Cilastatin ammonium salt is primarily used in combination with the antibiotic imipenem to enhance its efficacy. It works by inhibiting the enzyme dehydropeptidase-I, which is found in the kidneys. This enzyme would otherwise break down imipenem, reducing its effectiveness. By blocking this enzyme, cilastatin ensures that imipenem remains active in the body for a longer period, improving its antibacterial activity. This combination is particularly valuable in treating severe infections caused by susceptible bacteria, including those in the respiratory tract, urinary tract, abdomen, and bloodstream. It is also effective in managing infections in immunocompromised patients. The use of cilastatin ammonium salt helps to minimize the risk of kidney damage that can occur with imipenem alone, making it a critical component in combination therapy for serious bacterial infections.