reference to the prevention of recurrences over an observation period of 6 months, the treatment being given for the first 3 months. The five studies were similar in design. The analysis by means of the Wilcoxon–Mann–Whitney test showed superiority of Uro-Vaxom in all five studies, (P<1%). The summarising Mann–Whitney (MW) statistics also indicated superiority with the Mann–Whitney value being 0.684. In all studies, the Uro-Vaxom group was statistically significant and clinically relevant superior to control with respect to the reduction of the frequency of UTIs and to dysuria, bacteriuria and leucocyturia. The confidence intervals (CI)s were small (0.64–0.72). The drug was well tolerated and compliance of patients was excellent in all studies. Oral immunotherapy with the Uro-Vaxom Escherichia coli (E. coli) extract is an effective prophylactic approach in the prevention of UTIs.     

Antimicrobial susceptibility of clinical isolates of aerobic gram-positive cocci and anaerobic bacteria in 2008

The activity of antibacterial agents against aerobic Gram-positive cocci (25 genus or species, 1029 strains) and anaerobic bacteria (21 genus or species, 187 strains) isolated from clinical specimens in 2008 at 16 clinical facilities in Japan were studied using either broth microdilution or agar dilution method. The ratio of methicillin-resistant strains among Staphylococcus aureus and Staphylococcus epidermidis was 59.6% and 81.2%, suggesting that resistant strains were isolated at high frequency. Vancomycin (VCM), linezolid (LZD) and quinupristin/dalfopristin (QPR/DPR) had good antibacterial activity against methicillin-resistant S. aureus and methicillin-resistant S. epidermidis, with MIC90s of < or = 2 microg/mL. The ratio of penicillin (PC) intermediate and resistant strains classified by mutations of PC-binding proteins among Streptococcus pneumoniae was 92.0% that was highest among our previous reports. Cefpirome, carbapenems, VCM, teicoplanin (TEIC), LZD and QPR/DPR had MIC90s of < or = 1 microg/mL against PC-intermediate and resistant S. pneumoniae strains. Against all strains of Enterococcus faecalis and Enterococcus faecium, the MICs of VCM and TEIC were under 2 microg/mL, and no resistant strain was detected, suggesting that these agents had excellent activities against these species. 15.9% of E. faecalis strains and 1.2% of E. faecium strains showed intermediate to LZD. 17.1% of E. faecium strains showed intermediate or resistant to QPR/DPR. Against all strains of Clostridium difficile, the MIC of VCM was under 1 microg/mL, suggesting that VCM had excellent activity. Carbapenems showed good activity against Clostridiales, Bacteroides spp., and Prevotella spp., but one strain of Bacteroides fragilis showed resistant to carbapenems. And so, the susceptibility of this species should be well-focused in the future at detecting continuously.     

Antimicrobial susceptibility of clinical isolates of aerobic Gram-positive cocci and anaerobic bacteria in 2006

The activity of antibacterial agents against aerobic Gram-positive cocci (26 species, 1022 strains) and anaerobic bacteria (23 species, 184 strains) isolated from clinical specimens in 2006 at 16 clinical facilities in Japan were studied using either broth microdilution or agar dilution method. The ratio of methicillin-resistant strains among Staphylococcus aureus and Staphylococcus epidermidis was 53.0% and 65.8%, suggesting that resistant strains were isolated at high frequency. Vancomycin (VCM) and quinupristin/dalfopristin (QPR/DPR) had good antibacterial activity against methicillin-resistant S. aureus and methicillin-resistant S. epidermidis, with MIC90s of < or = 2 micrcog/mL. The ratio of penicillin (PC) intermediate and resistant strains classified by mutations of PC-binding proteins among Streptococcus pneumoniae was 87.6%. Ceftriaxone, cefpirome, cefepime, carbapenem antibiotics, VCM, teicoplanin, linezolid(LZD) and QPR/DPR had MIC90s of < or = 1 microg/mL against PC-intermediate and resistant S. pneumoniae strains. Against all strains of Enterococcus faecalis and Enterococcus faecium, the MICs of VCM and TEIC were under 2 microg/mL, and no resistant strain was detected, suggesting that these agents had excellent activities against these species. 10.9% of E. faecalis strains or 3.5% of E. faecium strains showed intermediate or resistant to LZD. 24.4% of E. faecium strains showed intermediate or resistant to QPR/DPR. Against all strains of Clostridium difficile, the MIC of VCM were under 1 microg/mL, suggesting that VCM had excellent activity against C. difficile. Carbapenems showed good activity against Peptococcaceae, Bacteroides spp., and Prevotella spp. However since several strains of Bacteroides fragilis showed resistant to carbapenems and the susceptibility of this species should be well-focused in the future.     

Antibacterial activity of combined cefotaxime and desacetyl-cefotaxime against aerobic and anaerobic gram-negative bacilli

Synergy between cefotaxime and desacetyl-cefotaxime was evaluated against 12 strains (9 Enterobacteriaceae and 3 Bacteroides fragilis) by the chequerboard technique. A 1:1 combination of cefotaxime and desacetyl-cefotaxime was synergistic against two-thirds of the 12 strains tested. The in vitro activity of the combination was compared with that of four other beta-lactam antibiotics against 96 recent clinical isolates: 78 Enterobacteriaceae, 8 Haemophilus influenzae, 10 B. fragilis. The MICs of the combination for Gram-negative bacilli were similar to those of ceftazidime. Cefotaxime/desacetyl-cefotaxime was more active than cefotetan, cefonicid and piperacillin against Enterobacteriaceae and H. influenzae.     

Comparison of minimal inhibitory and mutant prevention drug concentrations of 4 fluoroquinolones against clinical isolates of methicillin-susceptible and -resistant Staphylococcus aureus

Staphylococcus aureus remains an important human pathogen affecting both outpatients and those hospitalized. Increasing antimicrobial resistance is global but prevalence rates are variable for different geographical areas. Fluoroquinolones have been used to treat S. aureus infections and the newer quinolones have enhanced in vitro activity against this organism. The mutant prevention concentration (MPC) defines the antimicrobial drug concentration threshold that would require an organism to simultaneously possess two mutations for growth in the presence of the drug. We tested clinical isolates of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) S. aureus by minimum inhibitory concentration (MIC) and MPC against gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin. For MSSA strains, the rank order of potency based on MIC(90) values were gemifloxacin (0.063 mg/l) = moxifloxacin (0.063 mg/l) > gatifloxacin (0.05 mg/l) = levofloxacin (0.25 mg/l) and by MPC values moxifloxacin (0.25 mg/l) > gemifloxacin (0.5 mg/l) > gatifloxacin (1 mg/l) = levofloxacin (1mg/l). For 87% of the isolates the MPC value was 0.5 mg/l for gatifloxacin. The rank order of potency based on the time the serum drug concentration exceeded the MPC(90), was as follows: moxifloxacin (>24 h) > levofloxacin (>18 h) > gatifloxacin (12 h) > gemifloxacin (9 h). Serum drug concentration remained in excess of the MPC(87) for 24 h for gatifloxacin. Both MIC(90) and MPC(90) values were higher against MRSA strains and the time above the MPC(90) was significantly shorter for all agents.     

Antimicrobial activity of dactimicin against aerobic and anaerobic bacteria isolated from intra-abdominal infections

The in vitro antimicrobial activity of dactimicin against aerobic and anaerobic bacteria isolated from intra-abdominal infections was compared to those of gentamicin and metronidazole. The data obtained show that dactimicin is a promising new aminoglycoside covering aerobic bacteria and that it may be used together with an antianaerobic agent in the treatment of these infections.     

L-656,575 (OCP-9-176): a novel oxacephem. In vitro activity against aerobic and anaerobic clinical bacterial isolates

L-656,575 (OCP-9-176) is a novel oxacephem superior to ceftazidime in in vitro activity against clinical isolates of Enterobacter species, methicillin-susceptible Staphylococcus aureus and Staphylococcus epidermidis, and multiply-resistant Pseudomonas aeruginosa. Our results suggest that L-656,575 has a high affinity for penicillin binding proteins of Pseudomonas and may bind preferentially to PBP-3 in this organism. L-656,575 is active against beta-lactamase derepressed Enterobacteriaceae and ceftazidime-resistant P. aeruginosa.     

The effect of a combination of ampicillin and sulbactam against clinical anaerobic isolates

Effect of a Combination of Ampicillin and Sulbactam on Clinical Isolates of Anaerobic Bacteria. The antimicrobial susceptibility of 182 recent clinical isolates of anaerobic bacteria to ampicillin alone, ampicillin plus 1 mg/l sulbactam, ampicillin plus 5 mg/l sulbactam, and cefoxitin was studied by means of agar dilution tests. The ampicillin-sulbactam combination (Unacid) was most effective against species of the Bacteroides fragilis group, the MIC90 of ampicillin plus 5 mg/l sulbactam for B. fragilis being less than or equal to 1 mg/l, compared to 256 mg/l of ampicillin, 4 mg/l of ampicillin plus 1 mg/l sulbactam, and 8 mg/l of cefoxitin. No significant difference between ampicillin alone and in combination with sulbactam was observed against gram-positive anaerobic rods or cocci.     

哌拉西林／舒巴坦对临床分离菌的体外抗菌作用

目的 对哌拉西林／舒巴坦进行体外抗菌活性研究。方法 采用琼脂二倍稀释法测定最低抑菌浓度,采用肉汤稀释法测定最低杀菌浓度,并对其影响因素进行测定。结果 本品对肠杆菌科细菌、非发酵菌、葡萄球菌、粪肠球菌抗菌活性均低于亚胺培南,对不产酶流感嗜血杆菌和粘膜莫拉氏菌抗菌活性高于亚胺培南2－16倍。对肺炎链球菌和嗜麦芽黄单胞菌的抗菌活性同本次所研究的所有对照药。对临床常见5种致病菌（铜绿假单胞菌、大肠埃希氏菌、肺炎克雷伯氏菌、金葡球菌和粪肠球菌）的MIC和MBC非常接近,差异在0－2之间,表明本品为一杀菌剂。     

In vitro synergism of beta-lactams with ciprofloxacin and moxifloxacin against genetically distinct multidrug-resistant isolates of Pseudomonas aeruginosa

In vitro combinations of beta-lactams with fluoroquinolones against multidrug-resistant (MDR) Pseudomonas aeruginosa were tested. From a total of 200 isolates, 24 genetically distinct isolates defined by pulsed-field gel electrophoresis (PFGE) were selected. The isolates were exposed over time to imipenem, meropenem and ceftazidime as well as to their combinations with ciprofloxacin and moxifloxacin. All isolates were resistant to all agents tested at concentrations equal to their average serum level. Synergy of any of the tested combinations was found in 10 isolates (41.7%). This was shown after 4h and 6h of exposure accompanied by re-growth after 24h. Not all the tested combinations were active against the same isolates. The combinations of imipenem+ciprofloxacin, ceftazidime+ciprofloxacin and imipenem+moxifloxacin were the most active. When time-kill assays were repeated for the latter isolates at antimicrobial concentrations equal to their maximum serum levels, synergy was prolonged to 24h. The present findings should be interpreted with caution for the management of infections by MDR P. aeruginosa. They underscore the potential interest of reporting synergism between beta-lactams and fluoroquinolones in the nosocomial setting when a MDR isolate emerges.     

Antibacterial effects of moxifloxacin and levofloxacin simulating epithelial lining fluid concentrations against community-acquired methicillin-resistant Staphylococcus aureus

BACKGROUND AND OBJECTIVE: Current North American guidelines advocate the use of respiratory fluoroquinolones for the empirical management of community-acquired pneumonia (CAP). While community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as a pathogen frequently encountered in skin and skin structure infections, it has also now been recognised as a causative pathogen in CAP. Since fluoroquinolones may be used empirically to treat unsuspected CA-MRSA pneumonia, the objective of this study was to evaluate the antibacterial properties of levofloxacin and moxifloxacin using human simulated drug exposures in epithelial lining fluid (ELF). METHODS: An in vitro model was used to simulate the ELF concentrations, previously determined in older adults receiving multiple doses, of levofloxacin 500 mg once daily and moxifloxacin 400mg once daily. Four CA-MRSA isolates were studied at a starting inoculum of 10(6) colony-forming units (CFU)/mL; selected isolates were also studied at 10(8) CFU/mL. Bacterial density and resistance were quantitatively assessed over 48 hours. Drug exposure (area under the concentration-time curve [AUC]) was confirmed using validated drug assays. RESULTS: At a standard 10(6) starting inoculum, sustained bacterial kill (3.6-4.5 log) with both fluoroquinolones was noted for CA-MRSA isolates 27 and 44 (AUC/minimum inhibitory concentration [MIC] = 383-3923). Despite an MIC of 8 microg/mL (AUC/MIC = 25) for isolate 3, levofloxacin displayed a 2.8 log kill, while moxifloxacin (MIC 1 microg/mL) sustained a 4.5 log kill (AUC/MIC = 207) over 48 hours. Against isolate 59, levofloxacin displayed no antibacterial effect (AUC/MIC = 3), while moxifloxacin with an MIC of 8 microg/mL (AUC/MIC = 31) killed 4.6 log. At a high inoculum (10(8)), both fluoroquinolones showed 5.2-5.6 log kill for the susceptible isolate (44), while moxifloxacin showed no antibacterial activity against isolate 59. Drug exposure (AUC/MIC) appeared to correlate well (r(2) = 0.99) with the change in log CFU/mL. Maximal activity was observed for both drugs at an AUC/MIC of approximately 30. CONCLUSION: When evaluated at human simulated ELF concentrations, both levofloxacin and moxifloxacin appeared to demonstrate sustained antibacterial activity for CA-MRSA isolates with MICs 相似文献   

利奈唑胺、万古霉素对甲氧西林耐药的金黄色葡萄球菌的防耐药突变体选择浓度的研究

目的：比较利奈唑胺、万古霉素对耐甲氧西林金黄色葡萄球菌的防耐药突变选择能力;研究防耐药突变体选择浓度（MPC）和最低抑菌浓度（MIC）的相关性。方法：采用琼脂微量稀释法测定利奈唑胺、万古霉素对35株耐甲氧西林金黄色葡萄球菌（MRSA）临床分离菌株的MPC和MIC;采用线性回归法比较利奈唑胺、万古霉素对MRSA的MPC和MIC的相关性;结合人体药代动力学数据,预测利夺唑胺、万古霉素对MRSA的防耐药突变体选择能力。结果：利奈唑胺、万古霉素对35株MRSA的MPC90值（抑制90％的细菌发生细菌耐药的最低防耐药突变体选择浓度）分别为16.8μg／mL,选择指数（MPC90／MIC90）均为8。两药对MRSA的MPC和MIC的线性相关系数R^2分别为0．32和0．008。结合两药药代动力学参数,利奈唑胺药物浓度在整个给药间隔落在耐药突变选择窗理论（MSW）中,万古霉素药物浓度在大部分给药间隔落在MPC之上。结论：万古霉素对MRSA的防耐药选择能力强于利奈唑胺;MPC和MIC的相关性差。     

Mutant prevention concentrations of garenoxacin against Streptococcus pneumoniae isolates from otorhinolaryngological infections

The minimum inhibitory concentrations (MICs) and the mutant prevention concentrations (MPCs) of garenoxacin (GRNX), were compared to those of levofloxacin (LVFX), and moxifloxacin (MFLX) against 78 Streptococcus pneumoniae isolates from otorhinolaryngological infections in Japan during the period January 2007 to June 2007. The MIC and MPC for 90% of the isolates (MIC90 and MPC90) of GRNX were 0.06 and 0.12 microg/mL, respectively, and were the lower values than LVFX and MFLX MIC90s and MPC90s. The ratios of MPC/MIC of GRNX were the lower values than those of LVFX and MFLX.     

Human serum activity of telithromycin, azithromycin and amoxicillin/clavulanate against common aerobic and anaerobic respiratory pathogens

Telithromycin is a new ketolide antimicrobial with a good in vitro activity against both aerobic and anaerobic respiratory pathogens. In this study, we evaluated the antibacterial activity over time of telithromycin (800mg), azithromycin (500mg), and amoxicillin/clavulanate (875/125mg) in serum following single oral doses of these agents to 10 healthy subjects. Inhibitory and bactericidal titers were determined at 2, 6, 12, and 24h after each dose and the median titer was used to determine antibacterial activity. Against two azithromycin-resistant strains of Streptococcus pneumoniae, both telithromycin (MIC=0.25 and 0.5 microg/mL) and amoxicillin/clavulanate exhibited inhibitory and cidal activity for at least 6h. All three antibiotics provided prolonged (>or=12h) inhibitory activity against strains of Hemophilus influenzae (telithromycin MIC=4.0 microg/ml). Both telithromycin and amoxicillin/clavulanate exhibited rapid and prolonged inhibitory activity (>or=12h) against each of the anaerobes studied (Finegoldia [Peptostreptococcus] magna Peptostreptococcus micros, Prevotella bivia, and Prevotella melaninogenica). Moreover, both agents provided bactericidal activity against both Prevotella species. In this ex vivo pharmacodynamic study, we found that telithromycin provided rapid and prolonged antibacterial activity in serum against macrolide-resistant strains of S. pneumoniae, beta-lactamase-positive and -negative strains of H. influenzae, and common respiratory anaerobic pathogens. These findings suggest that telithromycin could have clinical utility in the treatment of community-acquired mixed aerobic-anaerobic respiratory tract infections, including chronic sinusitis and aspiration pneumonia.     

盐酸莫西沙星脂质体的制备及包封率测定方法研究

目的：制备盐酸莫西沙星脂质体,建立盐酸莫西沙星脂质体包封率测定方法。方法：乙醇注入法制备盐酸莫西沙星脂质体,正交试验优选脂质体的最佳处方。采用葡聚糖凝胶柱法、超滤离心法分离脂质体与游离药物,并进行方法学考察,优选出测定盐酸莫西沙星脂质体包封率的方法。结果：盐酸莫西沙星脂质体的最佳处方为：卵磷脂与胆固醇比为 3：1,药脂比为 1：7,水合介质中聚山梨酯20的用量为1%,优化后的包封率为90.73%。葡聚糖凝胶柱法和超滤离心法都能将脂质体与游离药物分离,葡聚糖凝胶柱法的平均柱加样回收率为85.54%~88.15%,超滤离心法的平均加样回收率为94.40%~97.35%。结论：盐酸莫西沙星脂质体的制备工艺稳定,包封率较高。葡聚糖凝胶柱法不适于盐酸莫西沙星脂质体的包封率测定,超滤离心法可高效、准确、方便地测定盐酸莫西沙星脂质体包封率。     

Comparative in vitro bacteriostatic and bactericidal activity of trovafloxacin, levofloxacin and moxifloxacin against clinical and environmental isolates of Legionella spp.

The susceptibility of 140 Legionella spp isolates (106 clinical and 34 environmental isolates) to trovafloxacin (TRFX), levofloxacin (LEVX), moxifloxacin (MOFX), ciprofloxacin (CIPX), ofloxacin (OFLX), erythromycin (ERY), azithromycin (AZI) and rifampicin (RIF) was studied using a standard microdilution method and buffered yeast extract broth (BYE) supplemented with 0.1% alpha-ketoglutarate. The post-antibiotic effects (PAEs) of the study drugs against 10 clinical isolates of Legionella pneumophila sg.1 were compared. The MIC inhibiting 90% of strains tested on BYEalpha broth were 0.008, 0.016, 0.016, 0.06, 0.125, 0.5, 0.5, and 0.004 mg/l for TRFX, LEVX, MOXX, CIP, OFLX, ERY, AZI, and RIF, respectively. The MBC/MIC ratios ranged from one to eight depending on the antibiotic tested: TRFX [1x-2 x MIC], LEVX, MOFX, CIPX and OFLX [1x-4 x MIC], RIF [2x-4 x MIC], ERY and AZI [2x-8 x MIC]. TRFX, RIF, LEVX, MOFX, CIPX, OFLX, ERY and AZI showed similar activity against Legionella species other than L. pneumophila. One-hour exposures to the study antimicrobial agents at a concentration of 4 x MIC resulted in PAEs as follows (average in hours): TRFX: 2.68 h; RIF: 2.63 h; CIPX: 2.62 h; MOFX: 2.56 h; LEVX: 2.41 h; OFLX: 2.25 h; AZI: 1.65 h; and ERY: 1.54 h. In conclusion, our in vitro data confirm that trovafloxacin, levofloxacin, moxifloxacin and rifampicin have excellent bacteriostatic and bactericidal activity against Legionella spp and show significant post-antibiotic effect.     

Antibacterial activity of liposomal gentamicin against Pseudomonas aeruginosa: a time-kill study

Cystic fibrosis (CF) is a common and lethal genetic disorder with a carrier frequency of 1 in 29 Caucasians. Chronic respiratory infections with Pseudomonas aeruginosa are the leading cause of morbidity and mortality in individuals with CF. Aminoglycoside antibiotics, including gentamicin, are highly effective against P. aeruginosa, but severe toxicity limits their use. One potential strategy for avoiding this problem is to encapsulate aminoglycosides in liposomes. In this study, we compared the bactericidal capacity of liposome-encapsulated gentamicin with that of free antibiotic against clinical isolates of P. aeruginosa. Liposome size, encapsulation efficiency and minimal inhibitory concentrations (MICs) of the free and liposomal gentamicin against gentamicin-sensitive and -resistant strains of P. aeruginosa were determined. In vitro time-kill studies were performed using free and liposomal gentamicin at 1, 2 or 4 times the MICs. The average liposomal size was 426.25 +/- 13.56 nm, with a gentamicin encapsulation efficiency of 4.51 +/- 0.54%. The MICs for liposomal gentamicin were significantly lower than those of corresponding free gentamicin. In addition, the time-kill values for liposomal gentamicin were either equivalent to or better than those of the free antibiotic. In conclusion, our liposomal gentamicin formulation is a more potent antipseudomonal drug with an improved killing time and prolonged antimicrobial activity.