In Vitro Models for Prediction of Antimicrobial Activity: a Pharmacokinetic and Pharmacodynamic Perspective

Bioinspired drug delivery strategies for repurposing conventional antibiotics against intracellular infections

Bacteria have developed a wealth of strategies to avoid and resist the action of antibiotics, one of which involves pathogens invading and forming reservoirs within host cells. Due to the poor cell membrane permeability, stability and retention of conventional antibiotics, this renders current treatments largely ineffective, since achieving a therapeutically relevant antibiotic concentration at the site of intracellular infection is not possible. To overcome such challenges, current antibiotics are 'repurposed' via reformulation using micro- or nano-carrier systems that effectively encapsulate and deliver therapeutics across cellular membranes of infected cells. Bioinspired materials that imitate the uptake of biological particulates and release antibiotics in response to natural stimuli are recently explored to improve the targeting and specificity of this 'nanoantibiotic' approach. In this review, the mechanisms of internalization and survival of intracellular bacteria are elucidated, effectively accentuating the current treatment challenges for intracellular infections and the implications for repurposing conventional antibiotics. Key case studies of nanoantibiotics that have drawn inspiration from natural biological particles and cellular uptake pathways to effectively eradicate intracellular pathogens are detailed, clearly highlighting the rational for harnessing bioinspired drug delivery strategies.

Pharmacodynamic effects of simulated standard doses of antifungal drugs against Aspergillus species in a new in vitro pharmacokinetic/pharmacodynamic model

In conventional ΜΙC tests, fungi are exposed to constant drug concentrations, whereas in vivo, fungi are exposed to changing drug concentrations. Therefore, we developed a new in vitro pharmacokinetic/pharmacodynamic model where human plasma pharmacokinetics of standard doses of 1 mg/kg amphotericin B, 4 mg/kg voriconazole, and 1 mg/kg caspofungin were simulated and their pharmacodynamic characteristics were determined against three clinical isolates of Aspergillus fumigatus, Aspergillus flavus, and Aspergillus terreus with identical MICs (1 mg/liter for amphotericin B, 0.5 mg/liter for voriconazole) and minimum effective concentrations (0.5 mg/liter for caspofungin). This new model consists of an internal compartment (a 10-ml dialysis tube made out of a semipermeable cellulose membrane allowing the free diffusion of antifungals but not galactomannan) inoculated with Aspergillus conidia and placed inside an external compartment (a 700-ml glass beaker) whose content is diluted after the addition of antifungal drugs by a peristaltic pump at the same rate as the clearance of the antifungal drugs in human plasma. Fungal growth was assessed by galactomannan production. Despite demonstrating the same MICs, amphotericin B completely inhibited (100%) A. fumigatus but not A. flavus and A. terreus, whose growth was delayed for 7.53 and 22.8 h, respectively. Voriconazole partially inhibited A. fumigatus (49.5%) and Α. flavus (27.9%) but not Α. terreus; it delayed their growth by 3.99 h (A. fumigatus) and 5.37 h (Α. terreus). Caspofungin did not alter galactomannan production in all of the species but A. terreus. The new model simulated human pharmacokinetics of antifungal drugs and revealed important pharmacodynamic differences in their activity.

In vitro pharmacodynamic models to determine the effect of antibacterial drugs

In vitro pharmacodynamic (PD) models are used to obtain useful quantitative information on the effect of either single drugs or drug combinations against bacteria. This review provides an overview of in vitro PD models and their experimental implementation. Models are categorized on the basis of whether the drug concentration remains constant or changes and whether there is a loss of bacteria from the system. Further subdifferentiation is based on whether bacterial loss involves dilution of the medium or is associated with dialysis or diffusion. For comprehension of the underlying principles, experimental settings are simplified and schematically illustrated, including the simulations of various in vivo routes of administration. The different model types are categorized and their (dis)advantages discussed. The application of in vitro models to special organs, infections and pathogens is comprehensively presented. Finally, the relevance and perspectives of in vitro investigations in drug discovery and clinical research are elucidated and discussed.

New criteria for selecting the proper antimicrobial chemotherapy for severe sepsis and septic shock

The mortality rate resulting from severe bacterial sepsis, particularly that associated with shock, still approaches 50% in spite of appropriate antimicrobial therapy and optimum supportive care. Bacterial endotoxins that are part of the cell wall are one of the cofactors in the pathogenesis of sepsis and septic shock and are often induced by antimicrobial chemotherapy even if it is administered rationally. Not all antimicrobial agents are equally capable of inducing septic shock; this is dependant on their mechanism of action rather than on the causative pathogen species. The quantity of endotoxin released depends on the drug dose and whether filaments or spheroplast formation predominates. Some antibiotics such as carbapenems, ceftriaxone, cefepime, glycopeptides, aminoglycosides and quinolones do not have the propensity to provoke septic shock because their rapid bactericidal activity induces mainly spheroplast or fragile spheroplast-like bacterial forms.

The in vitro activity of moxifloxacin against Haemophilus influenzae and Moraxella catarrhalis explored using a pharmacodynamic model

OBJECTIVE: To assess the antibacterial action of moxifloxacin on Haemophilus influenzae and Moraxella catarrhalis using an in vitro pharmacodynamic model of infection. METHODS: Serum concentrations in humans associated with doses of 400 mg once a day for 48 h were simulated and the antibacterial effect measured by the log change in viable count at intervals through the simulation compared to time zero and also the area under the bacterial kill curve (AUBKC). Wild-type strains of H. influenzae and M. catarrhalis with varying beta-lactam susceptibilities (moxifloxacin MICs </=0.1 mg/L) and laboratory-generated mutants with moxifloxacin MICs of 0.5-1.0 mg/L were tested. RESULTS: H. influenzae strains with MICs of </=0.06 mg/L were eradicated by 12 h; strains with MICs of 0.5-1.0 mg/L were eradicated by 24-36 h. M. catarrhalis strains with MICs of </=0.08 mg/L were eradicated by 24-36 h, while the less susceptible laboratory mutant (MIC 1.0 mg/L) was not eradicated even at 48 h. Although we used only a single dosing simulation, the AUC/MIC ratio was strongly related to the AUBKC. CONCLUSIONS: These data indicated that once daily dosing of moxifloxacin holds promise for the treatment of infection due to H. influenzae or M. catarrhalis but bacterial killing is related to MIC.