Drug & supplement interaction

Bacillus Subtilis + Colistimethate

Colistimethate brand name: Coly-Mycin M.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Bacillus Subtilis has a moderate interaction with Colistimethate. Theoretically, taking Bacillus subtilis with antibiotic drugs might decrease the effectiveness of B.

Read the full interaction report
SeverityModerate
LikelihoodProbable
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Bacillus Subtilis and Colistimethate

Here is the interaction we found between these two, with the evidence behind it.

Moderate

ANTIBIOTIC DRUGS

Why this applies to Colistimethate

Colistimethate falls under ANTIBIOTIC DRUGS — the group Bacillus Subtilis interacts with.

Theoretically, taking Bacillus subtilis with antibiotic drugs might decrease the effectiveness of B. subtilis.
Since B. subtilis preparations usually contain live and active organisms, simultaneously taking antibiotics might kill a significant number of the organisms. Tell patients to separate administration of antibiotics and B. subtilis preparations by at least 2 hours.
Severity Moderate Likelihood Probable Evidence D

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the simple version: Bacillus subtilis is a live probiotic, and Colistimethate is an antibiotic whose whole job is to kill bacteria. So the concern runs in one direction. The colistimethate doesn't get weaker or stronger here; instead, it may wipe out a good chunk of the friendly probiotic organisms, leaving you with less benefit from the supplement. This is a theoretical worry based on how both products work, not something proven in studies, so it's a moderate, common-sense caution rather than a danger.

The easy fix is timing. Try to space them out by at least 2 hours. Colistimethate is usually given by injection in a hospital or clinic setting, so it's worth checking with your pharmacist or nurse on how to fit the probiotic in around your doses.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Pierce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York: The Stonesong Press, 1999:19.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Bacillus Subtilis Also Interacts With Other Medications

Bacillus Subtilis has 181 moderate known drug interactions in our database — the Colistimethate one above is one of them. If you take anything else, check it against the full list below.

Moderate 181 No known interaction 2,649 (incl. Colistimethate)
Taking anything else?

Check Another of Your Medications Against Bacillus Subtilis

Covers the 2,830 medications we’ve checked against Bacillus Subtilis. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Colistimethate

This page covers Bacillus Subtilis only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Colistimethate page lists 27 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Bacillus Coagulans (moderate), Bifidobacterium Animalis Subsp. Lactis (moderate), Bifidobacterium Bifidum (moderate), Bifidobacterium Breve (moderate) and Bifidobacterium Longum (moderate).

By severity: 26 moderate · 1 minor.

Open the Colistimethate interaction page

One more smart check

Taking Bacillus Subtilis as Part of a Dietary Supplement Product? Check It for Interactions

We hold 786 real supplement products containing Bacillus Subtilis, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Bacillus Subtilis. Your product may carry other ingredients that interact with Colistimethate too, on top of Bacillus Subtilis — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Bacillus Subtilis and Colistimethate Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Bacillus Subtilis
Top 25%

#253 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Colistimethate
Steady interest

#2,681 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Bacillus Subtilis

What is Bacillus Subtilis?

  • Digestive health and bloating
  • Diarrhea support
  • Immune support
  • Gut microbiome balance

Bacillus subtilis is a spore-forming probiotic bacterium found in soil and some fermented foods, and it is used mainly to support gut health and digestion. Early research is promising for certain digestive and immune uses, but evidence is still limited and not strong enough to make firm claims. Talk to a pharmacist or doctor before using it, especially if you have a weak immune system.

Read the full Bacillus Subtilis monograph & all interactions
Medication

About Colistimethate Injection

What Is Colistimethate Injection Used For?

Brand name: Coly-Mycin M

Colistimethate for Injection is used to treat acute (sudden) or chronic (long-lasting) infections caused by specific gram-negative bacteria. It is particularly effective against Pseudomonas aeruginosa and is also used for infections caused by Escherichia coli, Klebsiella pneumoniae, and Enterobacter aerogenes.

It may be used to start treatment when a serious infection is suspected to be caused by gram-negative bacteria, even before lab results are back. It is not used for infections caused by Proteus or Neisseria bacteria.

See full Colistimethate Injection drug information
Keep checking

Other Drugs & Bacillus Subtilis

Browse every other medication we’ve checked against Bacillus Subtilis — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
181Moderate
0Minor
2,648No known interaction
181 Moderate 2,648 No interaction
Moderate

181 interactions

Showing 60 of 181 moderate interactions — see all 181 on the Bacillus Subtilis page.

No interaction 2,648 drugs checked — show the list

We also checked Bacillus Subtilis against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,648 medications checked with no known interaction — see the full Bacillus Subtilis list.

See the full Bacillus Subtilis interactions page
See every supplement checked against Colistimethate, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Bacillus Subtilis monograph › Uses, safety, and every drug interaction in one place Colistimethate supplement interactions › Every supplement checked against Colistimethate, ranked by severity Colistimethate Injection drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Bacillus Subtilis and Colistimethate Together: Common Questions

Can you take Bacillus Subtilis with Colistimethate?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Bacillus Subtilis and Colistimethate interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Colistimethate and Bacillus Subtilis?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.