A pharmacokinetic-pharmacodynamic assessment of oral antibiotics for pyelonephritis

Amoxicillin-Clavulanate Breakpoints Against Enterobacterales: Rationale for Revision by the Clinical and Laboratory Standards Institute

Amoxicillin-clavulanate (AMC) is among the most frequently prescribed antibiotics globally. It has broad antibacterial activity against gram-positive, gram-negative, and anaerobic bacteria and has been used to treat infections caused by a broad range of pathogens. AMC breakpoints against Enterobacterales were initially set in the 1980s. However, since that time, increases in antibiotic resistance, advances in pharmacokinetic/pharmacodynamic analyses, and publication of additional clinical data prompted a reassessment by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing. Based on this contemporary reappraisal, the CLSI retained the Enterobacterales breakpoints but revised comments regarding dosing associated with use of the AMC breakpoints in the 2022 supplement of M100. This viewpoint provides insight into the CLSI breakpoint reevaluation process and summarizes the data and rationale used to support these revisions to the AMC Enterobacterales breakpoint.

Evaluation of Oral Amoxicillin/Clavulanate for Urinary Tract Infections Caused by Ceftriaxone Non-Susceptible Enterobacterales

Urinary tract infections (UTIs) are one of the most common infections and are frequently caused by Gram-negative organisms. The rise of resistant isolates has prompted evaluation of alternative therapies, including amoxicillin-clavulanate which has potent activity against Ambler class A enzymes. This study sought to evaluate clinical outcomes of patients with ceftriaxone non-susceptible UTIs receiving amoxicillin-clavulanate or standard of care (SOC). This was a single-center, retrospective, cohort study of adult patients with urinary tract infections caused by a ceftriaxone non-susceptible pathogen who received amoxicillin-clavulanate or SOC. The primary outcome was clinical failure at 90 days. Secondary outcomes included time to failure, isolation of a resistant organism, and hospital length of stay. Fifty-nine patients met study inclusion: 26 received amoxicillin/clavulanate and 33 received SOC. Amoxicillin-clavulanate recipients did not have higher failure rates compared to SOC recipients. For patients requiring hospital admission, hospital length of stay was numerically shorter with amoxicillin-clavulanate. The frequency of amoxicillin-clavulanate and carbapenem-resistant organisms did not differ significantly between groups. Amoxicillin-clavulanate may be a useful alternative therapy for the treatment of ceftriaxone non-susceptible Enterobacterales UTIs.

Oral Antibiotics for Bacteremia and Infective Endocarditis: Current Evidence and Future Perspectives

Bacteremia and endocarditis are two clinical syndromes that, for decades, were managed exclusively with parenteral antimicrobials, irrespective of a given patient's clinical condition, causative pathogen, or its antibiotic susceptibility profile. This clinical approach, however, was based on low-quality data and outdated expert opinions. When a patient's condition has improved, gastrointestinal absorption is not compromised, and an oral antibiotic regimen reaching adequate serum concentrations is available, a switch to oral antibacterials can be applied. Although available evidence has reduced the timing of the oral switch in bacteremia to three days/until clinical improvement, there are only scarce data regarding less than 10-day intravenous antibiotic therapy in endocarditis. Many standard or studied oral antimicrobial dosages are smaller than the approved doses for parenteral administration, which is a risk factor for treatment failure; in addition, the gastrointestinal barrier may affect drug bioavailability, especially when the causative pathogen has a minimum inhibitory concentration that is close to the susceptibility breakpoint. A considerable number of patients infected by such near-breakpoint strains may not be potential candidates for oral step-down therapy to non-highly bioavailable antibiotics like beta-lactams; different breakpoints should be determined for this setting. This review will focus on summarizing findings about pathogen-specific tailoring of oral step-down therapy for bacteremia and endocarditis, but will also present laboratory and clinical data about antibiotics such as beta-lactams, linezolid, and fosfomycin that should be studied more in order to elucidate their role and optimal dosage in this context.

Outcomes of high-dose oral beta-lactam definitive therapy compared to fluoroquinolone or trimethoprim-sulfamethoxazole oral therapy for bacteremia secondary to a urinary tract infection

Objective

Compare outcomes of patients receiving high-dose oral beta-lactam versus standard oral therapy for Enterobacterales bacteremia from a urinary tract infection (UTI).

Design

Retrospective, multicenter, observational cohort.

Setting

Three Michigan community teaching hospitals.

Patients

Adult patients admitted between February 1, 2020, and October 1, 2022, with gram-negative bacteremia from a urinary source were evaluated. Patients receiving active empiric intravenous (IV) antibiotics and transitioned to appropriately dosed oral cephalexin, amoxicillin, fluoroquinolone (FQ), or trimethoprim/sulfamethoxazole (TMP/SMX) were included. Patients receiving less than 72 hours of oral therapy, diagnosed with renal abscess, lobar nephronia, or expired during admission were excluded.

Methods

Standard oral therapy was defined as FQ or TMP/SMX. The primary outcome compared the composite of recurrent bacteremia or mortality within 30 days of therapy between groups. Secondary outcomes compared recurrent UTI, emergency department or hospital readmission, and Clostridioides difficile within 30 days.

Results

194 patients were included (beta-lactam, n = 75 vs standard therapy, n =119). Patients in both groups were treated for a median of 11 days, with 4 days IV and 7 days oral therapy. There was no difference in the primary outcome between groups (beta-lactam 1.3% vs standard therapy 1.7%, OR 1.27 [95% CI 0.11-14.2]). No patients experienced C. difficile in either group (p = 1.0). Infectious disease consultation was independently associated with standard therapy prescribing (OR 4.4 [95% CI 2.24-8.26]).

Conclusion

High-dose oral beta-lactams were as safe and effective as oral FQ or TMP/SMX for the treatment of bacteremia from a urinary source. Most patients received 8-10 days of therapy in both groups.

Shedding Light on Amoxicillin, Amoxicillin-clavulanate, and Cephalexin Dosing in Children from a Pharmacist's Perspective

Selection of an antibiotic and dosing regimen requires consideration of multiple factors including microbiological data, site of infection, pharmacokinetics, and how it relates to the pharmacodynamic target. Given the multiple dosage regimens of amoxicillin with/without clavulanate and cephalexin, we review the principles of dose selection from a pharmacist's perspective.

A retrospective review of oral cephalosporins versus fluoroquinolones for the treatment of pyelonephritis

Background

The current Infectious Diseases Society of America guidelines for the treatment of acute uncomplicated pyelonephritis (AUP) advise caution when using oral beta-lactams due to concern for potentially inferior efficacy compared to fluoroquinolones (FQs) and trimethoprim-sulfamethoxazole; however, studies specifically evaluating the efficacy of oral cephalosporins (CPs) in AUP are limited.

Objective

To assess the safety and efficacy of oral CPs versus FQs for the treatment of AUP.

Design, setting and participants

This is a retrospective, chart review study conducted at a single-center, tertiary care hospital.

Measurements

The primary endpoint was treatment failure within 30 days, defined as a change in antibiotic or return to ED or clinic due to persistent symptoms. Secondary endpoints included adverse drug reactions (ADRs) and C. difficile infection (CDI) within 30 days.

Results

Of the 343 patients included in the study, treatment failure occurred in 54/338 (16.0%) patients and was similar between oral CPs and FQs (35/229 [15.3%] vs. 19/109 [17.4%]). A higher percentage of treatment failures were observed for third generation (3GC) and first generation (1GC) CPs compared to second generation CPs (2GC) (3GC: 15/65 [23.4%]; 1GC: 11/49 [22.4%]; 2GC: 9/115 [7.8%]). Documented ADRs were low (6/343 [1.7%]) and no cases of CDI were documented.

Conclusions

Oral CPs appear to be as safe and effective as FQs for the treatment of AUP. Fewer treatment failures were noted with 2GCs as compared to 3GCs and 1GCs.

Optimizing the Management of Uncomplicated Gram-Negative Bloodstream Infections: Consensus Guidance Using a Modified Delphi Process

Background

Guidance on the recommended durations of antibiotic therapy, the use of oral antibiotic therapy, and the need for repeat blood cultures remain incomplete for gram-negative bloodstream infections. We convened a panel of infectious diseases specialists to develop a consensus definition of uncomplicated gram-negative bloodstream infections to assist clinicians with management decisions.

Methods

Panelists, who were all blinded to the identity of other members of the panel, used a modified Delphi technique to develop a list of statements describing preferred management approaches for uncomplicated gram-negative bloodstream infections. Panelists provided level of agreement and feedback on consensus statements generated and refined them from the first round of open-ended questions through 3 subsequent rounds.

Results

Thirteen infectious diseases specialists (7 physicians and 6 pharmacists) from across the United States participated in the consensus process. A definition of uncomplicated gram-negative bloodstream infection was developed. Considerations cited by panelists in determining if a bloodstream infection was uncomplicated included host immune status, response to therapy, organism identified, source of the bacteremia, and source control measures. For patients meeting this definition, panelists largely agreed that a duration of therapy of ~7 days, transitioning to oral antibiotic therapy, and forgoing repeat blood cultures, was reasonable.

Conclusions

In the absence of professional guidelines for the management of uncomplicated gram-negative bloodstream infections, the consensus statements developed by a panel of infectious diseases specialists can provide guidance to practitioners for a common clinical scenario.

Orally Administered Amoxicillin/Clavulanate: Current Role in Outpatient Therapy

Oral amoxicillin/clavulanate is a community workhorse antibiotic, routinely prescribed for respiratory tract infections, skin infections as well as urinary tract infections (UTIs). Multiple adult and paediatric dose formulations of amoxicillin/clavulanate are available in different parts of the world. In adult formulations, clavulanic acid dose is restricted to 125 mg because of tolerability issues. Despite its popular use for 40 years, few pharmacokinetic/pharmacodynamic (PK/PD) studies were undertaken to justify the doses and breakpoints currently in use for various infections. Clavulanate has a minimal role in the combination’s use for respiratory infections. In the context of rising extended spectrum beta-lactamase (ESBL) prevalence globally, empirical and overuse of orally administered amoxicillin/clavulanate may select resistance in Gram-negative pathogens. The susceptibility test methods and interpretive criteria differ between the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST). Third-generation oral cephalosporins such as ceftibuten or cefpodoxime can be combined with amoxicillin/clavulanate to tackle UTIs involving ESBL producing Escherichia coli and Klebsiella spp. Clinicians who routinely prescribe amoxicillin/clavulanate in outpatient settings should be aware of potential benefits and limitations of this combination.

Oral β-Lactam Antibiotics vs Fluoroquinolones or Trimethoprim-Sulfamethoxazole for Definitive Treatment of Enterobacterales Bacteremia From a Urine Source

Importance

Oral β-lactam antibiotics are traditionally not recommended to treat Enterobacterales bacteremia because of concerns over subtherapeutic serum concentrations, but there is a lack of outcomes data, specifically after initial treatment with parenteral antibiotics. Given the limited data and increasing limitations of fluoroquinolones or trimethoprim-sulfamethoxazole (TMP-SMX), oral β-lactam antibiotics may be a valuable additional treatment option.

Objective

To compare definitive therapy with oral β-lactam antibiotics vs fluoroquinolones or TMP-SMX for Enterobacterales bacteremia from a suspected urine source.

Design, Setting, and Participants

A retrospective cohort study was conducted from January 1, 2007, to September 30, 2015, at 114 Veterans Affairs hospitals among 4089 adults with Escherichia coli, Klebsiella spp, or Proteus spp bacteremia and matching urine culture results. Additional inclusion criteria were receipt of active parenteral antibiotic(s) followed by conversion to an oral antibiotic. Exclusion criteria were previous Enterobacterales bacteremia, urologic abscess, or chronic prostatitis. Data were analyzed from April 15, 2019, to July 26, 2020.

Exposures

Conversion of therapy to an oral β-lactam antibiotic vs fluoroquinolones or TMP-SMX after 1 to 5 days of parenteral antibiotics.

Main Outcomes and Measures

The main outcome was a composite of either 30-day all-cause mortality or 30-day recurrent bacteremia. Propensity-based overlap weights were used to adjust for differences between groups. Log binomial regression models were used to estimate adjusted relative risks (aRRs) and adjusted risk differences (aRDs).

Results

Of the 4089 eligible patients (3731 men [91.2%]; median age, 71 years [interquartile range, 63-81 years]), 955 received an oral β-lactam antibiotic, and 3134 received fluoroquinolones or TMP-SMX. The primary outcome occurred for 42 patients (4.4%) who received β-lactam antibiotics and 94 patients (3.0%) who received fluoroquinolones or TMP-SMX (aRD, 0.99% [95% CI, -0.42% to 2.40%]; aRR, 1.31 [95% CI, 0.87-1.95]). Mortality rates were 3.0% (n = 29) for patients receiving β-lactam antibiotics vs 2.6% (n = 82) for those receiving fluoroquinolones or TMP-SMX (aRD, 0.06% [95% CI, -1.13% to 1.26%]; aRR, 1.02 [95% CI, 0.67-1.56]). Recurrent bacteremia rates were 1.5% (n = 14) among those receiving β-lactam antibiotics vs 0.4% (n = 12) among those receiving fluoroquinolones or TMP-SMX (aRD, 1.03% [95% CI, 0.24%-1.82%]; aRR, 3.43 [95% CI, 0.42-27.90]).

Conclusions and Relevance

In this cohort study of adults with E coli, Klebsiella spp, or Proteus spp bacteremia from a suspected urine source, the relative risk of recurrent bacteremia was not significantly higher with β-lactam antibiotics compared with fluoroquinolones or TMP-SMX, and the absolute risk and risk difference were small (ie, <3%). No significant difference in mortality was observed. Oral β-lactam antibiotics may be a reasonable step-down treatment option, primarily when alternative options are limited by resistance or adverse effects. Further study is needed because statistical power was limited owing to a low number of recurrent bacteremia events.

A Critical Review of Cephalexin and Cefadroxil for the Treatment of Acute Uncomplicated Lower Urinary Tract Infection in the Era of "Bad Bugs, Few Drugs"

First-generation oral cephalosporins (cephalexin and cefadroxil) have traditionally been considered second-line treatment options for uncomplicated lower urinary tract infections (uLUTIs).  However, in the current age of "bad bugs, few drugs", where there are increasingly limited oral options against resistant Enterobacteriaceae, there is an urgent need to rethink how best to utilize the available antibiotic armamentarium.  This review examines the historical clinical trials and experimental studies of cephalexin and cefadroxil, particularly through the modern lens of pharmacokinetics/pharmacodynamics (PK/PD), to better appreciate the efficacy of these drugs in uLUTIs.  Furthermore, newer cefazolin-cephalexin surrogate testing, as recommended by the Clinical and Laboratory Standards Institute (CLSI) and the United States Committee on Antimicrobial Susceptibility Testing (USCAST), has recategorized cephalexin in many instances from resistant to susceptible.  We conclude that cephalexin and cefadroxil have very good early bacteriological and clinical cures in uLUTIs due to non-extended-spectrum beta-lactamase-producing (ESBL) Enterobacteriaceae comparable to many traditionally first-line agents.  Cephalexin can be conveniently administered as 500 mg twice or thrice daily, similar to cefadroxil (500 mg twice daily); therefore, either agent may be used as a fluoroquinolone-sparing alternative. Cephalexin may be the more practical choice for many clinicians because reliable antimicrobial susceptibility test interpretative criteria (STIC) are provided by CLSI, USCAST, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST), whereas direct cefadroxil STIC is offered only by EUCAST.

Process Development and Synthesis of Process-Related Impurities of an Efficient Scale-Up Preparation of 5,2'-Dibromo-2,4',5'-Trihydroxy Diphenylmethanone as a New Acute Pyelonephritis Candidate Drug

Based on a foregoing gram-scale laboratory process, an efficient scale-up preparation process of 5,2'-dibromo-2,4',5'-trihydroxydiphenylmethanone (LM49-API), a new acute pyelonephritis candidate drug, was developed and validated aiming to reduce by-products and achieve better impurity profiles. Meanwhile, the polymorph of LM49-API and process-related impurities were also investigated. Ultimately, the optimal reaction conditions were verified by evaluating the impurity profiles and their formation during the synthesis. Six process-related impurities were synthesized and identified, being useful for the quality control of LM49-API. Its finalized preparation process was further validated at 329-410 g scale-up production in 53.4-57.1% overall yield with 99.95-99.98% high-performance liquid chromatography (HPLC) purity, and it is currently viable for commercial production. LM49-API-imC and LM49-API-imX were identified as the main single impurities in LM49-API, with the content controlled to be less than 0.03%.