All Roads Lead to Rome: Enhancing the Probability of Target Attainment with Different Pharmacokinetic/Pharmacodynamic Modelling Approaches

Interaction of the Atypical Tetracyclines Chelocardin and Amidochelocardin with Renal Drug Transporters

Antimicrobial resistance is expected to increase mortality rates by up to several million deaths per year by 2050 without new treatment options at hand. Recently, we characterized the pharmacokinetic (PK) and pharmacodynamic properties of two atypical tetracyclines, chelocardin (CHD) and amidochelocardin (CDCHD) that exhibit no cross-resistance with clinically used antibacterials. Both compounds were preferentially renally cleared and demonstrated pronounced effects in an ascending urinary tract infection model against E. coli. Renal drug transporters are known to influence clearance into the urine. In particular, inhibition of apical transporters in renal tubular epithelial cells can lead to intracellular accumulation and potential cell toxicity, whereas inhibition of basolateral transporters can cause a higher systemic exposure. Here, selected murine and human organic cation (Oct), organic anion (Oat), and efflux transporters were studied to elucidate interactions with CHD and CDCHD underlying their PK behavior. CHD exhibited stronger inhibitory effects on mOat1 and mOat3 and their human homologues hOAT1 and hOAT3 compared to CDCHD. While CHD was a substrate of mOat3 and mOct1, CDCHD was not. By contrast, no inhibitory effect was observed on Octs. CDCHD rather appeared to foster enhanced substrate transport on mOct1. CHD and CDCHD inhibited the efflux transporter hMRP2 on the apical side. In summary, the substrate nature of CHD in conjunction with its autoinhibition toward mOat3 rationalizes the distinct urine concentration profile compared to CDCHD that was previously observed in vivo. Further studies are needed to investigate the accumulation in renal tubular cells and the nephrotoxicity risk.

Aerosolized delivery of ESKAPE pathogens for murine pneumonia models

Murine pneumonia models for ESKAPE pathogens serve to evaluate novel antibacterials or to investigate immunological responses. The majority of published models uses intranasal or to a limited extent the intratracheal instillation to challenge animals. In this study, we propose the aerosol delivery of pathogens using a nebulizer. Aerosol delivery typically results in homogeneous distribution of the inoculum in the lungs because of lower particle size. This is of particular importance when compounds are assessed for their pharmacokinetic and pharmacodynamic (PK/PD) relationships as it allows to conduct several analysis with the same sample material. Moreover, aerosol delivery has the advantage that it mimics the 'natural route' of respiratory infection. In this short and concise study, we show that aerosol delivery of pathogens resulted in a sustained bacterial burden in the neutropenic lung infection model for five pathogens tested, whereas it gave a similar result in immunocompetent mice for three out of five pathogens. Moreover, a substantial bacterial burden in the lungs was already achieved 2 h post inhalation. Hence, this study constitutes a viable alternative for intranasal administration and a refinement of murine pneumonia models for PK/PD assessments of novel antibacterial compounds allowing to study multiple readouts with the same sample material.

Translational PK/PD for the Development of Novel Antibiotics-A Drug Developer's Perspective

Antibiotic development traditionally involved large Phase 3 programs, preceded by Phase 2 studies. Recognizing the high unmet medical need for new antibiotics and, in some cases, challenges to conducting large clinical trials, regulators created a streamlined clinical development pathway in which a lean clinical efficacy dataset is complemented by nonclinical data as supportive evidence of efficacy. In this context, translational Pharmacokinetic/Pharmacodynamic (PK/PD) plays a key role and is a major contributor to a "robust" nonclinical package. The classical PK/PD index approach, proven successful for established classes of antibiotics, is at the core of recent antibiotic approvals and the current antibacterial PK/PD guidelines by regulators. Nevertheless, in the case of novel antibiotics with a novel Mechanism of Action (MoA), there is no prior experience with the PK/PD index approach as the basis for translating nonclinical efficacy to clinical outcome, and additional nonclinical studies and PK/PD analyses might be considered to increase confidence. In this review, we discuss the value and limitations of the classical PK/PD approach and present potential risk mitigation activities, including the introduction of a semi-mechanism-based PK/PD modeling approach. We propose a general nonclinical PK/PD package from which drug developers might choose the studies most relevant for each individual candidate in order to build up a "robust" nonclinical PK/PD understanding.