Mezlocillin Sodium is a broad-spectrum antibiotic primarily used in the treatment of severe bacterial infections, especially in hospital settings. It is effective against a wide range of Gram-positive and Gram-negative bacteria, including Pseudomonas aeruginosa, Escherichia coli, Proteus species, and certain strains of Klebsiella and Enterobacter.

It is commonly used to treat infections in the respiratory tract, urinary tract, abdomen, and bloodstream, particularly when caused by susceptible organisms. Due to its activity against Pseudomonas, it is often included in treatment regimens for infections in immunocompromised patients or those with complicated infections such as sepsis or nosocomial pneumonia.

Mezlocillin Sodium is often combined with a beta-lactamase inhibitor like sulbactam to enhance its stability against bacterial enzymes that can inactivate the antibiotic. This combination broadens its effectiveness, especially against beta-lactamase-producing strains.

Because it is administered parenterally (intravenously or intramuscularly), it is mainly used in clinical environments where rapid and high concentrations of the drug are needed. Its use has declined somewhat with the introduction of newer antibiotics, but it remains an option in specific multi-drug resistant infections or when culture results indicate susceptibility.