Serum bactericidal activity of mezlocillin, ceftazidime, mezlocillin/ceftazidime and mezlocillin/amikacin against Klebsiella pneumoniae and Pseudomonas aeruginosa

Pseudomonas aeruginosa prosthetic joint-infection outcomes: Prospective, observational study on 43 patients

Objectives

Analysis the outcomes of Pseudomonas aeruginosa prosthetic joint infection (PJI), and of their clinical and microbiological characteristics, surgical strategies and antibiotic treatments.

Methods

Monocenter cohort study in a Bone-and-Joint-Infection Referral Center (08/2004 to 10/2018) including all consecutive P. aeruginosa PJIs. Data were extracted from the prospective database, including the following events: relapses, new PJIs, related deaths.

Results

Median [IQR]: among the 43 patients included (28 females; 72 [63-80] years old; 27 hip, 15 knee, and 1 shoulder PJIs), 29 (67%) had underlying comorbidities, 12 (28%) had previously been treated for another PJI and 9 (21%) had undergone previous surgeries for their P. aeruginosa PJI. Eleven (26%) PJIs were polymicrobial, 16 (37%) strains were wild type, 8 (19%) ciprofloxacin-resistant. PJIs were classified as late chronic (n = 33), early postoperative (n = 9) or acute hematogenous infection (n = 1). Forty patients underwent surgery: 27 one-stage and 5 two-stage exchanges, 3 debridement and implant retention, and 5 other surgical strategies. Antibiotic treatments were: 29 received 41 [37-43] days of combination therapy (IV anti-pseudomonal β-lactam and 3-5 days of amikacin, then β-lactam and oral ciprofloxacin), followed by oral ciprofloxacin for a total of 12 weeks; 10 received only IV antibiotics for 83 [77-86] days, including 37 [32-46] days of combination therapy; 49 days of ceftazidime alone for 1. During follow-up lasting 33 [24-64.5] months, 2 relapses, 3 new PJIs, and 2 related deaths occurred. Thirty-three (82%) patients and 93% of those managed with one-stage exchange experienced no event.

Conclusion

Outcomes of our cohort's P. aeruginosa PJIs-predominantly monomicrobial, chronic, ciprofloxacin-susceptible, treated with one-stage exchange and prolonged IV antibiotics-were 82% favorable.

Comparative study of pharmacokinetics and serum bactericidal activities of cefpirome, ceftazidime, ceftriaxone, imipenem, and ciprofloxacin

We compared the pharmacokinetics and the serum bactericidal activities of cefpirome, ceftazidime, ceftriaxone, imipenem, and ciprofloxacin. Fifteen healthy volunteers received 1 g of cefpirome, ceftazidime, and ceftriaxone intravenously, 500 mg of imipenem-cilastatin intravenously, and 500 mg of ciprofloxacin orally. High-performance liquid chromatographic assays were used to quantitate unchanged antibiotic in plasma and urine. Serum bactericidal activities were determined against six clinical isolates each of Staphylococcus aureus, Enterobacter cloacae, and Pseudomonas aeruginosa by using a modified microdilution method of Reller and Stratton (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977). Overall, cefpirome exhibited pharmacokinetics similar to those of ceftazidime: half-life (t1/2), 1.95 h; concentration at 1 h (C1h), 47 to 49 micrograms/ml for both antibiotics. Ceftriaxone displayed the longest t1/2 (7.65 h) and the highest C1h (137.8 micrograms/ml), while we observed the shortest t1/2 (1.05 h) and the lowest C1h (19.85 micrograms/ml) with imipenem. At 1 h, cefpirome and, even more so, imipenem showed significantly better serum bactericidal activities against S. aureus (1:273 and 1:80) than did the other antibiotics (P less than 0.0005; analysis of variance with randomized block design and Bonferroni correction). Against E. cloacae, we observed the highest serum bactericidal titers at 1 h with cefpirome, and this superiority vis-à-vis the other antibiotics tested was maintained for up to 8 h after dosing. Ceftazidime remained the most active agent tested against P. aeruginosa (serum bactericidal activity titers, 1:43 at 1 h) up to 8 h. In summary, the study showed that cefpirome and imipenem provide more potent serum bactericidal activities than do broad-spectrum cephalosporins against S. aureus; thus, both of these antibiotics should be adequate against serious S. aureus infections. In addition, cefpirome appears to be a promising alternative for treatment of infections caused by E. cloacae and P. aeruginosa.

Antibiotic combinations: should they be tested?

When antibiotic combinations are used to provide a broader spectrum of antimicrobial activity or in an attempt to prevent the emergence of resistant organisms, it is rarely necessary or practical to perform tests of drug interactions in vitro. In vitro testing of combinations may be useful when combinations are used in an attempt to attain synergistic interactions. In some cases, screening methods can be used as substitutes for formal synergy testing. This paper examines the mechanisms of antibiotic interaction leading to synergism or antagonism, surveys attempts to correlate in vitro observations with efficacy in animal models, and reviews clinical data providing evidence for or against a useful role of synergistic antibiotic interactions in the treatment of human infections.

Serum bactericidal test in volunteers--a review

A review is given of work utilizing the serum bactericidal test for preclinical evaluation of agents considered for treatment of gram-negative sepsis among neutropenic cancer patients. Following a description of the methodology of the two major groups, the results of the various antibiotic trials are summarized. First the extended-spectrum cephalosporins (cefotaxime, cefoperazone, and moxalactam) were tested and found to be, at best, of limited value as single agents for Pseudomonas aeruginosa, a common pathogen of neutropenic cancer patients. When the extended-spectrum penicillins became available, the serum bactericidal levels in volunteers of mezlocillin and piperacillin were compared alone or in combination with an aminoglycoside to ticarcillin with or without aminoglycoside against the same organisms. Piperacillin proved to be most effective followed by mezlocillin and then ticarcillin; in each case the addition of the aminoglycoside improved serum bactericidal activity. Recent studies suggest that imipenem alone is as active as the combination of a broad-spectrum penicillin plus an aminoglycoside and is worthy of a carefully controlled clinical trial. These types of volunteer-based evaluations of the serum bactericidal activity of new compounds may help predict useful clinical approaches for the future.