Axel Dalhoff

Effects of Amoxicillin, Gentamicin, and Moxifloxacin on the Hemolytic Activity of Staphylococcus aureus In Vitro and In Vivo

ABSTRACT In Staphylococcus aureus infection hemolysis caused by the extracellular protein α-toxin encoded by hla is thought to contribute significantly to its multifactorial virulence. In vitro, subinhibitory concentrations of β-lactam antibiotics and fluoroquinolones increase the levels of hla and α-toxin expression, whereas aminoglycosides decrease the levels ofhla and α-toxin expression. In the present study we investigated the effects of subinhibitory concentrations of amoxicillin, gentamicin, and moxifloxacin on hla and α-toxin expression and total hemolysis of S. aureusstrain 8325-4, a high-level α-toxin producer, and its α-toxin-negative mutant, DU 1090, in vitro and in a rat model of chronic S. aureus infection. The levels of expression ofhla and α-toxin and total hemolysis did not differ significantly when amoxicillin, gentamicin, or moxifloxacin was added to cultures of S. aureus strain 8325-4. In vivo, strain 8325-4 induced a significantly increased level of hemolysis in infected pouches compared to that in uninfected control pouches, but the hemolysis was reduced to control levels by treatment with doses of amoxicillin, gentamicin, or moxifloxacin that reduced bacterial numbers by 2 orders of magnitude. Additionally, the effects of subinhibitory concentrations of the three antibiotics on total hemolysis of four methicillin-resistant S. aureus and three methicillin-sensitive S. aureus (MSSA) clinical isolates were assessed in vitro. A significant increase in total hemolysis was observed for only one MSSA strain when it was treated with amoxicillin but not when it was treated with moxifloxacin or gentamicin. When purified α-toxin was incubated with purified human neutrophil elastase, α-toxin was cleaved nearly completely. The results suggest that the penicillin-induced increases in S. aureusα-toxin expression are strain dependent, that reduction of bacterial numbers in vivo counteracts this phenomenon effectively, and finally, that in localized S. aureus infections α-toxin activity is controlled by neutrophil elastase.

In vitro activities of quinolones

Quinolones were first introduced to clinical use in the early 1960s [1]; nalidixic acid was the first quinolone used on a large scale, but its use was limited firstly by its pharmacokinetics, as nalidixic acid achieves good urinary tract levels but only low serum concentrations, and secondly by the rapid development of resistance against nalidixic acid resulting in clinical failures. With the introduction of a 6-fluorine and a 7-piperazine substituent into the quinolone ring, norfloxacin, the first of an ever growing number of fluoroquinolones, was synthesised and used clinically [2].

Moxifloxacin and Azithromycin but not Amoxicillin Protect Human Respiratory Epithelial Cells against Streptococcus pneumoniae In Vitro when Administered up to 6 Hours after Challenge

ABSTRACT We determined the protective effect of moxifloxacin, azithromycin, and amoxicillin against Streptococcus pneumoniae infection of respiratory cells. Moxifloxacin and azithromycin effectively killed intracellular S. pneumoniae strains and protected respiratory epithelial cells significantly even when given 6 h after S. pneumoniae challenge. Amoxicillin was less effective.

Pharmacodynamics of Finafloxacin, Ciprofloxacin, and Levofloxacin in Serum and Urine against TEM- and SHV-Type Extended-Spectrum-β-Lactamase-Producing Enterobacteriaceae Isolates from Patients with Urinary Tract Infections

ABSTRACT The pharmacodynamics of finafloxacin, ciprofloxacin, and levofloxacin against extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae isolates were compared. Since quinolones lose activity in acidic media, and particularly in urine, their activities were tested in parallel under conventional conditions and in acidic artificial urine. For this purpose, TEM- and SHV-type ESBL-producing Escherichia coli and Klebsiella pneumoniae strains and their wild-type counterparts were exposed in a modified Grasso model to simulated concentrations of drugs in serum and urine following oral doses of either finafloxacin at 800 mg once a day (q.d.), immediate-release ciprofloxacin at 500 mg twice a day (b.i.d.), extended-release ciprofloxacin at 1,000 mg q.d., or levofloxacin at 500 or 750 mg q.d. The concentrations of the drugs in urine were fitted by compartmental modeling. Bacteria were cultivated in Mueller-Hinton broth (MHB) at pH 7.2 or 5.8 or in artificial urine at pH 5.8. Bacteria were counted every 2 h until 10 h and at 24 h; the areas under the bacterial-count–versus–time curves were calculated. It was found that finafloxacin eliminated all strains within 2 h under all the conditions studied. At all doses studied, ciprofloxacin and levofloxacin were highly active against wild-type strains in MHB at pH 7.2 but lost activity in MHB, and particularly in urine, at pH 5.8. Viable counts of ESBL producers were reduced for 6 to 8 h by 3 log10 titers, but the bacteria regrew thereafter. Ciprofloxacin and levofloxacin were almost inactive against the SHV producer grown in artificial urine. We conclude that pharmacodynamic models using artificial urine may mirror the physiology of urinary tract infections more closely than those using conventional media. In contrast to ciprofloxacin and levofloxacin, finafloxacin gained activity in this model at an acidic pH, maintained activity in artificial urine, and was active against TEM and SHV producers.

Activity of Moxifloxacin, Imipenem, and Ertapenem against Escherichia coli, Enterobacter cloacae, Enterococcus faecalis, and Bacteroides fragilis in Monocultures and Mixed Cultures in an In Vitro Pharmacokinetic/Pharmacodynamic Model Simulating Concentrations in the Human Pancreas

ABSTRACT The activities of moxifloxacin, imipenem, and ertapenem against pathogens causing severe necrotizing pancreatitis were studied in an in vitro pharmacokinetics/pharmacodynamics (PK/PD) model. Escherichia coli, Enterobacter cloacae, Enterococcus faecalis, and Bacteroides fragilis were exposed in monocultures and mixed cultures to concentrations of the three agents comparable to those in the human pancreas. Moxifloxacin was more active than the two carbapenems in monocultures and mixed cultures, reducing the numbers of CFU more drastically and more rapidly.

Population Pharmacokinetics of Finafloxacin in Healthy Volunteers and Patients with Complicated Urinary Tract Infections

ABSTRACT Finafloxacin is a novel fluoroquinolone with increased antibacterial activity at acidic pH and reduced susceptibility to several resistance mechanisms. A phase II study revealed a good efficacy/safety profile in patients with complicated urinary tract infections (cUTIs), while the pharmacokinetics was characterized by highly variable concentration-versus-time profiles, suggesting the need for an elaborated pharmacokinetic model. Data from three clinical trials were evaluated: 127 healthy volunteers were dosed orally (n = 77) or intravenously (n = 50), and 139 patients with cUTI received finafloxacin intravenously. Plasma (2,824 samples from volunteers and 414 samples from patients) and urine (496 samples from volunteers and 135 samples patients) concentrations were quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). NONMEM was used to build a population pharmacokinetic model, and pharmacokinetic/pharmacodynamic relationships were investigated via simulations and logistic regression. A two-compartment model with first-order elimination described the data best (central volume of distribution [Vc] and peripheral volume of distribution [Vp] of 47 liters [20%] and 43 liters [67%], respectively, and elimination clearance and intercompartmental clearance of 21 liters/h [54%] and 2.8 liters/h [57%], respectively [median bootstrap estimates {coefficients of variation}]). Vc increased with body surface area, and clearance was reduced in patients (−29%). Oral absorption was described best by parallel first- and zero-order processes (bioavailability of 75%). No pharmacodynamic surrogate parameter of clinical/microbiological outcome could be identified, which depended exclusively on the MIC of the causative pathogens. Despite the interindividual variability, the present data set does not support covariate-based dose adjustments. Based on the favorable safety and efficacy data, the clinical relevance of the observed variability appears to be limited. (This study has been registered at ClinicalTrials.gov under identifier NCT01928433.)

Does the use of antifungal agents in agriculture and in food foster polyene-resistance development? A reason for concern.

Environmental fungicides are used in agriculture to reduce fungal spoilage of crops to a minimum, and the polyene macrolide natamycin is used as a food preservative. The use of natamycin in yoghurt has recently been authorised in the USA and some other countries. However, resistance development is a serious risk associated with the use of antimicrobials as food additives and environmental fungicides. Cross-resistance between agricultural and medical azoles and between azoles and amphotericin B (AMB) not being used in agriculture has been demonstrated in clinical and environmental isolates. Polyene resistance can be elicited in vitro by the use of subinhibitory polyene concentrations and a large number of transfers. This condition may mirror the exposure of faecal Candida spp. to natamycin following consumption of natamycin-containing food. A large number of environmental and clinical isolates are resistant to AMB, and strong evidence linking farm antibiotic use and multidrug resistance, including AMB resistance, in human infections has been provided. In contrast to the acquisition of resistant environmental strains, consumption of natamycin-containing food may expose the gastrointestinal fungal flora directly to resistance selective pressure. So far, whether natamycin itself may cause the emergence of polyene resistance in gastrointestinal fungal flora and/or may act as an AMB resistance selector is probable but speculative. Use of any anti-infective agent as a food preservative should be limited to an absolute minimum as the clinical efficacy of anti-infectives used to treat serious life-threatening infections has to be preserved.