High-Dosage Fosfomycin Results in Adequate Plasma and Target-Site Exposure in Morbidly Obese and Nonobese Nonhyperfiltration Patients

Development and validation of an LC-MS/MS assay for quantification of fosfomycin in Mueller-Hinton broth for application in profiling antibacterial efficacy against clinical bacterial isolates

Multidrug-resistant (MDR) bacterial infections pose a global public health threat, intensified by the declining efficacy of commonly used antibiotics. The reassessment of neglected antibiotics, such as fosfomycin (FOS), presents a promising strategy against MDR infections. Investigations in in vitro infection models (IVIMs) generate crucial knowledge for treatment optimisation. However, reliable bioanalytical assays for quantification of FOS in Mueller-Hinton broth (MHB), a standard bacterial growth medium used for IVIM experiments, are essential. Therefore, an LC-MS/MS assay for quantification of FOS in MHB was developed and validated according to criteria of the EMA guideline on bioanalytical method validation. The calibration range of 10-2000 mg/L FOS (in original samples; corresponding to 0.04-8 mg/L after sample preparation) covered clinically relevant concentrations. The assay employed a simple and rapid sample preparation consisting of a precipitation and dilution step. Within-run mean accuracy ranging from 91.3 %-108 % and within-run precision with a maximum coefficient of variation of 11.7 % were acceptable across all concentration levels (n = 126). The assay was successfully applied to samples from IVIM experiments using a clinical Escherichia coli isolate. Additionally, thermal stability of FOS in MHB was confirmed under relevant conditions (24 h at 37 °C and 15 min at 50 °C). Overall, the developed assay is best suitable for application in IVIM set-ups, which are a prerequisite for the reassessment of FOS as a promising antibiotic combination treatment option for MDR infections.

Updated antimicrobial dosing recommendations for obese patients

The prevalence of obesity has increased considerably in the last few decades. Pathophysiological changes in obese patients lead to pharmacokinetic (PK) and pharmacodynamic (PD) alterations that can condition the correct exposure to antimicrobials if standard dosages are used. Inadequate dosing in obese patients can lead to toxicity or therapeutic failure. In recent years, additional antimicrobial PK/PD data, extended infusion strategies, and studies in critically ill patients have made it possible to obtain data to provide a better dosage in obese patients. Despite this, it is usually difficult to find information on drug dosing in this population, which is sometimes contradictory. This is a comprehensive review of the dosing of different types of antimicrobials (antibiotics, antifungals, antivirals, and antituberculosis drugs) in obese patients, where the literature on PK and possible dosing strategies in obese adults was critically assessed.

Parenteral Fosfomycin in Gastrointestinal Surgery: A Systematic Review

BACKGROUND

To investigate if perioperative parenteral administration of fosfomycin given before or during gastrointestinal surgery could protect against postoperative infectious complications and characterise the administration of fosfomycin and its harms.

METHODS

This systematic review included original studies on gastrointestinal surgery where parental administration of fosfomycin was given before or during surgery to≥5 patients. We searched three databases on March 24 2023 and registered the protocol before data extraction (CRD42020201268). Risk of bias was assessed with Cochrane Handbook risk of bias assessment tool or the Newcastle-Ottawa Scale. A narrative description was undertaken. For infectious complications, results from emergency and elective surgery were presented separately.

RESULTS

We included 15 unique studies, reporting on 1,029 patients that received fosfomycin before or during gastrointestinal surgery. Almost half of the studies were conducted in the 1980s to early 1990s, and typically a dose of 4 g fosfomycin was given before surgery co-administered with metronidazole and often repeated postoperatively. The risk of bias across studies was moderate to high. The rates of infectious complications were low after fosfomycin; the surgical site infection rate was 0-1% in emergency surgery and 0-10% in elective surgery. If reported, harms were few and mild and typically related to the gastrointestinal system.

CONCLUSION

There were few postoperative infectious complications after perioperative parenteral administration of one or more doses of 4 g fosfomycin supplemented with metronidazole in various gastrointestinal procedures. Fosfomycin was associated with few and mild harms.

Population pharmacokinetics and pharmacodynamics of cefazolin using total and unbound serum concentrations in patients with high body weight

The objective of this study was to evaluate the steady state pharmacokinetics and pharmacodynamics of cefazolin in patients with a high body weight. Cefazolin was administered by 0.5-h infusions to 11 patients with total body weight (TBW) ≥120 kg receiving 3 g q8h, and 12 patients with TBW <120 kg receiving 2 g q8h. Total and unbound serum concentration-time data obtained from serial blood samples were analysed simultaneously by population pharmacokinetic modelling using NONMEM. Probability of target attainment (PTA) was calculated for various dosing regimens through Monte Carlo simulations based on the cumulative percentage of the dosing interval that the unbound concentration exceeds the minimum inhibitory concentration (MIC) value for the pathogen at steady state (fT_MIC) ≥40%, ≥60% and 100%. A two-compartment model with non-linear protein binding and allometric scaling of the central volume of distribution using TBW best characterized both total and unbound concentration-time data. Unbound clearance was significantly associated with creatinine clearance, and maximum protein binding constant was significantly associated with serum albumin concentration and body mass index (P <0.05). Based on unbound concentration-time profiles, all simulated regimens achieved PTA >90% at MIC values ≤2 mg/L using fT_MIC ≥40%, at MIC values ≤1 mg/L using fT_MIC ≥60%, and at MIC values ≤0.5 mg/L using fT_MIC of 100%. At fT_MIC ≥60%, 0.5-h infusion of cefazolin 1 g q8h achieved PTA <90% at MIC values ≥2 mg/L in patients with TBW≥120 kg; however, prolonged-infusion and higher-dose regimens improved PTA to >90%. Overall, cefazolin pharmacokinetics are altered considerably in obese patients. Higher-dose and/or prolonged-infusion cefazolin regimens should be considered in patients with TBW ≥120 kg, particularly those with less-susceptible Gram-negative infections.