What Is Imipenem/Cilastatin? Uses, Dosage, and What You Need to Know in 2026

If you or someone you know has been prescribed Imipenem/Cilastatin, you might be wondering what it is and why it's such a significant medication. Here's what you need to know about this powerful antibiotic — in plain English.

What Is Imipenem/Cilastatin?

Imipenem/Cilastatin (brand name Primaxin) is a combination antibiotic belonging to the carbapenem class — one of the broadest-spectrum and most potent groups of antibiotics available. It was the first carbapenem ever approved by the FDA, receiving approval in 1985. Since then, it has been a cornerstone of treatment for serious bacterial infections in hospitals worldwide.

The drug has two active components:

• Imipenem: A carbapenem antibiotic that kills bacteria by preventing them from building their cell walls.

• Cilastatin: Not an antibiotic — it's a kidney-protective "helper" drug that blocks an enzyme in the kidneys (dehydropeptidase I) that would otherwise break down imipenem before it can do its job. Cilastatin lets approximately 70% of imipenem be excreted unchanged in urine, where it can treat urinary tract infections.

What Infections Does Imipenem/Cilastatin Treat?

Imipenem/Cilastatin is FDA-approved to treat serious infections caused by susceptible bacteria in adults and children. It is effective against a very wide range of bacteria — both gram-positive and gram-negative, aerobic and anaerobic. Common uses include:

• Intra-abdominal infections (peritonitis, appendicitis, bowel perforations)

• Lower respiratory tract infections including hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP)

• Septicemia (serious bloodstream infections / sepsis)

• Complicated skin and soft tissue infections

• Bone and joint infections (osteomyelitis, septic arthritis)

• Urinary tract and urogenital infections caused by multi-drug resistant organisms

• Endocarditis (heart valve infections)

• Febrile neutropenia in immunocompromised patients (off-label but widely used)

Important: Imipenem/Cilastatin is NOT used for meningitis — it does not adequately cross into the brain and spinal fluid, and it increases seizure risk at high doses.

How Is Imipenem/Cilastatin Given?

Imipenem/Cilastatin is only available as an injectable medication — there is no pill or liquid version you can take by mouth. It is given in two ways:

• Intravenous (IV): The most common route. Typically given as a 20–60 minute infusion every 6–8 hours in a hospital or infusion center. Available in 250 mg/250 mg and 500 mg/500 mg vial strengths.

• Intramuscular (IM): A less common option for some mild-to-moderate infections or when IV access isn't available. Maximum dose 1.5 g/day IM. Available in 500 mg and 750 mg vials.

What Is the Typical Dosage?

The IV dose for adults is typically 250 mg to 1 gram every 6–8 hours, based on the severity of the infection and the patient's kidney function. Total daily doses should not exceed 4 grams in most cases. Treatment usually lasts 5–14 days, depending on the type and severity of infection.

Dose adjustments are essential for patients with impaired kidney function (reduced creatinine clearance). Using the normal adult dose in a patient with kidney disease can cause drug accumulation and increase the risk of seizures.

Is Imipenem/Cilastatin a Controlled Substance?

No. Imipenem/Cilastatin is not a controlled substance. It is an antibiotic, not a drug with abuse potential. You do not need a DEA-special prescription, and there are no quantity limits based on controlled substance regulations. However, because of antibiotic stewardship requirements, many hospitals require infectious disease specialist approval before prescribing carbapenems.

Why Isn't Imipenem/Cilastatin Available Over the Counter?

Because it's a powerful antibiotic that must be used appropriately to remain effective. Overuse of broad-spectrum antibiotics contributes to antibiotic resistance — making these drugs less effective against the bacteria they're meant to treat. Using a carbapenem when a narrower antibiotic would suffice is exactly what antibiotic stewardship programs aim to prevent.

Is Imipenem/Cilastatin Currently in Shortage?

Yes. As of 2026, Imipenem/Cilastatin for Injection is on the FDA's active shortage list. See our Imipenem/Cilastatin shortage update for patients for the latest details on why it's in short supply and what you can do. If you're having difficulty filling your prescription, medfinder calls pharmacies near you to check current availability.