Drug & supplement interaction

Bifidobacterium Longum + Penicillin G

Penicillin G brand name: Pfizerpen.

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

Bifidobacterium Longum has a moderate interaction with Penicillin G. Theoretically, taking Bifidobacterium longum 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

Bifidobacterium Longum and Penicillin G

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

Moderate

ANTIBIOTIC DRUGS

Why this applies to Penicillin G

Penicillin G falls under ANTIBIOTIC DRUGS — the group Bifidobacterium Longum interacts with.

Theoretically, taking Bifidobacterium longum with antibiotic drugs might decrease the effectiveness of B. longum.
Since B. longum 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. longum 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 thing to keep in mind: this interaction works in one direction, and it's the probiotic that loses out, not your antibiotic. Penicillin G is designed to kill bacteria, and Bifidobacterium longum is a live, friendly bacterium. So if you take them at the same time, the penicillin can wipe out a good chunk of those probiotic organisms before they ever get a chance to do their job.

The good news is your penicillin will still work just fine against the infection it was prescribed for. To get value from the probiotic, a simple fix helps: space the two apart by at least 2 hours. This is based on how these products work rather than hard studies, so it's a sensible precaution. When in doubt, check with your pharmacist.

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.
  2. Xiao JZ, Takahashi S, Odamaki T, et al. Antibiotic susceptibility of bifidobacterial strains distributed in the Japanese market. Biosci Biotechnol Biochem. 2010;74(2):336-42. PubMed

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

Bifidobacterium Longum Also Interacts With Other Medications

Bifidobacterium Longum has 181 moderate known drug interactions in our database — the Penicillin G 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. Penicillin G)
Taking anything else?

Check Another of Your Medications Against Bifidobacterium Longum

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

Everything else you take

See Every Supplement That Interacts With Penicillin G

This page covers Bifidobacterium Longum only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Penicillin G page lists 56 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Siberian Cocklebur (major), Aristolochia (moderate) and Bacillus Coagulans (moderate).

By severity: 3 major · 42 moderate · 11 minor.

From our pharmacist’s overview on the Penicillin G page

“My concern with penicillin G (Pfizerpen), an injectable antibiotic reserved for serious infections such as syphilis and endocarditis, centers on a few supplements that deserve genuine respect. Siberian cocklebur and asarabacca can each harm the kidneys, extra strain nobody fighting a severe infection needs, while activated charcoal can…”

Reviewed by 2 · Jul 18, 2026

Open the Penicillin G interaction page

One more smart check

Taking Bifidobacterium Longum as Part of a Dietary Supplement Product? Check It for Interactions

We hold 3,189 real supplement products containing Bifidobacterium Longum, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Bifidobacterium Longum. Your product may carry other ingredients that interact with Penicillin G too, on top of Bifidobacterium Longum — 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 Bifidobacterium Longum and Penicillin G 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 Bifidobacterium Longum
Top 10%

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

29 days ago today
Medication Penicillin G
Top half

#984 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 Bifidobacterium Longum

What is Bifidobacterium Longum?

  • Digestive health and regularity
  • Irritable bowel syndrome (IBS)
  • Diarrhea (including antibiotic-related)
  • Immune support
  • Mood and stress (gut-brain axis)

Bifidobacterium longum is a 'friendly' bacterium found naturally in the human gut and used as a probiotic. It is generally well tolerated and is most studied for digestive issues, though evidence for many uses is still limited or mixed. Talk to your pharmacist or doctor before using it, especially if you have a weakened immune system.

Read the full Bifidobacterium Longum monograph & all interactions
Medication

About Penicillin G (Potassium, Sodium) Injection

What Is Penicillin G (Potassium, Sodium) Injection Used For?

Brand name: Pfizerpen

Penicillin G Potassium for Injection is used to treat serious infections caused by bacteria that are susceptible to penicillin. It covers a wide range of conditions, including bloodstream infections (septicemia), meningitis, pneumonia, endocarditis (heart valve infection), and pericarditis (infection around the heart).

It is also used for infections such as syphilis (including neurosyphilis and congenital syphilis), anthrax, diphtheria, botulism, tetanus, gas gangrene, disseminated gonococcal infections, listeria infections, and rat-bite fever, among others. Some uses are as adjunctive therapy — meaning penicillin G supports, but does not replace, other treatments like antitoxins.

See full Penicillin G (Potassium, Sodium) Injection drug information
Keep checking

Other Drugs & Bifidobacterium Longum

Browse every other medication we’ve checked against Bifidobacterium Longum — 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 Bifidobacterium Longum page.

No interaction 2,648 drugs checked — show the list

We also checked Bifidobacterium Longum 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 Bifidobacterium Longum list.

See the full Bifidobacterium Longum interactions page
See every supplement checked against Penicillin G, 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
Bifidobacterium Longum monograph › Uses, safety, and every drug interaction in one place Penicillin G supplement interactions › Every supplement checked against Penicillin G, ranked by severity Penicillin G (Potassium, Sodium) 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 Bifidobacterium Longum and Penicillin G Together: Common Questions

Can you take Bifidobacterium Longum with Penicillin G?
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 Bifidobacterium Longum and Penicillin G 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 Penicillin G and Bifidobacterium Longum?

Our pharmacists answer your medication & supplement questions — free.

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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.