# A freely accessible, adaptable hollow-fiber setup to reproduce first-order absorption: illustration with linezolid cerebrospinal fluid pharmacokinetic data

## TL;DR

Researchers created a new hollow-fiber setup to simulate drug absorption in cerebrospinal fluid, matching clinical data and enabling better antibiotic dosing studies.

## Contribution

A novel hollow-fiber setup and algorithm were developed to simulate first-order absorption pharmacokinetics in vitro, with open-source tools for easy implementation.

## Key findings

- The setup successfully replicated linezolid concentrations in cerebrospinal fluid and plasma within 20% of clinical targets.
- The system uses a programmable infusion pump and algorithm to simulate absorption phases in a traditional hollow-fiber model.
- An open-source web application was developed to design hollow-fiber experiments, enhancing accessibility and reproducibility.

## Abstract

The main objective of this study was to validate an algorithm and experimental setup to simulate first-order absorption pharmacokinetic profiles without altering the standard in vitro hollow-fiber infection model (HFIM). For that, clinical cerebrospinal fluid (CSF) linezolid concentrations after 30 min infusions at dosing regimens 600 mg q12 h, 900 mg q12 h, and 900 mg q8 h were reproduced in the HFIM over 4 days. To approximate the apparent first-order absorption observed on CSF pharmacokinetic profiles, we split the dosing interval into a series of sub-intervals during which continuous infusions were delivered to the system. During each sub-interval, the same amount of linezolid was delivered, but the sub-intervals had different durations and flow rates, which were computed by a newly developed algorithm. In addition, we independently reproduced plasma concentrations to validate our system. Samples were collected from the central reservoir and the extracapillary space (ECS) of the cartridge of the HFIM and assayed by liquid chromatography-tandem mass spectrometry. Observed pharmacokinetic parameters and concentrations in the ECS were compared with the target clinical pharmacokinetic parameters and concentrations. Observed pharmacokinetic parameters were within 20% of target pharmacokinetic parameters for all experiments, thus validating the ability of our experimental setup to reproduce plasma and CSF linezolid pharmacokinetic profiles. The algorithm and setup are available in the open-source web application (https://varacli.shinyapps.io/hollow_fiber_app/) to easily design other HFIM experiments.

We developed and validated a novel hollow-fiber setup that enables in vitro simulation of mono-compartmental pharmacokinetics with an absorption phase. This novel experimental setup was easily implemented on top of the traditional one since it only requires the addition of a programmable infusion pump. Using this streamlined approach, we successfully replicated pharmacokinetics at the infection site, specifically cerebrospinal fluid concentrations of linezolid, consistent with those observed in intensive care unit patients. Thus, this study addresses the challenge of accurately reproducing target site concentrations, rather than relying solely on plasma levels, offering a valuable tool for optimizing dosing regimens in antibiotic therapy. Importantly, this setup also allows for the reproduction of plasma pharmacokinetics following oral (or any other extravascular) administration, broadening its applicability. The algorithm and setup developed in this study were incorporated into an open-source web application designed to facilitate the design of hollow-fiber experimental protocols (https://varacli.shinyapps.io/hollow_fiber_app/).