Alternatives to Colistin If You Can't Fill Your Prescription

When Colistin Isn't Available: What Are Your Options?

Being told that Colistin — the antibiotic your doctor specifically prescribed — isn't available is frightening, especially when you're dealing with a serious, drug-resistant infection. Colistin (Colistimethate Sodium) is often prescribed as a last-resort treatment, so hearing "we don't have it" can feel like hitting a wall.

The good news: there are alternatives. Not every substitute will work for every infection, but your infectious disease specialist has options to consider. In this guide, we'll explain what Colistin does, how it works, and walk through the most common alternatives available in 2026.

What Is Colistin?

Colistin, also sold under the brand name Coly-Mycin M, is a polymyxin antibiotic (specifically Polymyxin E). It was first introduced in the 1950s and fell out of favor for decades due to its toxicity — particularly kidney damage (nephrotoxicity) and nerve damage (neurotoxicity).

However, as multidrug-resistant gram-negative bacteria have become more common, Colistin has made a comeback as one of the few antibiotics that still works against these dangerous organisms. It's primarily used in hospital settings for serious infections caused by:

• Pseudomonas aeruginosa (including multidrug-resistant strains)
• Acinetobacter baumannii (a major hospital-acquired infection threat)
• Klebsiella pneumoniae (including carbapenem-resistant strains)
• Escherichia coli and Enterobacter species resistant to other treatments

For a complete overview, see What Is Colistin? Uses, Dosage, and What You Need to Know.

How Does Colistin Work?

Colistin works by binding to lipopolysaccharides (LPS) in the outer membrane of gram-negative bacteria. Think of it as a detergent that dissolves the bacterial cell wall. Once the membrane is disrupted, the bacteria's internal contents leak out and the cell dies.

This unique mechanism is why Colistin still works against bacteria that have developed resistance to other antibiotic classes — the membrane target is different from what most modern antibiotics attack. You can read a detailed breakdown in our post: How Does Colistin Work? Mechanism of Action Explained.

Alternatives to Colistin

If Colistin is unavailable due to shortages or supply issues, your doctor may consider one of the following alternatives. Important: These decisions depend entirely on the specific bacteria causing your infection, its susceptibility profile, and your overall health. Never switch medications on your own — always work with your prescriber.

1. Polymyxin B

Drug class: Polymyxin antibiotic (Polymyxin B Sulfate)

Polymyxin B is the closest relative to Colistin. Both are polymyxin antibiotics that work through the same membrane-disrupting mechanism. Key differences:

• Polymyxin B is administered directly as the active drug, while Colistin is given as a prodrug (Colistimethate Sodium) that converts to active Colistin in the body.
• Polymyxin B may have more predictable pharmacokinetics, meaning blood levels are easier to manage.
• Nephrotoxicity risk is comparable between the two, though some studies suggest Polymyxin B may have slightly lower kidney toxicity rates.

Polymyxin B is available as an injectable and is used for many of the same multidrug-resistant gram-negative infections as Colistin. It may also face supply challenges, but it provides another option your doctor can explore.

2. Tobramycin

Drug class: Aminoglycoside antibiotic

Tobramycin is an aminoglycoside that is particularly effective against Pseudomonas aeruginosa. It's available in several forms:

• IV/IM injection for systemic infections
• Inhaled (TOBI, TOBI Podhaler) for chronic Pseudomonas in cystic fibrosis patients
• Ophthalmic for eye infections

Tobramycin shares some toxicity concerns with Colistin — it can also cause nephrotoxicity and ototoxicity (hearing damage). However, it's more widely manufactured and generally easier to find. If your infection is susceptible to Tobramycin, it can be a viable substitute, especially for pulmonary infections.

3. Amikacin

Drug class: Aminoglycoside antibiotic

Amikacin is a broad-spectrum aminoglycoside with activity against many gram-negative bacteria, including some strains resistant to other aminoglycosides like Gentamicin and Tobramycin. It's available as:

• IV/IM injection for serious systemic infections
• Inhaled (Arikayce) — an FDA-approved liposomal inhaled form for Mycobacterium avium complex (MAC) lung infections

Amikacin is often used in combination with other antibiotics for multidrug-resistant gram-negative infections. Like Tobramycin, it carries risks of kidney and hearing damage, and blood levels must be monitored.

4. Ceftazidime-Avibactam (Avycaz)

Drug class: Cephalosporin/beta-lactamase inhibitor combination

Ceftazidime-Avibactam is a newer option that combines a cephalosporin antibiotic with a beta-lactamase inhibitor. This combination works against some carbapenem-resistant Enterobacteriaceae (CRE) — a type of infection that often leads doctors to prescribe Colistin.

• Administered IV in hospital settings
• Effective against many KPC-producing organisms (a common carbapenem resistance mechanism)
• Generally better tolerated than Colistin, with lower nephrotoxicity risk
• Significantly more expensive — often $500 to $1,000+ per day of treatment

This may be preferred when susceptibility testing shows the bacteria responds to it, as it's less toxic than polymyxin antibiotics.

How Your Doctor Decides

The right alternative depends on:

• Culture and sensitivity results: Lab tests that show exactly which antibiotics the bacteria responds to
• Infection site: Lung infections, bloodstream infections, and urinary tract infections may respond differently to each antibiotic
• Your kidney function: Since most alternatives also carry nephrotoxicity risk, your kidneys' baseline function matters
• Drug availability: Even alternatives can face supply issues; your hospital pharmacist can check current stock

If you're currently searching for Colistin, don't give up — use Medfinder to check pharmacy availability in real time. Also check our guide on how to find Colistin in stock near you.

Final Thoughts

Colistin shortages are stressful, but they don't mean you're out of options. Polymyxin B, Tobramycin, Amikacin, and Ceftazidime-Avibactam are real alternatives that your infectious disease doctor can evaluate based on your specific situation.

The most important step: talk to your medical team immediately if you can't access Colistin. Time matters with serious infections, and your doctors can help you find the best available treatment quickly.

For more information about Colistin, explore our other guides:

• Colistin Side Effects: What to Expect and When to Call Your Doctor
• Colistin Drug Interactions: What to Avoid
• How to Save Money on Colistin