# In vitro and in vivo synergistic effects of cyclizine and piroxicam in combination with linezolid against methicillin-resistant Staphylococcus aureus

## TL;DR

This study finds that combining linezolid with cyclizine or piroxicam effectively treats linezolid-resistant Staphylococcus aureus in lab and animal tests.

## Contribution

The study introduces two novel synergistic combinations (linezolid/cyclizine and linezolid/piroxicam) for treating linezolid-resistant S. aureus.

## Key findings

- Linezolid/cyclizine and linezolid/piroxicam combinations showed strong synergy against linezolid-resistant S. aureus isolates.
- The combinations provided complete protection and improved lung health in a murine model of lung infection.
- The synergistic combinations significantly enhanced bacterial eradication compared to monotherapy.

## Abstract

Linezolid (LNZ) is considered one of the last-resort antimicrobial agents reserved for treating methicillin resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Staphylococcus aureus (VRSA). The development of resistance against linezolid necessitates the exploration of novel therapies.  Aim: This study aims to investigate the synergistic activity of various combinations of linezolid with non-antibiotic through in vitro and in vivo approaches.

In our research, 44 S. aureus isolates were obtained from various clinical sources. S. aureus isolates presented high levels of resistance to β-lactams and moderate resistance to doxycycline and erythromycin. Among the isolates, 43 (97.73%) were MRSA, 10 (22.73%) were linezolid resistant S. aureus (LRSA), and 17 (38.64%) were classified as VRSA. A total of 97.73% of the isolates presented the mecA gene (MRSA), whereas the optrA gene was detected in 9.09% of the isolates (LRSA).  The synergistic activity of nine compounds with linezolid was assessed in vitro against LRSA isolates using broth microdilution and checkerboard microdilution methods. Linezolid/cyclizine and linezolid/piroxicam combinations showed fractional inhibitory concentration indexes (FICIs) ranging from 0.28 to 0.5 against LRSA isolates. Time-kill curves were used to confirm their bactericidal activity. Promising combinations (linezolid/cyclizine and linezolid/piroxicam) were further evaluated in vivo LRSA-induced lung infection murine animal model. Compared with monotherapy, combination therapies significantly enhance bacterial eradication and increase sensitivity to linezolid, resulting in superior bacterial eradication. Linezolid/cyclizine and linezolid/piroxicam combinations provided complete protection (100% survival), improved lung pathology, and enhanced clinical scores.

This study presents two novel combination therapies (linezolid/cyclizine and linezolid/piroxicam) with promising applications in treating severe LRSA infections.

optrA gene was detected in four linezolid S. aureus–resistant isolates (LRSA)Linezolid/cyclizine and linezolid/piroxicam synergism was detected against LRSA.Combinations revealed complete lung protection in lung-infected LRSA murine model.

optrA gene was detected in four linezolid S. aureus–resistant isolates (LRSA)

Linezolid/cyclizine and linezolid/piroxicam synergism was detected against LRSA.

Combinations revealed complete lung protection in lung-infected LRSA murine model.

The online version contains supplementary material available at 10.1007/s00253-026-13738-9.