Imipenem/Cilastatin Shortage: What Providers and Prescribers Need to Know in 2026

Imipenem/Cilastatin (Primaxin) — the first carbapenem approved in the United States — remains on the FDA's active drug shortage list in 2026. For providers and stewardship teams, this shortage has real clinical implications: patients with serious gram-negative infections, polymicrobial sepsis, and multidrug-resistant organisms may need alternative or conservation strategies when primary supply is disrupted. This briefing summarizes the current shortage landscape, evidence-based alternatives, and practical stewardship approaches.

Current Shortage Status and Manufacturer Landscape

As of 2026, the FDA Drug Shortage Database and ASHP Shortage List both classify Imipenem/Cilastatin for Injection as "Currently in Shortage." The two primary generic manufacturers — Fresenius Kabi USA and Pfizer (Hospira) — have both cited supply constraints: Fresenius Kabi due to increased demand, Hospira due to manufacturing delays. Merck's branded Primaxin IV may have different availability than generics. No confirmed resolution date has been provided by any manufacturer or the FDA.

Key presentations: 250 mg/250 mg and 500 mg/500 mg vials (IV); 500 mg/750 mg vials (IM). Availability may differ by strength and presentation. Institutions should query their GPO and distributor (McKesson, AmerisourceBergen, Cardinal Health) to identify which specific SKUs are available.

Clinical Context: When Is Imipenem/Cilastatin the Drug of Choice?

Imipenem/Cilastatin is indicated for serious infections caused by susceptible organisms, including:

• Lower respiratory tract infections (HAP, VAP) including Pseudomonas aeruginosa

• Complicated intra-abdominal infections (polymicrobial, peritonitis)

• Septicemia and febrile neutropenia in immunocompromised patients

• Complicated UTIs and urogenital infections

• Complicated skin and soft tissue infections, bone and joint infections

• ESBL-producing Enterobacteriaceae and certain multidrug-resistant (MDR) organisms

Notably, Imipenem/Cilastatin is NOT indicated for meningitis — it does not adequately penetrate the blood-brain barrier and carries higher seizure risk than other carbapenems, particularly at high doses or in patients with renal impairment (seizure incidence reported up to 6%).

Evidence-Based Alternatives for Prescribers

The following alternatives should be considered based on the infection type, causative organism, and patient-specific factors:

• Meropenem (Merrem): The preferred substitute in most clinical scenarios. Superior CNS safety profile, active against Pseudomonas, can be used for meningitis. Typical dosing: 1 g IV q8h (or 2 g IV q8h for CNS, lung, or highly resistant organisms). Extended infusion (3-hour) can optimize pharmacodynamics.

• Ertapenem (Invanz): Appropriate for community-acquired or healthcare-associated infections with Enterobacteriaceae or anaerobes, when Pseudomonas and Acinetobacter have been ruled out. Once-daily dosing (1 g IV/IM q24h) is advantageous for OPAT programs. Do not use if Pseudomonas is suspected or isolated.

• Piperacillin-Tazobactam (Zosyn): Consider for susceptible gram-negative infections, polymicrobial intra-abdominal infections, or HAP when ESBL-producers have been excluded by susceptibility testing. Not appropriate for CRE or carbapenem-resistant organisms.

• Ceftazidime-Avibactam (Avycaz): Reserve for documented KPC- or OXA-48-producing CRE, or MDR Pseudomonas aeruginosa. Expensive; requires ID specialist oversight. Coverage of MBL-producing organisms requires combination with aztreonam.

Key Drug Interaction Warning: Valproic Acid

A critical interaction all prescribers must be aware of: carbapenems (including imipenem, meropenem, and ertapenem) significantly reduce serum valproic acid/divalproex concentrations — often by more than 50% — through inhibition of glucuronide hydrolysis. This can precipitate breakthrough seizures in epilepsy patients who are otherwise well-controlled. Avoid all carbapenems in patients on valproic acid when possible, or consult neurology for alternative anticonvulsant management if carbapenem therapy is unavoidable.

Stewardship Conservation Strategies

When Imipenem/Cilastatin is in limited supply, stewardship programs can implement several conservation measures:

1. Prospective audit and feedback: Review all imipenem/cilastatin orders to confirm the indication is appropriate and a carbapenem is truly the drug of choice based on available susceptibility data.

2. De-escalation protocols: Switch to a narrower agent as soon as culture and sensitivity data are available and the patient is clinically improving.

3. Extended infusion strategies: Administer imipenem/cilastatin over extended periods (though note that imipenem stability in solution limits extended infusion times compared to meropenem — check current stability data with your pharmacy).

4. Renal dose optimization: Ensure all patients with CrCl ≤70 mL/min receive appropriate dose adjustments per labeling, reducing unnecessary drug use and seizure risk.

How medfinder Supports Your Patients During Shortage

For patients transitioning to outpatient IV therapy, finding a pharmacy with Imipenem/Cilastatin in stock is a major challenge. medfinder for providers helps your discharge team locate infusion pharmacies with current stock before the patient leaves the hospital — reducing the risk of treatment gaps during OPAT.

For the patient-facing shortage update, see our Imipenem/Cilastatin shortage update for patients.