Apostolos Georgopoulos

Application of microdialysis to clinical pharmacokinetics in humans

Measurement of drug concentrations in tissues would be useful for clinical pharmacokinetic studies, but appropriate experimental methods are not available at present. The aim of this study was to assess the scope and limitations of the microdialysis technique for human tissue pharmacokinetic studies.

Distribution and Antimicrobial Activity of Fosfomycin in the Interstitial Fluid of Human Soft Tissues

ABSTRACT Fosfomycin is a broad-spectrum antibiotic which is established as therapy for uncomplicated lower urinary tract infections. In addition, preliminary data indicate that fosfomycin has a potential role in the treatment of soft tissue infections. However, the use of fosfomycin has not been established for this condition, and it is unclear whether the level of fosfomycin penetration into human soft tissues is high enough to eradicate relevant pathogens. To better characterize the antibiotic potential of fosfomycin, we applied a combined in vivo pharmacokinetic-in vitro pharmacodynamic model to human volunteers. For this purpose fosfomycin concentrations in vivo in the fluid of the interstitial space of human soft tissues were measured by microdialysis following intravenous infusion of 4 or 8 g of fosfomycin (n = 6). Subsequently, bacterial isolates with relevance for soft tissue infections were exposed to concentrations according to the in vivo pharmacokinetic profile in the interstitial space fluid obtained by microdialysis. Our experiments indicated a high degree of soft tissue penetration for fosfomycin, with ratios of the area under the concentration-time curve from 0 to 8 h for muscle (AUC0–8muscle)/AUC0–8serumof 0.48 ± 0.08 and 0.53 ± 0.04 and ratios of AUC0–8adipose tissue/AUC0–8serum of 0.74 ± 0.12 and 0.71 ± 0.11 following administration of 4 and 8 g, respectively. In corresponding in vitro simulation experiments with selected isolates of Staphylococcus aureus,Enterobacter cloacae, and Serratia marcescensfor which MICs were 16 μg/ml, organisms were undetectable after a single dosing interval. Fosfomycin exhibits a strong ability to penetrate into the fluid of the interstitial space of soft tissues and reaches levels sufficient to substantially inhibit the growth of relevant bacteria at the target site. We therefore conclude that fosfomycin might qualify as an alternative candidate for the therapy of soft tissue infections.

In vitro activity of naftifine, a new antifungal agent.

Naftifine exhibits an interesting in vitro spectrum of activity against dermatophytes (38 strains; minimal inhibitory concentration [MIC] range 0.1 to 0.2 microgram/ml), aspergilli (6 strains; MIC range, 0.8 to 12.5 microgram/ml), Sporothrix schenckii (2 strains; MICs, 0.8 and 1.5 microgram/ml), and yeasts of the genus Candida (77 strains; MIC range, 1.5 to greater than 100 microgram/ml). Its degree of efficacy is unaffected by the organism density in the test medium, and it is primarily fungicidal against dermatophytes as well as yeasts. Its in vitro efficacy is pH dependent and rises with increasing pH values.

Antimicrobial Activities of 81.723 hfu, a New Pleuromutilin Derivative

The new pleuromutilin derivative 81.723 hfu is extremely active against gram-positive organisms such as streptococci, staphylococci, and against mycoplasmas. A number of Shigella, Klebsiella, and Escherichia coli strains were also found to be quite susceptible to this new agent, whereas other gram-negative organisms like Pseudomonas aeruginosa, Proteus species, and Alcaligenes faecalis proved to be naturally resistant to 81.723 hfu. The new compound acts bacteriostatically. Bactericidal effects have been observed only at concentrations which are 100-fold higher than the minimal inhibitory concentrations. The new antibiotic is well tolerated in all animal species tested so far and has been successfully used in the treatment of experimental infections with gram-positive organisms and with mycoplasmas in mice and rats. Resistance against this new compound arose gradually in all microorganisms investigated. It is noteworthy that the rate at which resistance against 81.723 hfu emerged in mycoplasmas (Mycoplasma gallisepticum and Mycoplasma hyorhinis) was significantly slower than the corresponding rate at which resistance against tylosin tartrate appeared. Mycoplasma strains which became insensitive to 81.723 hfu were also resistant to tylosin tartrate, whereas mycoplasmas which developed resistance against tylosin tartrate, although less sensitive to 81.723 hfu than wild-type strains, were still eliminated by this drug. In a strain of Klebsiella pneumoniae, complete cross-resistance was observed between the pleuromutilin derivative on one hand and lincomycin and erythromycin on the other. Modest degrees of cross-resistance were also observed with chloramphenicol. However, it appears unlikely that the latter phenomenon is sufficiently pronounced to affect treatment with either antibiotic.

Pharmacokinetics and Pharmacodynamics of Cefpirome in Subcutaneous Adipose Tissue of Septic Patients

ABSTRACT The objective of the present study was to evaluate whether cefpirome, a member of the latest class of broad-spectrum cephalosporins, sufficiently penetrates subcutaneous adipose tissue in septic patients. After the administration of the drug at 2 g, tissue cefpirome concentrations in septic patients (n = 11) and healthy controls (n = 7) were determined over a period of 4 h by means of microdialysis. To assess the antibacterial effect of cefpirome at the target site, the measured pharmacokinetic profiles were simulated in vitro with select strains of Staphylococcus aureus and Pseudomonas aeruginosa. The tissue penetration of cefpirome was significantly impaired in septic patients compared with that in healthy subjects. For subcutaneous adipose tissue, the area under the concentration-versus-time curve values from 0 to 240 min were 13.11 ± 5.20 g · min/liter in healthy subjects and 6.90 ± 2.56 g · min/liter in septic patients (P < 0.05). Effective bacterial growth inhibition was observed in all in vitro simulations. This was attributed to the significantly prolonged half-life in tissue (P < 0.05), which kept the tissue cefpirome levels above the MICs for relevant pathogens for extended periods in the septic group. By consideration of a dosing interval of 8 h, the values for the time above MIC (T > MIC) in tissue were greater than 60% for pathogens for which the MIC was ≤4 mg/liter in all septic patients. The present data indicate that cefpirome is an appropriate agent for the treatment of soft tissue infections in septic patients. However, due to the high interindividual variability of the pharmacokinetics of cefpirome in tissue, dosing intervals of not more than 8 h should be preferred to ensure that susceptible bacterial strains are killed in each patient.

Relevance of Soft-Tissue Penetration by Levofloxacin for Target Site Bacterial Killing in Patients with Sepsis

ABSTRACT Antimicrobial therapy of soft tissue infections in patients with sepsis sometimes lacks efficiency, despite the documented susceptibility of the causative pathogen to the administered antibiotic. In this context, impaired equilibration between the antibiotic concentrations in plasma and those in tissues in critically ill patients has been discussed. To characterize the impact of tissue penetration of anti-infective agents on antimicrobial killing, we used microdialysis to measure the concentration-versus-time profiles of levofloxacin in the interstitial space fluid of skeletal muscle in patients with sepsis. Subsequently, we applied an established dynamic in vivo pharmacokinetic-in vitro pharmacodynamic approach to simulate bacterial killing at the site of infection. The population mean areas under the concentration-time curves (AUCs) for levofloxacin showed that levofloxacin excellently penetrates soft tissues, as indicated by the ratio of the AUC from time zero to 8 h (AUC0-8) for muscle tissue (AUC0-8 muscle) to the AUC0-8 for free drug in plasma (AUC0-8 plasma free) (AUC0-8 muscle/AUC0-8 plasma free ratio) of 0.85. The individual values of tissue penetration and maximum concentration (Cmax) in muscle tissue were highly variable. No difference in bacterial killing of a select Staphylococcus aureus strain for which the MIC was 0.5 μg/ml was found between individuals after exposure to dynamically changing concentrations of levofloxacin in plasma and tissue in vitro. In contrast, the decrease in the bacterial counts of Pseudomonas aeruginosa (MIC = 2 μg/ml) varied extensively when the bacteria were exposed to levofloxacin at the concentrations determined from the individual concentration-versus-time profiles obtained in skeletal muscle. The extent of bacterial killing could be predicted by calculating individual Cmax/MIC and AUC0-8 muscle/AUC0-8 plasma free ratios (R = 0.96 and 0.93, respectively). We have therefore shown in the present study that individual differences in the tissue penetration of levofloxacin may markedly affect target site killing of bacteria for which MICs are close to 2 μg/ml.

Morphologic changes correlating to different sensitivities of Escherichia coli and enterococcus faecalis to Nd:YAG laser irradiation through dentin.

Previous studies demonstrated the disinfecting potential of Nd:YAG laser irradiation on the root canal system from an overall quantitative viewpoint. The aim of this study was to evaluate the specific effect of irradiation through dentin on gram‐negative and gram‐positive bacteria with regard to their cell structure.

Pharmacokinetics of Intravenous Linezolid in Cerebrospinal Fluid and Plasma in Neurointensive Care Patients with Staphylococcal Ventriculitis Associated with External Ventricular Drains

ABSTRACT The pharmacokinetic profile of linezolid in cerebrospinal fluid (CSF) in five neurointensive care patients with staphylococcal ventriculitis was studied. The mean area under concentration-time curve (± standard deviation) was 63 ± 18.9 mg · h/liter, with a CSF-to-plasma ratio of 0.8 ± 0.3. Times above MIC in CSF were 99.8% and 57.2% for pathogens with MICs of 2 mg/liter and 4 mg/liter, respectively.

Polymorphic Membrane Protein (PMP) 20 and PMP 21 of Chlamydia pneumoniae Induce Proinflammatory Mediators in Human Endothelial Cells In Vitro by Activation of the Nuclear Factor-κB Pathway

We tested whether polymorphic membrane proteins (PMPs) of Chlamydia pneumoniae might play a role in triggering an inflammatory response in human endothelial cells. Of 15 purified, recombinant chlamydial PMPs tested, 2 (PMP 20 and PMP 21) dose-dependently increased the production of the inflammatory mediators interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1), in cultured human endothelial cells; production of IL-8 was also increased. When endothelial cells were infected by live C. pneumoniae, an increase in the production of IL-6, IL-8, and MCP-1 was seen. We used adenovirus-induced overexpression of IkappaBalpha-an inhibitor of nuclear factor (NF)-kappaB-to demonstrate that PMP 20 and PMP 21 increase the production of IL-6 and MCP-1 in human endothelial cells by activation of the NF-kappaB pathway, because, in cells overexpressing IkappaBalpha, treatment with the respective PMP did not result in increased production of IL-6 and MCP-1. Thus, C. pneumoniae could, by interactions of its PMPs with the endothelium, contribute to the process of vascular injury during the development and progression of atherosclerotic lesions.

In vivo antimycotic activity of naftifine.

Naftifine, a new antifungal agent belonging chemically to the allylamines, was tested for its in vivo activity after topical application against guinea pig skin infections caused by Trichophyton mentagrophytes, T. mentagrophytes var. quinckeanum, or Microsporum racemosum. Compared with standard compounds, naftifine proved to be highly effective mycologically and clinically after topical application in the above models.