Plasma and soft tissue pharmacokinetics of ceftolozane/tazobactam in healthy volunteers after single and multiple intravenous infusion: a microdialysis study.

OBJECTIVES: To investigate ceftolozane/tazobactam pharmacokinetics (PK) in plasma and interstitial space fluid (ISF) of muscle and subcutaneous tissue and establish a population PK model. METHODS: Eight healthy volunteers received four IV doses of 1000/500 mg ceftolozane/tazobactam q8h in a prospective, open-labelled PK study. ISF concentration-time profiles were determined via in vivo microdialysis up to 8 h post-dose and efficacy of unbound ceftolozane and tazobactam was estimated using the time above MIC (%ƒT>MIC) and time above threshold concentration (%T>CT), respectively. A population PK model was established by merging derived plasma and soft tissue PK data. RESULTS: Ceftolozane reached %ƒT>MIC values of 100% in plasma, muscle and subcutaneous ISF for Enterobacteriaceae and 87%, 89% and 87%, respectively, for Pseudomonas aeruginosa. Tazobactam %T>CT was 21%, 22% and 21% in plasma, muscle and subcutaneous ISF, respectively. Plasma protein binding was 6.3% for ceftolozane and 8.0% for tazobactam. Multiple-dose ceftolozane AUC0-8 ISF/plasma ratios were 0.92 ±â€Š0.17 in muscle and 0.88 ±â€Š0.18 in subcutis, and tazobactam ratios were 0.89 ±â€Š0.25 in muscle and 0.87 ±â€Š0.21 in subcutis, suggesting substantial soft tissue penetration. CONCLUSIONS: Tazobactam %T>CT values were distinctly below proposed target values, indicating that tazobactam might be underdosed in the investigated drug combination. However, ISF/unbound plasma ratios of ceftolozane and tazobactam support their use in soft tissue infections. A plasma and soft tissue PK model adds important information on the PK profile of ceftolozane/tazobactam. Further investigations in patients suffering from wound infections are needed to confirm these findings.

Colistin Reduces LPS-Triggered Inflammation in a Human Sepsis Model In Vivo: A Randomized Controlled Trial.

The previously described anti-endotoxin effect of colistin has not been investigated in humans yet. We performed a randomized, double-blind, placebo-controlled crossover trial to determine the degree of colistin-driven modulation of inflammatory response in blood of lipopolysaccharide (LPS)-challenged healthy volunteers in a human endotoxemia model. After a single intravenous dose of 2.5 million IU colistin methanesulfonate, interleukin (IL)-6, IL-8, tumor necrosis factor alpha (TNF-α), and IL-1ß concentrations as well as other biomarkers of inflammation such as C-reactive protein, differential leukocyte counts, and body temperature were measured up to 24 h postdose. Colistin significantly decreased the inflammatory cytokine response to LPS in blood of healthy volunteers. This effect was most evident for IL-6, IL-8, and TNF-α. This study is the first to confirm the anti-endotoxin effect of colistin in humans in vivo. Further studies might increase our knowledge on the interaction between colistin and the effectors of the immune system.

Differential in vivo activation of monocyte subsets during low-grade inflammation through experimental endotoxemia in humans.

Human monocytes are a heterogeneous cell population, which can be divided into a classical (CD14++CD16-), a non-classical (CD14+CD16+), and an intermediate (CD14++CD16+) subset. We hypothesized that low-grade inflammation may differentially affect monocyte subsets. We used a human lipopolysaccharide (LPS) infusion model to mimic low-grade inflammation to identify, which monocyte subsets are preferentially activated under these conditions. Monocyte subsets were identified by staining for CD14 and CD16, activation status of monocytes was analyzed by staining for CD11b and a novel in situ mRNA hybridization approach to detect IL-6 and IL-8 specific mRNA at the single-cell level by flow cytometry. After LPS challenge, cell numbers of monocyte subsets dropped after 2 h with cell numbers recovering after 6 h. Distribution of monocyte subsets was skewed dramatically towards the intermediate subset after 24 h. Furthermore, intermediate monocytes displayed the largest increase of CD11b expression after 2 h. Finally, IL-6 and IL-8 mRNA levels increased in intermediate and non-classical monocytes after 6 h whereas these mRNA levels in classical monocytes changed only marginally. In conclusion, our data indicates that the main responding subset of monocytes to standardized low-grade inflammation induced by LPS in humans is the CD14++CD16+ intermediate subset followed by the CD14+CD16+ non-classical monocyte subset. Circulating classical monocytes showed comparably less reaction to LPS challenge in vivo.

Simultaneous assessment of the pharmacokinetics of a pleuromutilin, lefamulin, in plasma, soft tissues and pulmonary epithelial lining fluid.

BACKGROUND: Lefamulin is a pleuromutilin antibiotic under evaluation for the treatment of bacterial infections, including respiratory tract infections. Currently, there are no high-quality pharmacokinetic data on drug tissue concentrations of lefamulin available. METHODS: A single dose of intravenous lefamulin (150 mg) was given to 12 healthy men. The registered EudraCT number for this study was 2010-021938-54. Lefamulin concentrations were simultaneously measured in plasma, skeletal muscle tissue, subcutaneous adipose tissue and epithelial lining fluid (ELF) over 24 h, and corresponding pharmacokinetic parameters were calculated. Microdialysis was used to measure unbound lefamulin concentrations in skeletal muscle tissue and subcutaneous adipose tissue, which were similar to unbound lefamulin concentrations in plasma. Bronchoalveolar lavage was performed 1, 2, 4 and 8 h post-dose to determine lefamulin concentrations in ELF. RESULTS: Unbound lefamulin levels showed a 5.7-fold higher exposure in ELF compared with that in plasma, demonstrating good penetration to the target site. CONCLUSIONS: Lefamulin may be an addition to the therapeutic armamentarium for the treatment of infections. Simultaneous measurements of unbound drug concentration can guide target attainment for future therapeutic trials.

Target site antimicrobial activity of colistin might be misestimated if tested in conventional growth media.

Cation-dependent inhibition of antimicrobial activity was reported for polymyxin antibiotics. Ca(2+) and Mg(2+) concentrations recommended by the Clinical and Laboratory Standards Institute (CLSI) for the supplementation of Müller-Hinton broth (MHB) are markedly lower than interstitial space fluid (ISF) concentrations in vivo. Hence, it was speculated that the antimicrobial activity of colistin might be overestimated if tested using conventional cation-adjusted MHB. The antimicrobial activity of colistin against n = 100 clinical isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae and Escherichia coli (n = 25 each) was evaluated by broth microdilution and, for selected isolates, by time-kill curves, in MHB without cations (MHB(ONLY)), MHB supplemented with 25 mg/L Ca(2+) and 12.5 mg/L Mg(2+) according to CLSI recommendations (MHB(CLSI)), and in MHB adjusted to 50 mg/L Ca(2+) and 20 mg/L Mg(2+) simulating ISF concentrations (MHB(ISF)). The minimum inhibitory concentration (MIC) values of colistin against the vast majority of isolates of both P. aeruginosa and A. baumannii increased significantly with higher cation concentrations. The susceptibility of K. pneumoniae isolates to colistin did not show significant changes between cation-supplemented media, while the MICs of E. coli decreased with ascending cation concentrations. These findings were confirmed in time-kill studies, where colistin killing against P. aeruginosa 1514 and A. baumannii 1485 declined with increasing cation concentrations. Contrarily, the killing of selected concentrations of colistin against K. pneumoniae 15 and E. coli 16 was enhanced in the presence of increasing cation concentrations. The present data suggest that the clinical antimicrobial activity of colistin might be misestimated in vitro if tested in conventional growth media.

Blood, tissue, and intracellular concentrations of azithromycin during and after end of therapy.

Although azithromycin is extensively used in the treatment of respiratory tract infections as well as skin and skin-related infections, pharmacokinetics of azithromycin in extracellular space fluid of soft tissues, i.e., one of its therapeutic target sites, are not yet fully elucidated. In this study, azithromycin concentration-time profiles in extracellular space of muscle and subcutaneous adipose tissue, but also in plasma and white blood cells, were determined at days 1 and 3 of treatment as well as 2 and 7 days after the end of treatment. Of all compartments, azithromycin concentrations were highest in white blood cells, attesting for intracellular accumulation. However, azithromycin concentrations in both soft tissues were markedly lower than in plasma both during and after treatment. Calculation of the area under the concentration-time curve from 0 to 24 h (AUC(0-24))/MIC(90) ratios for selected pathogens suggests that azithromycin concentrations measured in the present study are subinhibitory at all time points in both soft tissues and at the large majority of observed time points in plasma. Hence, it might be speculated that azithromycin's clinical efficacy relies not only on elevated intracellular concentrations but possibly also on its known pleotropic effects, including immunomodulation and influence on bacterial virulence factors. However, prolonged subinhibitory azithromycin concentrations at the target site, as observed in the present study, might favor the emergence of bacterial resistance and should therefore be considered with concern. In conclusion, this study has added important information to the pharmacokinetic profile of the widely used antibiotic drug azithromycin and evidentiates the need for further research on its potential for induction of bacterial resistance.

Blood, tissue, and intracellular concentrations of erythromycin and its metabolite anhydroerythromycin during and after therapy.

For macrolides, clinical activity but also the development of bacterial resistance has been attributed to prolonged therapeutic and subtherapeutic concentrations. Although erythromycin is a long-established antimicrobial, concomitant determination of the pharmacokinetics of erythromycin and its metabolites in different compartments is limited. To better characterize the pharmacokinetics of erythromycin and its anhydrometabolite (anhydroerythromycin [AHE]) in different compartments during and after the end of treatment with 500 mg of erythromycin four times daily, concentration-time profiles were determined in plasma, interstitial space of muscle and subcutaneous adipose tissue, and white blood cells (WBCs) at days 1 and 3 of treatment and 2 and 7 days after end of therapy. In WBCs, concentrations of erythromycin exceeded those in plasma approximately 40-fold, while free concentrations in plasma and tissue were comparable. The observed delay of peak concentrations in tissue might be caused by fast initial cellular uptake. Two days after the end of treatment, subinhibitory concentrations were observed in plasma and interstitial space of both soft tissues, while 7 days after the end of treatment, erythromycin was not detectable in any compartment. This relatively short period of subinhibitory concentrations may be advantageous compared to other macrolides. The ratio of erythromycin over AHE on day 1 was highest in plasma (2.81 ± 3.45) and lowest in WBCs (0.27 ± 0.22). While the ratio remained constant between single dose and steady state, after the end of treatment the concentration of AHE declined more slowly than that of the parent compound, indicating the importance of the metabolite for the prolonged drug interaction of erythromycin.

Pgp-mediated interaction between (R)-[11C]verapamil and tariquidar at the human blood-brain barrier: a comparison with rat data.

Using positron emission tomography (PET) imaging we assessed, in vivo, the interaction between a microdose of (R)-[(11)C]verapamil (a P-glycoprotein (Pgp) substrate) and escalating doses of the Pgp inhibitor tariquidar (3, 4, 6, and 8 mg/kg) at the blood-brain barrier (BBB) in healthy human subjects. We compared the dose-response relationship of tariquidar in humans with data obtained in rats using a similar methodology. Tariquidar was equipotent in humans and rats in its effect of increasing (R)-[(11)C]verapamil brain uptake (expressed as whole-brain volume of distribution (V(T))), with very similar half-maximum-effect concentrations. Both in humans and in rats, brain V(T) approached plateau levels at plasma tariquidar concentrations >1,000 ng/ml. However, Pgp inhibition in humans led to only a 2.7-fold increase in brain V(T) relative to baseline scans (before administration of tariquidar) as compared with 11.0-fold in rats. The results of this translational study add to the accumulating evidence that there are marked species-dependent differences in Pgp expression and functionality at the BBB.

Antimicrobial effect of statins: organic solvents might falsify microbiological testing results.

OBJECTIVES: Statins possess a variety of pleiotropic effects. Direct antimicrobial effect of simvastatin and, to a smaller degree, fluvastatin, has been reported for Gram-positive bacteria. The present study investigated antimicrobial activity of all statins available on the European market on Gram-positive and -negative organisms, with particular attention on the possible impact of organic solvents on bacterial growth. METHODS: Simvastatin was dissolved both in 100% methanol (simvastatin 100%) and in 5% methanol (simvastatin 5%), the latter solution requiring pH adjustment for solubility reasons. Antimicrobial activity of both simvastatin solutions and of five other statins was evaluated against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 by broth microdilution testing. In addition, time-kill curves of methanol alone, simvastatin 100% and simvastatin 5% were performed for S. aureus ATCC 29213. RESULTS: Relevant antimicrobial activity was observed only for simvastatin 100% when tested against S. aureus (MIC = 31 mg/l). MIC of simvastatin 5% was more than 10-fold higher (500 mg/l). In analogy, time-kill rates of simvastatin against S. aureus decreased markedly when the methanol content in the test solutions was reduced. In both experimental settings, antimicrobial activity observed for pure methanol was only slightly inferior to that of simvastatin 100%. CONCLUSION: Previously published results about the antimicrobial effect of statins relied on the use of pure methanol as solvent. Present data indicate that the observed antimicrobial effect must be attributed, at least to a very large extent, to the solvent. Toxicity of solvents may influence microbiological evaluation of poorly water-soluble substances. pH adjustment to enhance solubility and thus reduce the need for using organic solvent might sometimes overcome this problem.

The third-generation P-glycoprotein inhibitor tariquidar may overcome bacterial multidrug resistance by increasing intracellular drug concentration.

OBJECTIVES: The use of efflux pump inhibitors may be a powerful strategy to overcome transporter-mediated bacterial multidrug resistance. In the present study, we set out to investigate the potency of tariquidar, a third-generation P-glycoprotein inhibitor in clinical development, for overcoming bacterial resistance towards ciprofloxacin. METHODS: Staphylococcus aureus 29213 (SA29213) and S. aureus 1199B (SA1199B), which overexpresses the multidrug transporter NorA, as well as Pseudomonas aeruginosa 27853 and Stenotrophomonas maltophilia BAA-85, which expresses SmeDEF, were exposed to ciprofloxacin in the presence and absence of tariquidar or, for comparative reasons, elacridar. Activity of both P-glycoprotein inhibitors was evaluated by determination of MICs and time-kill curves, and by quantification of uptake of ciprofloxacin into bacterial cells. RESULTS: Activity of tariquidar and elacridar was comparable for S. aureus strains, and both dose-dependently increased susceptibility towards ciprofloxacin. Highest effects were observed for SA1199B, where the addition of tariquidar resulted in a 10-fold reduction of the ciprofloxacin MIC, while no effect was observed for P. aeruginosa. For S. maltophilia, elacridar but not tariquidar improved susceptibility. Uptake of [14C]ciprofloxacin and modification of susceptibility showed significant correlations (r=0.89, P<0.0001). Tariquidar had no intrinsic activity against any strain tested. CONCLUSIONS: We conclude that tariquidar has potent inhibitory effect against certain bacterial efflux pumps in vitro. Their high activity at clinically achievable concentrations might yield this class of drugs promising for future applications in infectious diseases.