Methicillin sodium salt is primarily used as an antibiotic in the treatment of bacterial infections, particularly those caused by penicillinase-producing staphylococci. It is effective against strains of bacteria that are resistant to other penicillins due to its ability to resist degradation by bacterial enzymes. This makes it a crucial agent in combating infections such as skin and soft tissue infections, respiratory tract infections, and septicemia. It is typically administered via injection to ensure rapid and effective delivery into the bloodstream. However, its use has declined over time due to the emergence of methicillin-resistant Staphylococcus aureus (MRSA), which has led to the development of alternative antibiotics. Despite this, it remains an important historical and clinical reference in the study of antibiotic resistance and bacterial infections.