MRX-I is a potent oxazolidinone antibiotic against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus, penicillin-resistant Streptococcus pneumoniae, penicillin-intermediate S. pneumoniae, and vancomycin-resistant enterococci. MRX-I demonstrated comparable or slightly higher activity than linezolid and was active against enterococci resistant to both vancomycin and teicoplanin. In addition, MRX-I exhibited bactericidal activities against staphylococci and streptococci but was bacteriostatic against enterococci. MRX-I inhibits formation of functional 70S initiation complex essential for bacterial protein synthesis, leading to the cessation of bacterial growth. Oral MRX-I was associated with a greater bioavailability and exposure when administered with food, and minimal accumulation of MRX-I occurred after multiple-dose administration. Oral MRX-I was well tolerated at single doses of up to 1,200 and 800 mg q12h for up to 28 days; all adverse events were mild to moderate in severity, and there was no drug discontinuation due to adverse events.