Synergy of ciprofloxacin and azlocillin in vitro and in a neutropenic mouse model of infection

Comparison of clinical, para-clinical and laboratory findings in survived and deceased patients with COVID-19: diagnostic role of inflammatory indications in determining the severity of illness

BACKGROUND

Since December 2019, when a cluster of pneumonia cases due to SARS-CoV-2 initially emerged in Wuhan city and then rapidly spread throughout the world, the necessity for data concerning the clinical and para-clinical features of Iranian patients with COVID-19 was highlighted. Therefore, we aimed to compare the clinical, para-clinical and laboratory evidences of deceased patients with survival group.

METHODS

We extracted data regarding 233 patients with laboratory-confirmed COVID-19 from Buali Hospital in Iran; clinical/para-clinical and inflammatory indexes data were collected and analyzed. The data of laboratory examinations and chest CT findings were compared between deceased and survived patients.

RESULTS

The mean age of the patients was 49.8 years and 64% of our patients were male. The acute respiratory distress syndrome occurred in 64 patients, 52 who were admitted to the ICU, which all of them underwent invasive mechanical ventilation, and 28 who died. Lymphopenia (79%), neutrophilia (79%), and thrombocytopenia (21%) were the most frequently observed laboratory findings of the deceased group on admission. Most patients (68%) had a high systematic immune-inflammation (SII) index of > 500 and increased C-reactive protein level (88%). Levels of inflammatory indexes such as neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR) and SII were documented to be significantly elevated in the deceased group when compared with the patients who survived (P < 0.0001, P < 0.001, P < 0.0001, respectively). The most commonly presented symptoms were fever (70%) and cough (63%) on admission. Headache was uncommon (11%). Ground-glass opacity with consolidation (mixed) was the most common radiologic finding on chest CT (51%). No radiographic or CT abnormality was found in 15 of 204 patients (7%).

CONCLUSION

Small fraction of patients with COVID-19 may present without fever and abnormal radiologic findings. Elevated NLR, PLR and SII can be considered as prognostic and risk stratifying factor of severe form of disease.

Comparison of the in vitro activity of ampicillin and moxifloxacin against Listeria monocytogenes at achievable concentrations in the central nervous system

PURPOSE

The aim of this study was to compare the in vitro activity of ampicillin and moxifloxacin against six isolates selected from 154 invasive clinical isolates of Listeria monocytogenes and evaluate their intra- and extracellular activities with achievable central nervous system concentrations obtained using Monte Carlo simulations with conventional and unconventional dosages.

METHODOLOGY

The MICs and minimal bactericidal concentrations (MBCs) of ampicillin and moxifloxacin were determined by using the broth microdilution method. The intra- and extracellular activities were compared using time-kill curves and inhibition of intracellular growth assays.

RESULTS

The MICs50/90 of ampicillin were 0.125/0.5 mg l-1 and the MBC50/90 was ≥16 mg l-1, while the moxifloxacin MICs50/90 were 0.25/0.5 mg l-1 and the MBC50/90 was 0.5 mg l-1. Ampicillin did not show any extracellular bactericidal activity at 24 h, although bactericidal activity was detected at 48 h. For moxifloxacin, the bactericidal effect was evident after 6 h of incubation. Both antibiotics achieved significant reductions in intracellular inoculum after 1-24 h of incubation; however, moxifloxacin becomes bactericidal more rapidly, producing a much greater reduction in the inoculum in the first hour than ampicillin. There were no differences among the MIC and MBC values of moxifloxacin and ampicillin among the strains belonging to different serotypes and/or epidemic clones. This fact was also found in the intra- and extracellular studies.

CONCLUSION

The results of this study demonstrated the faster bactericidal activity of moxifloxacin at achievable central nervous system concentrations against intra- and extracellular forms of L. monocytogenes in comparison with ampicillin.

Modification of mitogen-driven lymphoproliferation by ceftriaxone in normal and immunocompromised mice

Cyclophosphamide-treated mice are proposed as a model to assay immunomodulation by antimicrobial agents in immunocompromised animals. Cyclophosphamide-treated BALB/c mice developed temporary leukopenia, myelopenia and spleen atrophy that was followed by splenomegaly. Cells from both atrophic and hypertrophic spleens exhibited impaired responses to mitogens and suppressed the mitogen-driven proliferation of normal splenocytes. This experimental model was applied to the study of immunomodulation by ceftriaxone. Ceftriaxone did not worsen the cyclophosphamide-damaged immunity mechanisms. On the contrary, cyclophosphamide-induced suppression of lymphoproliferation in response to concanavalin A was attenuated by ceftriaxone.

Synergistic activity of the novel des-fluoro(6) quinolone, garenoxacin (BMS-284756), in combination with other antimicrobial agents against Pseudomonas aeruginosa and related species

Non-fermentative Gram-negative bacteria (Pseudomonas aeruginosa, Burkholderia cepacia, Stenotrophomonas maltophilia and Acinetobacter spp.) are intrinsically less susceptible to many antimicrobial agents. Two-drug combinations have been used to treat infections caused by less susceptible pathogens. In this study, the antibacterial activity of garenoxacin (GARX) with non-quinolones was examined. The non-quinolones evaluated were cefepime (CEPI), imipenem (IMIP), aztreonam (AZTR), piperacillin-tazobactam (PIPC/TZ), amikacin (AMK), ceftazidime (CTAZ), trimethoprim-sulphamethoxazole (TMP/SMX) and ticarcillin-clavulanate (TICC/CA). Synergism was determined by time-kill analysis using GARX (at 2 x its MIC, not to exceed 4 mg/l) and the second drug (at 1 x MIC, not to exceed its susceptible MIC breakpoint), and is defined as > or = 2 log(10) enhanced killing at 24 h with the combination. Partial synergy is defined as > or = 1.5 log(10) but < 2 log(10) enhanced killing with the drug combination. Synergy/partial synergy was observed most often with GARX plus: CEPI, AZTR, PIPC/TZ, IMIP (five strains each) or AMK (four strains) vs. eight P. aeruginosa; CTAZ, AZTR (five strains each) vs. six B. cepacia; TICC/CA (six strains), CEPI, CTAZ or AMK (five strains each) vs. eight S. maltophilia; and CEPI, AMK (three strains each) or CTAZ, TICC/CA (two strains each) vs. four Acinetobacter spp. In conclusion, synergistic killing was observed frequently with GARX plus a non-quinolone bactericidal agents against non-fermentative Gram-negative bacteria, including strains intermediately susceptible/resistant to one or both agents.

Synergistic activities of gatifloxacin in combination with other antimicrobial agents against Pseudomonas aeruginosa and related species

Drug combinations have been used to treat serious infections caused by Pseudomonas, Burkholderia, Stenotrophomonas, and Acinetobacter. In this study, the combined drug effects of gatifloxacin (GAT) and nonquinolones were determined by time-kill analysis at clinically achievable drug concentrations. Synergy (>or=2 log(10)-enhanced killing at 24 h) was observed with GAT plus amikacin or a beta-lactam against 50 to 75% of strains, including strains nonsusceptible to one or both drugs.

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.

Timed killing kinetic studies of the interaction between ciprofloxacin and beta-lactams against gram-negative bacilli

Timed killing kinetic studies were performed with ciprofloxacin in combination with aztreonam, ceftazidime, piperacillin/tazobactam, and ticarcillin/clavulanic acid against three isolates each of Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, and Pseudomonas aeruginosa. Each antimicrobial agent in the combination was tested at its MIC and at one-half and one-quarter of its MIC. Colony counts were determined at 0, 3, 5, and 7 hours. Synergy occurred most frequently at 7 hours and, when present, was most likely to occur when ciprofloxacin and the beta-lactam were tested at concentrations equal to their respective MICs. Synergy after 3 hours of incubation was not predictive of a synergestic interaction at 5 or 7 hours. Antagonism was noted in several instances, particularly when ciprofloxacin and the beta-lactam were combined at one-quarter of their respective MICs.

Comparison of the bactericidal activities of ofloxacin and ciprofloxacin alone and in combination with ceftazidime and piperacillin against clinical strains of Pseudomonas aeruginosa

On the basis of MIC data, ciprofloxacin exhibits superior activity against Pseudomonas aeruginosa than the other currently available fluoroquinolones do. Despite the antipseudomonal advantage noted for ciprofloxacin monotherapy, it is unknown whether this advantage is maintained when the fluoroquinolones are used in combination with antipseudomonal beta-lactams such as ceftazidime and piperacillin. Twelve healthy volunteers were enrolled in this open-label, randomized, steady-state, six-way cross-over, comparative trial. All subjects received the following regimens: (i) 400 mg of ofloxacin given intravenously (i.v.) every 12 h (q12h), (ii) 400 mg of ciprofloxacin given i.v. q12h, (iii) 400 mg of ofloxacin given i.v. q12h plus 1 g of ceftazidime given i.v. every 8 h (q8h), (iv) 400 mg of ciprofloxacin given i.v. q12h plus 1 g of ceftazidime given i.v. q8h, (v) 400 mg of ofloxacin given i.v. q12h plus 4 g of piperacillin given i.v. q8h, and (vi) 400 mg of ciprofloxacin given i.v. q12h plus 4 g of piperacillin given i.v. q8h. Serum bactericidal titers with subsequent calculation of the area under the bactericidal curve were determined against three clinical isolates of P. aeruginosa. As monotherapy, ciprofloxacin demonstrated superior antipseudomonal activity than ofloxacin did; however, combination of these agents with ceftazidime yielded remarkably similar and statistically comparable activity profiles. In contrast, ciprofloxacin-piperacillin retained a bactericidal advantage over ofloxacin-piperacillin. Although ciprofloxacin exhibits superior antipseudomonal activity when used as monotherapy, combination of ofloxacin or ciprofloxacin with ceftazidime yielded equivalent activity profiles against susceptible strains of P. aeruginosa.

In vitro pharmacodynamics of piperacillin, piperacillin-tazobactam, and ciprofloxacin alone and in combination against Staphylococcus aureus, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa

The time-kill curve methodology was used to determine the pharmacodynamics of piperacillin, ciprofloxacin, piperacillin-tazobactam and the combinations piperacillin-ciprofloxacin and ciprofloxacin-piperacillin-tazobactam. Kill curve studies were performed for piperacillin, ciprofloxacin, and piperacillin-tazobactam at concentrations of 0.25 to 50 times the MICs for 13 strains of bacteria: four Pseudomonas aeruginosa, three Enterobacter cloacae, three Klebsiella pneumoniae, and three Staphylococcus aureus isolates (tazobactam concentrations of 0.5, 4, and 12 micrograms/ml). By using a sigmoid Emax model and nonlinear least squares regression, the 50% lethal concentrations and the maximum lethal rates of each agent were determined for each bacterial strain. For piperacillin-ciprofloxacin and ciprofloxacin-piperacillin-tazobactam, kill curve studies were performed with concentrations obtained by the fractional maximal effect method (R. C. Li, J. J. Schentag, and D. E. Nix, Antimicrob. Agents Chemother. 37:523-531, 1993) and from individual 50% lethal concentrations and maximum lethal rates. Ciprofloxacin-piperacillin-tazobactam was evaluated only against the four P. aeruginosa strains. Interactions between piperacillin and ciprofloxacin were generally additive. At physiologically relevant concentrations of piperacillin and ciprofloxacin, ciprofloxacin had the highest rates of killing against K. pneumoniae. Piperacillin-tazobactam (12 micrograms/ml) had the highest rate of killing against E. cloacae. Piperacillin-ciprofloxacin with relatively higher ciprofloxacin concentrations had the greatest killing rates against S. aureus. This combination had significantly higher killing rates than piperacillin (P < 0.002). For all the bacterial strains tested, killing rates by ciprofloxacin were significantly higher than those by piperacillin-tazobactam (4 and 12 micrograms/ml had significantly higher killing rates than piperacillin alone (P < 0.02 and P < 0.004, respectively). The effect of the combination of piperacillin-ciprofloxacin, in which piperacillin concentrations were relatively higher, was not statistically different from that of piperacillin alone (p > or = 0.71). The combination of ciprofloxacin-piperacillin-tazobactam achieved greater killing than other combinations or monotherapies against P. aeruginosa. The reduction in the initial inoculum was 1 to 4 logs greater with ciprofloxacin-piperacillin-tazobactam at 4 and 12 micrograms/ml than with any other agent or combination of agents. On the basis of the additive effects prevalently demonstrated in the in vitro study, the combinations of piperacillin-ciprofloxacin and piperacillin-tazobactam are rational therapeutic options. Greater killing of P. aeruginosa was demonstrated with ciprofloxacin-piperacillin--tazobactam. Since treatment failure of P. aeruginosa pneumonia is a significant problem, clinical studies are warranted.

Antipseudomonal penicillins

Antipseudomonal penicillins retain most of the antibacterial activity of penicillin and aminopenicillins. This group of penicillins has added activities against many gram-negative rods, including P. aeruginosa. Similar to the earlier penicillins, this group continues to be susceptible to hydrolysis by many beta-lactamases and are, therefore, not consistently active against Staphylococcus, some gram-negative rods, and certain beta-lactamase-producing gram-negative anaerobes. The ureidopenicillins, especially piperacillin, appear to have better activity against Enterococcus, Klebsiella, and P. aeruginosa than ticarcillin. The advantages over the newer cephalosporins are (1) better activity against Enterococcus, (2) more consistent activity against Clostridium, and (3) more consistent synergy with aminoglycosides. The ureidopenicillins have certain advantages over carboxypenicillins, including lower sodium load, less frequent hypokalemia, reduced platelet dysfunction, minimal dosage adjustment in patients with renal failure, and a wider spectrum of antibacterial activity, especially against Enterococcus, Pseudomonas, and Klebsiella. The utility of the antipseudomonal penicillins by themselves is limited as agents for monotherapy when the infecting organism is not known. In addition, monotherapy is not recommended in certain infections to avoid the development of resistance. When combined with a beta-lactamase inhibitor or with an aminoglycoside, however, some of the weaknesses can be overcome.

Comparative efficacies of ciprofloxacin and pefloxacin alone or in combination with fosfomycin in experimental endocarditis induced by multidrug-susceptible and -resistant Pseudomonas aeruginosa

The in vivo efficacy of ciprofloxacin or pefloxacin alone or in combination with fosfomycin was evaluated in experimental aortic valve endocarditis induced in 133 rabbits by a multidrug-susceptible or multidrug-resistant strain of Pseudomonas aeruginosa. Therapy was initiated early (12 h after infection), when bacterial counts in aortic valve vegetations were relatively low, or late (48 h after infection), when vegetations contained a larger inoculum. Antibodies were administered as a continuous 24-h intravenous infusion. Mean steady-state levels of ciprofloxacin (64 mg/kg), pefloxacin (64 mg/kg), and fosfomycin (300 mg/kg) in serum were 2.5, 4.2, and 63.9 mg/liter, respectively. For the multidrug-susceptible strain, all regimens except pefloxacin alone significantly reduced the number of CFU per gram of vegetation versus controls, whether treatment was performed early or late. For the multidrug-resistant strain, none of the regimens showed differences from untreated controls, except ciprofloxacin-fosfomycin, which significantly reduced bacterial counts in vegetations compared with controls when therapy was begun early (4.1 +/- 1.1 log10 CFU/g of vegetation; P < 0.001 versus the control). These data suggest that combination of fosfomycin with ciprofloxacin or pefloxacin is more effective than ciprofloxacin or pefloxacin alone for the therapy of severe infections caused by multidrug-susceptible P. aeruginosa.

Increased susceptibility of Pseudomonas aeruginosa to ciprofloxacin in the presence of vancomycin

Vancomycin in combination with ciprofloxacin exhibited synergy against 7 of 10 strains of Pseudomonas aeruginosa. MICs for the microbial strains used in this study ranged from 0.0325 to 3.0 micrograms/ml for ciprofloxacin and from 23.5 to > 188 micrograms/ml for vancomycin. Combinations of these antibiotics, tested in a checkerboard pattern, gave fractional inhibitory concentrations of 0.5 or less for 7 of the 10 strains tested.

The postantibiotic suppressive effect of L-ofloxacin, an optically active isomer of ofloxacin

The postantibiotic suppressive effect (PAE) of L-ofloxacin was studied and compared with those of ciprofloxacin and norfloxacin. The PAE of L-ofloxacin was observed against all Gram-positive organisms tested: Staphylococcus aureus, S. epidermidis, and Enterococcus faecalis. At the achievable serum concentrations L-ofloxacin showed a longer PAE than ciprofloxacin and norfloxacin. Exposure of organisms to 4 micrograms/ml of L-ofloxacin for 2 hr produced a 3.1 and 4.2 hr PAE for methicillin-sensitive and methicillin-resistant staphylococci, respectively. Against E. faecalis and S. epidermidis, the PAEs of L-ofloxacin were 1.9 and 1.6 hr, respectively.

A pilot study of piperacillin and ciprofloxacin as initial therapy for fever in severely neutropenic leukemia patients

We studied the efficacy of piperacillin and ciprofloxacin as initial parenteral therapy in 41 adult patients with leukemia who developed 47 febrile episodes during severe neutropenia following chemotherapy. 40 patients (98%) survived their febrile episode(s), whereas 1 patient died of infection. When assessed at 72 h after initiation of treatment (early evaluation), 24/47 episodes (51%) had been successfully treated. These 24 favourable responses were seen in 15/24 (63%) microbiologically documented infections and 9/19 (47%) fever of unknown origin (FUO). At the resolution of fever (late evaluation) 46 episodes were evaluable, and 28 (61%) had responded successfully to piperacillin and ciprofloxacin. Successful treatment was most frequently observed in microbiologically defined infections, 18/23 (78%). Three of 5 (60%) Gram-positive, 11/12 (92%) Gram-negative and 1 of 2 mixed bacteremias were successfully treated. In contrast, only 10/19 (53%) FUO and none of 4 clinically defined infections had responded. Thus, this pilot study indicates that piperacillin and ciprofloxacin may be a safe and effective combination for the treatment of febrile episodes in severely neutropenic leukemia patients, which merits further investigation in randomized trials.

Synergy and antagonism of combinations with quinolones

Combinations of fluoroquinolones with other antimicrobial agents have been extensively investigated. Combinations of fluoroquinolones with aminoglycosides, beta-lactams, imidazoles, macrolides and clindamycin infrequently show synergy against Enterobacteriaceae and gram-positive bacteria. These combinations rarely show antagonism. Combinations of rifampin with fluoroquinolones tested against Staphylococcus aureus have been reported to show synergy and antagonism, and in vitro results have not correlated with results of animal infection experiments. Against Pseudomonas aeruginosa combinations of antipseudomonas penicillins or imipenem with fluoroquinolones are synergistic for 20% to 50% of isolates in vitro and also are synergistic in animal models of infection, whereas combinations of aminoglycosides with fluoroquinolones rarely show synergy against Pseudomonas aeruginosa. Against anaerobic species such as Bacteroides fragilis combinations of fluoroquinolones with clindamycin, anti-anaerobic penicillins, cephalosporins or imidazoles are occasionally synergistic but usually indifferent. Ciprofloxacin and ofloxacin combined with antituberculosis agents have activity against Mycobacterium tuberculosis and atypical mycobacteria. In general, fluoroquinolones should be combined with other agents not to achieve synergy, which is extremely variable, but to provide activity against bacteria inadequately inhibited by the fluoroquinolones.

Combination of ofloxacin and other antimicrobial agents

We evaluated the combination of ofloxacin with piperacillin, gentamicin, vancomycin, rifampin, clindamycin, and metronidazole by the checkerboard agar dilution method against 165 isolates which included Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa, Providencia stuartii, Acinetobacter, Staphylococcus aureus, Bacteroides fragilis, and Citrobacter perfringens. Synergy of piperacillin-ofloxacin was demonstrated for 50% and 40% respectively of E. cloacae and P. aeruginosa. Some ofloxacin and piperacillin-resistant isolates were susceptible with the combination. Ofloxacin-gentamicin was indifferent for aerobic gram-negative species. Ofloxacin and vancomycin or gentamicin was indifferent for S. aureus and E. faecalis, but rifampin-ofloxacin showed addition. Combination of ofloxacin and metronidazole or clindamycin or erythromycin was indifferent for aerobic and anaerobic species. Ofloxacin could be combined with piperacillin with benefit against P. aeruginosa, but combination with aminoglycosides is not of benefit.

An unusual presentation of staphylococcal pericarditis

An atypical presentation of purulent pericarditis caused by Staphylococcus aureus is described. A bacterial etiology was initially not taken into consideration because the clinical course was torpid and afebrile. Therefore, the appropriate treatment was delayed. The patient recovered after percutaneous pericardial drainage of his purulent pericardial effusion and antimicrobial therapy. The importance of a high index of suspicion of a bacterial cause in patients with pericardial effusion of unexplained etiology is emphasized.

Ciprofloxacin in combination with other antimicrobials

Combinations of ciprofloxacin with aminoglycosides or beta-lactams are infrequently synergistic and only rarely antagonistic against Enterobacteriaceae or gram-positive bacteria. Against Pseudomonas aeruginosa, combinations of ciprofloxacin with an aminoglycoside are synergistic for a minority of isolates, whereas rates of synergistic interactions between ciprofloxacin and beta-lactams against this group of organisms vary over a wide range.

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.

In vitro synergy studies with ciprofloxacin and selected beta-lactam agents and aminoglycosides against multidrug-resistant Pseudomonas aeruginosa

In order to determine the effect of combining ciprofloxacin with beta-lactam and aminoglycoside agents against multidrug-resistant P. aeruginosa, ciprofloxacin was tested in vitro with the checkerboard broth microdilution technique with various current beta-lactam and aminoglycoside agents. In both inhibitory and bactericidal testing, the combination of ciprofloxacin with a beta-lactam agent (ceftazidime, piperacillin, mezlocillin, azlocillin, or imipenem) was more likely to show a synergistic effect or additive effect and lack of antagonism (96.5% of all inhibitory and cidal tests) than was a combination of ciprofloxacin with an aminoglycoside [(amikacin, tobramycin, or gentamicin), 90% of all inhibitory and cidal tests]. Finding of antagonism in some testing, especially with aminoglycosides, indicates that results are unpredictable. These results may influence selection of agents for selection in clinical situations.

Listeria monocytogenes infections--therapeutic possibilities and problems

Listeriosis in humans is a rare disease, which, however, is known to be epidemic and endemic. The prognosis has remained unsatisfactory up to today, the fatality being at least 10% and often considerably higher depending on the clinical features of the disease and the patient's age. Three population groups are at risk: pregnant women, fetuses and newborn infants. Furthermore, immunosuppression in older patients due to disease, therapy, or age also plays a role. The incidence of Listeria infections in patients over 45 is clearly increasing. Due to the nature of the pathogen (in vivo bactericidal concentrations of antibiotics are often not attainable; intracellular growth) a high dosage of ampicillin is recommended. Although the present therapeutic possibilities are not satisfactory, a combination of ampicillin and an aminoglycoside appears to be the best therapy at present. Other combinations such as rifampicin and beta-lactam antibiotics have exhibited in vitro antagonism. The preferred therapy, ampicillin, can only be recommended with reservations because it is not optimally effective.

Analysis of the interaction between piperacillin and ciprofloxacin or tobramycin against thirteen strains of Pseudomonas aeruginosa, using killing curves

Time-kill studies were made with thirteen strains of Pseudomonas aeruginosa, comparing the activity of ciprofloxacin plus piperacillin with the combination of tobramycin and piperacillin. Synergism was demonstrated in an equal number of strains with both combinations. No antagonism was demonstrated. The reproducibility of the killing-curve method suggests that at least two different concentrations should be used and that a decrease in viable counts below 2 log10 after 24 hours does not exclude a synergistic action.

Synergism of the combinations of imipenem plus ciprofloxacin and imipenem plus amikacin against Pseudomonas aeruginosa and other bacterial pathogens

The combinations of imipenem plus ciprofloxacin and imipenem plus amikacin were investigated for their activity against Pseudomonas aeruginosa and other bacterial pathogens. For imipenem-susceptible P. aeruginosa, synergy of imipenem plus ciprofloxacin and imipenem plus amikacin was observed against 36 and 45% of the strains, respectively. The incidence of synergy against imipenem-resistant isolates of P. aeruginosa was 10% for both combinations. Antagonism was not observed with either combination.