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Rabbits are frequently used for the examination of the pharmacokinetics and effectiveness of antibiotic substances. However, antibiotics vary substantially in protein binding affecting the concentration of the antimicrobially effective unbound drug. We hypothesized that the binding properties of vancomycin, meropenem and ceftriaxone might vary between human and rabbit plasma. In an in-vitro study we observed dose dependent variability in protein binding of antibiotics between species. Thus, in-vitro-pre-studies are required to guarantee for translational conditions.

There is evidence that Staphylococcus aureus colonisation is linked to severity of atopic dermatitis. As no gold standard for S. aureus sampling on atopic dermatitis skin lesions exists, this study compared three commonly used methods. In addition, effectiveness of standard skin disinfection to remove S. aureus colonisation from these inflamed skin lesions was investigated. In 30 atopic dermatitis patients, three different S. aureus sampling methods, i.e. detergent scrubbing, moist swabbing and tape stripping, were performed on naïve and disinfected skin lesions. Two different S. aureus selective media, mannitol salt agar and chromID agar, were used for bacterial growing. Quantifying the S. aureus load varied significantly between the different sampling methods on naïve skin lesions ranging from mean 51 to 1.5 × 104 CFU/cm2 (p p S. aureus load (p S. aureus selection agar plates to implement further clinical studies for the effectiveness of topical anti-staphylococcal antibiotics. Other disinfection regimes should be considered in atopic dermatitis patients when complete de-colonisation of certain skin areas is required, e.g. for surgical procedures.

Background and Objective In microdose studies, drug pharmacokinetics is measured in humans after administration of subtherapeutic doses. While previous microdose studies focused primarily on plasma pharmacokinetics, we set out to evaluate the feasibility of microdosing for a pharmacokinetic assessment in subcutaneous tissue and epithelial lining fluid. Methods Healthy subjects received a single intravenous bolus injection of a microdose of [14C]ciprofloxacin (1.1 µg, 7 kBq) with (cohort A, n = 9) or without (cohort B, n = 9) a prior intravenous infusion of a therapeutic dose of unlabeled ciprofloxacin (400 mg). Microdialysis and bronchoalveolar lavage were applied for determination of subcutaneous and intrapulmonary drug concentrations. Microdose [14C]ciprofloxacin was quantified by accelerator mass spectrometry and therapeutic-dose ciprofloxacin by liquid chromatography–tandem mass spectrometry. Results The pharmacokinetics of therapeutic-dose ciprofloxacin (cohort A) in plasma, subcutaneous tissue, and epithelial lining fluid was in accordance with previous data. In plasma and subcutaneous tissue, the dose-adjusted area under the concentration–time curve of microdose ciprofloxacin was similar in cohorts A and B and within an 0.8-fold to 1.1-fold range of the area under the concentration–time curve of therapeutic-dose ciprofloxacin. Penetration of microdose ciprofloxacin into subcutaneous tissue was similar in cohorts A and B and comparable to that of therapeutic-dose ciprofloxacin with subcutaneous tissue-to-plasma area under the concentration–time curve ratios of 0.44, 0.44, and 0.38, respectively. Penetration of microdose ciprofloxacin into epithelial lining fluid was highly variable and failed to predict the epithelial lining fluid penetration of therapeutic-dose ciprofloxacin. Conclusions Our study confirms the feasibility of microdosing for pharmacokinetic measurements in plasma and subcutaneous tissue. Microdosing combined with microdialysis is a potentially useful tool in clinical antimicrobial drug development, but its applicability for the assessment of pulmonary pharmacokinetics with bronchoalveolar lavage requires further studies. Clinical Trial Registration ClinicalTrials.gov NCT03177720 (registered 6 June, 2017).

Although fungal infections play a central role in severely ill and immunosuppressed patients, in contrast to antibiotics immunomodulatory effects of antifungals have not been sufficiently investigated. The present study sets out to compare the effect of different antimycotics on immunologic reaction towards mold in vitro. Aspergillus fumigatus ATCC204305 was used to develop a model of invasive aspergillosis in vitro in whole blood. Since autoclaved hyphal suspension demonstrated the most potent cytokine release, they were used for the further study including blood of 20 male volunteers. Impact on IL-6, IL-8 and TNF-α time concentration profiles by 5 mg/mL conventional and liposomal amphotericin B, 20 mg/mL fluconazole, 5 mg/mL voriconazole, 2 mg/mL posaconazole or saline solution was investigated over 4 h of incubation at 37 °C. Compared to baseline, cytokine levels increased by addition of hyphal suspension over 4 h approximately: 54-fold for IL-6, 1000-fold for IL-8 and 270-fold for TNF-α. While conventional amphotericin B further increased IL-6 and to a smaller extent IL-8 levels, this was not the case for its liposomal formulation. Congruently amphotericin B increased cytokines in blood without fungus substantially. Fluconazole reduced cytokine increase for all three cytokines compared to stimulation with hyphae without antifungal agent. Our data indicate significant differences in the immunomodulatory potency of different antimycotics. While fluconazole had the highest anti-inflammatory potential, conventional amphotericin even increased cytokine release. This preliminary information might have clinical implication, since cytokine dysregulation plays a major role in the pathogenesis and outcome of fungal infections. Clinical studies are warranted to confirm our findings.

It has been shown that protein binding, temperature, and pH influence in vitro pharmacodynamic (PD) models. The fact that corpuscular blood compounds might also have an important impact is something which has, until now, often been neglected. We investigated if the addition of human erythrocytes to standard growth media (Mueller Hinton Broth, MHBII) has an influence on bacterial growth behavior and on antibiotic efficacy. We did this by using bacterial growth assays and time kill curves (TKC) of selected strains (Escherichia coli ATCC25922, Staphylococcus aureus ATCC29213, and Pseudomonas aeruginosa ATCC27853) over 24 h. The final concentration of erythrocytes was set to match the physiological concentrations in the blood of a healthy human, i.e., 3 × 10^6 cells/μl in MHBII. Meropenem, ciprofloxacin, and tigecycline were tested with concentrations several-fold above and below the minimal inhibitory concentration (MIC). Moreover, HPLC analysis of antibiotic stability and distribution in erythrocytes was performed. Meropenem, ciprofloxacin, and tigecycline showed the greatest decline in activity against E. coli when erythrocytes were present. A mean difference in log10 bacterial killing between pure MHBII and 50%-Ery of 3.83, 1.33, and 2.42 was found for ciprofloxacin, meropenem, and tigecycline, respectively. In the case of ciprofloxacin, HPLC analysis revealed that less extracellular antibiotic is available in the presence of erythrocytes. We have demonstrated that erythrocytes do influence antimicrobial activity and that this might have an impact on the extrapolation of in vitro activity testing to in vivo efficacy in patients.

In vitro pharmacodynamic models are used to optimize in vivo dosing regimens in antimicrobial drug development. One limiting factor of such models is the lack of host factors such as corpuscular blood components as erythrocytes which have already been shown to impact activity of antibiotics and/or growth of the pathogen. However, the impact of thrombocytes has not previously been investigated. We set out to investigate if the addition of thrombocytes (set to physiological concentrations in blood of healthy human, i.e., 5 × 105 thrombocytes/μL standard growth media Mueller Hinton Broth, MHB) has an influence on bacterial growth and on the efficacy of antibiotics against Gram+ and Gram− bacteria. Growth assays and time-killing-curves (TKC) were performed with ATCC-strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa in triplicate over 24 h. The same approach was followed for 5 clinical isolates of Escherichia coli. Meropenem, ciprofloxacin, and tigecycline were tested as representatives of broad-spectrum antibiotics, and concentrations several-fold above and below the minimal inhibitory concentration (MIC) were simulated. No significant impact of thrombocytes was found on bacterial growth or antimicrobial stability for the investigated agents. Bacteria reduced thrombocyte content to different degree, indicating direct interaction of pathogens and thrombocytes. Impact on bacterial killing was observed but was not fully reproducible when thrombocytes from different donors where used. While interaction of bacteria and thrombocytes was evident in the present study, interaction between antibiotic activity and thrombocytes seems unlikely. Whether variability was caused by different thrombocyte concentrates needs further investigation.

P-glycoprotein (P-gp), a transmembrane transporter expressed at the blood–brain barrier, restricts the distribution of diverse central nervous system-targeted drugs from blood into brain, reducing their therapeutic efficacy. The third-generation P-gp inhibitor tariquidar (XR9576) was shown to enhance brain distribution of P-gp substrate drugs in humans. Oral bioavailability of tariquidar was found to be low in humans requiring the compound to be administered intravenously, which hinders a broader clinical use. The objective of the present study was to investigate the plasma pharmacokinetics of tariquidar in rats after single intravenous, oral, and intraperitoneal administration. Two different tariquidar formulations (A and B) were used, both at a dosage of 15 mg/kg, respectively. Formulation A was a solution and formulation B was a microemulsion which was previously shown to improve the oral bioavailability of the structurally related P-gp inhibitor elacridar in mice. In contrast to human data, the present study found a high bioavailability of tariquidar in rats after oral dosing. Oral bioavailability was significantly higher (p = 0.032) for formulation B (86.3%) than for formulation A (71.6%). After intraperitoneal dosing bioavailability was 91.4% for formulation A and 99.6% for formulation B. The present findings extend the available information on tariquidar and provide a basis for future studies involving oral administration of this compound.

It has been known from previous studies that body fluids, such as cerebrospinal fluid, lung surfactant, and urine, have a strong impact on the bacterial killing of many anti-infective agents. However, the influence of human bile on the antimicrobial activity of antibiotics is widely unknown. Human bile was obtained and pooled from 11 patients undergoing cholecystectomy. After sterilization of the bile fluid by gamma irradiation, its effect on bacterial killing was investigated for linezolid (LZD) and tigecycline (TGC) against Enterococcus faecalis ATCC 29212. Further, ciprofloxacin (CIP), meropenem (MEM), and TGC were tested against Escherichia coli ATCC 25922. Time-kill curves were performed in pooled human bile and Mueller-Hinton broth (MHB) over 24 h. Bacterial counts (in CFU per milliliter after 24 h) of bile growth controls were approximately equal to MHB growth controls for E. coli and approximately 2-fold greater for E. faecalis , indicating a promotion of bacterial growth by bile for the latter strain. Bile reduced the antimicrobial activity of CIP, MEM, and TGC against E. coli as well as the activity of LZD and TGC against E. faecalis . This effect was strongest for TGC against the two strains. Degradation of TGC in bile was identified as the most likely explanation. These findings may have important implications for the treatment of bacterial infections of the gallbladder and biliary tract and should be explored in more detail.

Cellular growth inhibition exerted by thiosemicarbazones is mainly attributed to down-regulation of ribonucleotide reductase (RNR) activity, with RNR being responsible for the rate-limiting step of de novo DNA synthesis. In this study, we investigated the antineoplastic effects of three newly synthesized thiosemicarbazone derivatives, thiazolyl hydrazones, in human HL-60 promyelocytic leukemia cells. The cytotoxicity of compounds alone and in combination with arabinofuranosylcytosine (AraC) was determined by growth inhibition assays. Effects on deoxyribonucleoside triphosphate (dNTP) concentrations were quantified by HPLC, and the incorporation of radio-labeled 14C-cytidine into nascent DNA was measured using a beta counter. Cell cycle distribution was analyzed by FACS, and protein levels of RNR subunits and checkpoint kinases were evaluated by Western blotting. VG12, VG19, and VG22 dose-dependently decreased intracellular dNTP concentrations, impaired cell cycle progression and, consequently, inhibited the growth of HL-60 cells. VG19 also lowered the protein levels of RNR subunits R1 and R2 and significantly diminished the incorporation of radio-labeled 14C-cytidine, being equivalent to an inhibition of DNA synthesis. Combination of thiazolyl hydrazones with AraC synergistically potentiated the antiproliferative effects seen with each drug alone and might therefore improve conventional chemotherapeutic regimens for the treatment of human malignancies such as acute promyelocytic or chronic myelogenous leukemia.