# Enhanced In Vitro Stability of Bedaquiline with Ascorbic Acid and Pyruvate During Long-Term Incubation in Mycobacterium Species

## TL;DR

This study shows that adding ascorbic acid and pyruvate helps keep bedaquiline stable during long-term testing in mycobacteria.

## Contribution

The study introduces a new stabilization method for bedaquiline during drug susceptibility testing.

## Key findings

- Bedaquiline showed significant MIC variation after pre-incubation.
- Combining bedaquiline with ascorbic acid and pyruvate prevented MIC variation.
- Other antibiotics remained stable without additional stabilizers.

## Abstract

Background: Drug susceptibility testing in Mycobacterium species typically requires prolonged incubation periods during which the chemical integrity of antibiotics may not be maintained, potentially compromising the reliability and accuracy of minimum inhibitory concentration (MIC) determinations. Objectives: This study evaluated the in vitro stability of several antibiotics, including recently introduced agents (bedaquiline [BDQ], pretomanid, delamanid and clofazimine) used for treating multidrug-resistant mycobacteriosis (linezolid and moxifloxacin), and those commonly included in combination regimens (rifampicin, isoniazid, ethambutol and clarithromycin). Methods: Antibiotics were pre-incubated at 37 °C before MIC determination and those exhibiting two or more dilutions in MIC were further tested in combination with ascorbic acid (AA) and pyruvate (P). Results: All antibiotics demonstrated stability except BDQ, which showed significant MIC variation after pre-incubation, which was prevented when BDQ was combined with AA and P. Conclusions: These findings suggest that the combined use of AA and P may serve as an effective stabilizing strategy for BDQ during MIC determination.