Imipenem and cilastatin injection comes as a powder to be mixed with liquid to be injected intravenously (into a vein) or intramuscularly (into a muscle). When imipenem and cilastatin is injected intravenously, it is usually infused (injected slowly) over a period of 20 minutes to 1 hour every 6 or 8 hours. When imipenem and cilastatin is given intramuscularly, it is injected into the muscles of the buttocks or thigh once every 12 hours. The length of treatment depends on the type of infection being treated. Your doctor will tell you how long to use imipenem and cilastatin injection. After your condition improves, your doctor may switch you to another antibiotic that you can take by mouth to complete your treatment.