Bactericidal activity and killing rate of serum from volunteers receiving pefloxacin alone or in combination with amikacin

Tracing the Antibacterial Performance of Bis-Imidazolium-based Ionic Liquid Derivatives

Ionic liquid (IL) cationic species have recently captivated the attention of pharmacists, biochemists, and biomedical scientists as promising antibacterial agents to deal with the multidrug resistance bacteria crisis. The structure and functional groups of ILs influence their physiochemical properties and biological activities. However, a comprehensive study is required to fully understand the details of the antibacterial activity of ILs carrying various functional groups. Herein, dicationic ILs (DCILs) are reported based on imidazolium rings as efficient antibacterial agents. The DCILs carried various functionalities such as 2-hydroxybutyl (DCIL-1), 2-hydroxy-3-isopropoxypropyl (DCIL-2), 2-hydroxy-3-(methacryloyloxy)propyl (DCIL-3), 2-hydroxy-2-phenylethyl (DCIL-4), and 2-hydroxy-3-phenoxypropyl (DCIL-5). The structure-antibacterial activity relationships of the DCILs against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) were comprehensively studied through antibacterial tests, morphology analysis, and adhesion tests. The experimental assays revealed an antibacterial efficacy order of DCIL-5 > DCIL-1 > DCIL-4 > DCIL-2 > DCIL-3. The all-atom molecular dynamics (MD) simulation showed a deep permeation of the hydrophobic -OPh functional group of DCIL-5 through the E. coli membrane model in agreement with the experimental observations. Current findings assist scientists in designing new task-specific DCILs for effective interactions with biological membranes for different applications.

Bactericidal effect of pefloxacin and fosfomycin against Pseudomonas aeruginosa in a rabbit endocarditis model with pharmacokinetics of pefloxacin in humans simulated in vivo

The bactericidal activity of pefloxacin and fosfomycin alone and in combination against Pseudomonas aeruginosa was evaluated in an experimental rabbit endocarditis model after 24 h of treatment. Two strains with intermediate susceptibility to pefloxacin and good susceptibility to fosfomycin were tested. The serum kinetics obtained during administration of 400 mg every 12 h in humans were simulated in the animals using computer-controlled variable-flow infusion. Fosfomycin was administered as a continuous infusion at a constant flow, allowing a steady-state concentration of 47.4 +/- 11.9 mg/ml to be reached in serum. In valvular vegetations, pefloxacin was less bactericidal than fosfomycin, and in combination treatment, it reduced (but did not abolish) the bactericidal effect of fosfomycin. The duration of the pretreatment interval (12-48 h) had a negative effect on the bactericidal activity of both drugs, especially that of fosfomycin.

Clinical and microbiological evaluation of pefloxacin in lower respiratory tract infections

Patients with Gram-negative lower respiratory tract infections (acute exacerbation of chronic bronchitis (n = 23), pneumonia (n = 4), and bronchiectasis (n = 5) were treated with pefloxacin, 400 mg twice daily, given either intravenously or orally. Symptoms, signs and sputum volume and colour were monitored daily. Chest X-rays, sputum culture and Gram-stain examinations were carried out on days 1 and 5, and immediately after the end of the treatment. There was a clinical improvement, as indicated by the incidence of cough, dyspnoea and rales, and by sputum volume and colour in 31 patients (97%). Microbiological improvement, as indicated by the complete elimination of sputum pathogens and pus cells, was achieved in 28 of the patients (88%). In one patient, an adverse effect, renal failure, occurred. These results suggest that pefloxacin is both clinically and microbiologically effective for the treatment of Gram-negative lower respiratory tract infections.

Pharmacokinetics and bactericidal activities of one 800-milligram dose versus two 400-milligram doses of intravenously administered pefloxacin in healthy volunteers

Pefloxacin pharmacokinetics and serum bactericidal activities (SBA) against Escherichia coli and Staphylococcus aureus were compared after intravenous infusion of either a single 800-mg dose or twice-daily 400-mg doses into 16 healthy volunteers. Plasma pefloxacin concentrations were measured for up to 60 h, and SBAs were determined 1, 12, and 24 h after the start of the infusion. The mean areas under the concentration-versus-time curve for plasma were not different (138 versus 136 h.mg/liter). The mean clearances, volumes of distribution, and half-lives were also comparable. The mean (+/- standard deviation) maximal concentration after the 800-mg infusion was 12.11 +/- 1.35 versus 6.51 +/- 0.73 mg/liter after the first 400-mg infusion and 7.42 +/- 0.76 mg/liter after the second 400-mg infusion. Mean trough concentrations at 24 h were significantly different: 2.77 +/- 0.63 (800 mg) versus 1.93 +/- 0.49 (400 mg twice) mg/liter (P = 0.0007). Mean SBAs against E. coli after 800 mg of pefloxacin were higher than 1/128 (1 h), 1/32 (12 h), and 1/16 (24 h). Mean SBAs against S. aureus under the same conditions were higher than 1/64 (1 h), 1/16 (12 h), and 1/8 (24 h). Mean SBAs at 1 and 12 h were significantly higher after the 800-mg infusion than after the 400-mg infusion but were similar at 24 h for both regimens. Comparison of SBAs according to National Committee for Clinical Laboratory Standards criteria showed a similar adequacy at 24 h for both regimens against both strains. Administration of 800 mg of pefloxacin once a day is bioequivalent to 400 mg twice a day, and bactericidal activity of the 800-mg infusion is not less than that of two 400-mg infusions.

Determination of optimal dosage regimen for amikacin in healthy volunteers by study of pharmacokinetics and bactericidal activity

The pharmacokinetics and serum killing curves of amikacin, which was administered by a 30-minute intravenous infusion of single doses of 7.5 mg/kg and then 15 mg/kg, were investigated in six healthy volunteers who received the two doses in a crossover study with a washout period of 20 days. The serum killing curves were determined for four bacterial species: Escherichia coli, Serratia marcescens, Enterobacter cloacae, and Pseudomonas aeruginosa. All strains were serum resistant, and the bactericidal activity was analyzed by separating the early phase (first 5 h) and the late phase (24 h) of the killing curve. For the early phase, the bactericidal activity was evaluated by correlating an index of surviving bacteria with amikacin concentrations. This methodology allowed determination of two parameters: the maximal effective concentration and the lowest effective concentration. For the late phase, the threshold values separating bacteriostatic and bactericidal activities were lower than 10 mg/liter for each strain. The concentration dependence of amikacin bactericidal activity was confirmed for Escherichia coli and Enterobacter cloacae and, to a lesser extent, for Serratia marcescens and Pseudomonas aeruginosa. Correlation of these data with amikacin pharmacokinetic data in volunteers indicated that a daily dose of 15 mg/kg may be effective in the treatment of Escherichia coli and Enterobacter cloacae infections. For Pseudomonas aeruginosa and Serratia marcescens, the partially time-dependent activity probably necessitates two daily administrations and combination with another antibiotic.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Concentrations of ofloxacin in serum and cerebrospinal fluid of patients without meningitis receiving the drug intravenously and orally

The cerebrospinal fluid (CSF) penetration of ofloxacin given orally or or intravenously was studied in cancer patients without meningitis. Each patient was assigned to a different sampling time to assess the relation between time and penetration. Ofloxacin was measured in serum and CSF by high-pressure liquid chromatography and bioassay. In addition, the bactericidal titers were measured in CSF and serum against a set of relevant bacteria. Concentrations measured by high-pressure liquid chromatography and bioassay were well correlated. Peak concentrations in CSF (0.4 to 1 microgram/ml) were observed 2 to 4 h after infusion or oral administration. Peak concentrations in serum were observed just after infusion (2 to 3.5 micrograms/ml) or 1 to 2 h after oral administration (1.7 to 4 micrograms/ml). Measured bactericidal titers were well correlated with the titers expected from the MBC and concentration. High CSF bactericidal titers were observed against Neisseria meningitidis, Haemophilus influenzae, and Escherichia coli, whereas low or no bactericidal titers were obtained against Staphylococcus aureus, Listeria monocytogenes, and Streptococcus pneumoniae.

Antipseudomonal activity of simulated infusions of gentamicin alone or with piperacillin assessed by serum bactericidal rate and area under the killing curve

The objectives of this study were to (i) determine which of three simulated dosing regimens (gentamicin alone, simultaneous infusions of gentamicin and piperacillin, or staggered infusions of gentamicin and piperacillin) produced the fastest killing rate of Pseudomonas aeruginosa in serum, using the serum bactericidal rate (SBR) assay; and (ii) describe an alternative method of analysis of killing curves, the area under the killing curve (AUKC). Gentamicin alone or combined with piperacillin was added to heat-inactivated human serum to approximate drug concentrations achieved after the above-mentioned types of infusion. By a microdilution technique, seven strains of P. aeruginosa were exposed to no drug (control) and gentamicin alone or with piperacillin; colony counts were determined at hourly intervals for 5 h, and log10 CFU per milliliter was plotted versus time. Linear regression was used to calculate the slope (SBR) of each timed killing curve for each drug concentration tested alone or in combination. In addition, the AUKC for each curve was calculated. To compare simulated infusion regimens further, the cumulative AUKC (the sum of AUKCs for specific time points along the serum concentration-time curve for each simulated regimen) was calculated. With the SBR assay or AUKC determination, there was a significant increase in the rate of killing of all test strains by the combination compared with gentamicin alone only at gentamicin concentrations which exceeded the MIC (8, 5, and 2.5 micrograms/ml). Mean cumulative AUKC of the simultaneous-infusion regimen was significantly less (indicating faster killing) than either the staggered-infusion regimen or the gentamicin infusion alone. Both the SBR and AUKC have the potential for integration of in vitro microbiologic effects and in vivo pharmacokinetics of antimicrobial agents.

Pefloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Pefloxacin is a fluorinated quinolone that is structurally related to nalidixic acid. It can be administered both orally and intravenously, and has a broad spectrum of in vitro activity against Gram-negative organisms and staphylococci. The pharmacokinetic profile of pefloxacin is characterised by high bioavailability after oral administration, a long half-life and good penetration of tissue and body fluids. Data from mainly non-comparative studies suggest that pefloxacin has the potential for use in a variety of serious or difficult-to-treat and nosocomially acquired infections in hospitalised and immunocompromised patients. Such infections have included respiratory tract, urogenital tract, and bone and joint infections, septicaemia and surgical infections, in addition to severe Gram-negative infections in neutropenic cancer patients. Pefloxacin demonstrates comparable efficacy with ampicillin combined with gentamicin in upper gynaecological tract infections, ceftazidime in nosocomially acquired Gram-negative infections and co-trimoxazole (trimethoprim + sulphamethoxazole) in uncomplicated urinary tract infections and typhoid fever. Although the place of pefloxacin in this new and expanding class of 4-quinolone antibacterial drugs has yet to be defined and it appears to be a well-tolerated and useful drug for the treatment of serious infections in hospitalised patients, further studies are awaited with interest for confirmation of these preliminary results.

[Bactericidal activity of enoxacin and ciprofloxacin in body fluids]

Until present studies are lacking which investigate the bactericidal activity of new quinolones in body fluids. Therefore, we determined bactericidal titers of enoxacin (en) and ciprofloxacin (cip) against a typical pathogen in urinary tract infections (Escherichia coli) in urine and against a typical pathogen in respiratory tract infections (Streptococcus pyogenes) in sputum, in each case at the time of peak and trough levels (In vitro data of the test strains: E. coli - MICen = 0.06 mg/l, MICcip = 0.06 mg/l, MBCen = 0.5 mg/l, MBCcip = 0.25 mg/l; Streptococcus pyogenes - MICen = 32 mg/l, MICcip = 1 mg/l, MBCen greater than 64 mg/l, MBCcip greater than 64 mg/l). Following a randomization list, ten healthy volunteers took either 400 mg enoxacin b.i.d. for three days, then (after a break of at least three days) 500 mg ciprofloxacin b.i.d. for three days, or vice versa. Two and 12 hours after the final dose, samples of sputum were taken, urine was collected 2-4 h and 10-12 h after the final dose. The bactericidal titers against E. coli in urine were greater than 1:512 (2-4 h after the final dose) and greater than 1:64 (10-12 h after the final dose) for both quinolones in all cases. On the other hand, as to S. pyogenes were found growth in every dilution of sputum. These results confirm the scepticism against quinolone therapy of respiratory tract infections caused by streptococci.

Serum bactericidal test

The serum bactericidal test represents one of the few in vitro tests performed in the clinical microbiology laboratory that combines the interaction of the pathogen, the antimicrobial agent, and the patient. Although the use of such a test antedates the antimicrobial era, its performance, results, and interpretation have been subject to question and controversy. Much of the confusion concerning the serum bactericidal test can be avoided by an understanding of the various factors which influence bactericidal testing. In addition, the methodologic aspects of the serum bactericidal test have recently been addressed and should place this test on firmer ground. New information on the clinical utility of this test is becoming available; additional data are needed to establish more clearly the usefulness of the serum bactericidal test in specific infections. Such clinical trials from multiple centers will enable firmer recommendations for the future use of the serum bactericidal test.

In vitro antistaphylococcal activity of pefloxacin alone and in combination with other antistaphylococcal drugs

MICs of pefloxacin and nine antistaphylococcal drugs were determined for 200 isolates of Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus hominis, and Staphylococcus saprophyticus. All the strains were susceptible to pefloxacin, vancomycin, and rifampin. Oxacillin-resistant strains were uniformly resistant to cephalothin and were more likely to be resistant to gentamicin, erythromycin, clindamycin, doxycycline, and trimethoprim-sulfamethoxazole than were oxacillin-susceptible strains. Time-kill studies with 23 strains of S. aureus, S. epidermidis, and S. haemolyticus indicated that the relative order of bactericidal activities was gentamicin greater than or equal to pefloxacin greater than oxacillin greater than vancomycin greater than rifampin. Pefloxacin combined with oxacillin or vancomycin killed staphylococci more rapidly than oxacillin or vancomycin alone but less rapidly than pefloxacin alone. Gentamicin combined with oxacillin, vancomycin, or pefloxacin resulted in the most rapid killing of gentamicin-susceptible strains. Rifampin combined with oxacillin, vancomycin, or pefloxacin reduced the bactericidal activities of those drugs, but rifampin resistance was not observed as it was with rifampin alone. Pefloxacin is a potentially useful antistaphylococcal agent.

Serum bactericidal activity and postantibiotic effect in serum of patients with urinary tract infection receiving high-dose amikacin

Ten patients received a 30-min infusion of amikacin (30 mg/kg) on day 1 and 15 mg/kg on day 2. Mean serum creatinine was 1.1 +/- 0.3 (standard deviation) mg/dl before and 1.0 +/- 0.3 mg/dl 3 days after the second infusion. Mean serum amikacin concentrations before, at the end of infusion, and 1, 6, 12, and 24 h after 30 and 15 mg/kg were 0, 157, 79, 31, 16, 5, 5, 85, 51, 19, 12, and 5 mg/liter, respectively. Five strains each of Staphylococcus aureus, Staphylococcus epidermidis susceptible and resistant to oxacillin, Streptococcus (Enterococcus) faecalis, corynebacterium sp. strain JK, Listeria monocytogenes, Mycobacterium fortuitum (three strains), Klebsiella pneumoniae, Serratia marcescens, Acinetobacter calcoaceticus, and Pseudomonas aeruginosa were tested. Serum bactericidal activities (SBAs) were greater than or equal to 1:8 in greater than or equal to 80% of the sera 1 and 6 h after 30 mg/kg and in greater than or equal to 60% of the sera 1 and 6 h after 15 mg/kg against Staphylococcus aureus and Staphylococcus epidermidis susceptible to oxacillin, A. calcoaceticus, and K. pneumoniae. L. monocytogenes, Serratia marcescens, and P. aeruginosa had lower SBAs. Very low or no activity was observed against oxacillin-resistant staphylococci and Streptococcus faecalis. The study of the killing rate in serum confirmed these results. Postantibiotic effect was studied by incubating a strain from each species in serum samples obtained 1 and 6 h after both regimens for 0.5, 1, or 2 h. The duration of postantibiotic effect depended on the duration of contact and the concentration of amikacin for the following organisms: oxacillin-susceptible staphylococci, L. monocytogenes, P. aeruginosa, A. calcoaceticus, K. pneumoniae, and Serratia marcescens. M. fortuitum was killed after 30 min of contact. No postantibiotic effect was observed with Streptococcus faecalis, Corynebacterium sp. strain JK, or oxacillin-resistant staphylococci. Amikacin at 30 mg/kg provided high levels and SBAs against susceptible pathogens. Prolonged postantibiotic effects were observed. No signs of nephrotoxicity occurred.

Serum bactericidal rate as measure of antibiotic interactions

The serum bactericidal rate (SBR) assay was used to assess the antipseudomonal activity of gentamicin with or without piperacillin. Heat-inactivated donor serum was spiked with gentamicin, piperacillin, or a combination at concentrations representative of levels in serum and tested against five P. aeruginosa strains isolated from blood. The SBR assay was performed as follows: colony counts in test samples (control, gentamicin, piperacillin, and combination) were determined at 0, 2, 4, 6, and 8 h after inoculation of a test strain. Log10 CFU per milliliter was plotted versus time, and linear regression analysis was performed; the slope of the regression line was defined as the SBR. The SBRs of agents alone and in combination were compared statistically. The SBR of gentamicin was dependent on the serum concentration. The combination of gentamicin and piperacillin always resulted in a higher SBR than did either drug alone. However, this difference was not statistically significant for highly gentamicin-susceptible strains (MIC, less than or equal to 2 micrograms/ml) until the gentamicin concentration was reduced below the MIC. For a gentamicin-resistant strain (MIC, 8 micrograms/ml), the combination of gentamicin and piperacillin produced mean SBRs similar to that found with gentamicin-susceptible strains. These results provide evidence that the SBR assay may be a useful method of evaluating antibiotic interactions, since it can be done by using serum and since it compares the antibacterial activity of drugs statistically rather than requiring arbitrary criteria to define interactions.

Serum bactericidal activity of ciprofloxacin and ofloxacin in volunteers

The serum bactericidal activity of two newer quinolones, ciprofloxacin and ofloxacin, against 206 clinical bacterial isolates was determined in six male volunteers after oral administration of either 500 mg of ciprofloxacin or 200 mg of ofloxacin respectively. The highest bactericidal titers were achieved against Enterobacteriaceae 1 h after ciprofloxacin administration, ranging from 1:121 for indole-positive Proteus species to 1:30 for Serratia spp. Ofloxacin generated lower titers, ranging from 1:14 for indole-positive Proteus spp. to 1:2.5 for Enterobacter spp. Only low serum bactericidal titers were found for Pseudomonas aeruginosa, Acinetobacter spp. and gram-positive cocci. It is concluded that the activity of orally administered ciprofloxacin is superior to that of orally administered ofloxacin in the serum bactericidal test.

Serum bactericidal activity and killing rate for volunteers receiving imipenem, imipenem plus amikacin, and ceftazidime plus amikacin against Pseudomonas aeruginosa

Serum bactericidal activity against 20 strains of Pseudomonas aeruginosa was studied in 10 volunteers after administration of imipenem (25 mg/kg), imipenem (25 mg/kg) plus amikacin (7.5 mg/kg), and ceftazidime (25 mg/kg) plus amikacin (7.5 mg/kg). Eight strains were susceptible and 12 were resistant to ticarcillin. Serum levels were measured microbiologically after 30 and 60 min and were, respectively, 97 and 46 micrograms/ml for imipenem given alone and 79 and 45 micrograms/ml for imipenem given with amikacin. Despite the very large dose of imipenem used, imipenem and imipenem plus amikacin appeared slightly less active than ceftazidime plus amikacin (P less than or equal to 0.1; Wilcoxon matched-pairs test), with respective median titers at 30 min of 1:128, 1:128, and 1:256 against ticarcillin-susceptible strains and 1:32, 1:32, and 1:64 against ticarcillin-resistant strains; however, more than 90% of the serum determinations, regardless of the regimen, had a serum bactericidal activity greater than or equal to 1:8. Amikacin significantly increased the rate of killing in serum of P. aeruginosa by imipenem. Imipenem plus amikacin appeared as effective as ceftazidime plus amikacin in reducing the viable counts of P. aeruginosa after 24 h of incubation.

BRL-36650: in vitro studies and assessment of serum bactericidal activity after single-dose administration in volunteers

Ten healthy volunteers received 1 g of BRL-36650, a new formamido-penicillin derivative, given by intravenous infusion over 15 min. Levels in serum were measured microbiologically 30, 60, and 120 min after the start of the 15-min infusion and were (mean +/- standard deviation) 102.7 +/- 28.4, 59.7 +/- 11.5, and 9.6 +/- 1.9 mg/liter, respectively. A total of 10 strains each of Escherichia coli, Klebsiella pneumoniae, Serratia spp., and Enterobacter spp. and 14 strains of Pseudomonas aeruginosa were selected according to their susceptibility or resistance to piperacillin for the study of serum bactericidal activity (SBA). The MICs and MBCs of these strains were influenced by the choice of medium. Median SBA against E. coli and K. pneumoniae were greater than or equal to 1:2,048 and 1:512, respectively. The SBA against piperacillin-susceptible Serratia spp. (1:256), Enterobacter spp. (1:128), and P. aeruginosa (1:32) were significantly higher than against piperacillin-resistant strains (1:32, 1:8, and 1:4, respectively). Killing curves confirmed the high bactericidal activities obtained against the majority of strains. In the case of one Enterobacter sp. and one P. aeruginosa isolate with an MBC greater than or equal to 32, the absence of killing was noted.