Comprehensive medication guide to Imipenem/Cilastatin including estimated pricing, availability information, side effects, and how to find it in stock at your local pharmacy.
Estimated Insurance Pricing
$0–$50 copay typical for commercial or Medicaid plans when administered in hospital or infusion center (medical benefit, not pharmacy benefit); prior authorization typically required for outpatient OPAT home infusion. Medicare Part B covers 80% of outpatient infusion charges after deductible.
Estimated Cash Pricing
$46–$303 retail per course of vials (250 mg or 500 mg generic); as low as $129.78 for 12 × 500 mg vials with a SingleCare coupon at participating pharmacies. Brand Primaxin IV is significantly more expensive (>$800 for 25 vials).
Medfinder Findability Score
25/100
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Imipenem/Cilastatin (brand name Primaxin) is a combination carbapenem antibiotic — the first carbapenem ever approved by the FDA (1985). It is used to treat serious and life-threatening bacterial infections caused by a broad spectrum of gram-positive, gram-negative, and anaerobic organisms, including many drug-resistant bacteria. The drug is administered intravenously (IV) or by intramuscular (IM) injection, almost always in a hospital, infusion center, or through an outpatient IV therapy (OPAT) program.
The combination product has two components: imipenem, the active antibiotic, and cilastatin, a kidney-protective agent that prevents the breakdown of imipenem in the renal tubules and allows approximately 70% of the drug to reach target tissues and the urine unchanged. Without cilastatin, imipenem would be destroyed by the kidney before it could fight the infection.
FDA-approved indications include severe infections of the lower respiratory tract, intra-abdominal cavity, skin and soft tissue, bones and joints, urinary tract, bloodstream (septicemia), and reproductive organs. It is also widely used off-label for febrile neutropenia in immunocompromised patients.
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Imipenem kills bacteria by binding to penicillin-binding proteins (PBPs) — enzymes that bacteria use to build and repair their cell walls. By inactivating these proteins (particularly PBPs 1A, 1B, 2, 4, 5, and 6), imipenem blocks cell wall synthesis. Without an intact cell wall, bacteria cannot survive osmotic pressure and burst and die — a process called bacteriolysis. This is called a bactericidal (bacteria-killing) mechanism of action.
Imipenem is resistant to most beta-lactamases — enzymes produced by bacteria to destroy antibiotics — including cephalosporinases and many extended-spectrum beta-lactamases (ESBLs). This makes it effective against bacteria that have developed resistance to penicillins, cephalosporins, and many other antibiotics. However, it is susceptible to carbapenemases (KPC, NDM, OXA), which some highly resistant organisms (CRE) produce.
Cilastatin works by competitively inhibiting dehydropeptidase I (DHP-I), an enzyme in the kidney's brush border cells that would otherwise break imipenem down into a toxic, inactive metabolite. By blocking DHP-I, cilastatin preserves imipenem's antibacterial activity, prevents kidney damage from the metabolite, and allows adequate urinary concentrations of active imipenem. Both drugs have a half-life of approximately 1 hour and are eliminated primarily through the kidneys.
250 mg/250 mg — IV powder for injection
Intravenous use; 250 mg imipenem + 250 mg cilastatin per vial
500 mg/500 mg — IV powder for injection
Intravenous use; 500 mg imipenem + 500 mg cilastatin per vial — most commonly used strength
500 mg/500 mg — IM powder for injection
Intramuscular use; formulated with lidocaine for IM injection
750 mg/750 mg — IM powder for injection
Intramuscular use; for mild-to-moderate infections via IM route
Finding Imipenem/Cilastatin in 2026 is very challenging. The drug is listed as "Currently in Shortage" on both the FDA Drug Shortage Database and the ASHP Drug Shortage Database. Both major generic manufacturers — Fresenius Kabi and Pfizer (Hospira) — have faced supply constraints due to increased demand and manufacturing delays, respectively. No resolution timeline has been announced.
Compounding the challenge: Imipenem/Cilastatin is an IV antibiotic, so it is not stocked at standard retail pharmacies like CVS or Walgreens. Patients and caregivers must contact hospital outpatient pharmacies and specialty infusion pharmacy networks. Availability varies significantly by region, by vial strength (250 mg vs 500 mg), and by manufacturer — requiring real-time verification to find actual stock.
The most efficient way to locate Imipenem/Cilastatin is through medfinder — a paid service that calls pharmacies and infusion centers near you to find which ones currently have the medication in stock, then texts you the results.
Imipenem/Cilastatin is not a controlled substance and does not require a DEA-special prescription. However, because it is an IV antibiotic used for severe infections and because most hospitals have antibiotic stewardship programs that restrict carbapenem use, prescriptions are almost exclusively written by physicians or advanced practice providers in hospital, critical care, or infectious disease settings.
Infectious Disease (ID) Specialists — primary prescribers of carbapenems; required or preferred for stewardship approval at most institutions
Hospitalists — manage acutely ill inpatients and may initiate empiric carbapenem therapy in consultation with ID
Intensivists / Critical Care Physicians — prescribe in ICU settings for septic shock and ventilator-associated pneumonia
Surgeons — general surgeons prescribe for complex intra-abdominal infections and polymicrobial post-surgical infections
Pulmonologists — for hospital-acquired and ventilator-associated pneumonia due to resistant gram-negatives
Oncologists / Hematologists — for febrile neutropenia in cancer patients on chemotherapy
Nurse Practitioners and Physician Assistants — can prescribe within scope of practice, though typically in consultation with or supervised by a physician in this context
Telehealth: Imipenem/Cilastatin cannot be meaningfully prescribed via telehealth. It requires IV administration through an OPAT program, which requires in-person clinical setup, home nursing assessment, and specialty infusion pharmacy coordination that cannot be initiated through a remote visit alone.
No. Imipenem/Cilastatin is not a controlled substance and is not scheduled under the DEA Controlled Substances Act. It is an antibiotic with no abuse potential or addiction risk. There are no special DEA prescription requirements, no refill restrictions under controlled substance regulations, and no quantity limits based on scheduling.
However, even though it is not controlled, access to Imipenem/Cilastatin is regulated in a different way: most hospitals have antibiotic stewardship programs that require physician documentation of the clinical indication, and many institutions require infectious disease (ID) specialist consultation or approval before carbapenems can be prescribed. This is a clinical quality and antimicrobial resistance prevention measure, not a DEA requirement.
Most patients tolerate Imipenem/Cilastatin reasonably well. Common side effects include:
Nausea and vomiting (most common GI effect)
Diarrhea (mild; watch for C. diff if severe)
Injection site pain, redness, and phlebitis
Fever and chills
Dizziness and drowsiness
Transient elevated liver enzymes (seen in ~6% of patients)
Seizures — risk up to 6% at high doses or with renal impairment; higher risk in patients with prior seizure history or brain injury
C. difficile-associated diarrhea (CDAD) — severe colitis; can occur up to 2 months after completing antibiotic course
Anaphylaxis — severe allergic reaction; cross-reactivity with penicillin allergy (~1–2%)
CNS toxicity — confusion, encephalopathy, tremors, myoclonus (especially in elderly or renally impaired patients)
Cholestatic hepatitis — rare; onset 1–3 weeks post-treatment; jaundice, dark urine, pale stools
Stevens-Johnson syndrome — very rare; severe blistering skin rash affecting mucous membranes
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Meropenem (Merrem)
Closest carbapenem alternative; lower seizure risk, can be used for meningitis, slightly more active against Pseudomonas. Most commonly substituted during imipenem shortage.
Ertapenem (Invanz)
Once-daily carbapenem ideal for OPAT; however, has NO activity against Pseudomonas aeruginosa or Acinetobacter — only appropriate when these organisms are excluded.
Piperacillin-Tazobactam (Zosyn)
Broad-spectrum beta-lactam/BLI combination for susceptible polymicrobial infections; not appropriate for ESBL-producers or carbapenem-resistant organisms.
Ceftazidime-Avibactam (Avycaz)
Reserve drug for carbapenem-resistant Enterobacterales (CRE) and MDR Pseudomonas; requires ID specialist oversight and prior authorization; very expensive.
Doripenem (Doribax)
Another carbapenem with similar spectrum to meropenem; less commonly used but may be available when other carbapenems are scarce.
Prefer Imipenem/Cilastatin? We can find it.
Valproic acid / Divalproex sodium (Depakote)
majorMAJOR: Carbapenems reduce valproic acid levels by >50%, risking breakthrough seizures in epilepsy patients. Avoid this combination. Consult neurology if carbapenem therapy is unavoidable.
Ganciclovir / Valganciclovir (Cytovene, Valcyte)
majorMAJOR: Combination significantly increases risk of generalized seizures. Avoid concurrent use unless benefit clearly outweighs risk.
Probenecid (Probalan)
majorMAJOR: Increases plasma levels and half-life of imipenem by blocking renal clearance, raising toxicity and seizure risk. Coadministration not recommended.
Cyclosporine (Neoral, Sandimmune)
moderateMODERATE: Cyclosporine may increase imipenem neurotoxic effects; combination may alter cyclosporine levels unpredictably. Monitor both levels closely.
BCG intravesical (bladder cancer treatment)
majorMAJOR: Imipenem/cilastatin may reduce effectiveness of BCG intravesical therapy. Avoid concurrent use.
Live bacterial vaccines (oral typhoid, cholera)
moderateMODERATE: Antibiotics may reduce the efficacy of live bacterial vaccines. Wait until antibiotic course is complete before vaccination.
Imipenem/Cilastatin (Primaxin) remains one of the most important antibiotics in medicine — a broad-spectrum carbapenem that has been saving lives from serious drug-resistant infections since 1985. Its active shortage in 2026 is a stark reminder of how fragile the supply chain for critical sterile injectable antibiotics can be. When this drug is unavailable, patients with serious infections face real risks, and clinical teams must pivot quickly to alternatives like meropenem and ertapenem.
For patients and caregivers: if you're having trouble sourcing this medication, do not wait. Contact your prescribing physician immediately, ask your hospital pharmacy team about sourcing options, and consider alternative infusion pharmacies in your area.
And if you need help finding Imipenem/Cilastatin in stock near you, medfinder is here to help — calling pharmacies and infusion centers on your behalf and texting you the results so you can get the treatment you need, when you need it.
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Our medication guides are researched and written to help patients make informed decisions. All content is reviewed for accuracy and updated regularly. Learn more about our standards
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