Are polymyxin B and colistin FDA-approved, and what does the research show?

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What are polymyxin B and colistin?

Polymyxin B and colistin are antibiotics, drugs that kill bacteria, and they are used for serious infections ¹, ². Polymyxin B's label calls it "one of a group of basic polypeptide antibiotics," produced by growing a bacterium, Bacillus polymyxa ¹. A polypeptide is a chain of amino acids, the building blocks of proteins.

The colistin injection cited here is colistimethate sodium; its label describes it as "a polypeptide antibiotic" and states its strength as "colistin base activity," that is, in terms of colistin ². Its label also names it "pentasodium colistinmethanesulfonate," and NLM files it as a derivative of colistin ², ¹¹. Colistin sulfate is a second form, listed in FDA's drug database in a combination ear drop and an oral suspension ⁵.

Neither drug is a wellness, weight-loss, immune-boosting or performance peptide. Both labels name bacterial infections as the only use ¹, ². The polymyxin B injection label says some of its uses apply "when less potentially toxic drugs are ineffective or contraindicated" ¹.

Each injection label warns of harm to the kidneys and to the nerves ¹, ². The polymyxin B label also says that using it with colistin, at the same time or in sequence, "should be avoided" ¹. Colistin is itself a polymyxin: NLM's medical vocabulary says it is "composed of Polymyxins E1 and E2" ¹².

Are polymyxin B and colistin FDA-approved?

Polymyxin B sulfate injection ³, colistimethate sodium injection ⁴ and a colistin sulfate combination ear drop ⁵ are FDA-approved and listed "Prescription" in Drugs@FDA as of November 9, 2026; colistimethate's brand, Coly-Mycin M, is listed "Discontinued" ⁶. Drugs@FDA is the agency's database of approved drug applications, and November 9, 2026 is the date of its data. The two injection applications cited here are generics from Xellia, with its polymyxin B application approved January 15, 2014, and its colistimethate application May 29, 2015 ³, ⁴. Each label is marked for prescription use only ¹, ².

Under the heading "Acute Infections Caused by Susceptible Strains of Pseudomonas aeruginosa," the polymyxin B injection label calls the drug "a drug of choice in the treatment of infections of the urinary tract, meninges, and blood-stream caused by susceptible strains of Ps. aeruginosa" ¹. Pseudomonas aeruginosa is a gram-negative bacterium, gram-negative being a laboratory grouping of bacteria by how they take up a stain. The meninges are the membranes around the brain and spinal cord. The label's indications also include Pseudomonas aeruginosa infections of the eye, with the drug put on the eye or injected under its surface membrane ¹.

The label then says polymyxin B "may be indicated in serious infections caused by susceptible strains of the following organisms, when less potentially toxic drugs are ineffective or contraindicated" ¹. It lists four: H. influenzae (Haemophilus influenzae) in infections of the meninges, Escherichia coli in urinary tract infections, and Aerobacter aerogenes and Klebsiella pneumoniae in bacteremia ¹. Bacteremia means bacteria in the blood.

The colistimethate injection label says the drug is "indicated for the treatment of acute or chronic infections due to sensitive strains of certain gram-negative bacilli," bacilli being rod-shaped bacteria ². It is "particularly indicated when the infection is caused by sensitive strains of Pseudomonas aeruginosa" and "not indicated for infections due to Proteus or Neisseria," two other groups of bacteria ². The label names four bacteria against which the drug "has proven clinically effective": Enterobacter aerogenes (the polymyxin B label's Aerobacter aerogenes, another name for the same species ¹³), Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa ². It adds that the drug "may be used to initiate therapy in serious infections that are suspected to be due to gram-negative organisms" ².

Both labels say the drug should be used "only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria" ¹, ². The stated aim is to "reduce the development of drug-resistant bacteria" ¹, ².

Both drugs are decades old, with many generic versions ⁹, ¹⁴. On Drugs@FDA's data of November 9, 2026, 97 applications name polymyxin B sulfate as an active ingredient, ten of them for polymyxin B alone ⁹. Eight of the ten are injections: four are listed "Prescription" and four "Discontinued," the record's word for a product no longer marketed ⁹. FDA has withdrawn the approvals of two of them ¹⁵, ¹⁶. The oldest of the eight carries an approval dated June 29, 1964 ⁹.

For colistimethate sodium the same data show seven applications, all injections ¹⁴. Four generics are listed "Prescription" and two "Discontinued" ¹⁴. FDA withdrew the approval of one, ANDA 065177, as of October 23, 2025 ¹⁵.

The brand, Coly-Mycin M, approved June 4, 1970, is also listed "Discontinued" ⁶. FDA's label dataset on openFDA, updated November 9, 2026, holds a Coly-Mycin M label from Par Health USA, LLC, effective June 8, 2026 ¹⁷. Its maker's DailyMed listing gives the product a marketing end date of May 31, 2027 ¹⁷.

Outside the injections, the same data of November 9, 2026 list polymyxin B sulfate as an ingredient in 87 combination applications ⁹. Among their products, 16 for the eye, 9 for the ear and 3 irrigation solutions are listed "Prescription" ⁹. One of the three irrigation solutions is under ANDA 060707, whose approval FDA withdrew as of January 12, 2026 ⁹, ¹⁸. They pair it with drugs such as neomycin, trimethoprim, dexamethasone or hydrocortisone ⁹.

The record also lists nine combinations for the skin, all "Discontinued" ⁹. FDA's first aid rule also permits polymyxin B without prescription, only in combination with bacitracin, neomycin or oxytetracycline, in ointments, creams, powders and aerosols ⁷, ⁸.

On Drugs@FDA's data of November 9, 2026, colistin sulfate appears in two applications under the brand Coly-Mycin S ⁵. One is a prescription ear drop, approved May 17, 1962, that combines it with neomycin, hydrocortisone and thonzonium bromide ⁵. The other, an oral suspension, is listed "Discontinued" ⁵. FDA withdrew its approval, NDA 50-355, effective September 29, 1995, after its holder told the agency it was "no longer being marketed under the NDA" ¹⁹.

How do polymyxin B and colistin work?

For its approved use, polymyxin B's FDA label reads: "Polymyxins increase the permeability of bacterial cell membrane leading to death of the cell" ¹. Put plainly, the bacterium's membrane becomes leaky and the cell dies. The label calls this a bactericidal action, one that kills, "against almost all gram-negative bacilli except the Proteus group" ¹.

The label also says what the drug does not reach: "All gram positive bacteria, fungi, and gram-negative cocci are resistant to polymyxin B" ¹. Gram-positive bacteria are the other grouping by that stain, and cocci are round bacteria.

Colistimethate sodium, by its label, "is a surface active agent which penetrates into and disrupts the bacterial cell membrane" ². A surface active agent acts at a surface, as a detergent does. The label reports bactericidal activity against most strains of four gram-negative bacteria "both in vitro and in clinical infections," in vitro meaning in the laboratory ².

The labels also describe how the body handles each drug. Polymyxin B "is not absorbed from the normal alimentary tract," the gut, and "loses 50 percent of its activity in the presence of serum," the liquid part of blood ¹. It "does not pass the blood brain barrier into the cerebrospinal fluid," and the kidneys excrete it slowly ¹. Colistimethate's level in serum fell with a half-life, the time taken to halve, of 2 to 3 hours after injection into a vein or a muscle ². That held in adults and in children, premature infants included, and the drug leaves mainly through the kidneys ².

What does the research show?

Each drug is approved by FDA for bacterial infections, and none of the three labels cited here reports a trial by its number of patients ¹, ², ¹⁷. The colistimethate label says clinical studies gave the drug to newborns, infants, children and adolescents ². It also says those studies "did not include sufficient numbers of subjects aged 65 and over" to tell whether older people respond differently ².

Studied in people: a randomized trial, published online in February 2018, asked whether adding meropenem to colistin helps adults with severe infections ¹⁰. The infections were caused by gram-negative bacteria that resist carbapenems, the antibiotic family meropenem belongs to ¹⁰. The trial ran in six hospitals in Israel, Greece and Italy ¹⁰. The adults enrolled had bacteremia, pneumonia acquired in hospital or on a ventilator, or urosepsis, a life-threatening reaction to an infection starting in the urinary tract ¹⁰. Between October 2013 and December 2016, 406 patients were randomly assigned to intravenous colistin alone or to colistin plus meropenem ¹⁰.

The trial was open-label: patients and doctors knew the treatment, while the people who assessed outcomes did not ¹⁰. Most patients, 355 of 406, had pneumonia or bacteremia, and 312 of 406 infections were caused by Acinetobacter baumannii ¹⁰. The main outcome was clinical failure 14 days after randomization ¹⁰. A patient counted as a failure unless every criterion of success was met, among them survival, stable circulation and an organ-failure score that had not worsened ¹⁰.

Clinical failure occurred in 156 of 198 patients (79 percent) given colistin alone and 152 of 208 (73 percent) given the combination ¹⁰. The risk ratio, one arm's failure rate divided by the other's, was 0.93 ¹⁰. Its 95 percent confidence interval ran from 0.83 to 1.03, and the difference was not significant ¹⁰. A confidence interval is the range in which the true figure plausibly lies; this one includes 1, so the trial did not show a difference between the two arms.

The authors concluded: "Combination therapy was not superior to monotherapy" ¹⁰. They added that the trial "was unpowered to specifically address other bacteria" ¹⁰. Unpowered means the trial enrolled too few such patients to answer the question. Both groups received colistin, so the trial measures what meropenem adds, not how colistin compares with another antibiotic or with none ¹⁰.

None of the sources cited here studies polymyxin B in a randomized trial. None studies either drug for weight, immune function, aging or athletic performance.

What are the side effects?

Polymyxin B's injection label opens with a boxed warning, a warning set in a box at the head of the label ¹. Its subjects are nephrotoxicity, harm to the kidneys, and neurotoxicity, harm to the nerves ¹. For intramuscular or intrathecal use, an injection into a muscle or into the spinal fluid, it says the drug "should be given only to hospitalized patients, so as to provide constant supervision by a physician" ¹. On the kidneys, it says "renal function should be carefully determined" and that "diminishing urine output and a rising BUN are indications for discontinuing therapy with this drug" ¹. BUN, blood urea nitrogen, is a blood test of kidney function.

On the nerves, the box says "neurotoxic reactions may be manifested by irritability, weakness, drowsiness, ataxia, perioral paresthesia, numbness of the extremities, and blurring of vision" ¹. Ataxia is unsteady movement, and perioral paresthesia is tingling around the mouth. The box warns that this neurotoxicity "can result in respiratory paralysis from neuromuscular blockade, especially when the drug is given soon after anesthesia and/or muscle relaxants" ¹. Neuromuscular blockade means the nerve signal to the muscles, the breathing muscles included, is cut off.

The box says the use of other drugs that harm nerves or kidneys, at the same time or in sequence, "should be avoided" ¹. It names eleven, among them bacitracin, neomycin, gentamicin, tobramycin, amikacin and colistin ¹. It ends: "The safety of this drug in human pregnancy has not been established" ¹. The label lists one contraindication, a condition in which the drug is not to be given: "a prior history of hypersensitivity reactions to polymyxins" ¹. Hypersensitivity is an allergic-type reaction.

Colistimethate's label carries no boxed warning; its kidney and nerve warnings sit in the Warnings section ². It says "transient neurological disturbances may occur," among them numbness or tingling around the mouth and in the limbs, generalized itching, vertigo, dizziness and slurred speech ². Patients "should be warned not to drive vehicles or use hazardous machinery while on therapy" ². On the kidneys it says: "Nephrotoxicity can occur and is probably a dose-dependent effect of colistimethate sodium" ². It calls these kidney effects "reversible following discontinuation of the antibiotic" ².

The same label says "respiratory arrest has been reported following intramuscular administration of colistimethate sodium" ². Poor kidney function, it adds, raises the chance of apnea, a pause in breathing, and of neuromuscular blockade ². Its overdose section says "respiratory muscle paralysis may lead to apnea, respiratory arrest and death" ². Its contraindication is "a history of sensitivity to the drug or any of its components" ². In pregnancy, it says the drug crosses the placenta and should be used "only if the potential benefit justifies the potential risk to the fetus" ².

Two warnings appear on both labels. Clostridium difficile associated diarrhea, a bowel infection that follows antibiotic use, "may range in severity from mild diarrhea to fatal colitis," inflammation of the colon ¹, ². Both labels also report cases, after marketing, of a kidney disorder called pseudo-Bartter syndrome with intravenous use ¹, ². All the cases had low blood potassium and blood that had turned too alkaline ¹, ². Neither label gives a rate for any adverse reaction in patients ¹, ².

In the 2018 trial, diarrhea was reported in 56 patients (27 percent) given colistin plus meropenem and 32 (16 percent) given colistin alone ¹⁰. Mild renal failure was less frequent with the combination ¹⁰. Among patients at risk of or with kidney injury, it occurred in 37 of 124 (30 percent) in one arm and 25 of 125 (20 percent) in the other ¹⁰.

In sport

Neither polymyxin B nor colistin is named on WADA's 2026 Prohibited List ²⁰. WADA is the World Anti-Doping Agency. Both drugs can be given into a vein, polymyxin B by drip and colistimethate by infusion ¹, ². The list's method rule M2.2 prohibits "Intravenous infusions and/or injections of more than a total of 100 mL per 12-hour period except for those legitimately received in the course of hospital treatments, surgical procedures or clinical diagnostic investigations" ²⁰.

What JumpstartMD offers

JumpstartMD does not prescribe polymyxin B or colistin. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 10, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.

v2 changes

Cold read folded by J Writer (b13-fold-polymyxin) from "CRO-101 BATCH 13 — COLD READ — polymyxin b and colistin — 2026-11-10 16:17 CET", 34 items. Sources: v1's text and writer's notes only; nothing was opened.

1. Applied. At a glance line 1 names colistimethate sodium, the member ² describes; line 3 now reads "Polymyxin B and colistimethate sodium are injected" for the same blur.
2. Applied. The colon is gone; the two halves are joined by "and".
3. Applied. The line is the new status sentence, word for word; each injection stands on its one application, ³ and ⁴, with no plural.
4. Applied in part. The line names the three infection types and the outcome (clinical failure at 14 days). "Gram-negative" is added to the body's sentence on the bacteria, not to At a glance, where the term is not yet explained.
5. Applied. The reason sentence names the two injection labels and the trial's two arms; the entry block's evidence reason is identical.
6. Applied. "Each is a polypeptide" is cut; the gloss follows polymyxin B's quotation, and "a polypeptide antibiotic" is given as the colistimethate label's words for colistimethate sodium.
7. Applied. "Colistin's injected form is" became "The colistin injection cited here is colistimethate sodium" with a new GAP beside it for the relation; "pentasodium colistinmethanesulfonate" is cut from the body and the FAQ (it stays an alias in the entry block).
8. Applied. "colistin base activity" is kept as the label's one stated link to colistin, glossed "in terms of colistin", inside the sentence of item 7.
9. Applied. The paraphrase is replaced by the label's quoted clause, "when less potentially toxic drugs are ineffective or contraindicated"; the full sentence keeps its home under "Are … FDA-approved?". The "last-line" GAP stays as the unit wrote it.
10. Applied. Cut as a repeat; the box is quoted under "What are the side effects?".
11. Applied. "The two drugs share their main risks:" is cut; the sentence reads "Each injection label warns of harm to the kidneys and to the nerves".
12. Applied in part. The qualifier is restored as "at the same time or in sequence", the wording the page uses under side effects; the box's own words for it are not in the notes, so it is not quoted. The sentence stays because it is the one place the polymyxin B label names colistin, and the class GAP sits beside it.
13. Applied. "Yes:" is gone. The new status sentence has 30 words outside quotation marks and citation tokens (34 if its four tokens are counted as words).
14. Applied. The heading no longer stands as the indication. The first sentence carries the status only; polymyxin B's indication sentence (named under its heading) and its "less potentially toxic" sentence follow in the next two paragraphs in the label's words, and colistimethate's "indicated for the treatment of acute or chronic infections …" quotation moved to the head of its own paragraph, whole.
15. Applied. The first sentence carries the colistin sulfate ear drop ⁵ and the "Discontinued" Coly-Mycin M ⁶; status_proposed.source_n is now P3, P4, P6, P8.
16. Applied (same sentence as item 3).
17. Applied. "Gram-negative" is explained in the page's own voice before the colistimethate quotation that uses it; "bacilli" is glossed at that quotation and its later gloss under "How do … work?" is removed.
18. Applied by cut. The route instruction cannot be quoted from the notes and is an instruction to the prescriber; "intrathecal" is glossed at its first use under side effects (item 30).
19. Applied. Reworded as an indication ("The label's indications also include …"), not an instruction; not quoted because the notes carry only the label's word "subconjunctivally".
20. Applied. "H. influenzae (Haemophilus influenzae)"; Enterobacter aerogenes is linked to the polymyxin B label's Aerobacter aerogenes as an older name, in the colistimethate paragraph.
21. Applied. "two other groups of bacteria".
22. Applied. A visible sentence states the June 8, 2026 Coly-Mycin M label beside Drugs@FDA's "Discontinued"; reference ¹⁷ is added from the notes (set id, version, effective date, read through openFDA's label dataset); the one GAP stays, now also saying the label's title and DailyMed address are not in the notes.
23. Applied. Both paragraphs name Drugs@FDA's data of November 9, 2026.
24. Applied. The opening sentence is cut; the first quotation is introduced "For its approved use, polymyxin B's FDA label reads".
25. Applied. "Proteus" is glossed at its first use under "Are … FDA-approved?"; "gram positive" is glossed after its quotation.
26. Applied. Urosepsis is glossed without the word "sepsis".
27. Applied. The colon is gone; "risk ratio" is glossed; the interval has its own sentence.
28. Applied. "so the trial did not show a difference between the two arms".
29. Applied. "than A. baumannii" is cut; "unpowered" is glossed. The paragraph is split in three to stay within five sentences.
30. Applied.
31. Applied.
32. Applied.
33. Applied. "the abstract gives" is cut; the figures stay, as "in one arm" and "in the other", with one GAP for Checker that states the possible contradiction.
34. Applied. "Not quite" is cut; the answer is the records' (two ingredients in Drugs@FDA ⁵, ¹⁴), and the body now says it under "What are …?" (colistimethate sodium the injection, colistin sulfate "a second form").

Also changed with these: the reference list and the entry block's references are in the new order first cited (P1, P2, P3, P4, P6, P8, P5, 1, P7, P9, W). word_count is 2590 by the fold's script (H1 to the line before References; headings, citation tokens and markers excluded); the same script reads v1 at 2420 against the 2312 its unit recorded. The badge is unchanged. No date is changed.

New GAPs (1): the relation of colistimethate sodium to colistin ("What are …?"). Reworded GAPs (2): Coly-Mycin M (adds the label's title and address); the renal figures (arms; Checker confirms from the source).

Glosses for Dr. Bourke, new in v2: "colistin base activity" as "in terms of colistin"; Proteus and Neisseria as "two other groups of bacteria"; Haemophilus influenzae for H. influenzae; Aerobacter aerogenes as an older name of Enterobacter aerogenes; gram-positive as "the other grouping by that stain"; urosepsis as "a life-threatening reaction to an infection starting in the urinary tract" (At a glance: "a life-threatening infection starting in the urinary tract"); risk ratio; a confidence interval that includes 1; unpowered; intramuscular and intrathecal; contraindication; hypersensitivity as "an allergic-type reaction"; colitis as "inflammation of the colon".