Surotomycin_Dosage, benefits & legal status
Also known as CB-183,315, CB-183315
A worked example of why one trial never settles anything.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Surotomycin?
Plain language first. The technical label stays, but it never stands alone.Overview
Nothing, now. This drug was tested for the gut infection that often follows antibiotic treatment, it failed to beat the cheap existing option, and it was dropped in 2017. The page exists for two reasons. The first is a class error: several widely used reference sources, Wikipedia among them, call surotomycin a macrolide, and it is not one. The second is more useful. Two of its phase 3 trials were run to the same design against the same comparator, and they disagreed. One concluded the drug was non-inferior to vancomycin. The other concluded it was not. Same drug, same question, two answers.
Surotomycin, developed as CB-183,315 by Cubist Pharmaceuticals and inherited by Merck when Merck acquired Cubist, is an orally administered bactericidal cyclic lipopeptide that was taken through phase 3 for Clostridioides difficile infection. Both of its pivotal trial reports describe it as a cyclic lipopeptide, and the paper that first characterized it is titled as a lipopeptide antibiotic. It is structurally related to daptomycin, and it acts on the bacterial cell membrane rather than on protein synthesis. It was given as 250 mg twice daily by mouth for 10 days against oral vancomycin at 125 mg four times daily. Development stopped in 2017. It was never approved anywhere.
What it's used for
Nothing. It was investigated for Clostridioides difficile infection and was never approved in any country. Development was discontinued in 2017.
How does Surotomycin work?
What it does in the body, and where.Two things are worth getting right here: what kind of antibiotic this is, and why two identical trials of it disagreed.
- 01It is a lipopeptide, not a macrolideA macrolide, such as azithromycin or erythromycin, is built on a large lactone ring and works by jamming the bacterial ribosome so protein synthesis stops. A lipopeptide is a different thing entirely: a short peptide ring carrying a fatty tail, and it attacks the cell membrane instead of the ribosome. Surotomycin is the second kind. Both of its pivotal trial papers call it a cyclic lipopeptide, and the paper that first characterized it is titled as a lipopeptide antibiotic. The class matters because it predicts everything downstream: what the drug interacts with, how resistance arises, and which other drugs it resembles.
- 02What it does to the membraneThe characterization paper from Cubist reported that the compound depolarized the membrane potential of Staphylococcus aureus without making the membrane leaky to small molecules. That is the useful detail. It discharges the electrical gradient the cell depends on rather than punching holes in it, and that is the same broad approach daptomycin takes. In the laboratory, spontaneous resistance in C. difficile sat below the limit of detection, and 15 days of serial passage shifted susceptibility by no more than twofold.
- 03Why it was built for this infectionC. difficile lives in the gut, so a drug that stays in the gut rather than entering the bloodstream can work at the site and leave the rest of the body alone. That is why this one was given by mouth. The hope was lower recurrence than vancomycin, because recurrence, not initial cure, is what makes this infection hard. In the hamster model the compound performed comparably to vancomycin, including a similar pattern of recurrence once dosing ended, and that result turned out to anticipate the human trials.
- 04The two trials that disagreedTwo pivotal phase 3 trials asked whether surotomycin was non-inferior to vancomycin for clinical cure at the end of treatment. In one, cure was 79.0 percent against 83.6 percent for vancomycin, a difference of minus 4.6 percent with a 95 percent confidence interval running from minus 11.0 to 1.9, and non-inferiority was not met. In the other, cure was 83.4 percent against 82.1 percent, a difference of 1.4 percent with an interval from minus 4.9 to 7.6, and non-inferiority was met. Same drug, same comparator, same endpoint, opposite conclusions.
- 05What that disagreement teachesNeither trial was broken. Look at the intervals rather than the verdicts and the two results overlap heavily, and both are consistent with the drug being roughly as good as vancomycin and not better. The verdicts diverged because a non-inferiority test turns a continuous range of plausible values into a yes or a no, and the two point estimates happened to fall on either side of the threshold. This is the clearest example on this site of why a single trial, read as a verdict, misleads. Neither trial showed any advantage on recurrence, and that is what ended the program.
A schematic of the compound's mechanism, not a diagnostic image.
What else is it used for?
Each group carries its own evidence level.Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
Two pivotal trials, opposite verdicts
tested-and-failed- Human trialNCT01597505: clinical cure at end of treatment 79.0 percent against vancomycin's 83.6 percent, difference minus 4.6 percent, 95 percent confidence interval minus 11.0 to 1.9. Non-inferiority was not met.
- Human trialNCT01598311: clinical cure at end of treatment 83.4 percent against vancomycin's 82.1 percent, difference 1.4 percent, 95 percent confidence interval minus 4.9 to 7.6. Non-inferiority was met.
- Human trialNeither trial showed any advantage on sustained response or recurrence. Minus 0.8 percent in the first and 4.3 percent in the second, both intervals crossing zero, with superiority not demonstrated in either.
- No dataThe two sets of confidence intervals overlap substantially. The verdicts diverged because a non-inferiority margin converts a range of plausible values into a single yes or no, not because the underlying results conflicted.
What class of antibiotic it is
none- lab-analysisThe 2012 characterization paper is titled as a lipopeptide antibiotic, and the 2017 phase 3 report calls it a bactericidal cyclic lipopeptide. It is structurally related to daptomycin.
- No dataWikipedia's article calls it a macrolide antibiotic in those words. A macrolide targets the ribosome; a lipopeptide targets the cell membrane. The two classes share neither a structure nor a mechanism.
Laboratory behavior
none- Lab studyDepolarized the membrane potential of Staphylococcus aureus without changing permeability to small molecules.
- Lab studySpontaneous resistance in C. difficile fell below the limit of detection, and 15 days of serial passage moved susceptibility no more than twofold.
- Animal studyIn a hamster model, efficacy was comparable to vancomycin, including a similar pattern of recurrence after dosing stopped. The human trials went on to show the same lack of advantage on recurrence.
Three things. The class is the most common error, and it is on Wikipedia in plain words: surotomycin is called a macrolide there, and it is a cyclic lipopeptide. Second, the reason it was dropped gets compressed into the drug failing, when what happened is narrower. One pivotal trial met non-inferiority and one did not, neither showed any gain on recurrence, and a drug that merely matches a cheap generic has no route to market. Third, a single one of those two trials is sometimes quoted on its own as the result for this drug. Quoting either alone misrepresents the evidence, because the honest summary is that two trials of the same design disagreed and the drug was probably about as good as vancomycin and no better.
The published record
Papers and trials about Surotomycin
Searched: surotomycin, CB-183,315, CB-183315.
Left out: daptomycin (has its own slug and a large literature; surotomycin is described as structurally related to it, which is exactly why the term would contaminate this row); lipopeptide (a chemical class term); Clostridium difficile (an enormous clinical literature in which this molecule is a footnote); Cubist (the developer's name, returning corporate and acquisition coverage); macrolide (the class that Wikipedia and several reference databases wrongly assign to this drug; including it would import unrelated macrolide papers and reinforce the very error the card corrects).
40 papers tagged human · 16 not reviews or lab · 5 clinical trial publications
4 registered trials · 2 with posted results
Furthest stage reached: Phase 3, results posted
Counted from Europe PMC indexing, not read by a person; a human tag can land on reviews, commentary or lab papers; clinical trial publications is the narrower count.
At a glance
Four things to know about Surotomycin
Evidence
Investigational
Category
Immune support
Common vial
Varies
Half-life
Not published
How much, and do you cycle it?
The range, and whether you take breaks.500 mg a day in trials, twice daily for 10 days, in trials. A 10-day course Trial dose
An antibiotic for an acute gut infection was given as a fixed 10-day course in the trials, not continuously and not in cycles.
Not publishedNo figure
No human half-life figure was found in the sources read for this page. The drug was designed to stay in the gut rather than to circulate, so systemic half-life was not the measure the program was built around.
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.Surotomycin is not injected in the forms covered here
It is taken by mouth, in trials only. The figure is the phase 3 trial protocol, 250 mg by mouth twice daily for 10 days, and it is recorded here as history rather than as guidance. The comparator arm took oral vancomycin at 125 mg four times daily. There is no approved product and therefore no recommended dose.
How do you store it?
Before mixing, and after.Nothing to store: it is not sold anywhere.
Surotomycin has never been marketed, so there is no vial, pen or bottle to keep at home. Supplies for a trial are made, stored and dispensed by the sponsor and the trial pharmacy under conditions set in the protocol. Anything offered for sale under this name did not come from that supply chain.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Any use at all: this compound was never approved and is not available as a medicine
- Reading it as a macrolide and reasoning from macrolide properties, since it is a lipopeptide and behaves like one
Stop and get help
- Not applicable. There is no approved product to take.
Common effects
- Nothing to list for current use. In trials the tolerability profile was reported as comparable to oral vancomycin.
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Surotomycin approved?
And where the numbers on this page come from.No. Surotomycin was never approved, and its development has ended. There is no legal route to obtain it as a medicine.
- Approval statusInvestigational
- RouteBy mouth, in trials only
- Checked26 October 2026
- DoseFrom published clinical trials. Not approved by a regulator for this dose.
- Vial sizeFrom what vendors typically list; not a recommendation.
- SourcesMascio and colleagues, Antimicrobial Agents and Chemotherapy, characterization of CB-183,315Boix and colleagues, Open Forum Infectious Diseases, the phase 3 trial that missed non-inferiorityDaley and colleagues, Journal of Antimicrobial Chemotherapy, the phase 3 trial that met non-inferiorityLee and colleagues, Journal of Antimicrobial Chemotherapy, the phase 2 trialWikipedia article on surotomycin, cited as the error rather than as a source
What has happened recently
Never approved in any country. Cubist Pharmaceuticals developed it as CB-183,315, and Merck inherited the program when it acquired Cubist. Two phase 3 trials reported their primary outcomes in 2017, and development stopped that year on the grounds that the drug was not superior to existing treatment. Note what that reasoning means: the bar it failed was not safety and not effectiveness in absolute terms, but whether it improved on a cheap generic already in use. A drug can work and still be dropped.
You can compare this against the whole library, or read how to check a seller.
What else is like Surotomycin?
Others in Immune support, side by side.If you're weighing Surotomycin, it's worth reading Teixobactin, Thymopentin (TP-5), and Tuftsin in the same class.
A worked example of why one trial never settles anything.
- Dose
- 500 mg a day in trials
- How often
- Twice daily for 10 days, in trials
A decade-long lesson in what 'no resistance detected' actually means.
- Dose
- No human dose exists
- How often
- Not applicable
Five amino acids that carry the whole activity of a thymus hormone.
- Dose
- 50 mg per dose
- How often
- 3x per week
A four-amino-acid immune peptide from the 1970s, and the parent of Selank.
- Dose
- Research only
- How often
- Not established
Guides for this compound
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
- How to Read a Peptide COA
What the purity number does and does not tell you, and how to spot an edited report.
- How to Vet a Peptide Vendor
Independent COAs, HPLC purity, and the red flags that mean walk away.
Sources
- Mascio and colleagues, Antimicrobial Agents and Chemotherapy, characterization of CB-183,315(2012)In Vitro and In Vivo Characterization of CB-183,315, a Novel Lipopeptide Antibiotic for Treatment of Clostridium difficile, volume 56, issue 10, pages 5023 to 5030, October 2012. All ten authors were at Cubist Pharmaceuticals. The title itself establishes the drug class. The abstract states the compound is structurally related to daptomycin, that it depolarized the membrane potential of Staphylococcus aureus without changing permeability to small molecules, that spontaneous resistance in C. difficile was below the detection limit, and that serial passage over 15 days changed susceptibility no more than twofold. Efficacy in a hamster model was comparable to vancomycin, including similar patterns of disease recurrence after dosing ended. Note that this paper uses only the code CB-183,315 and never the name surotomycin. DOI resolved at Crossref.
- Boix and colleagues, Open Forum Infectious Diseases, the phase 3 trial that missed non-inferiority(2017)Primary Outcomes From a Phase 3, Randomized, Double-Blind, Active-Controlled Trial of Surotomycin in Subjects With Clostridium difficile Infection, volume 4, issue 1, article ofw275, published online January 19, 2017. Clinical cure at end of treatment was 79.0 percent for surotomycin against 83.6 percent for vancomycin, a difference of minus 4.6 percent with a 95 percent confidence interval of minus 11.0 to 1.9. Sustained clinical response at day 40 to 50 was 60.6 percent against 61.4 percent, a difference of minus 0.8 percent with an interval of minus 8.8 to 7.1. The stratified log-rank test for clinical response over time gave P of 0.832. The abstract states that surotomycin failed to meet the criteria for non-inferiority against vancomycin for the primary and key secondary endpoints, and did not meet superiority criteria in the microbiological modified intent-to-treat population. Trial registration NCT01597505. DOI resolved at Crossref.
- Daley and colleagues, Journal of Antimicrobial Chemotherapy, the phase 3 trial that met non-inferiority(2017)Surotomycin versus vancomycin in adults with Clostridium difficile infection: primary clinical outcomes from the second pivotal, randomized, double-blind, Phase 3 trial, volume 72, issue 12, pages 3462 to 3470, published online September 6, 2017. 285 patients received surotomycin and 292 received vancomycin, randomized 1 to 1, with surotomycin at 250 mg twice daily and vancomycin at 125 mg four times daily for 10 days, and follow-up 30 to 40 days after the end of treatment. Clinical cure at end of treatment was 83.4 percent against 82.1 percent, a difference of 1.4 percent with a 95 percent confidence interval of minus 4.9 to 7.6, and non-inferiority was met. Sustained response was 63.3 percent against 59.0 percent, a difference of 4.3 percent with an interval of minus 3.6 to 12.2, and superiority was not demonstrated, log-rank P of 0.277. The abstract describes the drug as a bactericidal cyclic lipopeptide. Trial registration NCT01598311. DOI resolved at Crossref.
- Lee and colleagues, Journal of Antimicrobial Chemotherapy, the phase 2 trial(2016)Surotomycin versus vancomycin for Clostridium difficile infection, a phase 2 randomized controlled trial, volume 71, issue 10, pages 2964 to 2971. This is the earlier trial that the phase 3 reports refer back to as having shown non-inferiority to vancomycin, and it is cited here for that chain of reasoning rather than for its own numbers, and we did not read those. DOI resolved at Crossref.
- Wikipedia article on surotomycin, cited as the error rather than as a source(2026)Included to document the class error this page corrects, not as evidence for anything. The article states verbatim: This macrolide antibiotic was under investigation by Merck and Co. Surotomycin is a cyclic lipopeptide, as both of its own pivotal trial papers state. The article is accurate on other points: it gives the developer chain through Merck's acquisition of Cubist, records that the drug reached phase 3, and states that production was discontinued in 2017 on the grounds of non-superiority to current therapies.
Beyond these, 56 records are indexed. Browse the records