In vitro comparison of cefoperazone/sulbactam with selected antimicrobials against 300 bacteroides isolates. Inhibitory activity and time-kill kinetic studies

Multicenter study on clinical outcomes and poor prognostic factors in patients with Klebsiella pneumoniae bacteremia receiving cefoperazone/sulbactam treatment

BACKGROUND

Infections caused by Klebsiella pneumoniae are common and result in high mortality rates. In vitro studies demonstrated the potency of cefoperazone/sulbactam (CPZ/SUL) against Klebsiella pneumoniae. However, the clinical efficacy of CPZ/SUL for the treatment of K. pneumoniae bacteremia has not been studied.

OBJECTIVES

This study aimed to associate the clinical outcomes of patients with bacteremia with the minimal inhibitory concentrations (MICs) of CPZ/SUL against the causative K. pneumoniae isolates.

METHODS

This multicenter, retrospective study was conducted in Taiwan between July 2017 and April 2021. Patients with K. pneumoniae bacteremia treated with CPZ/SUL were enrolled in this study. CPZ/SUL MICs were determined using the agar dilution method. Data on the patients' clinical outcomes and characteristics were collected and analyzed.

RESULTS

In total, 201 patients were enrolled. Among the causative K. pneumoniae isolates, 180 (89.5%) were susceptible to CPZ/SUL. Most patients (n = 156, 77.6%) had favorable outcomes. The 30-day mortality rate was 11.9% (n = 24). Multivariate risk analyses showed that higher APACHE II score (Odds Ratio [OR], 1.14; Confidence Interval [CI], 1.07-1.21; p < 0.001), metastatic tumors (OR, 5.76; CI, 2.31-14.40; p < 0.001), and causative K. pneumoniae CPZ/SUL MICs > 16 µg/ml (OR, 4.30; CI, 1.50-12.27; p = 0.006) were independently associated with unfavorable outcomes.

CONCLUSION

Patients with K. pneumoniae bacteremia treated with CPZ/SUL at a ratio 1:1 had favorable outcomes when the CPZ/SUL MICs were ≤ 16 µg/ml. Patients with higher APACHE II scores and metastatic tumors had unfavorable outcomes.

Current antimicrobial therapy of anaerobic infections

The treatment of many anaerobic infections involves antimicrobial therapy, appropriate surgical drainage of abscesses, and debridement of devitalized tissue. Most anaerobic infections are polymicrobial and require treatment with agents active against an array of aerobic and anaerobic bacteria. Bacterial resistance, especially to penicillins and tetracyclines, but also to newer agents of other classes, continues to increase. As a result, treatment with more than one drug is often required. Combination therapy is often necessary in serious infection, and is indicated for empiric treatment before receiving culture results. In the past combination therapy has been the mainstay of antimicrobial therapy, but more recent studies suggest that monotherapy for anaerobic infections may dominate the future. Selection of an agent requires consideration of the site of infection and the most likely etiologic agents. In vitro susceptibility is important, but it is not the only determinant of antimicrobial effectiveness. The pharmacology of the drug--absorption, distribution, concentrations in body fluids and tissues, excretion and metabolism--also plays an important role. The nature and severity of the underlying illness are important factors in selecting empiric therapy. Although it is a clinical judgement, in patients considered to have mild to moderate infections, several factors in selecting antimicrobial agents may be considered, including cost, whereas in patients judged to have severe or life-threatening infections, the most potent agents should be chosen as initial therapy, regardless of cost. Finally, the toxicities of the agent must also be considered.

Inhibitory and bactericidal activity of selected beta-lactam agents alone and in combination with beta-lactamase inhibitors compared with that of cefoxitin and metronidazole against cefoxitin-susceptible and cefoxitin-resistant isolates of the Bacteroides fragilis group

The inhibitory activity of five beta-lactam agents, alone and in combination with a beta-lactamase inhibitor, was compared with that of cefoxitin and metronidazole against 300 beta-lactamase producing Bacteroides fragilis group isolates. Each of the beta-lactamase inhibitors significantly potentiated the activity of the respective beta-lactam. In the presence of clavulanate, the MIC90 (minimum inhibitory concentration) values of amoxicillin and ticarcillin were reduced 64-fold and 32-fold, respectively. Similarly, sulbactam enhanced the activity of ampicillin and cefoperazone 16-fold and 8-fold, respectively, whereas tazobactam potentiated the activity of piperacillin 16-fold. Few strains were resistant to the beta-lactam-beta-lactamase inhibitor combinations and were comprised of strains of B. fragilis, B. thetaiotamicron, and B. distasonis. Of the strains, 7% were resistant to cefoxitin, and none to metronidazole. Using time-kill kinetic studies, the bactericidal activity of the various beta-lactam agents, with and without beta-lactamase inhibitors, was determined and compared with that of cefoxitin and metronidazole against cefoxitin-susceptible and cefoxitin-resistant isolates of the B. fragilis group. Overall, metronidazole was the most bactericidal agent with all isolates being killed with less than or equal to 4 micrograms/ml at 24 hr. Ampicillin-sulbactam was the next most bactericidal agent with all isolates being killed with less than or equal to 16/8 micrograms/ml of ampicillin-sulbactam at 24 hr. Amoxicillin-clavulanate and cefoperazone-sulbactam had bactericidal activity similar to that of ampicillin-sulbactam. Piperacillin-tazobactam and ticarcillin-clavulanate were bactericidal at higher concentrations with all isolates killed with 64 micrograms/ml of piperacillin and 128 micrograms/ml of ticarcillin combined with their respective beta-lactamase inhibitors. None of the beta-lactam agents alone was able to kill more than 19 of the 26 isolates. We conclude that beta-lactam agents combined with beta-lactamase inhibitors have both inhibitory and bactericidal activity against cefoxitin-resistant members of the B. fragilis group provided that the concentrations achieved for these combinations are at the upper limits for maximum recommended dosing. Although isolates of the B. fragilis group have been reported to produce unusual beta-lactamases that are refractory to beta-lactamase inhibitors, none of the cefoxitin-resistant isolates tested in this study were resistant to the beta-lactam-beta-lactamase inhibitor combinations.