Comparative pharmacodynamics for intravenous antibiotics against Gram-negative bacteria in Europe between 2002 and 2006: a report from the OPTAMA program

Antibiotic Treatment of Carbapenem-Resistant Acinetobacter baumannii Infections in View of the Newly Developed β-Lactams: A Narrative Review of the Existing Evidence

It is estimated that antimicrobial resistance (AMR) is responsible for nearly 5 million human deaths worldwide each year and will reach 10 million by 2050. Carbapenem-resistant Acinetobacter baumannii (CRAB) infections represent the fourth-leading cause of death attributable to antimicrobial resistance globally, but a standardized therapy is still lacking. Among the antibiotics under consideration, Sulbactam/durlobactam seems to be the best candidate to replace current back-bone agents. Cefiderocol could play a pivotal role within combination therapy regimens. Due to toxicity and the pharmacokinetics/pharmacodynamics (PK/PD) limitations, colistin (or polymyxin B) should be used as an alternative agent (when no other options are available). Tigecycline (or minocycline) and fosfomycin could represent suitable partners for both NBLs. Randomized clinical trials (RCTs) are needed to better evaluate the role of NBLs in CRAB infection treatment and to compare the efficacy of tigecycline and fosfomycin as partner antibiotics. Synergism should be tested between NBLs and "old" drugs (rifampicin and trimethoprim/sulfamethoxazole). Huge efforts should be made to accelerate pre-clinical and clinical studies on safer polymyxin candidates with improved lung activity, as well as on the iv rifabutin formulation. In this narrative review, we focused the antibiotic treatment of CRAB infections in view of newly developed β-lactam agents (NBLs).

Application of Pharmacodynamic Profiling for the Selection of Optimal β-lactam Regimens in a Large University Hospital

BACKGROUND

Infections caused by drug-resistant Gram-negative bacteria (GNB) are increasing worldwide and as a result, the selection of appropriate empiric antibiotics (ATBs) has been made increasingly difficult. The present study aimed to identify optimized dosing regimens of intravenous (IV) ATBs, defined by cumulative fraction response (CFR), against E. coli (EC), K. pneumoniae (KP), P. aeruginosa (PA), and A. baumannii (AB) at 2,300-bed University Hospital.

MATERIALS AND METHODS

The minimum inhibitory concentrations (MIC) of EC, KP, PA, and AB from clinical specimens, 250 each, were determined. Pharmacodynamic profiling using Monte Carlo Simulation was performed for standard, high dosage, and prolonged infusions (PI) of ceftriaxone, cefepime, ceftazidime, imipenem, meropenem, and doripenem. A CFR of ≥90% was targeted as providing a sufficiently high ATB exposure.

RESULTS

When considering the Enterobacteriaceae, the % susceptible for the cephalosporins ranged from 60% for ceftriaxone to 86% for cefepime, as a result only the 2g q8h regimens of ceftazidime and cefepime provided high CFRs. In contrast, all the carbapenems had % susceptible and CFRs ≥90% for EC and KP. While cefepime and ceftazidime demonstrated higher % susceptibility (82-83%) for PA relative to that of the carbapenems (61-69%) only doripenem 2g q8h (4h PI) achieved an optimal CFR (92%) against this organism. Due to the MIC profiles and dismal susceptibilities of AB (16-22%), none of the regimens studied achieved CFRs > 65%.

CONCLUSIONS

The pharmacodynamic profiling undertaken in the current study provides insights that allow prescribers to select more appropriate empirical antibiotic regimens for the treatment of infection caused by these common GNB pathogens at this Thai hospital. While higher doses and PI of β-lactams improve exposures against EC, KP and PA, this approach will not sufficiently enhance their potency against AB, thus alternative therapies should be considered for this organism.

Pharmacodynamic profiling of doripenem, imipenem and meropenem against prevalent Gram-negative organisms in the Asia-Pacific region

Carbapenems are increasingly being utilised owing to the escalating prevalence of antimicrobial-resistant Gram-negative bacteria from community and hospital settings. In this study, pharmacodynamic profiles of doripenem, imipenem and meropenem were evaluated against Gram-negative bacteria isolated from hospitalised patients. MICs for carbapenems were determined for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii obtained from the COMPACT II programme conducted in the Asia-Pacific region. Monte Carlo simulations were undertaken to assess the pharmacodynamic profile of carbapenems against each of the pathogens. All carbapenem regimens achieved optimal exposures [cumulative fraction of response (CFR) ≥90%] against E. coli and K. pneumoniae. Against P. aeruginosa, doripenem achieved 81.3-95.3% CFR, imipenem achieved 55.2-77.9% CFR and meropenem achieved 71.9-91.3% CFR; only doripenem regimens of 4-h infusion of 1000 mg every 8h (q8h) and 1-h and 4-h infusion of 2000 mg q8h and a meropenem regimen of 3-h infusion of 2000 mg q8h obtained optimal exposures; all carbapenem regimens showed slight (1-7%) improvement in CFRs in favour of isolates collected from ICU sources. Against A. baumannii, CFRs were much lower (25.9-46.7% CFR) and no carbapenem regimens achieved optimal exposure in or outside the ICU. Owing to the high potency of carbapenems against these Enterobacteriaceae populations, standard regimens are likely to perform well in the Asia-Pacific region. However, larger doses combined with prolonged infusions will be required to increase the CFR for these carbapenems against resistant non-fermenting Gram-negatives such as P. aeruginosa and A. baumannii that are prevalent in these countries.

Pharmacodynamic profiling of intravenous antibiotics against prevalent Gram-negative organisms across the globe: the PASSPORT Program-Asia-Pacific Region

Due to escalating antimicrobial resistance amongst Gram-negative organisms, the choice of effective empirical antimicrobial regimens has become challenging. Monte Carlo simulations were conducted for conventional and prolonged infusion regimens of doripenem, imipenem and meropenem using pharmacokinetic data from adult patients with conserved renal function. Minimum inhibitory concentration data against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii were incorporated from the COMPACT surveillance programme in the Asia-Pacific region of the world. The cumulative fraction of response (CFR) was determined for each regimen against each bacterial population. All simulated carbapenem regimens achieved an optimal CFR against E. coli and K. pneumoniae (94.5-100% CFR). Against P. aeruginosa, doripenem achieved 78.7-92.6% CFR, imipenem achieved 60.4-79.0% CFR and meropenem achieved 73.0-85.1% CFR. The only dosing regimen to achieve ≥ 90% CFR against P. aeruginosa was doripenem 1000 mg and 2000 mg every 8 h (4-h infusion). Carbapenem CFRs against A. baumannii were much lower (29.2-54.4% CFR). CFRs for non-fermenting isolates were ca. 10% lower for isolates collected in the Intensive Care Unit. Carbapenem resistance amongst Enterobacteriaceae remains low in the Asia-Pacific region and thus standard carbapenem dosing regimens had a high likelihood of achieving pharmacodynamic exposures. However, larger doses combined with prolonged infusion will be required to increase the CFR for these carbapenems against resistant non-fermenting Gram-negatives that are common in these countries. The safety and efficacy of these high dosing regimens will need to be confirmed in the clinical setting.

Approaches to improving antibiotic management

New information is available to improve antibiotic outcomes in severe sepsis where increasing resistance and reducing novel compound development make reaching the right decisions ever more difficult and important.

In vivo efficacy of 1- and 2-gram human simulated prolonged infusions of doripenem against Pseudomonas aeruginosa

Doripenem is a new carbapenem antimicrobial with activity against a range of gram-negative organisms, including Pseudomonas aeruginosa. Previous animal studies have shown efficacy of a 500-mg dose of doripenem given as a 4-h infusion against P. aeruginosa with MICs of < or = 4 microg/ml. The purpose of this study is to evaluate the efficacy of 1- and 2-g-dose prolonged infusions of doripenem against a wide range of P. aeruginosa isolates in the neutropenic murine thigh model. Eighteen clinical P. aeruginosa isolates (MIC range, 2 to 32 microg/ml) were used; 15 of these were multidrug resistant. After infection, groups of mice were administered doripenem doses designed to simulate the free time above the MIC (fT>MIC) observed in humans given 1 or 2 g of doripenem every 8 h as a 4-h infusion. Efficacy correlated well with published fT>MIC bactericidal targets of 40%. After 24 h, 1- and 2-g doses achieved approximately > or = 2 log decreases in CFU against isolates with MICs of < or = 8 and 16 microg/ml, respectively (fT>MIC range, 52.5 to 95%). Results with organisms with higher MICs, where fT>MIC was 0%, were variable, including both increases and decreases in CFU. Compared with 1-g doses, statistically greater efficacy was noted for 2-g doses against three of the eight isolates with MICs of > or =16 microg/ml. While MIC distributions of P. aeruginosa at present necessitate increased exposures for only the most-resistant isolates, the ability of increased doses to achieve pharmacodynamic targets and the efficacy observed when these targets were attained could prove useful when these resistant isolates are encountered.