Manuel Kussmann

Daptomycin plus Fosfomycin, a Synergistic Combination in Experimental Implant-Associated Osteomyelitis Due to Methicillin-Resistant Staphylococcus aureus in Rats

ABSTRACT The aim of this study was to evaluate the combination of daptomycin and fosfomycin in experimental chronic implant-associated osteomyelitis due to methicillin-resistant Staphylococcus aureus (MRSA). Infection was induced in the tibiae of rats by the insertion of a bacterial inoculum (1 to 5 × 108 CFU/ml) of a clinical MRSA isolate and a titanium wire. Four weeks after infection, each animal was assigned to a treatment group: daptomycin monotherapy at 60 mg/kg of body weight once daily (n = 10), fosfomycin monotherapy at 40 mg/kg once daily (n = 10), or daptomycin and fosfomycin combined at 60 mg/kg and 40 mg/kg, respectively, once daily (n = 9). Ten animals were left untreated. After a 3-week treatment period, the animals were euthanized, and the infected tibiae and implants were processed for quantitative bacterial cultures. The bacterial cultures from bones were positive for MRSA in all animals in the untreated group, the daptomycin group, and the fosfomycin group, with median bacterial counts of 2.34 × 106 CFU/g bone, 1.57 × 106 CFU/g bone, and 3.48 × 102 CFU/g bone, respectively. In the daptomycin-fosfomycin group, 6 out of 9 animals were positive for MRSA, with a median count of 7.92 CFU/g bone. Bacterial cultures derived from the titanium wires were negative in the fosfomycin- and daptomycin-fosfomycin-treated groups. Based on bacterial counts in bones, treatment with daptomycin-fosfomycin was statistically significantly superior to all that of the other groups (P ≤ 0.003). Fosfomycin was superior to daptomycin and no treatment (P < 0.0001). No development of resistance was observed in any treatment arm. The combination of daptomycin and fosfomycin demonstrated synergism against MRSA in experimental implant-associated osteomyelitis.

An Open, Randomized, Single-Center, Crossover Pharmacokinetic Study of Meropenem after Intraperitoneal and Intravenous Administration in Patients Receiving Automated Peritoneal Dialysis

ABSTRACT The objective of this study was to determine the pharmacokinetic profile of meropenem in automated peritoneal dialysis (APD) patients. In 6 patients without peritonitis, a single dose of 0.5 g of meropenem was applied intraperitoneally (i.p.) or intravenously (i.v.) and concentrations in serum and dialysate were measured at specified intervals over 24 h with high-performance liquid chromatography-mass spectrometry. The mean maximum concentrations of meropenem in serum (Cmax) were 27.2 mg/liter (standard deviation [SD], ±6.9) and 10.1 mg/liter (SD, ±2.5) and in dialysate were 3.6 mg/liter (SD, ±2.3) and 185.8 mg/liter (SD, ±18.7) after i.v. and i.p. administrations, respectively. The mean areas under the curve from 0 to 24 (AUC0–24) of meropenem in serum were 173.5 mg · h/liter (SD, ±29.7) and 141.4 mg · h/liter (SD, ±37.5) (P = 0.046) and in dialysate were 42.6 mg · h/liter (SD, ±20.0) and 623.4 mg · h/liter (SD, ±84.1) (P = 0.028) after i.v. and i.p. administrations, respectively. The ratios for dialysate exposure over plasma exposure after i.v. and i.p. treatments were 0.2 (SD, ±0.1) and 4.6 (SD, ±0.9), respectively (P = 0.031). A mean target value of 40% T>MIC (time for which the free meropenem concentration exceeds the MIC) for clinically relevant pathogens with EUCAST susceptibility breakpoints of 2 mg/liter was reached in serum after i.p. and i.v. administrations and in dialysate after i.p. but not after i.v. administration. The present data indicate that low i.p. exposure limits the i.v. use of meropenem for PD-associated peritonitis. In contrast, i.p. administration not only results in superior concentrations in dialysate but also might be used to treat systemic infections.

Influence of Different Peritoneal Dialysis Fluids on the In Vitro Activity of Cefepime, Ciprofloxacin, Ertapenem, Meropenem and Tobramycin Against Escherichia Coli

♦ Background: Peritonitis is a major problem among patients on peritoneal dialysis (PD). The influence of diverse PD fluids on the activity of frequently used antibiotics has been insufficiently investigated. Thus, the present study set out to investigate the impact of different PD fluids on the activity of cefepime, ciprofloxacin, ertapenem, meropenem, and tobramycin against Escherichia coli. ♦ Methods: Time-kill curves in 4 different PD fluids (Dianeal PDG4, Extraneal, Nutrineal PD4 and Physioneal 40, all Baxter Healthcare Corp., Deerfield, IL, USA) were performed over 24 hours with 4 different concentrations (1 × minimum inhibitory concentration [MIC], 4 × MIC, 8 × MIC, 30 × MIC) of each antibiotic evaluated and without antibiotics as control. Cation-adjusted Mueller Hinton broth (CA-MHB) was used as comparator solution. ♦ Results: In all PD fluids investigated, bacterial growth and antimicrobial activity of all antibiotics tested was significantly reduced compared with the CA-MHB comparator solution. Except at high concentrations of 30 × MIC, cefepime, ertapenem and meropenem demonstrated a strongly reduced activity in all PD fluids investigated. Ciprofloxacin and tobramycin were highly active and bactericidal in all PD fluids and demonstrated dose-dependent activity. ♦ Conclusion: The antimicrobial activity of cefepime, ertapenem and meropenem is limited or even nullified in certain PD fluids in vitro, whereas ciprofloxacin and tobramycin show excellent activity. The choice of PD fluids can impact the activity of antimicrobial agents and might influence microbiological outcome. Further studies are required to verify the clinical relevance of our findings.

Substantial diagnostic impact of blood culture independent molecular methods in bloodstream infections: Superior performance of PCR/ESI-MS

This study analyzed the performance of different molecular technologies along with blood culture (BC) in the diagnosis of bloodstream infections (BSI) in patients from internal medicine wards - including intensive care units (ICUs) - and the emergency room. Patients with systemic inflammatory response syndrome were prospectively included. BCs and EDTA whole blood were obtained simultaneously. The latter was analyzed by PCR combined with electrospray ionization mass spectrometry (PCR/ESI-MS; IRIDICA BAC BSI assay, Abbott) and by SeptiFast (Roche). Cases were classified as BSI according to adapted European Centre for Disease Prevention and Control criteria. Out of 462 analyzed episodes, 193 with valid test results fulfilled the inclusion criteria and were further evaluated. Sixty-nine (35.8%) were classified as BSI. PCR/ESI-MS showed a significantly better overall performance than BC (p = 0.004) or SeptiFast (p = 0.034). Only in patients from the ICU the performance of SeptiFast was comparable to that of PCR/ESI-MS. Mainly due to the negative effect of antimicrobial pre-treatment on BC results, the cumulative performance of each of the molecular tests with BC was significantly higher than that of BC alone (p < 0.001). SeptiFast and in particular the broad-range pathogen detection system PCR/ESI-MS proved to be an essential addition to BC-based diagnostics in BSI.

Dalbavancin for treatment of implant-related methicillin-resistant Staphylococcus aureus osteomyelitis in an experimental rat model

Dalbavancin is a new semisynthetic lipoglycopeptide with improved antimicrobial activity against various gram-positive pathogens. It demonstrates an extensive plasma half-life which permits outpatient parenteral antimicrobial therapy with weekly intervals and might therefore be an excellent treatment alternative for patients requiring prolonged antimicrobial therapy. The present study investigated dalbavancin monotherapy in an experimental implant-related methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis model. A clinical MRSA isolate and a Kirschner-wire were inserted into the proximal tibia of anaesthetized Sprague-Dawley rats. Four weeks after infection 34 animals were treated over 4 weeks with either dalbavancin (20 mg/kg loading-dose; 10 mg/kg daily), vancomycin (50 mg/kg twice daily) or left untreated. Twenty-four hours after the last treatment dose tibial bones and Kirschner-wires were harvested for microbiological examination. Based on quantitative bacterial cultures of osseous tissue, dalbavancin was as effective as vancomycin and both were superior to no treatment. No emergence of an induced glycopeptide-/lipoglycopeptide- resistance was observed after a treatment period of four weeks with either dalbavancin or vancomycin. In conclusion, monotherapy with dalbavancin was shown to be as effective as vancomycin for treatment of experimental implant-related MRSA osteomyelitis in rats, but both antimicrobials demonstrated only limited efficacy. Further studies are warranted to evaluate the clinical efficacy of dalbavancin for the treatment of periprosthetic S. aureus infections.

Compatibility of linezolid with commercial peritoneal dialysis solutions

Purpose Results of a compatibility and stability study of linezolid admixed in commercial peritoneal dialysis (PD) solutions stored at various temperatures are reported. Methods Test samples were prepared by adding linezolid i.v. injection (2 mg/mL) to infusion bags of 4 PD solutions (Extraneal, Nutrineal, Physioneal 40 Glucose 1.36%, and Physioneal 40 Glucose 2.27%, all from Baxter Healthcare Corporation). Assessments were conducted at various time points during storage of test samples at refrigeration temperature (6 °C) or room temperature (25 °C) for 14 days and at body temperature (37 °C) for 24 hours. Linezolid concentrations over time were determined by high‐performance liquid chromatography, physical compatibility was determined by pH measurement and visual inspection, and antimicrobial activity was monitored by a disk diffusion method. The influence of solution warming by heating plate on drug stability was investigated. Results Linezolid was stable in all tested solutions for 14 days at refrigeration and room temperatures and for 24 hours at body temperature. No linezolid adsorption to container material was detected. There were only minor variations in pH values, and visual inspection revealed no diluent abnormalities. With 1 exception, antimicrobial activity of >90% was retained in all PD solution samples for the duration of the study under all temperature conditions. Conclusion Linezolid injection 2 mg/mL remained stable and was compatible with the PD solutions studied for up to 2 weeks at refrigeration or room temperature and up to 24 hours at body temperature.

Compatibility of Meropenem with Different Commercial Peritoneal Dialysis Solutions

♦ Background: Intraperitoneal administration of antimicrobial agents is recommended for the treatment of peritoneal dialysis (PD)-related peritonitis. For home-based antimicrobial therapy it is common to supply patients with PD fluid bags with admixed antibiotic. Thus, the compatibility of meropenem with different PD fluids (PDFs), namely Extraneal, Physioneal 1.36% and Physioneal 2.27% (all Baxter Healthcare Corp., Deerfield, IL, USA), was investigated under varying storage conditions. ♦ Methods: Meropenem (Venus Pharma, Werne, Germany) was stored at 6°C and 25°C over 14 days and at 37°C over 24 hours. Drug concentration over time was determined using high performance liquid chromatography, drug activity by a diffusion disk method, diluent stability by visual inspection and drug adsorption was calculated. Blank PD fluids and deionized water were used as comparator solutions. ♦ Results: Compared to water, the stability of meropenem was minimally lower in Extraneal but markedly reduced in both Physioneal solutions. No significant drug adsorption was detected for any PDF investigated. ♦ Conclusions: Meropenem is stable and compatible with Extraneal and might be stored for up to a week at refrigeration temperature (6°C). A loss of ~20% of meropenem after 2 days at room temperature should be considered. Mixed Physioneal appears not suitable for storage at any temperature after meropenem has been admixed. A considerable drug degradation due to the warming up to body temperature through heating plates should further be taken into account in clinical practice.

Direct detection of Anaplasma phagocytophilum by polymerase chain reaction followed by electrospray ionization mass spectrometry from human blood

Bacterial pathogens not detectable via commercial blood culture assays represent an important challenge for infectious disease physicians, in particular if clinical symptoms of the illness are non-specific. In this report, Anaplasma phagocytophilum was detected directly in a peripheral blood sample from a febrile patient reporting a tick bite. This was done using a commercial system based on PCR followed by electrospray ionization mass spectrometry (ESI-MS). The diagnosis of a human granulocytic anaplasmosis infection was established using this diagnostic methodology for the first time. Human granulocytic anaplasmosis is a neglected zoonotic disease in Europe. Its seroprevalence is similar in North America and Europe, but in contrast to the USA, it is rarely diagnosed in the old world. PCR followed by ESI-MS is a novel, complex, but highly promising diagnostic methodology for the rapid assessment of rare or exotic pathogens, including intracellular bacteria.